Abstract
The plant vigour hypothesis (PVH) predicts that females of galling insects preferentially oviposit on the most vigorous plants or plant modules, where their offspring's performance is highest. In the years 1995 to 1998, we evaluated the responses of species of two different guilds, two chewing species, Pantomorus sp. and Naupactus lar (Coleoptera: Curculionidae) and one galling species, Contarinia sp. (Diptera: Cecidomyiidae), to the length of shoots that were assumed to show the vigour of the tropical shrub Bauhinia brevipes (Leguminosae). The abundance of the chewing herbivores was not influenced by shoot length, since attack rates were randomly distributed among shoot length classes. The abundance of Contarinia galls increased with increasing shoot length, as proposed by the PVH. However, when we related the attack rate to unit length of shoot (cm), which denotes the resource availability per unit length, there was no effect of shoot length on Contarinia sp. These data corroborate the idea of a continuum of responses to plant quality, even when different herbivores feed on the same host plant.
Highlights
Animal occurrence and feeding is influenced by plant geographical range and local abundance, their size, struc tural complexity and nutritional quality, secondary chem istry, and phenology, among other factors (Price et al, 1991)
The plant vigour hypothesis relates to within-plantspecies variation, and the fact that many herbivores attack the most vigorous plant parts or plant individuals in a population is well documented (Price, 1997)
Foresters have long recognized that young vigorous trees are often more susceptible than older plants to attack by herbivores. number
Summary
Animal occurrence and feeding is influenced by plant geographical range and local abundance, their size, struc tural complexity and nutritional quality, secondary chem istry, and phenology, among other factors (Price et al, 1991). Any or all of these parameters are important in determining the consequences of animal feeding patterns and intensity (Crawley, 1989). Studies on the effects of plant quality on the attack rates of herbivorous insects have shown opposite results that have been incorporated into two major hypotheses. The plant stress hypothesis (PSH) proposed by White (1984) and Mattson & Haack (1987) argues that herbivore abun dacacnocuenitsinhgigfohrerthoisnpsattrteesrsnedwohuolsdt bpelaantds.ecTrehaesemienchparnotiesmin synthesis coupled with an increase in soluble amino acid content in plant tissue. Stressed plants are less astbrleesst,osupcrhodauscwe actheermshicoarltadgeef,ehnassetsen(Rs hseonaedsecse,n1c9e7o9f),plaanndt tissues, and translocated nutrients benefit insect herbivore nutrition, growth and survival (Prada et al, 1995).
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