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1

A REVIEW OF ALTERNATIVES TO FENTHION FOR QUELEA BIRD CONTROL

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Robert A. Chekea* and Mohamed El Hady Sidattb

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a

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Maritime, Chatham, Kent, ME4 4TB, UK

Natural Resources Institute, University of Greenwich at Medway, Central Avenue, Chatham

89bSecretariat of the Rotterdam Convention, Plant Production and Protection Division (AGP

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Food and Agriculture Organization of the United Nations (FAO), Viale delle Terme di

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Caracalla, 00153 Rome, Italy

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*

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E-mail address: r.a.cheke@greenwich.ac.uk (R. A. Cheke)

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Corresponding author.

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Keywords: red-billed quelea, Quelea quelea, fenthion, fire-bombs, integrated pest

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management.

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ABSTRACT21

The red-billed quelea (Quelea quelea) is the most important avian pest of small grain crops in22

semi-arid zones of Africa. Fenthion, an organophosphate, is the main avicide used for

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controlling the pest but it is highly toxic to non-target organisms. The only readily available

24

pesticide that could replace fenthion is cyanophos, but this chemical is also highly toxic to25

non-target organisms, although less so than fenthion, and may be more expensive; however,26

more research on its environmental impacts is needed. Apart from chemical avicides, the only

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rapid technique to reduce the numbers of quelea substantially is the use of explosives

28

combined with fuel to create fire-bombs but these also have negative effects on the29

environment, can be dangerous and have associated security issues. The technique is labour

30

intensive and in practice can only be deployed against small (<5 ha) colonies and roosts. An

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integrated pest management (IPM) approach is the most environmentally benign strategy but,

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apart from when circumstances permit cultural control measures, most IPM activities only

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have realistic chances of succeeding in controlling quelea in small (<10 ha) areas. For

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instance, mass-trapping, which also has the advantage of providing a food source, is suitable

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when quelea roosts and colonies are less than 5 and 10 hectares in area, respectively.

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Nevertheless with both traps and mist nets, care is needed to minimise non-target casualties.

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Other IPM measures are also reviewed and the advantages and disadvantages of different

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methods tabulated. A related figure provides a decision tree for choosing appropriate

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measures for different circumstances. If fenthion has to be used, means of minimising its use

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include ensuring that spraying is only conducted when crops are threatened and that the41

lowest dosages necessary are applied. Regular training of pest control workers in how to use

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equipment correctly and in what to do in the case of accidental contamination of operators,

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and training of farmers on IPM principles and quelea biology through farmer field schools are

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recommended.

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1.

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The red-billed quelea (Quelea quelea Linnaeus) is the most important avian pest of small

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grain crops in Africa, causing damage up to the equivalent of US$ 88.6 million per annum at492018 prices throughout semi-arid zones (Elliott, 1989a,b). At present, control is mostly by50

aerial and / or ground-spraying of organophosphate avicides, with fenthion (Queletox®)

51

being the pesticide of choice. As the red-billed quelea is recognised as a migratory pest, such52

control is conducted by international agencies, Governments and commercial companies,53

although subsistence farmers can undertake other measures, included in this review, to reduce54

the birds’ depredations. Regrettably, fenthion is toxic to humans and to other non-target

55

organisms so alternatives to its use, reviewed here, are urgently sought.

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quelea feeds principally on native grasses but when these are scarce the birds will attack the57

seed heads of crops. Principal amongst the latter are millet, sorghum, wheat, rice and teff.

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There are three subspecies of red-billed quelea: the nominate form Q. q. quelea occurs in

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West Africa from Senegal in the west to Sudan in the east; Q. q. aethiopica (Sundevall)

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ranges in East Africa from Ethiopia to southern Tanzania and Q. q. lathamii (Smith) is

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restricted to southern Africa (Cheke, 2014). All three of the subspecies are migrant pests

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which follow rainfall systems. As meteorological conditions vary from year to year, the63

locations and severity of quelea infestations also vary between seasons. In general, the birds

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breed 2 or 3 times a year, but up to 5 times per annum in East Africa, during and just after

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rainy seasons. Quelea coming from huge communal breeding colonies may attack crops.

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Damage also occurs in dry seasons when the birds continue to flock together and may roost in67

very high numbers. Both breeding colonies and roosts are the targets of control operations

68

that take place after dark when the birds have settled down for the night. The birds also

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collect in “day-roosts” or “secondary roosts” during daytime (Ward and Zahavi, 1973) when70

they are susceptible to mass-trapping.

IntroductionThe

red-billed

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As the birds are migrant pests, responsibility for their control rests in some zones with72

international organisations. Thus, the Desert Locust Control Organization for Eastern Africa

73(DLCO-EA) uses its aircraft to treat member countries’ infestations and the International Red

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Locust Control Organisation for Central and Southern Africa (IRLCO-CSA) has a similar

75role for its areas of responsibility. However, some countries such as Botswana, the Republic76

of South Africa and affected West African countries now undertake their own control duties.

77

Although fire-bombs are used to destroy quelea breeding colonies and roosts in Botswana,

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South Africa, Kenya and elsewhere, the principal control agent in all areas is currently the

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organophosphate avicide fenthion (Queletox®; 640 UL; thiophosphoric acid or O,O-

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dimethyl-O-[3-methyl-4-(methylthio) phenylphosphorothiote], also known as Baytex,

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Lebaycid, Tignvon and OMS-2).

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Fenthion, like other organophosphate compounds, acts by inhibiting acetylcholinesterase,83

which is essential for normal nerve function. When acetylcholinesterase is inhibited a build-84

up of acetylcholine results causing prolonged transmission of nerve impulses leading to death85

from respiratory failure. Fenthion can therefore injure or kill indiscriminately, with

86

consequent adverse effects on non-target organisms (McWilliam and Cheke, 2004) including

87

humans. Fenthion residues are now known to have a half-life of 45 days, almost twice a88

previous figure given by Meinzingen et al. (1989), and rainfall after sprays can cause fenthion89

to leach out of the soil and still be detectable five months later (Cheke et al., 2013).

90

Additionally, persistence of fenthion residues in the air for 64 hours and in soil for 46 days91

was reported by van der Walt (2000).

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To date, measures to control quelea birds without using fenthion have included the use of

93(a) alternative pesticides; (b) explosives/fire-bombs; (c) a variety of mass trapping methods,

94

sometimes keeping the birds for food; (d) cultural control; (e) quelea resistant crops; (f)95protecting vulnerable crops with repellents and netting and (g) scaring the birds, including the

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use of falcons. These will be described and discussed below under main headings of97

Chemical Control, Mechanical Control, Cultural Control and Biological Control. The

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information for this review is based on published and unpublished documents, obtained99

following library and internet-based literature searches for relevant terms, and the authors’100

own observations that were collated for presentation at a workshop to discuss the subject of101

this paper organised by the FAO’s Rotterdam Convention Secretariat. The meeting was

102

attended by representatives of 11 African countries and held in Khartoum, Sudan, on 4-5

103

April

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http://www.pic.int/Implementation/TechnicalAssistance/Workshops/WorkshopSudanApr201

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7/tabid/5895/language/en-US/Default.aspx). The workshop was convened following concerns

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over human safety and a proposal to list fenthion in Annex 3 of the Rotterdam Convention

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which, if accepted, would have led to the pesticide being subject to the Prior Informed

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Consent

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http://www.pic.int/Procedures/PICProcedure/tabid/1364/language/en-US/Default.aspx). The

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Rotterdam Convention is a multilateral Environment Agreement. Its principal objective is

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promotion of shared responsibility and cooperative efforts among parties in the international

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trade of certain hazardous chemicals, in order to protect human health and the environment.

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By its article 6, the convention allows developing countries and countries with economies in

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transition that are experiencing problems caused by any specific pesticide formulation to115

propose it for consideration as a Severely Hazardous Pesticide Formulation (SHPF). Such

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SHPFs will then be subject to the Prior Consent Procedure (PIC) applicable to the 160 parties

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of the Rotterdam Convention. Fenthion is scheduled for consideration for inclusion in 2019.

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After the Khartoum meeting, the text of the initial review was revised to include additional

119

topics raised by the delegates, comments arising from the ensuing discussions and the120

reflections of the attendees. A summary of the advantages and disadvantages of the various

2017

(PIC)

(see

procedure

(see

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methods is tabulated (Table 1) and, aiming to minimise pesticide usage, a decision tree

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recommending different approaches according to circumstances is provided (Figure 1),123

thereby collating current evidence about the various control methods available for use against

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quelea.

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2.

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2.1. Chemical Control

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2.1.1. Alternative pesticides

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Alternatives to fenthion for quelea control

The most commonly used alternative avicide is another organophosphate, cyanophos

131(Falcolan

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phosphorothioate). Cyanophos is not registered for use in the United States of America where133

it is classified as an extremely hazardous substance. Similarly it is not registered for use in134

the European Union. Nevertheless, it has been used for quelea control in Senegal, Mauritania,

135

Botswana, Ethiopia and elsewhere since it has lower toxicities (e.g. acute oral LD50 for rats

136

730 mg.kg-1 and 3 mg.kg-1 for quelea) than those of fenthion (acute oral LD50 for rats 250

137

mg.kg-1 and 6-10 mg.kg-1 for quelea). Cyanophos was tested in Tanzania but was not

138

recommended for routine use. In contrast, it is a registered avicide in the Republic of South

139

Africa where it is used for the majority of quelea control operations since fenthion is no140

longer available there (E. van der Walt, pers. comm., Nov. 2016). Cyanophos has the141

disadvantage of a delayed effect on mortality in comparison with fenthion (Allan, 1997), so142

use of cyanophos could lead to more secondary poisoning of non-target organisms than143

control with fenthion but few studies of the effects of cyanophos use in the field have been144

conducted. Mullié et al. (1999) studied non-target organisms after cyanophos spraying

145

against quelea in Senegal and concluded that it seemed to be as damaging as fenthion but that

520

UL;

OMS

226,

C9H10NO3PS(O-(4-cyanophenyl)

O,O-dimethyl

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the data were insufficient for adequate comparisons. Cheke et al. (2013) found that147

cyanophos was still present in soil, at concentrations of from 0.009 to 0.169 g.g−1, 41 days

148

after a spray in Botswana (the maximum residue level for this compound is unknown but UK

149

pesticide authorities recommend a default maximum residue level on food of 0.01 μg.g−1; see150

https://secure.pesticides.gov.uk/MRLs/). Phoxim, also an organophosphate, has been tested151

as an alternative to fenthion (Pope and King, 1973) and Allan (1997) listed some other152

alternative chemicals such as mevinphos, another organophosphate. However, mevinphos is153even more toxic than fenthion (acute oral LD50 for rats 3-12 mg.kg-1 and 1.43 mg.kg-1 for154

quelea), so it does not present a suitable alternative.

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2.1.2. Bird repellents including narcotics

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Alphachloralose is a narcotic agent added to bait grain or water that has been used in South

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African trials (Garanito et al. 2000) which leaves birds so weak that they can be easily picked

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up or killed, but its potential for affecting non-target organisms renders it unsuitable except,

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perhaps, in urban areas. Other possible chemicals with repellent abilities that could be used,161

but which have similar strictures against them, include 4-aminopyradine and aluminium

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ammonium sulphate, curb (ammonium sulphate) and trimethacarb (predominantly

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trimethylphenyl methylcarbamate).

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repellent, molluscicide and insecticide, also listed by Allan (1997), doubled yields of165sorghum in Senegal and in Sudan reduced damage from 85 to 30% in experiments on

166sorghum and wheat. It is now banned by the EU either for direct use on crops or as a seed167

dressing. Use of repellents was reviewed by Bruggers (1989). The repellent 9,10

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Anthraquinone is in use in Zimbabwe but it is not approved for use in the EU. Attempts have

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been made in South Africa to spray birds with wetting agents such as dilute molasses to

Use of mesurol, the carbamate methiocarb, a bird

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prevent the birds from thermoregulating, but the large volumes required precluded regular171

use of the technique (E. van der Walt, pers. comm.).

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2.2. Mechanical Control

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2.2.1. Explosions

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Explosions/fire-bombs are or were used to control red-billed quelea in Botswana, the176

Republic of South Africa, Kenya, Zimbabwe and elsewhere. They are often used in or near177

wetlands, where spraying with organophosphates is contra-indicated. The technique requires

178

highly trained personnel, specialised equipment to transport the explosives safely, and time to179

deploy the firebombs at the base of vegetation where the birds are either roosting or nesting.

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This precludes their use except at small (<5 ha) sites. Cheke et al. (2013) described the181

method used in Botswana as follows: “The technique involves the detonation of 5 L plastic

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containers, filled with 2.5 L of a mixture of fuels: one-third diesel to two-thirds unleaded

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petrol was used in 2009 and 2010, but a 50 : 50 mixture of 1 L of diesel and 1 L of petrol was

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used in 2005; the addition of diesel keeps the flame alight longer than petrol alone, but also

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gives rise to smoke. Each plastic container (white opaque containers were used in 2005–

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2008, but green ones in 2009–2010) is placed beneath a bush where quelea birds are either187

nesting or expected to roost. Each container has an explosive charge placed beneath it. In

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2005, this consisted of 150 g of Trojan C150 cast boosters, 38 × 120 mm of pentolite and a189

mixture of TNT and RDX, encased in yellow plastic [manufactured by Ensign-Bickford,

190(Pty) Ltd, South Africa]. Each booster had a hole drilled in the middle, through which red

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detonating cord (plastic cord, 8 g.m−1; Auxim Tech. Ltd, China) was fed. At the ignition site,

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about 120 cm of yellow safety fuse of slow-burning (8–10 mm.s−1) gunpowder was placed at193

the beginning of the cord, giving approximately 2.5 min between ignition and detonation for

1941000 m of cord under >200 containers. The fuse was connected to an electric detonator cord

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containing a white powdered high-explosive core to set off the detonator. This created a

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shock wave to the detonating cord, along which it travelled at 6400 m.s−1, exploding each197

booster in turn. In 2009 and 2010 the explosive used was PowergelTM (see198

www.oricaminingservices.com/download/file id 4292/for information on its toxicology), a

199

commercially available ammonium nitrate product, with a detonation velocity of 1780 m.s−1

200[<6400 m.s−1 for TNT (see above), and <8400 m.s−1 for pentaerythritol tetranitrate (PETN),

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which was also used in years before 2006], mixed with aluminium powder to enhance its

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performance. These charges were connected by cordex fuse cord, made of powdered PETN,

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to a central electric detonator that started the reaction with 1 g of metallic-derived explosives

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or after being activated by a slow-burning safety fuse of gunpowder (black powder). When205

the explosion takes place, the fuel mixture is first splashed up onto the trees where it forms a

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mist and then ignites.” In South Africa, the main explosions are preceded a few milliseconds

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earlier by a small detonation to scare the birds into the air to improve control and, in reed

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beds, the firebombs are raised on poles. In Kenya, small stones are sometimes placed in

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packages above the explosive apparatus. Allan (1997) also describes the method with

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particular reference to reed beds and he also discussed the drawbacks of the method including211

its expense and dangers. There is also a security issue given the involvement of explosives

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and suitably trained military personnel are often required to oversee the operations. This may

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explain why explosions are not used in Tanzania, for instance.

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The method has obvious dangers for the operators and the environment immediately

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affected by the explosions, but provided that suitable precautions are taken threats to216

personnel, villagers and livestock can be minimised. It was long thought that explosions were217

less damaging to the environment than the use of fenthion (e.g. see Meinzingen et al., 1989,

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Allan, 1997) and Jaeger and Elliott (1989) describe people eating the blown-up birds as219

benefitting from “a much appreciated source of uncontaminated quelea for food”. However,

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Cheke et al. (2013) showed that explosions are by no means environmentally benign. Many

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non-target organisms can be killed or maimed (see also reports cited in McWilliam and222

Cheke, 2004), soil is contaminated with concentrations of total petroleum hydrocarbons

223(TPHs) and phthalates (from the plastic) ranging from 0.05 to 130.81 (mean 18.69) μg.g−1

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and from 0 to 1.62 (mean 0.55) μg.g−1, respectively, in the craters formed by the explosions,225

but the values declined to means of 0.753 and 0.027 μg.g−1 at 10m away. Dead birds will also226

be contaminated and thus unfit to eat. One year after an explosion, mean TPHs of 0.865 and227

mean phthalates of 0.609 were still detectable in the soil. In addition, remains of the plastic

228

did not degrade and littered the sites for years after an explosion, bushes and other vegetation229

were badly burnt, although the bushes tended to recover unless their trunks were broken, and230

craters were formed at each firebomb location damaging the soil. More than 1% of the area

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encompassed by the explosion was damaged in this way.

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2.2.2. Nest destruction and chick harvesting

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Bashir (1989) described how in some communities such as in western Sudan, quelea nests

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are destroyed by pulling them out of trees with hooks on the ends of long poles or by cutting

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down the nest trees or with fire including use of flame-throwers. Nest destruction is only237

useful if conducted after the birds have laid their eggs, otherwise the birds simply repair nests

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or move elsewhere to breed, and before any fledglings can fly. Amongst various control239

methods tried against birds in reed beds where chemical control was prohibited, Garanito et240

al. (2000) concluded that mechanical destruction of breeding and roosting habitat manually or

241using tractors dragging brushing equipment was the most cost-effective technique.

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Removal of chicks from nests for later consumption for food is also widely practised.

