Density and Dispersion of Insect Herbivores on Lamb's-Quarters (Chenopodium Album)

154 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.Seven species of leaf-feeding insects were found on lamb's-quarters plants (Chenopodium album L. Chenopodiaceae) in central Illinois. The two most abundant were the microlepidopteran leaf miner Chrysopora lingulacella Clemens (Lepidoptera: Gelechiidae), which was abundant in sheltered areas in the city, and the common sooty wing skipper, Pholisora catullus Fabricius (Lepidoptera: Hesperiidae), which was abundant in open fields. A variety of natural history observations were made for these two insect species, and captive rearing techniques were developed for the leaf miners.Field experiments were performed to examine the response of the skippers to the size and spacing of host plant patches. Measurements were made of patch encounter and oviposition frequencies, and of egg and larval mortality patterns. With patches widely spaced, more eggs and larvae were found per patch, but fewer per plant, in large patches than in small patches. This pattern could be explained by the effects of random search for patches and by the oviposition behavior of female skippers; egg and larval mortality did not differ between patch sizes. With patches closely spaced, proportionately more eggs were found in large patches, and fewer in smaller patches, and the numbers of eggs per plant did not differ among patch sizes. This shift in herbivore load was due to a tendency of females to ignore small patches when patches were close together.A stochastic computer simulation model of insect movement and oviposition was developed and run using parameter values based on field observations of skipper behavior. The model produced egg dispersion patterns similar to those observed in the field, thus supporting the contention that the patterns of herbivores in the field are largely determined by female behavior.The results of the skipper studies suggest that matters of scale should be considered in relation to the sensory capabilities and mobility of insects if ecologists are to obtain a general understanding of insect dispersion patterns.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD