Life history of the oligochaete Enchytraeus coronatus (Annelida, Enchytraeidae) in agar culture

Abstract. Life-history attributes and the reproductive biology of Enchytraeus coronatus (Oligochaeta, Enchytraeidae) were studied in agar cultures, as a basis for using this species in toxicity tests and other experimental studies. The use of agar allows daily examination of the behavior, reproduction, and mortality of the worms. At 20°C, E. coronatus had a generation time of 21–22 days and an embryonic period of 7–10 days. Hatch rate was high (>80%) and worms became sexually mature 8–10 days after hatching. Cocoon production and number of eggs per cocoon were positively correlated. Mortality in the first stages of the life cycle (embryonic period and first week after hatching) was about 38%. Three different periods of cocoon production were distinguished: a period characterized by a regular increase in the number of cocoons produced (weeks 4–9), a period of production at a constant high rate of ∼5 cocoons per week (weeks 10–20), and a period of decline in production rate (weeks 21–32), down to a mean value of 1.6 cocoons per adult in the last week. This study showed that synchronized agar cultures of cohorts can provide adults for long-term experimental tests, with the age for optimum reproduction being 8–20 weeks.     

Biological studies upon Enchytraeus variatus Bouguenec & Giani 1987 in breeding cultures

The life history of an enchytraeid worm, Enchytraeus variatus, was studied under laboratory conditions at 18–22 °C. This species can reproduce simultaneously by asexual (architomy) or sexual reproduction. The number of ova per cocoon varies from 5 to 20 (x = 10.9). The generation period (from cocoon to next cocoon) varies from 14 to 39 days (x = 26.1) according to the period of the year. The number of generations per year is between 7.3 and 26.1 (x = 14). A mature worm can lay between 23.7 and 25.8 cocoons during its life (254 days as maximum observed) at a mean rate of 0.12 cocoon worm^–1 day^–1. Experimental cultures were carried out to determine the structure, density and biomass of the populations. A maximal density of 1 396 314 worms was recorded after 85 days of culture. Net production reached 21.48 g m^–2 day^–1 after 26 days in a culture initiated from cocoons.     

Effects of chronic gamma irradiation on reproduction in the earthworm Eisenia fetida (Oligochaeta)

Eisenia fetida were exposed continuously to (60)Co gamma radiation during two generations (F(0) and F(1)). Adult F(0) reproduction capacity (i.e., number of cocoons produced, hatchability and number of F(1) hatchlings) in controls and at five dose rates (0.18, 1.7, 4, 11 and 43 mGy/h) was measured over a 13-week exposure period. Survival, growth and sexual maturation of F(1) hatchlings were observed for 11 weeks. F(1) adults were exposed for a further 13 weeks to determine their reproduction capacity. There was no radiation-induced effect on the cocoon production rate in either F(0) or F(1). For F(0), hatchability of cocoons produced during the first 4 weeks was reduced to 60% at 43 mGy/h (98% in controls), and none of the cocoons produced at 5-13 weeks hatched. At 11 mGy/h the cocoon hatchability was reduced to 25% at 9-13 weeks. In addition, the number of hatchlings per hatched cocoon was reduced at 11 and 43 mGy/h. Correspondingly, at these dose rates, the total number of F(1) hatchlings per adult F(0) was significantly lower than in the control. This number was also reduced at 4 mGy/h, but the effect was of borderline significance. For adult F(1), the hatchability of cocoons at 11 mGy/h was reduced to 45-69% during the 13-week exposure period. The number of hatchlings (F(2)) per cocoon and the total number of F(2) individuals produced was also reduced. However, and in contrast to the results observed for F(0), hatchability increased with time, suggesting a possible acclimatization or adaptation of the F(1) individuals. In conclusion, chronic irradiation reduced the reproduction capacity of E. fetida, but extensive exposure periods (13 weeks) were needed for these effects to be expressed. The lowest dose rates at which an effect was observed were 4 mGy/h in F(0) and 11 mGy/h in F(1).     

Reproduction of Lumbricillus rivalis (Levinsen) in laboratory cultures and in decaying seaweed

The cocoon production of 144 Lumbricillus rivalis cultured in pairs at 10 ± 1 °C was high over the first 2 weeks of breeding activity and then declined, chiefly because of high mortality. Cocoon deposition lasted for between 1 and 16 weeks, eight pairs of worms producing cocoons for 9 weeks and one pair for 16 weeks. During the total period of cocoon deposition over 9000 eggs (mean 17·4 per cocoon) were deposited. Two decaying wrack bed populations of L. rivalis showed a low level of cocoon and egg production in autumn, rising to an annual maximum in late winter/early spring. In these populations the mean egg content varied seasonally from 17·1 to 47·8 eggs per cocoon. When cocoons in the laboratory were transferred from the site of deposition to incubation dishes 31% hatched, but those left in the substrate showed a 92% hatch. In the naturally occurring populations 19% of the cocoons detached from seaweed fronds hatched, but 62% of those left in situ. Eggs and worm embryos developed to relatively late stages in most cocoons, whatever the rate of hatching; development often continued for up to 2 months after deposition without hatching. Over 50% of the fertile eggs in cocoons from decaying wrack hatched and developed to 5 mm worms.     

Presence of Culturable Bacteria in Cocoons of the Earthworm Eisenia fetida

Viable bacteria were found to coexist with developing embryos in egg capsules (cocoons) of the earthworm Eisenia fetida. Earthworms were reared under standardized conditions, and bacterial densities were measured in distinct batches of cocoons collected weekly for 10 weeks. Cocoons weighing 12 mg contained a mean viable bacterial population of approximately 10⁸ CFU/g of cocoons. No difference was found in viable counts obtained from cocoons incubated at 15°C and cocoons incubated at 24°C. Viable bacterial numbers increased with cocoon age, while acridine orange direct counts of microbial cells were stable at approximately 10⁹ cells per g of cocoons. Bacteria isolated from cocoons were used to develop antisera in rabbits for the production of strain-specific fluorescent antibodies. Fluorescent antibody and selective plating techniques were used to monitor populations of these bacteria in earthworm bedding and to determine whether cocoons acquire bacteria from the environment in which they are formed. Cocoon isolates were readily recovered from cocoons formed in inoculated bedding at densities of 10⁸ CFU/g of cocoons. Bradyrhizobium japonicum USDA 110 and UMR 161 added to bedding were also recovered from cocoons, but at lower densities than cocoon isolates. Escherichia coli K-12(pJP4) inoculum was recovered from bedding but not from cocoons. The bacterial complement of Eisenia fetida cocoons is affected by inoculation of selected bacterial isolates in the worm growth environment.     

Studies on the Relationships Between Earthworms and Soil Fertility

The rate of cocoon production in British Lumbricidae differs considerably from species to species and is greatly affected by soil temperature, moisture and the food supply of the adult worms. Only two out of fourteen species studied frequently produced more than one worm per cocoon, and twins were only recorded once in many hundreds of observations on four species of the genus Lumbricus.
The incubation period of the cocoons and the growth period to sexual maturity varies from species to species and also depends on the time of year at which the cocoons are deposited and the young worms emerge.     

Seasonal population dynamics of Eisenia fetida (Savigny, 1826) (Oligochaeta, Lumbricidae) in the field

In order to assess the response of epigeic earthworms to seasonal changes we monitored the population dynamics of Eisenia fetida (Oligochaeta, Lumbricidae) in a manure heap in the field during a year. Earthworms were hand-sorted from five 0.25 x 0.25 x 0.20 m blocks around the heap in November (autumn) 1999 and in January (winter), April (spring) and August (summer) 2000 to determine earthworm population dynamics. Earthworms of each block were classified into different age classes: mature, preclitellate, juvenile, hatchling and cocoon, and afterwards counted and weighed. Seasonality had a strong effect on the density, biomass and reproductive activity of the population. The population of E. fetida was characterized by a high density of individuals and the predominance of mature individuals throughout the year. Maximum density, mating activity and size of cocoons were achieved in spring, but there were not changes in the number of cocoons per mature earthworm throughout the year. Unexpectedly, the smallest cocoons were produced in winter by the largest individuals. These results suggest that E. fetida is able to allocate resources to growth and/or reproduction in response to environmental fluctuations.     

