Substantially submaximal oviposition rates by a mymarid egg parasitoid in the laboratory and field
Abstract
Examined the foraging behaviour of the egg parasitoid Anagrus delicatus (Hymenoptera: Mymaridae) within patches of its planthopper host, Prokelisia marginata (Homoptera: Delphacidae) on leaves of Spartina alterniflora. Females discriminated between leaves with and without hosts. In field experiments with mixtures of newly mated and experienced females, the proportion of eggs laid was 4-26%. Available hosts far exceeded wasp fecundity. Hosts, were alive, available, and supported development of parasitoids if parasitized. Increasing numbers of female wasps visiting a patch led to increasing parasitism rate (average of 75% with 20 female wasps). Even though many hosts on a patch were probed and rejected by each wasp, rejected hosts were parasitized by subsequent wasps and yielded live parasitoid offspring. Single wasps dispersed before the ratio of unparasitized to parasitized hosts was much decreased by their efforts. Handing time constraints were small (2.2 min) in relation to total patch time (62 min). Anagrus passed up many suitable and available hosts in each patch and visited multiple patches during its lifetime; number of eggs laid increased linearly with the number of patches visited. This is apparently a foraging strategy built upon compromising the time rate of oviposition in favour of spreading ovipositions among patches and sites. There was high mortality of host-plant leaves, and thus of host-insect patches, in the field due to leaf senescence (20-30%), which would favour spreading of parasitoid offspring among leaves. -from Authors