IJERD – International Journal of Environmental and Rural Development (2017) 8-2

Research article
erd

Efficacy of the Entomopathogenic Fungus Nomuraea rileyi
in the Biological Control of Vegetable Pest Spodoptera litura(Lepidoptera: Noctuidae)
PATCHARIN KRUTMUANG
Department of Entomology and Plant Pathology, Faculty of Agriculture,
Chiang Mai University, Chiang Mai, Thailand

MALEE THUNGRABEAB*
Agricultural Technology Research Institute, Rajamangala University of Technology Lanna,
Lampang, Thailand
Email: sriwanmal@yahoo.com
Received 22 February 2016

Accepted 18 October 2017(*Corresponding Author)

Abstract Eight strains of the entomopathogenic of the fungus Nomuraea rileyi were screened
for control of the common cutworm, Spodoptera litura. The results showed that N. rileyi waspathogenic to S. litura, and that pathogenity significantly varied among the strains. The
mortalities ranged from 2.5 to 92.5% at 7 d after inoculation. The strains tested were classified
into three groups according to mortality percentage. High pathogenicity level was defined asa mortality greater than 75.79%, moderate pathogenicity was a mortality between 75.79 to49.50%, and low pathogenicity level less than 49.50% mortality. The high pathogenicity levelcontained two strains, BCC 14653 and BCC 14671, which were identified as highly virulent
and used in a secondary bioassay against various larval stages. Nomuraea rileyi could become
an important biopesticide agent in an integrated pest management program for insect pestcontrol.
Keywords Nomuraea rileyi, Spodoptera litura, Entomopathogenic Fungi,
Biological control

INTRODUCTION
The common cutworm, Spodoptera litura F (Lepidoptera: Noctuidae), is a highly polyphagous
migratory lepidopteran pest species. This insect is also known as the tobacco budworm, orientalleafworm moth, tropical armyworm, and taro caterpillar. It causes extensive losses in over 120
different plant species including many vegetables, fruits and ornamental crops. Some examples are:asparagus, beets, broccoli, cabbage, carrots, chrysanthemum, corn, cruciferous crops, eggplants,grapes, lettuce, orchid, potatoes, radish and sunflowers.
Insecticides for control S. litura have become ineffective because of the development ofresistance, and cause toxic residues in the crops.(Rajan and Muthukrishnan, 2009). Insecticide
resistance and the demand for reduced chemical inputs in agriculture have provided an impetus forthe development of alternative methods of pest control. Biological control offers an attractive
alternative or supplement to the use of chemical pesticides. Microbial control agents are naturally
occurring organisms and perceived as being less damaging to the environment. Furthermore, theirgenerally complex mode of action makes it unlikely that resistance could develop to a bio-pesticide.
Biological pest control agents include viruses, bacteria, fungi, and nematodes. The use ofmicroorganisms as selective pesticides has had some notable successes (Hong Wan, 2003).
Nomuraea rileyi is an important naturally-occurring, mortality-causing agent of many
lepidopterous pests in a variety of crop ecosystems throughout the world (Vimaladevi et al, 1996).
Natural occurrence of N. rileyi has been widely reported. N. rileyi has occurred in epizootics on
Spodoptera exiqua in black gram, S. litura in tobacco, Tricoplusia ni and Heliothis zeaⒸ ISERD

