Chapter 5 - Minor Miners and Major Miners: Population Dynamics of Leaf-Mining Insects

Abstract

This chapter discusses population dynamics of leaf-mining insects. Leaf mining is a means by which some insects consume foliage while simultaneously dwelling inside it. Worldwide approximately 10,000 species of insects are leaf miners, but density estimates and demographic data are available for only 1% of these species. Most leaf-mining species apparently suffer little egg mortality from natural enemies. Virtually every study examining mortality of leaf miners, whether at latent or eruptive densities, has identified parasitism of larvae, and sometimes pupae, as an important source of mortality. Interactions with conspecifics and other phytophagous insect species have generally been viewed as having little effect on the population dynamics, largely because the characteristically low densities of most phytophages were presumed to result in little competition for limiting resources. Tests of the regulatory role of dominant mortality sources, usually with regression-based tests for spatial and or temporal density dependence, have been equivocal. One additional caveat must be added to any discussion of population dynamics of leaf-mining insects. An extensive 3-year study of egg, larval, and pupal mortality revealed that most mortality occurred during the larval stage. In 1984, when population densities were 3.59 mines/leaf, intraspecific competition accounted for substantial mortality, and was spatially density dependent. Stilbosis quadricustatella is a univoltine leaf miner commonly found on Quercus geminata in northern Florida. No studies have simultaneously examined latent and eruptive populations of the same species over several years, so it is presently impossible to determine if these species have multiple stable states with low- and high-density populations regulated around different equilibrium levels.