Effects of host age and cocoon position on attack rate by the hyperparasitoid,Eurytoma sp. [Hym.: Eurytomidae], on cocoons of the parasitoid,Cotesia (=Apanteles) glomerata [Hym.: Braconidae]

Host age preference of the hyperparasitoid,Eurytoma sp., attacking the cocoons of the gregarious parasitoid wasp,Cotesia (=Apanteles) glomerata L., was investigated in the field and laboratory. Under laboratory conditions of 20°C and L16D8 photoperiod.Eurytoma sp. parasitized cocoons of all ages, laying 7 to 10 eggs per cluster during a 24 h period. Field-collected cocoons also indicated that the host was parasitized regardless of its developmental stage. However, the mortality ofEurytoma sp. laid in cocoons on the day before host emergence was as high as 60%. Furthermore, progeny sex ratio (proportion males) reached 0.708 in eggs laid in the oldest cocoon clusters, whereas that for younger cocoons was strongly female-biased. Together, these facts suggest that older hosts are less suitable forEurytoma sp. than are younger ones, even though there was no significant decreasing tendency in the number of parasitized cocoons per cluster. In addition, the effect of cocoon position within a cluster was apparent, outer cocoons being more easily parasitized than inner ones. TheEurytoma sp. female oviposited at random on the free surface ofC. glomerata cocoons.     

Spatio-temporal analysis of the population dynamics of the oriental moth,Monema flavescens (Lepidoptera: Limacodidae)

The comparative analysis of life tables of the oriental moth, Monema flavescens, obtained in 6 patches for 8 generations in 4 years revealed the following:

1. The ratio of maximum to minimum of cocoon density for each patch ranged from 5.34 to 22.50, each value being more than 3.20, the ratio for the whole study area.
2. The density change from adult to cocoon in the next generation caused most of the spatial variation in density change per patch. The rate of adult-to-cocoon population change showed spatial density dependence in some generations but not in others. When the change rate lacked spatial density dependence, it was the key-factor for spatial variation in adult density for the following few generations till the change rate recovered spatial density dependence. This was because of flooding, which killed the spatial density dependence existing potentially in the adult-to-cocoon change rate and damaged the same patches during the few successive generations.
3. The rate of population change from overwintered generation adults (summer ones) to first generation cocoons was not only the key-factor for the rate of throughout-the-year change but temporally density dependent in each patch. Therefore, the density for the whole study area is considered to fluctuate within a range. However, the strong equilibrium seen in the cocoon density for the whole study area was due to the floods that happened to occur when the density was near and at its maximum, and it is considered that such a strong equilibrium does not always occur.
4. In the population change from summer adults to first generation cocoons, temporal density dependence was found in all the patches, but it was found only in one patch in the population change from autumn adults to second generation cocoons. This was because the spatial density dependence seen in the former corresponded to the absolute density of adults, while that in the latter corresponded to the relative density.

     

体重、年龄和应激刺激对菲牛蛭繁殖性能的影响

采用单因素方差分析等方法探讨人工养殖条件下体重、年龄和环境应激对菲牛蛭繁殖性能的影响。结果表明,体重对卵茧大小和湿质量及幼蛭体长、体宽和湿体质量无显著影响(P>0.05),而亲蛭性腺系数、平均产茧数、孵化率和平均孵化数在各组间差异显著(P<0.05),其中体重10～15g组明显高于其他组(P<0.05);年龄对亲蛭平均产茧数、孵化率、平均孵化数和卵茧大小影响显著(P<0.05),其中2～3年龄亲本具有最高的平均产茧数、孵化率和平均孵化数,8月龄亲本所产卵茧个体明显大于其他年龄组(P<0.05),而卵茧湿质量及幼蛭体长、体宽和湿体质量在各年龄组间均无显著差异(P>0.05)。环境应激对亲蛭的平均产茧数、孵化率和平均孵化数影响显著(P<0.01),其中1～2次操作应激下的平均产茧数和孵化数最高,无操作刺激下的孵化率略高于1～2次操作刺激(P>0.05),而卵茧大小和湿质量及幼蛭体长、体宽和湿体质量在各应激处理组间无显著差异(P>0.05)。本研究获得了菲牛蛭繁殖的最佳体重和年龄,建议繁育生产中挑选10～15g和2～3年龄的个体作为亲本,期间进行1～2次操作刺激可提高其繁殖性能。     

The effects of feeding regime on the growth and reproduction of the medicinal leech Hirudo medicinalis

1. The feeding frequency, the size of meals, the number of meals required to attain reproductive maturity and the number of meals taken between iteroparous reproductive bouts were determined in the laboratory under optimal conditions for the medicinal leech Hirudo medicinalis fed exclusively on mammalian (bovine) blood. In addition the number of bouts of reproduction and the numbers of cocoons and hatchlings per cocoon produced were determined.
2. The average time for H. medicinalis to reach reproductive maturity at 20°C was 289 days, at an average wet biomass of 8143 mg with two–nine separate bouts of cocoon production. The number of meals to first reproduction was 8.9 (mean meal size of 3066.7 mg), with a significant correlation between total mass of blood ingested and the numbers of reproductive bouts and number of cocoons produced. Mean lifetime cocoon production per individual was 12.43, with 3.9 hatchlings per cocoon.
3. The significant positive relationships between ingestion, fecundity and developmental rate observed support the hypothesis that declining abundances of field populations of H. medicinalis are the result of lower available energy for growth, reflecting leeches now feeding predominantly on amphibian blood of lower energetic value than mammalian blood.     

The effects of feeding regime on the growth and reproduction of the medicinal leech Hirudo medicinalis

1. The feeding frequency, the size of meals, the number of meals required to attain reproductive maturity and the number of meals taken between iteroparous reproductive bouts were determined in the laboratory under optimal conditions for the medicinal leech Hirudo medicinalis fed exclusively on mammalian (bovine) blood. In addition the number of bouts of reproduction and the numbers of cocoons and hatchlings per cocoon produced were determined.
2. The average time for H. medicinalis to reach reproductive maturity at 20°C was 289 days, at an average wet biomass of 8143 mg with two–nine separate bouts of cocoon production. The number of meals to first reproduction was 8.9 (mean meal size of 3066.7 mg), with a significant correlation between total mass of blood ingested and the numbers of reproductive bouts and number of cocoons produced. Mean lifetime cocoon production per individual was 12.43, with 3.9 hatchlings per cocoon.
3. The significant positive relationships between ingestion, fecundity and developmental rate observed support the hypothesis that declining abundances of field populations of H. medicinalis are the result of lower available energy for growth, reflecting leeches now feeding predominantly on amphibian blood of lower energetic value than mammalian blood.     

Vermicomposting of cattle and goat manures by Eisenia foetida and their growth and reproduction performance

Vermicomposting is commonly adopted for the treatment of livestock organic wastes. In the present study, two types of livestock manure were used for culturing of the earthworm, Eisenia foetida. Each treatment group consisted of six replicates and worm vermicasts were examined after 5 weeks. The concentrations of total C, P and K in goat manure vermicasts were higher than those in cattle manure vermicasts. Cattle vermicasts had a higher N content than goat vermicasts but the C:N ratio of fresh manure was higher than that of vermicasts for both materials. Earthworm biomass and reproductive performance, in terms of number of worms after 5 weeks of experiment, were higher in cattle manure than in goat manure. The cocoon production per worm in cattle manure was higher than in goat manure. However, the hatchability of cocoons was not affected by manure treatments. In conclusion, cattle manure provided a more nutritious and friendly environment to the earthworms than goat manure.     

Artificial Food for Oak-Silkworm Raising

Oak-silkworms (Anthereae pernyi) were reared from hatching to the adult stage on a diet consisting of powder of dry leaves of oak trees (Quercus dentata T.), ‘kinako’ (powder of parched soy bean), sucrose, agar-agar, sodium dehydroacetate as an antiseptic, and water. Among 100 newly hatched oak-silkworms reared on the diet, 23 spun their cocoons. The weight of the cocoon fibres spun by one worm and the number of the eggs laid down by one moth were 0.34 g and 203, respectively, on the average.     

Growth and body weight of European hares in southern Sweden

Body weight and growth of European hares Lepus europaeus Pallas in relation to environmental conditions, population density, age, sex, and reproduction were studied in three populations in southern Sweden on the basis of hares shot during October-December. There were no significant differences in mean body weight of juveniles in the three areas. Differences in juvenile growth, as indicated by the correlation between eye lens weight (age indicator) and body weight, between areas and years were related to variations in nutrient conditions, in an island population it was probably also related to population density. Adult body weights did not differ between two mainland areas despite differences in food supply and population density, whereas island adult hares were, on average, significantly lighter than mainland hares. Also this difference was ascribed to nutrient conditions and/or population density. There were no significant differences in body weight between adult hares of different age classes. But reproductive females showed a significant positive correlation between number of litters produced annually and body weight. This relation indicates that reproduction is favoured by large body size and body weight, which also might explain the average higher mean body weight in females than in males. Juvenile hares showed no clear tendency in sex dimorphism of body weight.     

Role of a parasitoid with a low fecundity,Praestochrysis shanghaiensis (Hymenoptera: Chrysididae), in the population dynamics of its host

1. Analysis of life tables of the oriental moth, Monema flavescens, obtained for 8 generations over 4 years, disclosed that the cocoon parasitoid, Praestochrysis shanghaiensis, acted as a density-disruptive factor.
2. The density of the host cocoon remained stable (max./min.=3.2), whereas that of the host adult varied (max./min.=14.3) although both showed similar fluctation patterns.
3. Stability of the host population was associated with the density-dependence in the ratio of first generation cocoons to overwintered generation moths, which was the key factor for the rate of change throughout the year. Chrysidid parasitism among the first generation cocoons ranged from 37.7 to 70.1%, and that among the second generation cocoons from 16.7 to 63.2%, each showing an inverse density-dependence and acting as the main determinant (key-factor) of the between-year variation in the density of the adult moths.
4. The density-dependence of the rate of change from overwintered generation adults to first generation cocoons was so strong that the parasitism on the second generation hosts had not effect on the cocoon density of the first generation. On the other hand, the density-dependence of the rate of change from first generation adults to second generation cocoons was weak, and the parasitism on the first generation hosts became the key factor for the between-year variation of the second generation cocoons.
5. It is suggested that the stability of the parasitoid-host system will be disrupted without three parasitism-restricting factors: asynchrony in the parasitoid attack on the second generation hosts, high mortality among parasitoid larvae of the second generation, and the high proportion of those first generation parasitoids that enter diapause. These factors are considered to be effective only in cooler parts of the distribution of the parasitoid.

     

Intraspecific and Interspecific Competition Between Cotesia flavipes and Cotesia sesamiae (Hymenoptera: Braconidae), Gregarious Larval Endoparasitoids of Lepidopteran Stemborers

Super and multiple parasitism of Chilo partellus (Lepidoptera: Pyralidae) and Sesamia calamistis (Lepidoptera: Noctuidae) by Cotesia flavipes Cameron and Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) were investigated in the laboratory. Progeny production of Co. flavipes increased as a result of increasing the number of ovipositions, from one to three per one Ch. partellus host larva, then decreased as a result of four and five ovipositions per larva. Cocoon weight, sex ratio and emergence of the parasitoid progeny were not affected by superparasitism. Low progeny production of Co. sesamiae and poor survival of Ch. partellus host larvae were found as a result of superparasitism. When S. calamistis was the host, the duration of immature stages of Co. flavipes , parasitoid emergence, progeny production and sex ratio were not affected by superparasitism, but cocoon weight, adult longevity and the potential fecundity of adult females decreased. Superparasitism of S. calamistis by Co. sesamiae did not affect emergence, longevity or sex ratio of adult progeny of the parasitoid, but prolonged immature development, lowered cocoon weight and decreased potential fecundity of adult female progeny. Co. flavipes out-competed Co. sesamiae when Ch. partellus was parasitized by both species. The potential for local displacement of Co. sesamiae by Co. flavipes in areas dominated by Ch. partellus in East Africa is discussed.     

