Responses of the Common Sooty Wing Skipper to Patches of Host Plants

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Abstract
The dispersion patterns of eggs and larvae of the common sooty wing skipper (Pholisora catullus) changed when size of patches and distance between patches of its host plant (Chenopodium album) changed. With patches widely spaced, large patches had more eggs and larvae per patch but fewer per plant than did smaller patches. Behavioral observations showed that ovipositing females in widely spaced patches encountered patches at frequencies proportional to the patch diameters plus a small detection distance. Though females laid slightly more eggs per encounter in larger patches than in smaller patches, larger patches had many more plants and, therefore, fewer eggs per plant. Egg and larval mortality rates did not differ among patch sizes, so female behavior was sufficient to account for the observed egg and larval dispersion patterns of the skipper. When we reduced the spacing between patches, female skippers laid proportionately more eggs in large patches and fewer in smaller patches. As a result, the numbers of eggs per plant no longer differed among patch sizes. This shift was due to the greater tendency of females to fly by small patches without landing when the patches were closer together. In general, our results supported the hypothesis that differnt patch spacings can alter insect behavior, which in turn can produce different concentrations of herbivores in response to host patch size.