Testing optimal foraging for parasitoids: Perceived travel time influences the foraging behavior of Macrocentrus grandii in the field.
White, Jennifer *,1, Andow, David1, 1 University of Minnesota, St. Paul, MN
ABSTRACT- Optimal foraging theory predicts that animals should invest more time foraging in a patch when the travel time between patches is high than when travel time is low. While this prediction has been upheld in laboratory tests, it has rarely been tested under field conditions. We therefore manipulated Macrocentrus grandii's perception of travel time and observed subsequent patch-leaving behavior in the field. We found that wasps with 30 hours of exposure to high host density in field cages left subsequent patches twice as fast as wasps that received field cage experience without hosts, qualitatively matching the predictions of optimal foraging theory. This increased patch-leaving rate was detectable for at least 2 days after exposure to high host density, and was not driven by egg limitation: wasps in both groups had large numbers of eggs, and egg load did not differ significantly with treatment. A third group of wasps that had less exposure to the high host density treatment (6 hours) showed intermediate patch tenure, indicating that substantial exposure to high host density was needed before behavioral modification was observed. Furthermore, the wasps with 30 hours of high host density experience stayed longer on their patches than predicted by our foraging model, suggesting that even these wasps may have overestimated travel time and that there may be limitations to M. grandii's behavioral response to perceived travel time. In terms of biological control, these results suggest that M. grandii does not rapidly update its assessment of travel time, and may behave sub-optimally when exposed to a large range of host densities.
Key words: host density, parasitoid foraging behavior, patch tenure, travel time
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