8IJERD – International Journal of Environmental and Rural Development (2017) 8-2(Srisukchayakul, 2005). Furthermore, its occurrence has been reported on Helivoverpa armigera intomato and on S. litura in soybean, potato and cabbage (Patill and Abhilash, 2014).
OBJECTIVES
The objective of this study was to determine the pathogenicity of Nomuraea rileyi strains on larvaeof Spodoptera litura under laboratory conditions.
METHODOLOGY
Insects
Spodoptera litura populations including egg masses, larvae and adults were collected from
cruciferous vegetable crop plantations in Chiang Mai, Thailand. All stages were maintained underlaboratory conditions. The pupae were kept and used as a stock to build up new colonies. The adults
were reared in cages and fed with a 5% honey solution.
Fungal Preparations and Pathogenicity
Nomuraea rileyi strains from adult insects in the order Lepidoptera collected in natural environmentsof Thailand were obtained from the BIOTEC Culture Collection (BCC), National Center for Genetic
Engineering and Biotechnology (BIOTEC), Pathum Thani, Thailand. (Table 1). The fungal strains
were cultured on SMAY (Sabouraud’s maltose agar medium supplemented with 1% yeast extract)in 90 mm Petri dishes and incubated for 12-15 d at 25±1°C (Fig. 1). Conidial suspensions wereprepared by scraping conidia from petri plates into an aqueous solution of 0.002% Tween 80. The
conidial suspension was filtered through several layers of cheesecloth to remove mycelial mats.
Viability of conidia was assessed by germination tests before preparation of suspensions. The
concentration of conidia in the final suspensions was determined using a hemocytometer. The
conidial suspension used for the bioassays was adjusted by diluting conidia with the Tween 80
solution to final concentrations of 6x107, 6x108 and 6x109 conidia/ml. To determine pathogenicity,each of the conidial suspensions were sprayed on larvae of different instars (I-III). Three replications
were used with 10 larvae per replication including a non-treated control. The larval mortality wasrecorded at 7 d after inoculation.
Table 1 Strains of the entomopathogenic fungus Nomuraea rileyi collected from Thailand
and used in pathogenicity tests against larvae of Spodoptera litura
NoStrain number

TNCC number:Fungus species

Host insect

12345678BCC 14653
BCC 14658
BCC 14659
BCC 14660
BCC 14670
BCC 14671
BCC 14672
BCC 14673

4522
4685
4686
4687
4327
4328
4329
4318

Nomuraea rileyi
Nomuraea rileyi
Nomuraea rileyi
Nomuraea rileyi
Nomuraea rileyi
Nomuraea rileyi
Nomuraea rileyi
Nomuraea rileyi

Lepidoptera - adult
Lepidoptera - adult
Lepidoptera - adult
Lepidoptera - adult
Lepidoptera - adult
Lepidoptera - adult
Lepidoptera - adult
Lepidoptera - adultⒸ ISERD

9IJERD – International Journal of Environmental and Rural Development (2017) 8-2

Fig. 1 Colony and conidial characteristics of Nomuraea rileyi
RESULTS AND DISCUSSION
The results showed that N. rileyi was pathogenic to Spodoptera litura; the cumulative mortalities
ranged from 0 to 92.5% at 7 days after inoculation (Table 2). The corrected mortalities significantlydiffered (P≤0.05) between strains (Fig. 2).
Table 2 Cumulative mortality of the entomopathogenic fungus Nomuraea rileyi on each instarof Spodoptera litura at 7 d after inoculation
Nomuraea rileyi(conidia/ml)
Strain 1
Strain 2
Strain 3
Strain 4
Strain 5
Strain 6
Strain 7
Strain 8Control

6x107
6x108
6x109
6x107
6x108
6x109
6x107
6x108
6x109
6x107
6x108
6x109
6x107
6x108
6x109
6x107
6x108
6x109
6x107
6x108
6x109
6x107
6x108
6x109

I instar% Mortality
II instar

82.5
85.0
92.5
35.0
30.0
37.5
2.5
2.5
0
7.5
10.0
5.0
47.5
40.0
40.0
87.5
92.5
92.5
47.5
35.0
50.0
7.5
17.5
17.5
0

72.5
77.5
92.5
20.0
30.0
32.5
7.5
2.5
0
10.0
25.0
22.5
30.0
25.0
25.0
77.5
87.5
80.0
32.5
15.0
10.0
17.5
7.5
10.0
0III instar
72.5
55.0
70.0
20.0
37.5
32.5
7.5
2.50
10.0
5.0
2.5
2.5
7.5
25.0
75.0
67.5
82.5
12.5
15.0
10.0
7.5
2.5
12.5
0

