Host selection by an insect herbivore with spatially variable density dependence
Many species of phytophagous insects do not oviposit preferentially on plants that yield high offspring performance. One proposed explanation is that negatively density-dependent offspring performance would select for females that disperse eggs among plants to minimize competition. Recent work showing larval density dependence often varies substantially among plants suggests that ovipositing females should not only respond to the density of competitors but also to traits predictive of the strength of density dependence mediated by plants. In this study, we used field and greenhouse experiments to examine oviposition behavior in an insect herbivore that experiences density-dependent larval performance and variability in the strength of that density dependence among host-plant individuals. We found females moved readily among plants in the field and had strong preferences for plants that mediate weak offspring density dependence. Females, however, did not avoid plants with high densities of competitors, despite the fact that offspring performance declines steeply with density on most plants in natural populations. This means females minimize the effects of density dependence on their offspring by choosing plants that mediate only weak larval density dependence, not by choosing plants with low densities of competitors. Our results suggest that explaining the lack of positive preference-performance correlations in many systems may not be as simple as invoking density dependence. Resource selection behavior may depend not just on the presence or absence of density-dependent offspring performance but also on variation in the strength of offspring density dependence among sites within populations.
KeywordsHost-plant preference Offspring performance Oviposition behavior Tephritidae Plant–insect interaction
We thank R. Karban, J. Rosenheim, P. Grof-Tisza, M. Meek, I. Pearse, and the University of California (UC) Davis Insect Ecology Joint Lab Group for discussion and criticism. S. Krasnobrod, M. Cruz, R. Cox, A. Jordan, C. Kaplinsky, W. Zhang, and M. Meek provided field and lab assistance. We are grateful to D. Dawson of the UC VESR where this work was conducted. The UC Davis Center for Population Biology, the UC Natural Reserve Mathias Program, and the UC VESR provided funding. W. C. W. was supported by NSF DEB 081430, the REACH IGERT at UC Davis.
Conflict of interest
The authors declare that they have no conflict of interest.
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