Aggregation of a Leafminer, Cameraria Sp. Nov. (Davis): Consequences and Causes

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Abstract
Larvae of the leafminer, Cameraria sp. nov. Davis (Lepidoptera: Gracillariidae, agrifoliella group) were highly clumped at various spatial scales among and within trees of their host-plant, Quercus emoryi (Fagaceae) Torr. Larval distribution reflected ovipositional choice of adult females; inclusion of unhatched eggs did not alter the distributional patterns. Larval mortality increased, mainly due to interference competition, when there were more than two larvae per leaf. The mean pupal mass of survivors was inversely related to the number of mines per leaf, suggesting that fecundity was decreased for larvae sharing leaves. ''Winners'' in aggressive encounters between larvea occupying the same leaf did not have significantly larger pupae than when both miners survived, suggesting no clear advantage in killing and cannibalizing conspecifics. The hypothesis that leafminers clump because leaves vary in phytochemical quality was not supported; the density of leafminers among trees and leaves did not vary as predicted by variation in nutritional (protein and water) or ''defensive'' (tannin) content. Survival of leafminers in early instars was not related to phytochemistry of individual leaves as has been hypothesized. Morphological variation in leaf size and phenological variation in abscission and budbreak appeared to influence abundance, distribution and survival. Variation in these phenological factors may lead to apparent clumping either because some leaves are rejected based on size or propensity to abscise, or others are unavailable or inaccessible during the short ovispositional period.