土壤温度和湿度对外来种蚯蚓Pontoscolex corethrurus 产茧和幼蚓孵化的影响

通过采用主处理为土壤温度,副处理为土壤湿度的裂区区组实验设计,在室内微生态条件下控制土壤温度和湿度培养蚯蚓,探讨了3种土壤温、湿度对热带外来种蚯蚓Pontoscolex corethrurus成蚓产茧和蚓茧孵化的影响。研究结果表明,P.corethrurus成蚓在20—30℃土壤温度范围、25%—35%土壤湿度环境中均可持续产茧和孵化幼蚓,培养时间、土壤温湿度对蚯蚓的产茧和孵化呈现显著影响。20%土壤湿度下成蚓休眠或死亡。35%土壤湿度下呈现最大蚓茧产量和幼蚓孵化量。在较好(35%)土壤湿度下产茧数表现为高温好于低温,反之亦然;在适宜(25%—35%)土壤湿度下幼蚓孵化率随温度升高而增加,但呈现高、低温的限制作用,即25℃土壤温度和35%土壤湿度时出现最高幼蚓孵化率。在适宜的土壤温湿度范围内,湿度较温度对蚯蚓繁殖具有更显著的控制作用,温度的影响在一定程度上可通过土壤湿度加以调节。     

Growth,reproductive biology and life cycle of the vermicomposting earthworm, Perionyx ceylanensis Mich. (Oligochaeta: Megascolecidae)

In the present study, an attempt has been made to study the growth, reproduction and life cycle of the earthworm, Perionyx ceylanensis Mich. in cowdung for the period of 340 days. Results showed that the overall mean growth rate was 1.79, 1.57 and 1.34 mg/worm/day respectively for the worms cultured singly, in batches of four and eight. Cocoon production rate was found between 0.85 and 0.94 cocoons/worm/day and the hatching success between 74.67% and 82.67%. The majority of the cocoons (95.16–96.77%) hatched only one hatchling. Worms raised singly also produced viable cocoons indicating that P. ceylanensis reproduce parthenogenetically. The life cycle of the worms cultured singly was ±57 days and it was ±50 days for the worms cultured in batches of four and eight. There is a vast scope to utilize P. ceylanensis for vermiculture practices due to short period of life cycle.     

The role of spider cocoons in controlling desiccation

Summary The abilities of the cocoons of the spiders Mecynogea lemniscata and Argiope aurantia to protect the enclosed egg and spiderling stages from desiccation were investigated in the laboratory under controlled humidities, and in the field under ambient conditions. For M. lemniscata, which has a relatively small clutch (8–30 eggs) and remains in the cocoon for approximately 9–10 months, removal of the cocoon had no effect on water loss from the egg stage, nor did it adversely affect hatching or molting success. Cocoon removal did, however, significantly affect water loss and, consequently, survival in the spiderling stage at all humidities in the laboratory and in the field. The importance of the cocoon for survival is probably related to the unusually long time M. lemniscata spiderlings spend in the cocoon overwintering. For A. aurantia, which has a substantially larger clutch size (300–1400 eggs) and remains in the cocoon for a shorter 6–7 months, cocoon removal had no effect on water loss, egg hatching success, molting success, nor spiderling survival. The lack of an effect suggests that other factors (e.g., relative humidity at the oviposition site, or a large clutch size) may be more important in controlling water loss for A. aurantia.     

Susceptibility to insecticides of Glyptapanteles militaris (Hymenoptera: Braconidae), a Parasitoid of Pseudaletia unipuncta (Lepidoptera: Noctuidae)

The susceptibility of cocoons and adults of Glyptapanteles militaris (Walsh) were studied. One organophosphate insecticide (trichlorfon), one organochlorine insecticide (endosulfan), one pyrethroid (deltamethrin) and a commercial formulation of Bacillus thuringiensis subsp. Kurstaki were selected for testing. All the tests were carried out with fresh solutions of commercial insecticides applied on host larvae at the recommended concentration. One- and 6-day-old cocoons were sprayed with the insecticide solutions by means of a Potter Tower and held for adult emergence. Adults were exposed to residues of insecticides inside plastic vials. The B. thuringiensis formulation had no harmful effect on the cocoons nor on the adults. Trichlorfon and endosulfan were highly toxic to all the tested stages. Deltamethrin was highly toxic to adults but relatively safe when applied on parasitoid cocoons. Based on these results, field applications of deltamethrin would be least disruptive of tested insecticides to populations of G. militaris.