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Pelham (1998) reported that up to 3.78 kg of chicks could be harvested per person per hour in

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Zimbabwe. Reports of the use of quelea as a food source for the rural poor were reviewed and245

their implications discussed by McWilliam and Cheke (2004).

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2.2.3. Trapping248

It is well known that in many parts of Africa, people eat quelea as the birds provide a249

nutritious source of protein (Jaeger and Elliott 1989). Indeed quelea colonies are sometimes

250

not reported to pest control authorities when the villagers want to exploit them for food.

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Various means of trapping the birds are described below. Quelea consumption for food varies

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regionally and with the preferences of different ethnic groups but it is known to occur in parts

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of Botswana, Cameroon, Chad, Ethiopia, Kenya, Nigeria, Senegal, Tanzania, Zambia and254

Zimbabwe. With the exception of organised operations such as that described in Zimbabwe

255(Pelham, 1998), most harvesting for food is restricted to small colonies (<10 ha), but see

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section 2.2.3.1.

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2.2.3.1. Chad Traps

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In Chad, farmers adapted nets used for fishing to capture quelea. One of three types of nets

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used were triangular, suspended on long hand-held poles, and held open in front of roosts and261

closed to capture birds frightened into them. In this way, on moonless nights at tree roosts

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about 1,200,000 birds were caught over nine weeks (Mullié 2000). As many as 20,000 could263

be processed per day by a team of six men for later sale in markets as plucked, fried and dried

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products. The trapping had a negligible effect on the quelea populations, although many such265

actions conducted by teams can lead to 7,000,000 bird captures over the course of a year, but

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the revenue from sale of the quelea as food partly compensated the villagers for their crop

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losses.

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2.2.3.2. Kondoa basket traps

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In Kondoa District, near Dodoma in Tanzania, farmers catch quelea using basket traps

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woven in star grass Cynodon nlemfuensis Vanderyst (Cheke, 2011). The technique is only272

used in dry seasons when traps are usually placed with the funnel-shaped opening uppermost

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near water where the birds come to drink when they are attending “daytime or secondary274

roosts” or else they are placed in fields. Each basket is baited with grain and heads of millet

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and, sometimes, with a decoy quelea bird to entice others into the traps. In this way 800 or

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more birds can be caught per trap per day. The birds are then collected through the hole on277

the opposite side of the trap after the lid has been removed. The birds are slaughtered,278

plucked, de-gutted and then prepared as food in a variety of ways (Mtobesya, 2012). So

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successful are the captures that surplus birds are sold at roadsides and elsewhere leading to

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profits that help the farmers to buy goods and pay for school fees (Mtobesya, 2012, Manyama281

et al., 2014).

282
283

2.2.3.3. Kondoa basket traps made of wire mesh284

Given the success of the Kondoa basket traps in catching quelea, experiments were285

conducted with artificial versions made of wire-mesh (Mtobesya, 2012). The traps were286

deployed in the same manner as with the traditional model and found to be superior in their287

catching ability. Also, wire-mesh traps with 3 entrance holes caught more birds than those288with 1 or 2 holes and all of the wire mesh versions caught more than traditional grass basket

289

traps, with peak catches of all traps between 0800 and 1000 hours and between 1500 and

290

1700 hours (Mtobesya, 2012).

291
292

2.2.3.4. Funnel traps

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Mitchell (1963) described how very large funnel traps could be used to trap pest birds such294

as red-winged blackbirds Agelaius phoeniceus, common grackles Quiscalus quiscala,295

common starlings Sturnus vulgaris and brown-headed cowbirds Molothrusater in the United

296

States of America by luring them in with very bright lights (five 1,000 W floodlights). In 101

297

operations, 672,000 birds were caught and the three best catches yielded 80,000 – 120,000

298

birds per night. Similarly, such methods have been used to capture common starlings Sturnus

299

vulgaris in Tunisia in stands of broad-leaved trees such as Eucalyptus, with up to 15,000300

caught per night (Elliott et al. 2014). Trials of large funnel traps with attractant strong light301

have been conducted in Tanzania but with limited success (Elliott et al., 2014).

302
303

2.2.3.5. Miscellaneous indigenous trapping methods

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Allan (1997) illustrated a variety of basket trap and the means to catch termites to bait it305

with. Other methods include stick and box traps for which a string is pulled to close the box

306

onto the birds eating bait below, sticky bird lime attached to branches and throwing sticks

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into the midst of a quelea flock.

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309

2.2.3.6. Mist nets

310

Mist nets are efficient means of catching flying birds but run the risk of catching non-target

311

birds too, which may be killed or injured if not removed quickly from the nets by trained

312

personnel. In a trial of mist-netting operations to catch quelea in Tanzania, nearly 4000 were313

caught in 5 days using an average of 18 mist-nets (12m long x 3m tall) per day. Although this314

total is minimal compared with the totals in pest flocks and is unlikely to be feasible except at

315

small colonies (<5ha), the villagers nevertheless reported that attacks on their crops did

316

decline during the catching (Elliott et al., 2014). If the method is used repeatedly near

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colonies with eggs rather than chicks, the birds may desert the colony. Mist nets can also be

318

used to catch birds at roosts and have been deployed in Tanzania.

319
320

2.2.3.7. Roost traps

321

Mtobesya (2012) modified the trap roost concept (see section 2.3.6. below) by devising a322“roost trap” consisting of netting that could be drawn over a rigid frame erected over a “trap323

roost” of Typha sp. grass. Once the birds had settled to roost the net was pulled over the roost324

trapping the birds which could then be chivvied into a funnel at one end for capture.

325

Approximately 10,000 quelea were caught per night during trials conducted in Tanzania but

326

the catch also included some non-target species although the majority of these were weaver

327

bird species that sometimes also damage crops (Mtobesya, 2012).

