Compost Worm (Dendrobaena veneta)

## Source: tandfonline

The life-cycle of Dendrobaena veneta was studied to assess the potential of this species in vermicuhure. The

development, growth and reproduction were investigated by rearing worms at 25°C on urine-free cattle

manure with a moisture content of 80% over a period of 200 days. It was found that cocoons are produced at

a mean rate of 0,28 cocoons per worm per day and production can be sustained for at least 200 days. The

mean incubation period of the cocoons is 42,1 days with a very low hatching success. The mean number of

hatchlings per cocoon that hatched was 1, 1. Sexual maturity may be attained within 20 to 35 days but some

worms take up to 130 days. Dendrobaena veneta grew well on cattle manure. This species seems to be less

suitable than some other epigeic species for vermicuhure, at least in terms of its reproductive capacity in the

experimental climatic conditions.

Die lewensloop van Dendrobaena veneta is bestudeer ten einde vas te stel wat die potensiaal van hierdie

erdwurmspesie is vir sy benutting in vermikuhuur. Die ontwikkeling, groei en voortplanting is ondersoek deur

die wurms in 'n urienvrye beesmismedium met 'n voginhoud van 80%, by 25°C vir 200 dae te teel. Daar is

gevind dat kokonne teen 'n gemiddelde koers van 0,28 per wurm per dag geproduseer word en dat hierdie

produksie vir minstens 200 dae kan voortduur. Die gemiddelde inkubasieperiode van die kokonne is 42,1

dae met 'n baie swak uitbroeisukses. Die gemiddelde getal nakomelinge wat per kokon uitgebroei het, was

1,1. Volwassenheid word binne 20 tot 35 dae bereik maar sommige wurms het tot 130 dae geneem om

volwasse te word. Dendrobaena veneta het goed gegroei op die beesmismedium. lndien die voortplantings-

potensiaal van hierdie wurm met die van ander oppervlakvoeders vergelyk word, lyk dit egter asof dit nie so

'n groat potensiaal het vir vermikompostering as die ander spesies onder dieselfde omgewingstoestande nie.

• To whom correspondence should be addressed

With a rapidly expanding world population, and the grow-

ing use of intensive animal husbandry, the problem of waste

disposal has escalated. According to Hartenstein & Bisesi

(1989) it is important to manage animal wastes at minimal

cost, on minimal land, with minimal damage to the environ-

ment and with the production of a commodity from the

waste material. Earthworms are good candidates for fulfil-

ling these requirements (Loehr, Martin, Neuhauser & Ma-

lecki 1984) and the use of earthworm biotechnology for the

management of organic waste material is therefore receiving

increased attention from biologists and agriculturalists

(Graff 1974; Schulz & Graff 1977; Sabine 1983; Knierie-

men 1985; Haimi & Huhta 1986 ).

To achieve the best results with vermicultural enterprises

the correct species have to be selected. It is necessary to

investigate several species of earthworms, as environmental

conditions in different parts of the world vary. The optimal

requirements of species and their ability to handle different

wastes also vary (Knieriemen 1985; Loehr, Neuhauser &

Malecki 1985).

Dendrobaena veneta, an earthworm species from the

northern hemisphere, is one of the lesser known candidates

for vermiculture. After comparing the growth and cocoon

production of this species with that of four other candidates

for vermiculture, Loehr et a/. (1985) concluded that it does

not have a very high potential in this regard. Their work

was, however, done with a very small number of wonns on

a different type of substrate. Lofs-Holmin {1986) concluded

that this species does have potential to combat organic

waste problems. The complete life-cycle of D. veneta has

not been documented yet We therefore included this spe-

cies in a comprehensive investigation of earthworm species

with a potential for decomposing waste (Reinecke & Venter

1987; Venter & Reinecke 1988; Reinecke & Viljoen 1988;

Reinecke & Hallatt 1989; Viljoen & Reinecke 1989a;

Hallau, Reinecke & Viljoen 1990).

A fairly low mean temperature (- 15°C) is characteristic

of the natural habitat of D. veneta. To compare its potential

with that of other vermicomposting species that we have al-

ready investigated and also because of the promising results

obtained by Loehr et al. (1985) at 25°C, it was decided to

study the life-cycle of D. veneta at the same temperature

(25°C), and under the same conditions as were used for

Eiseniafetida (Venter & Reinecke 1988), Eudrilus eugeniae

(Viljoen & Reinecke 1989) and Perionyx excavatus {Hallatt,

Reinecke & Viljoen 1990).

Materials and Methods

The specimens of Dendrobaena veneta used during the

present study came from a stock maintained by Prof. 0.

Graff of Braunschweig, Germany. The experimental work

was conducted in an environmental control chamber at a

temperature of 25°C and a relative humidity of 80%.

A cattle manure medium, prepared from urine and straw-

free cattle droppings, was used as a substrate. It was sun-

dried, ground and sieved to a particle size of 500> <1000

J.Lm and wetted with distilled water to a moisture content of

75-80%. This medium was left to stabilize for at least 48 h

before the experimental animals were placed into it.

The worms ( = 55) were reared in groups of five or ten

in plastic containers with gauze lids. Fifty grams of the

stabilized culture medium per wonn was added when the

experiment was started. After 20 days an additional 2,5 g of

resh cattle manure per wonn was added; after 30 days a

further 10 g of fresh manure per worm was added and this

was repeated every 10 days until the end of the

experimental period. Some of the older substrate was

removed periodically to maintain the original volume of

substtate in each container as closely as possible. This was

deemed necessary to maintain a constant density-volume

ratio and to minimize possible effects of changes in this

factor.

The study was started with day-old hatchlings. The bio-

mass of each hatchling was determined before it was placed

in the medium and thereafter every five days up to the age

of 200 days, when the experiment was terminated. The bio-

mass was determined by removing the wonn from the sub-

strate, washing off all particles of medium, removing all

water from the surface of the wonn with tissue paper and

then weighing it in water in a weighing boat on a Sartorius

analytical balance.

At each weighing, clitellum development was assessed as

a measure of maturation. The containers were examined

regularly to observe the process of copulation.

Once clitellums began to develop the medium was

searched for cocoons every five days. Cocoons were coun-

ted and placed separately into multi-cell containers in the

same medium. These cocoons were incubated at 2S'C and

observed daily for hatchling emergence. The viability and

incubation period of the cocoons as well as the number of

offspring were determined in this way.

Resuhs

Growth

The growth rate of D. veneta over a period of 200 days is

illustrated in Figure 1. The mean biomass of newly hatched

wonns was 23,9 mg for 55 worms. Most of the worms

survived and grew well on the cattle manure substtate, but

at least one worm in ten did not gain weight and remained

much smaller than the rest during their whole life span.

None of these smaller worms reached maturity and some

did not survive the experimental period. The results

obtained for these worms were not used in the final

analysis.

The mean growth rate during the fll'St 30 days was slow,

about 7,6 mg per worm per day. Thereafter it increased

steadily up to a worm age of about 100 days, with a mean

growth rate of 19,4 mg per worm per day during this

period. After this period of fast biomass increase, growth

slowed to 9 mg per wonn per day between 100 and 140

days and then decreased still more, beginning to stabilize at

a mean biomass of about 2200 mg per wonn. The highest

biomass attained by an individual wonn was 3640 mg.

Maturation and copulation

The first indications of clite!!um development appeared

between Days 20 and 35. The worms were deemed sexually

mature when they had fully developed and swollen clitel-

lums. This was reached at Day 30 by some worms. One

hundred per cent maturation was attained after 130 days

(Figure 2 ).

Copulation was observed a number of times. In most

cases it occurred with the copulating wonns lying on the

surface of the substrate. A typical mucous band keeps the

two worms together during this process.

Cocoon production

The first cocoons were observed on Day 65 (Figure 3). In

the period between the first observation of maturation (i.e.

at about 30 days) and the beginning of cocoon production,

copulation was observed, but it can not be accurately stated

how long after copulation cocoon production commenced.

During the experimental period the rate of cocoon produc-

tion varied and cocoon production continued Lhrough to lhe

end of the experimental period of 200 days.

A peak cocoon production period occurred between Days

110 and 130, with a mean production rate of 0,4 cocoons

per wonn per day. Thereafter l.he production rate fluctuated

with the lowest production rate at 170 days, followed by an

increase to 0,43 cocoons per worm per day on Day 200.

Over the whole study period the mean production rate was

0,28 cocoons per worm per day.

It was noted that all the cocoons of D. veneta occur

within clumps of substrate (Figure 4a), and often more than

one cocoon can be found in the same clump. Ramisch &

Graff (1985) made extensive observations of the phenome-

non in Lumbricidae and concluded that the principal

importance lies in prOI.eCtion against Joss of water. The

cocoons are smooth and oval in shape with one end sharply

pointed and the other more blunL The colour of the cocoons

changed markedly with ageing, the freshly formed cocoons

Figure 4 4.1 Cocoon of D. ve~ta in a lump of substrate.

4.2 Micrograph of a cocoon of D. veneta.

having a light greenish yellow colour, changing to light

brown, reddish brown., dark brown and black, with age.

Cocoons in which embryos did not develop retained their

light colouring.

The cocoons are extremely fragile, making them difficult

46

to handle. The walls of the cocoons are thin, making it

possible to observe the development of the embryos and

young worms inside the cocoon, using a stereo microscope

(Figure 4b). Because of the fragility of the cocoons, weigh-

ing and measuring was not attempted and these parameters

were not used during the study.

Hatching success, incubation period and number of

offspring

Of the 643 cocoons incubated, a hatching success of only

19,6% was obtained at the constant temperature of 25°C.

The incubation period varied from 15 to 80 days with a

mean of 42,1 ± 1,03 days (Figure 5).

The number of hatchlings produced by all the cocoons

that hatched was 1,1 ± 0,05 hatchlings per cocoon. The

largest number of hatchlings to emerge from a single

cocoon was two (8%). Ninety-two per cent of the cocoons

produced only one hatchling (Figure 6). Upon emergence of

the hatchlings from the cocoon they had a pink colour and

the segments were well differentiated.

