Climatic unpredictability and parasitism of caterpillars: Implications of global warming

Abstract

Insect outbreaks are expected to increase in frequency and intensity with projected changes in global climate through direct effects of climate change on insect populations and through disruption of community interactions. Although there is much concern about mean changes in global climate, the impact of climatic variability itself on species interactions has been little explored. Here, we compare caterpillar-parasitoid interactions across a broad gradient of climatic variability and find that the combined data in 15 geographically dispersed databases show a decrease in levels of parasitism as climatic variability increases. The dominant contribution to this pattern by relatively specialized parasitoid wasps suggests that climatic variability impairs the ability of parasitoids to track host populations. Given the important role of parasitoids in regulating insect herbivore populations in natural and managed systems, we predict an increase in the frequency and intensity of herbivore outbreaks through a disruption of enemy-herbivore dynamics as climates become more variable.climate change ͉ herbivore ͉ outbreak ͉ parasitoid ͉ top-down

Evolution of alternative insect life histories in stochastic seasonal environments

“…This is surprising given the diversity and ecological significance of insects (Stork 2003), the effect of climate variability on biological processes where insects are involved (e.g., the parasitism rate of caterpillars: Stireman et al. 2005), the studies on various stochasticity and seasonality effects on life history evolution and plasticity in other arthropods (Arbačiauskas 2001; Varpe et al. 2009; Barbosa et al.…”

Caterpillar abundance and parasitism in a seasonally dry versus wet tropical forest of Panama

“…Dry-forest insect herbivores may also escape early wet-season mortality from natural enemies whose numbers may still be too low to track them (Aiello 1992, Coley 1998, Godfray 1994). In a study by Stireman et al (2005), the incidence of parasitism of caterpillars increased as year-to-year variability in precipitation decreased, providing strong evidence of a correlation between rainfall seasonality and intensity of top-down pressures. Parasitoid wasps in particular are negatively affected by dry conditions through desiccation due to their small size (Hance et al 2007, Shapiro & Pickering 2001.…”

Changes in the background losses of woody plant foliage to insects during the past 60 years: are the predictions fulfilled?

“…The existing scenarios generally predict that increasing temperature will cause faster increases in herbivory than in plant productivity [5][6][7], although the suggested mechanisms behind this prediction are diverse. Population densities of plant-feeding insects were predicted to increase because of direct beneficial effects of warmer climate on insect herbivores [8] and adverse effects of increased climatic variability on their natural enemies [9]. Furthermore, consumption of foliage was expected to intensify because of the nitrogen dilution effect associated with an increase in CO 2 concentrations [10] and increased metabolic demands of insects under higher temperatures [11].…”