Handling Time and the Functional Response of Aphelinus thomsoni, a Predator and Parasite of the Aphid Drepanosiphum platanoidis

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Abstract
The criterion of density-dependent mortality was used to show that A. thomsoni exhibited a type II functional response when confined with its host for 1 h but a type III response when free to leave at any time. Rogers'' (1972) random predator equation was extended to describe the predation and oviposition behavior of A. thomsoni. To give a type III functional response, instantaneous area of discovery, total time in patch or handling time must vary with prey density. In A. thomsoni only handling time was quantitatively shown to do so, although it is normally assumed to be constant in this context. A. thomsoni may either feed from or oviposit in its aphid prey but tends to feed first; thus the ratio of feeding to oviposition attacks decreases with prey density. Since feeding attacks take longer, the mean handling time decreases with aphid density. Variation in handling time can be an important factor in the production of a sigmoid functional response.

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