Laboratory studies on the life-histories of four enchytraeid worms (Oligochaeta) which inhabit sewage percolating filters

The life-histories of four enchytraeid worms, Lumbricillus rivalis, Enchy-traeus coronatus, E. buchholzi, and E. albidus which occur in sewage percolating filters, were studied under laboratory conditions at 8 , 15 and 20°C. The number of ova per cocoon varied from 0 to 50 (L. rivalis), 0 to 33 (E. coronatus), 1 to 9 (E. buchholzi) and 0 to 22 (E. albidus). The mean number of ova per cocoon was highest at 15°C for all species except E. coronatus which had a highest mean value at 8°C. The number of ova in cocoons was correlated with cocoon length (P < 0.001) for all species. Cocoon production usually increased with temperature ranging from 0.8 cocoons per adult per week at 8°C to 2.0 at 20°C for L. rivalis, and from 1–4 to about 2.6 for E. coronatus and E. buchholzi. The total number of ova produced by each E. coronatus (350 at 8°C to 550 at 20°C) was similar to that produced by each L. rivalis (600 at 8°C to 350 at 20°C) and was about five times greater than the total numbers produced by the other two species. Cocoon and ova production and the number of ova per cocoon varied with the age of the adult, usually reaching a peak soon after maturity. Hatching success was low and generally 40–50 % of ova failed to develop; subsequent mortality among immature worms was about 10–20%. Growth was more rapid at the higher temperatures; L. rivalis matured in about 26 days at 20°C, the clitellum forming when the worm was 13–14 mm long; data for the other species are 13 days and 5–6 mm (E. coronatus); 16 days and 3–4 mm (E. buchholzi); 28 days and 13–14 mm (E. albidus). The maturation period at 8°C was at least twice that at 20°C. The generation period (cocoon to cocoon) was about a month at 20°C for all species except E. albidus (2 months), but as some species had longer reproductive periods than others the actual number of generations per year was highest in E. buchholzi, 7.0 per year, and lowest in E. albidus, about 3.3 per year, At 8°C all four species had between 1.4 and 2.8 generations a year. A comparison of expected and observed population densities of L. rivalis and E. coronatus in a sewage percolating filter showed that neither achieved values approaching their potential summer densities although ample food was apparently available. Of the four species studied only E. buchholzi produced viable ova without pairing.     

Tghe tracheation of the wings of adult Lepidoptera

There is much variation in the extent of tracheation of the wings of adult Lepidoptera. This is surveyed. Significantly more tracheal branching is found in species with pupal cocoons. No correlation of tracheation with wing length is apparent. The concentrations of oxygen and carbon dioxide in the air inside cocoons of Antheraea pernyi Guér. (Saturniidae) before emergence are measured. Oxygen supply is probably not limited by the cocoon. Respiration rates per unit mass of wings of A. pernyi are similar to those of the whole, resting adult. The possible adaptive significance of this tracheation and its variation is discussed.     

The cocoon and hatchling of Nais variabilis (Naididae: Oligochaeta)

SUMMARY. 1. The cocoon of Nais variabilis is ovoid with an average length of 527.6±8.4 μm (95% CL) and an average breadth of 378.1±9.9 μm. The cocoon wall is about 7 μm thick and the average volume of the cocoon cavity is 0.035±0.002 mm³. Most cocoons contain one ovum; only single-ovum cocoons developed.
2. Cocoons hatch in about 80 days at room temperature (average 20°C. range 17–23°C). Hatchlings emerged posterior end first and were, on hatching, about one-third the adult live length of 8.5±10.3 mm.
3. It is estimated that adult Nais variabilis are unlikely to produce more than an average of ten cocoons each. Adults ceased asexual budding on becoming nature and died shortly after the completion of cocoon production. There was a brief co-existence of generations.