328
329

2.3. Cultural Control

330

2.3.1. Planting and harvest time manipulation

331

Elliott (1979) and Bullard and Gebrekidan (1989) drew attention to how crop damage by332

quelea can be minimised if the timings of planting and harvesting can be arranged such that333

the crop can be harvested when there are few or no quelea present. This method is apt when334

irrigation facilities are available. Thus in the lower Awash river valley in Ethiopia if irrigated335

sorghum is planted in September it can be harvested in December when quelea are absent

336(Bullard and Gebrekidan 1989). Similarly, irrigated rice can be timed for harvesting in mid-337

May to mid-June in parts of Chad and Cameroon when there are no quelea pests there (Elliott

3381979). Harvest time manipulation can also be achieved by growing early-maturing varieties339

of crops. Even if the latter do not completely escape attack they will be vulnerable for shorter

340

periods than conventional crops (Bullard and Gebrekidan 1989).

341

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2.3.2. Weeding343

It is important for farmers to keep their fields as weed-free as possible since quelea are344

attracted to weed seeds and may thus attack crops that they might otherwise ignore (Luder,345

1985, Rodenburg et al., 2014).

346
347

2.3.3. Alternative Crops

348

Crop substitution whereby a crop such as maize, which quelea birds do not attack, is349

planted instead of vulnerable crops such as millet or sorghum. As maize requires more water350

to thrive than do millet or sorghum, this measure will only succeed if there is adequate

351

rainfall or irrigation is possible. The socio-economic aspects of substituting for small grain352

crops and the movement away from winter wheat and barley in Zimbabwe due to quelea

353

attacks has been discussed by Mundy (2000). Other crops that are not attacked by quelea such354

as groundnuts could also be grown as substitutes.

355
356

2.3.4. Quelea resistant crops

357

Bullard and Gebrekidan (1989) described how plant breeders can produce crop cultivars

358

that have morphological or chemical characteristics that are unpalatable to quelea and Tarimo

359(2000) reported how bird resistance in sorghum is imparted by the cyanogenic glycoside360

known as dhurrin. However, unless the majority of farmers in an area plant resistant varieties361

the birds will simply move away from them to seek more palatable cultivars nearby.

362

Furthermore, resistant varieties with high concentrations of tannins are less palatable to363

people than conventional varieties. Gressel (2008) described possibilities for a genetic

364

engineering approach to either (a) make sorghum varieties that produce dhurrin only in the365

developing seeds, thereby preventing livestock eating sorghum forage from being poisoned;366

and then have dhurrin completely self-destruct on maturity or (b) manipulate the morphology

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16
367

of the seed head such that seeds are more difficult to peck apart or less accessible. At present,368

these suggestions remain unrealistic and (a) would not benefit subsistence farmers much.

369
370

2.3.5. Protecting crops with netting

371

Allan (1997) described a variety of methods whereby nets were used to cover crops and372

thus prevent birds from attacking them and Elliott and Bright (2007) recommended covering373

rice fields with nets to reduce quelea damage in Nigeria. This was tested and found to be374

worthwhile, with damage varying from 0 to 4% with netting compared with 2.7 to 18.8 %375with bird scaring. Yields ranged from 565 to 1,448 kg.ha-1 with netting, but were 296 to

376

1,250 kg.ha-1 with bird scaring (Ajayi et al., 2007).

377

Allan (1997) illustrated how black cotton threads and metallic tapes can be deployed over378

crops to deter quelea birds. Such methods may be appropriate for commercial farmers or for379

small-scale cropping but the expense and labour needed to erect and maintain the systems

380

negates their value for subsistence farmers in general. There is also a tendency for quelea to381

become habituated to such methods and after a few days they may ignore them.

382
383

2.3.6. Trap roosts

384

As it is known that quelea often roost in stands of sugar cane Saccharum officinarum L.

385

and Napier grass Pennisetum purpurum Schumach., these crops have been deliberately sown386

to act as “trap roosts” (Jarvis and La Grange, 1989, Allan, 1997). After settling into roosts,387

the birds then presented a discrete target that could be easily controlled with avicide. Ideally,388

the roosts should be planted 100m x 100m, with tracks for access on each side. They should389

also be grown within a few hundred metres of water where the birds can drink before roosting390

and away from other thickets or similar vegetation that the birds could move to.

391

16

17
392

2.3.7. Scaring393

2.3.7.1. Scaring by humans

394

Bird-scaring methods were reviewed by Bashir (1989). These include visual techniques

395such as scarecrows, flag-waving and loud noises, created by elaborate systems of tins and396

rattles activated by pulling a connecting string or by cracking whips. In addition, missiles397

may be hurled at the birds or shot from catapults or mud is sometimes flicked at the pests

398

from the ends of sticks. All such methods are time-consuming, often conducted by children399

who are thus absent from schools, and may be effective locally but scared birds will move to400

other fields where there are no scaring activities. In Ogun State, Nigeria, scaring costs may

401

account for as much as 50% of production costs (Elliott and Bright, 2007).

402
403

2.3.7.2. Scaring with falcons

404

In Botswana, experiments have been conducted using lanner falcons (Falco biarmicus) to405

scare quelea away from sorghum crops in the Pandamatenga area (H. Modiakgotla, pers.

406

comm., Gaemengwe, 2014). The farmers there reported that the method gave good results

407

and they supported use of the method as it had led to good and high tonnages due to reduced

408

bird damage (H. Modiakgotla, pers. comm., Oct 2016). The latter was estimated as 12.1% of409sorghum heads damaged on average in 13 fields where falcons were not deployed, but was

410

about half this figure at 6.3% in 6 fields where the falcons were flown (H. Modiakgotla, pers.

411

comm.). However, use of falcons has only been tested in the commercial farms in the412

Pandamatenga area and has not been applied to protect crops grown by subsistence farmers.

413
414

[Table 1 near here]

415
416

2.3.7.3. Commercial bird-scaring devices

17

18
417

In Europe and elsewhere, machines that produce loud bangs at set intervals are available

418

commercially419

http://www.nomorebirds.co.uk/bangalore%2Dbird%2Dscarer%7E230) and it is also possible420

to purchase varieties that produce species-specific alarm calls or predator calls to scare bird421

pests (e.g. http://www.birdstop.co.uk/bio-acoustic_bird_scarers.asp). This approach was422

tested against quelea using Bird X-Pellers (http://www.bird-x.com/) by Garanito et al. (2000)

423

and trials with similar devices have been conducted at Pandamatenga in Botswana (H.

