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

Abstract

The processes maintaining the enormous diversity of herbivore-parasitoid food webs depend on parasitism rate and parasitoid host specificity. The two parameters have to be evaluated in concert to make conclusions about the importance of parasitoids as natural enemies and guide biological control. We document parasitism rate and host specificity in a highly diverse caterpillar-parasitoid food web encompassing 266 species of lepidopteran hosts and 172 species of hymenopteran or dipteran parasitoids from a lowland tropical forest in Papua New Guinea. We found that semi-concealed hosts (leaf rollers and leaf tiers) represented 84 % of all caterpillars, suffered a higher parasitism rate than exposed caterpillars (12 vs. 5 %) and their parasitoids were also more host specific. Semi-concealed hosts may therefore be generally more amenable to biological control by parasitoids than exposed ones. Parasitoid host specificity was highest in Braconidae, lower in Diptera: Tachinidae, and, unexpectedly, the lowest in Ichneumonidae. This result challenges the long-standing view of low host specificity in caterpillar-attacking Tachinidae and suggests higher suitability of Braconidae and lower suitability of Ichneumonidae for biological control of caterpillars. Semi-concealed hosts and their parasitoids are the largest, yet understudied component of caterpillar-parasitoid food webs. However, they still remain much closer in parasitism patterns to exposed hosts than to what literature reports on fully concealed leaf miners. Specifically, semi-concealed hosts keep an equally low share of idiobionts (2 %) as exposed caterpillars.

Vertical canopy gradient shaping the stratification of leaf‐chewer–parasitoid interactions in a temperate forest

“…We expect both groups to be more parasitized lower in the canopy, but we expect semiconcealed hosts to be more abundant higher in the canopy, in accordance with the hypothesis that the harsh upper canopy environment favors concealed or semiconcealed feeders (Ribeiro & Basset, 2007). Moreover, in tropical forests, there are differences in parasitoid community composition between exposed and semiconcealed feeders (Hrcek, Miller, Whitfield, Shima, & Novotny, 2013), and here, we expect a similar pattern.…”

“…However, surprisingly, the parasitism rate did not significantly differ between the two guilds, contrasting with that found in the tropics, in which the latter group suffers higher parasitism (Gentry & Dyer, 2002; Hrcek et al., 2013). Moreover, an interesting trend occurred when comparing vertical trends in parasitism between guilds.…”

Is the globally rare frosted elfin butterfly (Lycaenidae) two genetically distinct host plant races in Maryland? DNA evidence from cast larval skins provides an answer

“…Microsatellite and mitochondrial DNA had previously been extracted from insect exuviae (Hrcek et al 2011(Hrcek et al , 2013Watts et al 2005) with similar rates of success in obtaining sequences. The difference in the methodology is that frosted elfin are of conservation concern, and we returned the larvae or pupae to the plant on which they had been found.…”

“…In this paper we examine DNA sequences from the mitochondrial CO1 gene as a maternally inherited proxy for female oviposition behavior that logically precedes the differentiation of host plant races. CO1 gene sequences are widely used to differentiate closely related species (Janzen et al 2009), and are reliably extracted from insect larval and pupal remains (Hrcek et al 2011(Hrcek et al , 2013. If it were possible to extract gene sequences from cast larval skins, one could take a caterpillar from the field to the lab, wait for it to molt (providing a cast larval skin), and return the caterpillar to the same plant in the field where it was found.…”

Eucharitid ant-parasitoid affects facultative ant-plant Leea manillensis: top-down effects through three trophic levels

“…Their species richness (and therefore possible functional relevance) has been markedly underestimated in the tropics (see, e.g. Veijalainen et al 2012;Hrcek et al 2013). The Eucharitidae is the only insect family known to comprise only parasitoids specialized on ant brood (Heraty 1985;Heraty and Darling 1984;reviewed in Lachaud and Pèrez-Lachaud 2012).…”