The effect of plant- and parasitoid-induced egg mortality on the interspecific distribution of an oligophagous herbivore.
1994
Rossi A.M. | Reeve J.D. | Cronin J.T.
Plant-mediated egg mortality varied greatly tor the oligophagous leafhopper, Carneocephala floridana, a common inhabitant of the salt marshes along Florida's Gulf coast. In the laboratory, survivorship from egg to first instar was generally greater on two herbaceous plants, Borrichia frutescens and Salicornia virginica (80 and 81% respectively) than it was on two grasses, Ditichlis spicata and Spartina alterniflora (41 and 77% respectively). Although C. floridana laid significantly more eggs per clutch on Sp. alterniflora than on the two herbaceous species, this increase in egg number was offset by the higher mortality of eggs laid on this species. The greatest source of identifiable plant-mediated egg mortality was death due to desiccation of the leaf tissue surrounding the egg clutch. In addition, field experiments in which the four host species were infested with eggs of C. floridana at natural densities consistently yielded higher parasitism rates by two mymarid wasps on the grasses, regardless of the background plants. C. floridana switches host plants seasonally, using the grass species mainly during the winter months, when the herbaceous species experience a substantial dieback. The herbaceous species are nutritionally superior to the two grass species as a food source for C. floridana. C. floridana reared on the herbs produce larger, more fecund, adults than they do on the grasses (Rossi 1991). However, during cold winter snaps the grasses, while less "attractive", may provide the most abundant nutritional and ovipositional resources available to C. floridana.
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