Leafminers on Oak: The Role of Immigration and In Situ Reproductive Recruitment

Abstract

The roles of overwintering reproductive recruitment and intertree immigration are examined for leaf—mining insects on oak trees. Full—exclusion caged trees that exclude immigrants, litter exclusion caged trees that exclude overwintering recruits, and control trees were sampled to determine leafminer abundance and species richness. Full—caged trees had little overwintering recruitment, and populations went extinct during the season's first generation. Litter exclusion trees recruited as many species as did control trees, but had lower leafminer densities. However, further experiments indicate that the lowered densities were a caging artifact. This result suggest that most leafminer populations on oak trees are maintained by yearly reimmigration from safe overwintering sites and not from in situ reproductive recruitment. Therefore, the distribution and abundance of leafminers on oak should not be viewed as the turnover of reproductive populations on individual trees, but rather as the immigration and failed colonization of species whose movements encompass several trees.