424

Modiakgotla, pers. comm.). However, such devices are expensive and the birds are likely to425

become habituated to them, as they will to other noises used for scaring such as drum beats426

and tractor horns. An additional possibility is to develop an unmanned aerial vehicle (UAV)427

or drone that can fly over quelea gatherings and scare them with appropriate noises or with428

predator-shaped machines. Two such devices have recently been developed for other bird429

pests (BirdX, 2016). Other novel methods include use of laser beams such as the Agrilaser,

430

either fixed or hand-held, to scare birds off crops (http://www.pestfix.co.uk/agrilaser-

431

autonomic-laser-bird-dispersal-system.asp). However, they have a limited range (approx

432600m) and are too expensive for use by subsistence farmers, but might be applicable in433

commercial farms.

forfarmers

(e.g.

the

Bangalore

bird-scarer,

434
435

2.4. Biological control

436

Barre (1974) reviewed the parasitology of Q. quelea to seek potential biological control

437

agents, but failed to identify any pathogen capable of causing an epizootic that might limit the438

bird’s populations. Barre recommended a worldwide survey of avian viruses occurring439

outside Africa and experimental checks to see if any were highly pathogenic to quelea.

440

Q. quelea are hosts to a variety of blood parasites (see Durrant et al., 2007 for surveys of441

some found in Q. q. lathamii), but none seem to cause morbidity. However, some taxa may

18

19
442

be species specific and, if so, there is a possibility that future progress in genetic

443

manipulation might allow the introduction of lethal forms of haematozoa.

444

Quelea are taken by a variety of predators (Thiollay, 1989) but these have a negligible

445

effect on the huge numbers of the pest birds, except occasionally when flocks of storks and446

birds of prey locate breeding colonies.

447

Quelea and their colonies have a sharp and distinct odour, quite unlike that of any other448

bird’s odour. Since many other species with acute olfactory abilities also have sharp odours,

449

this suggests that odour-based cues serve a communication function in quelea. Likely

450functions include acting as either a group-specific identification mechanism and/or as a451

colony- or roost-locating mechanism for either new entrants to colonies, or roosts, and birds

452

returning to their nests or roosts after foraging. In an attempt to identify any biologically453

active odours that might show promise as attractants to traps or as repellents, samples from454

birds of the nominate race Q. q. quelea were analysed but no compounds of interest were455

found (R. A. Cheke, D. R. Hall and D. Farman, unpublished data). Samples from other456

subspecies (Q. q. lathamii and Q. q. intermedia) were also analysed but again no promising457

compounds were detected. However, none of these samples were from actively breeding458

birds, which should be the subject of future research on this topic.

459

Feral pigeons (Columba livia) can now be controlled by using nicarbazin as a

460

contraceptive, dispensed in maize mixtures (Albonetti et al., 2015), but unless places where461

only Q. quelea would be feeding this method would pose dangers to non-target birds.

462
463

3.

464

preventive control approach

Comparison of red-billed quelea control methods with the desert locust

465

Control of quelea is only advised when the birds are posing a direct threat to a crop (Ward466

1972, 1973, 1979). The mere presence of the bird does not justify lethal control as they are

19

20
467

often innocuous, especially when their preferred grass food is plentiful. Thus, strategies for

468

dealing with the birds differ markedly from the “preventive control” approach (FAO 2001,

469

van Huis et al., 2007, Magor et al., 2008) applied to other migrant pests such as the desert

470

locust (Schistocerca gregaria), and the “strategic control” policy for control of the African

471

armyworm (Spodoptera exempta) (Rose et al., 2000, Cheke and Tucker, 1997). For locusts

472

and armyworm, control strategies require “off the crop monitoring” and lethal control as soon473

as the pest’s populations rise. In this way, if all proceeds according to plan, the pest’s474

population is prevented from reaching numbers high enough to cause severe damage to crops.

475

Also, locusts and armyworm are remarkable insofar as they change “phase” from the476solitarious state to the gregarious condition, a change associated with accelerating population

477

growth (Cheke, 1978, 1995) that does not occur in birds. One of the aims of the strategic

478

approach to locust and armyworm control is to ensure that the pests do not succeed in

479changing phase to become gregarious and swarm.

480

Elliott (2000a) pointed out that FAO’s approach to quelea control was to adopt Integrated

481

Pest Management (IPM) approaches whenever possible and only to use lethal control as a last482

resort. IPM approaches include many of the options listed above such as “modifying crop483

husbandry, planting time, weed reduction, crop substitution, bird scaring, exclusion netting

484

etc.” Elliott (2000b), in discussing management practices prevalent at the time in Eastern and

485

Southern Africa, also emphasised that economic constraints and the environmental impact of486

pesticides were leading to consideration of more sustainable IPM approaches.

487
488

4.

489

4.1. Forecasting and control planning

Recommendations for quelea control minimising the extent of fenthion use

490

Quelea breeding colonies are often not located in time to control them before the fledgling

491

birds, the juveniles responsible for much of the crop damage at this stage in the birds’ life

20

21
492

cycles, have left their nests. Similarly, if birds which are attacking crops can breed493

successfully then the populations available to attack crops will be augmented. However, if the494

efficiency of control operations could be improved, then the quantities of fenthion used could

495

be reduced. One way of improving the efficiency of control strategies is to detect the496

presence of suitable quelea breeding areas by satellite imagery (Wallin et al., 1992) or to497

forecast where the birds are likely to breed. Given that the birds’ migrations and breeding

498

opportunities are determined by patterns of rainfall (Ward, 1971), it is possible to devise499

forecasting systems to predict where the birds are likely to breed and, thus, to concentrate500

activities in search of the colonies to areas where the birds are likely to be for control

501

purposes (Cheke et al., 2007). A scheme based on the model described by Cheke et al. (2007)

502

that used satellite-derived rainfall data and knowledge of the threshold amounts of rainfall

503

needed to (a) initiate the migrations at the start of seasons (“early rains migrations”) and (b)504

to permit the birds to breed was maintained online as a forecasting system from 2001 to 2009,505

but fell into disuse when the funding for it ceased. That system was for southern Africa only,506

dealing with populations of Q. q. lathamii, but it is possible to develop a similar system for a507

pan-African set of forecasts and a prototype model for East Africa was developed (J. Venn

508

and R. A. Cheke, unpublished, Mtobesya, 2012). Regrettably, no system of forecasting where509

quelea roosts will appear in dry seasons has been devised, other than a recommendation to510

survey sites known to be traditional insofar as they are used regularly year after year.

