Determinants of multiple host use by a phytophagous insect population.

Abstract

The following question was asked of an oligophagous butterfly population: how does the use of several hosts arise from the behavior of individual insects? There are at least 3 mechanisms: 1) Some individuals behave as generalists themselves, and have almost equal likelihoods of depositing their eggs on different host species. 2) The population contains insects with different distinct preferences. This variation in preference affects variation in host use. 3) One of the most highly preferred hosts is sufficiently rare and localized that most insects which do prefer it search without finding it until other, less preferred hosts become acceptable. They then oviposit on these secondarily preferred species. The degree of host specialization (specificity) is a continuous variable in this population. While some butterflies show 'neutral' preference and fail to discriminate between potential host species, others are just as host-specific as individuals in strictly monophagous populations (of the same species). In such monophagous populations there is no variation of preference rank order and no undiscriminating insects (with 'neutral' preference) have been found. In consequence, the distribution and abundance of potential hosts does not usually affect breadth of host use by the population. -from Author