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

Abstract

Abstract:Rainfall seasonality can strongly influence biotic interactions by affecting host plant quality, and thus potentially regulating herbivore exposure to natural enemies. Plant defences are predicted to increase from dry to wet forests, rendering wet-forest caterpillars more vulnerable to parasitoids due to the slow-growth-high-mortality hypothesis. We collected and reared caterpillars from the understorey and trail edges of a wet forest and a seasonally dry forest to determine whether wet-forest caterpillars suffered a higher prevalence of parasitism and were less abundant than dry-forest caterpillars. In the two forests, caterpillar abundances (on average 8 h −1 ) and prevalence of parasitism (18%) were very similar regardless of feeding niche for both parasitism (27% versus 29% in shelter builders, and 16% versus 11% in external feeders) and caterpillar abundances (shelter builders: 1.42 versus 2.39, and external feeders: 8.27 versus 5.49 caterpillars h −1 ) in the dry and wet forests, respectively. A similar comparative analysis conducted in the canopy and understorey of the dry forest revealed a higher prevalence of parasitism in the canopy (43%) despite caterpillar densities similar to those in the understorey. Overall, shelter builders suffered higher parasitism than external feeders (32% versus 14.9%), and were attacked primarily by flies, whereas external feeders were more vulnerable to attack by parasitoid wasps.

Contrasting patterns of insect herbivory and predation pressure across a tropical rainfall gradient

“…Members of the family Geometridae feed on woody plants and are among the most commonly observed caterpillars in forests worldwide, including our Metropolitano site (Connahs et al . ).…”

“…, Richards & Coley , Connahs et al . ). The hypothesized tendency for insect abundance to be higher in wetter, less seasonal forests is likely to translate into higher herbivory.…”

“…Drier and more seasonal conditions could reduce insect abundance by increasing desiccation risk (Coley & Barone , Givnish , Connahs et al . ) and by causing resource limitation through decreased plant productivity (Coley & Barone , Leigh et al . , Richards & Coley , Connahs et al .…”

“…, Connahs et al . ), and we are unaware of studies documenting trends in herbivory and predation simultaneously across multiple sites.…”

Parasitism rate, parasitoid community composition and host specificity on exposed and semi-concealed caterpillars from a tropical rainforest

“…The comprehensive meta-analysis by Hawkins (1994) revealed general trends between parasitism rate and host concealment, but did not find a statistically significant difference between exposed and semi-concealed hosts. So far, two studies have shown higher parasitism rates in semi-concealed caterpillars (Connahs et al 2011;Gentry and Dyer 2002), while Le Corff et al (2000) found season to be more important than host concealment. Parasitism rate has also been found to depend on host abundance (Stireman and Singer 2003), as parasitoids could specialize on more common species or attack the more common species from their host range, and on the host plant species of the herbivores (Lill et al 2002).…”