Stage-specific parasitism of Diadegma semiclausum: Consequence for the parasitoid and its host, Plutella xylostella

摘要

The Ichneumon wasp, Diadegma semiclausum, is an important larval-prepupal endoparasitoid of the diamondback moth, Plutella xylostella. Parasitism of Plutella larvae of different instars and different developmental ages of the 4 th instar of the pest and the consequences for both the parasitoid and the host were investigated at 2A°C in laboratory. Diadegma semiclausum preferred parasitizing host larvae in 2nd and 3rd instars over 4th instars. Parasitism decreased with increasing host age of the 4lh instars. Development time, final adult size, adult fecundity and longevity of the parasitoid varied with the host instar at initialparasitization. Parasitoids with initial parasitism in the 4'" instar host naa tne snonesi ueveiopmcm. uuic, had the largest body size, followed by those in the 3 rd instar, and then by those in the 2"d instar. Parasitoid females starting parasitism in 3r,i instar host had the highest fecundity and the greatest longevity. However, the survival rate of the parasitoid during immature stages and the fecundity of the parasitoid adult female in the first day post-emergence did not vary with the host instar at initial parasitization. Parasitized host larvae exhibited longer development time compared with unparasitized ones, no matter when the larvae were parasitized initially. The host prepupae developed from parasitized larvae were not able to pupate, and the duration of the host staying in the prepupal stage increased with increase of host instar at parasitism. The parasitized larvae consumed similar amounts of cabbage leaf as the healthy larvae with the exception that parasitized larvae consumed significantly less cabbage leaf than healthy larvae during their 4* instar, when parasitism occurred at early 2 nd instar.