NUMBER OF HATCHLINGS/COCOON

Figure 6 Percentage occurrence of number of offspring of D.

veneta per cocoon. Mean number of hatchlings per cocoon =

1,1 ::!:: 0,05; n = 138.

Discussion

Growth

The population of D. veneta studied exhibited a typical

S.-Afr. Tydskr. Dierk. 1991, 26(1)

sigmoid growth pattern (Figure 1), indicating that the

environmental conditions were close to optimum and that

the duration of the study period was not too short for this

particular species. This growth pattern compares well with

that found by Loehr et al. (1985) but the growth rate was

higher in the latter case, with maximum biomass being

attained after 120 days, while the highest mean biomass

during our study was recorded on Day 200.

Loehr et al. (1985) however, used sludge as substrate and

they did not mention other environmental factors, except for

the temperature at which the growth study was conducted.

Earthworms grow differently on different substrates (Neu-

hauser, Kaplan, Malecki & Hartenstein 1980) and this

might explain the differences between the results of the two

studies. Although the influence of moisture on the growth

of D. veneta has not yet been studied, similar studies on

other earthworm species show that moisture availability has

a major influence on growth rate (Reinecke & Venter 1985;

Viljoen & Reinecke 1989b; Viljoen & Reinecke 1990).

Moisture availability during our experiment was probably

different from that in the study by Loehr et al. (1985) and

this could explain the differences in the results of the two

studies. It has been suggested that moisture could affect

food utilization by earthworms (Reinecke & Venter 1987)

and therefore influence growth.

The growth rate of D. veneta during the present study

compared favourably with that of the other vermicompost-

ing species E. fetida (Venter & Reinecke 1988) and P.

excavatus (Hallatt et al. 1990), but was somewhat lower

than that of E. eugeniae (Viljoen & Reinecke 1989a) on

the same substrate and under the same environmental con-

ditions.

Maturation

Reared under the conditions mentioned, the individual

worms varied considerably in the time needed to reach

maturity. The first indication of clitellum development was

at the age of 30 days and the last worms attained maturity

after 130 days although all were kept under the same

conditions and at the same densities. This differs from the

other vermicomposting species studied. All specimens of E.

eugeniae were mature after 45 days (Viljoen & Reinecke

1989a), 28 days were needed for maturation of P. excavatus

(Hallatt et al. 1990) and all specimens of E.fetida had well-

developed clitellums after 80 days (Venter & Reinecke

1988). Loehr et al. (1985) did not mention maturation in

their paper, but they -noted that D. veneta began to produce

cocoons only after 170 days, indicating that the worms

might have taken longer to reach maturity than in our study.

It has been shown that feeding status and the pattern of

feeding could influence the rate of maturation in

earthworms (Reinecke & Viljoen 1990).

Cocoon production

The mean rate of cocoon production, 0,28 cocoons per day,

was lower than that of some other epigeic earthworm

species. The maximum production of 0,43 cocoons per

worm per day was much lower than the 1,65 of E. eugeniae

(Viljoen & Reinecke 1989a), and the 1,1 of P. excavatus

(Hallatt et al. 1990), but compare favourably with the 0,35

of E.fetida (Venter & Reinecke 1988).

Although there were fluctuations in the cocoon produc-

tion rate, production was continuous after its commence-

ment on Day 65. During the study by Loehr et al. (1985)

cocoon production was also low, i.e 0,7 per worm per day,

with cocoons produced for the first time on Day 170.

Hatching

The very low hatching success of 19,6% obtained during

the present study cannot be explained readily and requires

further investigation. Apart from the direct role of the

substrate during incubation, low hatching success could also

be attributed to the fact that cocoons were incubated at

25°C. This temperature is much higher than the expected

optimum temperature for this species.

Loehr et al. (1985) obtained a very high hatching per-

centage (78%) but made no mention of the medium used

for the incubation of the cocoons. They incubated the

cocoons at 25°C. The number of hatchlings per cocoon that

hatched during their study was, however, the same as was

found during the present study, i.e. 1,1 hatchlings per

cocoon that hatched. This compares favourably with that of

P. excavatus but is much less than that of E. eugeniae and

E.fetida.

Life-cycle and vermicomposting potential

Our data show that D. veneta, in comparison with other

epigeic, vermicomposting species, has a fairly long life-

cycle when reared on a cattle manure substrate. This life-

cycle is presented diagrammatically in Figure 7.

The duration of the life-cycle described here will of

course be dependent on the various abiotic factors and on

the quality of the organic material used as feeding medium.

This worm species grew well at a temperature (25°C)

higher than that normally occurring in its natural habitat

(15°C). It is, however, possible that some reproductive

functions are affected by the higher temperatures,

explaining the lower hatching success and lower cocoon

65 doys

GROWTH

DURATION

manure with a moisture content of 75-80%.

47

production rate compared with the results of Loehr et al.

(1985).

Comparing the overall reproductive capacity and growth

with that of other detritus feeding species, D. veneta seems

to be less suitable for vermiculture at 25°C, in terms of its

reproductive rate and its ability to colonize organic waste,

but no account is taken of the species' activity in the sub-

strate or the rate at which the substrate is worked through.