Cronin, J. T. & D. R. Strong. 1990. Density-independent parasitism among host patches by Anagrus delicatus (Hymenoptera: Mymaridae): experimental manipulation of hosts. Journal of Animal Ecology 59: 1019-1026.

(1) Parasitism by Anagrus delicatus Dozier of the eggs of its host, Prokelisia marginata (Van Duzee) was examined experimentally in a north Florida salt marsh.

(2) By inducing planthopper oviposition into equal-sized sections of two leaves per potted plant, we controlled for variation in host-insect age, host-plant quality, number of hosts per patch and physical area (size) of patches. Potted plants were placed in the field and exposed to naturally occurring parasitoids for 72 h. The experiment was repeated twenty times over a 10-month period to account for seasonal or other environmental variation.

(3) Spatially, parasitism by A. delicatus was independent of host density for all experimental trials. Through time, a slight inverse reiationship between parasitism rate and density was apparent; higher overall host densities tended to have lower parasitism rates.

(4) These experimental results correspond to previous, observational findings for this system (Stiling & Strong l982; Strong l989).

(5) Parasitoids disperse from host clutches after laying only a small fraction of their eggs, and this behaviour appears to play an important role in producing the observed density-independent patterns of parasitism.

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