In support of the present investigation, Padanad and Krishnaraj, (2009) observed that all ten
isolates of N. rileyi were active against third instars of S. litura, resulting in 85 to 97% mortality.
Patil et al., (2014) stated that early instars were highly susceptible with a mortality of 70.17 percent,which decreased significantly as the age of the larvae advanced. However, there were statistically nosignificant differences among the strains with respect to the pathogenicity levels. The strains tested
could be classified into two groups according to mortality percentage (Table 3). Fungal strains BCCⒸ ISERD

10IJERD – International Journal of Environmental and Rural Development (2017) 8-2

14653 and BCC 1467 were identified as highly pathogenic and were used in the secondary bioassay
against various larval stages. The remaining strains were characterized as having low pathogenicity(Table 4).

% mortality
100aa8060b40bb20dbcBCC 3

BCC 4bc0
BCC 14653

BCC 2BCC 5

BCC 14671

BCC 7BCC 8Fig. 2 Percentages of corrected mortality of Spodoptera litura treated with different strains ofNomuraea riley at a concentration of 6x108 conidia/ml at 25 ±1oC
Table 3 Pathogenicity levels of different strains of Nomuraea rileyi toward Spodoptera litura as
expressed by percentage mortality
Pathogenicity level

Mortality (%)

Strain No.

High pathogenicity
Moderate pathogenicity
Low pathogenicity>75.7975.79 – 49.50<49.50

BCC 14653, BCC 14671
BCC 14658, BCC 14659, BCC 14660,BCC 14670, BCC 14672, BCC 14673

Table 4 shows the efficacy of two strains of Beauveria bassiana against various larval stages ofSpodoptera litura. All strains tested were effective against all larval stages of Spodoptera litura, but
the effectiveness varied with larval stage. There were significant differences (P≤ 0.05) among
different larval stages. No significant differences were found among concentrations.
Means in columns with different small letters indicate significant differences among different
concentrations of Nomuraea rileyi (one way ANOVA, P ≤ 0.05; Duncan’s multiple rang test). Meansin the same row followed by the different capital letters indicate significant differences between
instars of Spodoptera litura at P ≤ 0.05 (T- test).
Table 4 Efficacy of two strains of Nomuraea rileyi against various larval stages of Spodoptera
lituraStrains no.
BCC 14653
BCC 14671

Conc.
6x107
6x108
6x109
6x107
6x108
6x109

Corrected mortality of
1stinstar (%±SE)
82.5 ±5.77 bA
85.0±8.81 bA
92.5±3.33 aA
87.5±6.67 bA92.5±0.00 aA
92.5±5.77 aAⒸ ISERD

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Corrected mortality of
2ndinstar (%±SE)
72.5±3.33 bB
77. ±5.77 5 bB
92.5±5.77 aA
77.5±5.77 bB
87.5±8.81 aAB
80.0±5.77 abB

Corrected mortality of
3rd
instar (%±SE)
72.5±5.77 aB
55.0±8.81 bC
70.0±5.77 aB
75.0±5.77 abB
67.5±13.33 bBC
82.5±5.77 aB

IJERD – International Journal of Environmental and Rural Development (2017) 8-2

CONCLUSION
Research is needed to further characterize the use of Nomuraea rileyi as an effective biocontrol ofSpodoptera litura in vegetable crops. The results presented here suggest that some strains of thisfungus are effective in causing high mortality levels and (at sufficient dosages) could become animportant part of an integrated pest management program. Nomuraea rileyi treatment could be usefulin preventing the development of resistance if used in rotation with other effective therapeutic agents.
ACKNOWLEDGEMENTS
The authors would like to express their gratitude to the BIOTEC Culture Collection (BCC), National
Center for Genetic Engineering and Biotechnology (BIOTEC) Thailand for providing Nomuraearileyi. This study was supported by the Thailand Research Fund (TRF) and The Commission on
Higher Education (CHE).
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