Furlong M J, Pell J K
Department of Entomology and Nematology, IACR-Rothamsted, Harpenden, Hertfordshire AL5 2JQ, United Kingdom.
J Invertebr Pathol. 2000 Aug;76(2):85-94. doi: 10.1006/jipa.2000.4943.
Zoophthora radicans (Zygomycetes: Entomophthorales), Diadegma semiclausum (Hymenoptera: Ichneumonidae), and Cotesia plutellae (Hymenoptera: Braconidae) are all natural enemies of the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae). Adult C. plutellae are not susceptible to Z. radicans infection but the pathogen can infect and kill adult D. semiclausum. Infection of adult D. semiclausum prior to exposure to P. xylostella host larvae significantly reduced the number of parasitoid cocoons subsequently developing from the host larvae. Although Z. radicans infection of P. xylostella larvae prior to parasitism by D. semiclausum or C. plutellae always resulted in the death of the immature parasitoids, neither species discriminated between healthy and Z. radicans-infected host larvae in an oviposition choice experiment. However, host larvae recently killed by Z. radicans were always rejected by D. semiclausum but sometimes accepted by C. plutellae. At 20 degrees C, egg to pupa development took 6.7 and 7.8 days for D. semiclausum and C. plutellae, respectively. C. plutellae parasitism significantly increased host instar duration but D. semiclausum parasitism did not. Cadavers of P. xylostella larvae parasitized 1 day prior to fungal infection showed no reduction in Z. radicans conidia yield. However, cadavers of larvae parasitized 3 days prior to fungal infection demonstrated a marked decrease in Z. radicans conidia yield. Z. radicans infection of P. xylostella larvae < or = 4 days after parasitism resulted in 100% parasitoid mortality; thereafter, the reduction in parasitoid cocoon yield decreased as the time between parasitism and initiation of fungal infection increased. The extended duration of the host larval stage induced by C. plutellae parasitism increased the availability of the parasitoid to the pathogen. Estimates of interspecific competition indicated a similar pattern for the interaction between Z. radicans and each species of parasitoid.
根虫瘟霉（接合菌门：虫霉目）、半闭弯尾姬蜂（膜翅目：姬蜂科）和小菜蛾盘绒茧蜂（膜翅目：茧蜂科）均为小菜蛾（鳞翅目：菜蛾科）的天敌。小菜蛾盘绒茧蜂成虫不易受根虫瘟霉感染，但该病原菌可感染并杀死半闭弯尾姬蜂成虫。在接触小菜蛾寄主幼虫之前，半闭弯尾姬蜂成虫被根虫瘟霉感染，会显著减少随后从寄主幼虫发育而来的寄生蜂茧的数量。虽然在半闭弯尾姬蜂或小菜蛾盘绒茧蜂寄生之前，根虫瘟霉感染小菜蛾幼虫总会导致未成熟寄生蜂死亡，但在产卵选择实验中，这两种寄生蜂都不会区分健康的和被根虫瘟霉感染的寄主幼虫。然而，最近被根虫瘟霉杀死的寄主幼虫总是会被半闭弯尾姬蜂拒绝，但有时会被小菜蛾盘绒茧蜂接受。在20摄氏度下，半闭弯尾姬蜂和小菜蛾盘绒茧蜂从卵到蛹的发育分别需要6.7天和7.8天。小菜蛾盘绒茧蜂寄生会显著延长寄主龄期，但半闭弯尾姬蜂寄生则不会。在真菌感染前1天被寄生的小菜蛾幼虫尸体，根虫瘟霉分生孢子产量没有降低。然而，在真菌感染前3天被寄生的幼虫尸体，根虫瘟霉分生孢子产量显著下降。在寄生后≤4天，根虫瘟霉感染小菜蛾幼虫会导致100%的寄生蜂死亡；此后，随着寄生和真菌感染开始之间的时间增加，寄生蜂茧产量的减少幅度降低。小菜蛾盘绒茧蜂寄生导致寄主幼虫期延长，增加了寄生蜂被病原菌感染的可能性。种间竞争估计表明，根虫瘟霉与每种寄生蜂之间的相互作用模式相似。