511
512

4.2. Fenthion dosages

513

There is marked variation in the dosages used by different control organisations. For

514

instance at a workshop in Machakos, Kenya during May 2005, it was reported that Sudan

515

controlled their birds successfully at rates of 1 l.ha-1 (occasionally only 0.5 l.ha-1), DLCO-EA

516

usually used 2-4 l.ha-1 but South Africa reported use of dosages ranging from 7 l.ha-1 up to as

21

22
517

high as 14 l.ha-1. Clearly, less fenthion will be used if the dosage is minimised, with 2-4 l.ha-1

518

recommended. Amounts used by Tanzania during the 2012-2016 period were mostly within519

this range and were generally lower in the later years (Table 2), a difference which was

520

significant for the roosts (ANOVA, p < 0.0001) so an encouraging trend of gradual dosage

521

reductions was achieved. Interestingly the dosages sprayed on colonies (sample mean 2.66)

522

were consistently and significantly less than those deposited on roosts (sample mean 3.51;

523

Welch two sample t test, t = 8.82, d.f. = 171, p < 0.0001), so if this result is also true524

elsewhere other control teams could probably minimise potential environmental damage by

525

reducing dosages sprayed on roosts to the levels used on colonies without affecting control

526

rates.

527
528
529
530

[Table 2 near here]

531

4.3. Fenthion application methods

532

Studies of environmental effects of fenthion applications revealed that in some cases

533

sprays were conducted incorrectly with regard to speeds and directions of movements of534

ground-sprayers in relation to wind directions, failing to cease sprays when turning vehicles,

535

incorrect nozzle positioning, equipment maintenance and missed targets during aerial

536

applications (Cheke et al., 2013). Therefore regular training and supervision of pest control

537

workers is recommended, as is correct use of equipment to minimise excessive contamination

538

of the environment and risks to personnel. Furthermore use of the most appropriate

539

equipment may reduce quantities of fenthion needed. For instance, in Tanzania use of540

ground-based sprays with Micronair AU8000 sprayers required 10% of the volume used by541

aircraft (B. Mtobesya, pers. comm., October 2016). Training of farmers in quelea biology and542

IPM principles for damage avoidance and minimisation through farmer field schools is543

advised. Spray operators also need to know what to do in the case of accidental
22

23
544

contamination, which involves washing any affected area immediately with soap and water545

and discontinuing any further operations until the cause of the contamination has been546

corrected.

547

The use of unmanned aerial vehicles (drones) for spraying operations would ensure548

accurate targeting but to date the size of maximum possible payloads has precluded their use.

549

Recent developments have succeeded in increasing payload possibilities up to 80 litres (E.

550

van der Walt, pers. comm., Nov. 2016) so in future this technique may become usable.

551
552

5.

553

control using selected methods of control

Recommendations for quelea control without fenthion: a strategy for bird

554
555

The appropriate control measure to be adopted against quelea will vary depending upon the556

circumstances (Table 1). Most of the IPM measures described above will seldom be effective

557

on their own, except at scales when infestations are small relative to massive swarms of558

millions of birds or huge breeding colonies: one colony in March 1998 at Malilangwe in559

Zimbabwe was 20km long and 1km wide, with nests at densities of 30,000 nests per hectare

560(Dallimer, 2000). Ideally, an economic cost-benefit analysis should be made prior to each561

control operation as the overall objective is to find the optimal level of pesticide use, taking

562

into account the availability of non-pesticide alternatives and even compensation for crop

563

losses. As proposed by Agne et al. (1995), an economic assessment of pesticide use needs to564

be considered within a framework that covers both the farmer’s and society’s points-of-view.

565

Thus, the farmer would be expected to maximise expected net returns, with gross returns

566

from control equal to prevented crop losses in monetary terms. In contrast, the aim of society

567

in deciding how much pesticide or explosives to apply is to maximise net social benefit,

568

taking into account negative externalities such as environmental contamination and health.

23

24
569

However, by combining judicious planning of crop choice and of planting and harvesting

570

times before any expected quelea arrivals with environmentally benign control methods, the571

cultural control and IPM strategy will succeed under some circumstances. Nevertheless,572

faced with crop raids by huge quelea flocks, farmers and those in their country responsible

573

for the control will have little choice other than to authorise lethal control with pesticides

574(cyanophos or other alternatives to fenthion) or explosives. The scheme outlined in Figure 1

575

is an attempt to provide guidelines on how to minimise chemical use and their unintended576

effects, together with suggestions on the circumstances under which alternative methods

577

would be appropriate within the context of subsistence agriculture rather than commercial

578

operations.

24

Table 1. Summary information on alternatives to use of fenthion for quelea control.

MethodApplication

Mode of action

Advantages

Disadvantages

Socio-economic issues

Lethalorganophosphate
avicide.

Less toxic thanHigh risk of environmental
fenthion. Colonies and impacts. (Mullié et al.,roosts of any size can 1999, Cheke et al., 2013)
be treated
Killing action takes longer
than fenthion, so could
lead to more secondary
poisoning than fenthion.
(Allan, 1997)

More expensive thanfenthion. (Fenthion costs
approx. US$10 per litre[www.yufull.com]).
Requires trained personnel
and expensive equipment,
e.g. applied byGovernment personnel orinternational control
agencies.

Minimal pollution.

Labour intensive.

Chemical Methods
Cyanophos

Spray

Alphachloralose

Narcotic
Immobilises
added to bait birds.
grain
or
water
(Garanito etal., 2000)

Risk to non-target birds.
Requires birds to be foundand killed.
Only possible for small
sites (< 5ha)

26

Mesurol(Bruggers 1989)

Sprayed onseed heads ofcrops orapplied asseeddressing.

Carbamatepesticide, active
ingredientmethiocarb.
Repellent. Deters
birds from crops.
(Allan, 1997)

Risk to non-target birds
Expensive. Approx.
and mammals. Highly
US$300 per litre. Labour
toxic to aquatic fauna.
intensive.
Now not recommended for
direct use on crops, only as
seed dressing. Now
banned by the EU.

Mechanical Methods
Explosions(Cheke et al.,2013)

Diesel/petroleum
firebombs
detonatedbeneathbirds.

LethalNo organophosphates
or aircraft involved.

Risk to non-target birds
and mammals.
Petroleum productresidues pollute soil.

Expensive. Requires
trained personnel andexpensive equipment, e.g.
applied by Government
personnel.

Vegetation damage.
Fire and security risks.
Only possible for small
sites (< 5ha)

Nest destruction
and chickharvesting(Bashir 1989,
Jaeger andElliott, 1989)

Human
Lethalintervention
with sticks onpoles orflame
throwers

No pollution.
Provides source ofprotein.

Labour intensive. Often
possible only on small
scale (colonies <10ha) but
see Pelham (1998).

Profits possible, if surplus
chicks sold as food or
livestock feed.

26

27

Trapping with
Chad or basket
traps or othertrapping
methods (Mullié
et al., 2000,
Mtobesya, 2012)

Humanintervention
with various
trap designs.

LethalTrapping withmist nets (Elliott
et al., 2014)

Humanintervention
with various
trap designs.

LethalRoost traps(Jarvis and La
Grange, 1989,
Allan, 1997,
Mtobesya,2012).

No pollution.
Provides source ofprotein.

No pollution.
Provides source ofprotein.

Labour intensive. Often
possible only on small
scale (areas <10ha).

Profits possible, if surplus
birds sold as food or
livestock feed, e.g. annual
value of US$50,000 to
100,000 in Chad (Mullié
et al., 2000).

Labour intensive. Often
possible only on small
scale (areas <10ha).

Profits possible, if surplus
birds sold as food or
livestock feed.

Needs supervision to avoid Locally sourced nets at
non-target mortalities.
cost of only US$5 each.

Planting of
Lethalfodder crops
to attract
birds to roost,
followed byspraying.

High risk of environmental Loss of area where crops
impacts.
could be planted.
Possible only on small
scale (areas <10ha).

Cultural Methods
Planting andharvest datemanipulation(Elliott, 1979,

Planting of
fast-maturingcrop varieties
or early

Avoidance ofquelea attacks oncrops.

No pollution.
Can be done on large
scale

Not always possible.
Requires knowledge of
likely quelea movements
into and out of cropped

Agronomic advice needed.

27

28

Bullard andGebrekidan
1989)

harvesting tominimise riskof quelea at
harvest.

zone.
Alternative crops may notflourish in zone, especiallyin very arid areas.

Planting ofcrops that arenotsusceptible toattacks.
Netting crops(Elliott &Bright, 2007)

Covering
crops withnetting

Protective

No pollution.

Only on small scale. May
just divert birds to crops
with no netting present.

Expenditure on nets andpoles or gantry to rig themon

Scaring bypeople (Bashir,
1989)

Farmers andtheir children
scare birds

Birds frightenedaway from crops
by waving andnoise.

No pollution.

Labour intensive. Often
Prevents children
possible only on small
attending school. Labour
scale. May just divert birds intensive.
to crops with no scarers
present.

Scaring with
falcons(Gaemengwe,
2014)

Release ofBirds frightened
falcons nearaway from crops.
quelea flocks.

No pollution.

Requires trained birds andbird handlers. May justmove quelea to fields
where falcons not
deployed.

So far only used by large
scale commercial farmers
not by subsistence farmers.

Biological Methods
No successful biological control
28

29

agents identified to date.

29

30

Table 2. Dosages of fenthion (litres.ha-1) sprayed on quelea roosts and colonies in Tanzania
during the 2012-2016 seasons. Means and standard deviations calculated from raw data on
spraying operations reported by Mutahiwa (2016). n = sample size; SD = standard deviation.
Year

2012

2013

2014

2015

2016

4.79

4.03

4.20

2.72

2.98

n, SD

21, 3.95

12, 2.50

10, 2.85

30, 0.56

31, 1.92

Range

1.25 – 15

1.5 – 101.67 – 10

2.22 – 4.76

0.55 – 10

1.63

3.02

3.08

2.5

2.47

n, SD

11, 0.76

10, 2.92

33, 1.82

1, -31, 1.92

Range

0.67 – 3.33

1.43 – 11.11

0.73 – 10-

0.62 – 10

RoostsMean litres.ha-1

Colonies
Mean litres.ha-1

30

31

Figure 1. Flow diagram of decisions for planning quelea control by responsible authorities for
subsistence farmers.

31

32

Disclaimer
The views expressed in this information product are those of the authors and do not necessaryreflect the views or policies of FAO.

Acknowledgements
We are grateful to Hendrick Modiakgotla, Boaz Mtobesya, Etienne van der Walt and the late
Dr Clive Elliott for information and the latter for comments on an earlier draft. We thank Dr
Stephen Young for statistical help and the Rotterdam Convention Secretariat in FAO for
funding the preparation of this report. We are also grateful to Christine Fuell and Elisabetta
Tagliati of the Secretariat’s staff and to two anonymous referees for comments on an earlier
draft.

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