Plant Influences on Parasitism of Two Leafminers: A Test of Enemy‐Free Space

Abstract

We evaluated the importance of host plant traits as causes for a much greater parasitoid species richness on Tildenia inconspicuella (Lepidoptera: Gelechiidae), a leafminer on horsenettle, Solanum carolinense, than on tildenia georgei, a leafminer on groundcherry, Physalis heterophyllaa var. ambigua. In three field experiments, we found no evidence for short—term effects of host plants on parasitoids. None of the parasitoid species normally associated with the horsenettle miner successfully parasitized groundcherry miners transferred to horsenettle. Rates of parasitism and composition of parasitoid species did not differ for horsenettle miners on horsenettle vs. on eggplant, nor for groundcherry miners in tied vs. untied leaves. Instead, long—term effects of host plant morphology on leafminer behavior explained differences in parasitism between the two leafminer species. Whereas the mine structure of the groundcherry miner allows the larva to leave its mine and move freely over the leaf surface, the horsenettle miner stays within its mine, even when disturbed. We found that this difference has made the horsenettle miner vulnerable to more parasitoid species; it can be exploited, not only by parasitoids that can attack vagile hosts, but also by parasitoids restricted to concealed, sedentary hosts. Evidence further indicated that horsenettle trichome morphology has favored the evolution of this obligate endophytism in the horsenettle miner by selecting against mine architectures that would allow miners easy access to the leaf surface. When experimentally placed on leaf surfaces, miner larvae could not feed on horsenettle because they could not penetrate its meshwork of stellate trichomes. On groundcherry, where trichomes are thin and flexible, larvae easily initiated mines. We argue that obligate endophytism, which is uncommon among related gelechiids, is a specific adaption to horsenettle morphology that has made the horsenettle miner available to more parasitoid species than its vagile relatives.

Oviposition preference of two hoverfly species in response to risk of intraguild predation

“…For example, some herbivorous insects choose low quality rather than high quality plant species in terms of larval performance, because the low quality plant provide opportunity for chemical defense against predators (Gross and Price, 1988;Denno et al, 1990;Mira and Bernays, 2002). That oviposition site selection may be important not only for phytophagous insects but also predatory insects is suggested by previous studies (Nomikou et al, 2003;Blaustein et al, 2004).…”

Host shift and speciation in a coral-feeding nudibranch

“…Shifts to a new host may provide release from direct competition for resources and/or enemy-free space (Gross & Price 1988;Lill et al 2002). Most nudibranchs have diverse chemical and other defence mechanisms and are rarely victims of predation (Todd 1981).…”

Host behaviour and its influence on foraging and acceptance by the solitary parasitoid wasp,Venturia canescens (Hym: Ichneumonidae)

“…Koinobionts are parasitoids that allow the host to continue feeding and growing after parasitism, whereas idiobionts attack nongrowing host stages or paralyzed hosts (Askew & Shaw, 1986). The long-term responses of parasitoids to host defences may determine instar and species preference (Taylor, 1988), the species composition of parasitoid complexes and guilds (Gross & Price, 1988;Gross, 1993) and may also select for parasitoid counter defences in both koinobiont and idiobiont parasitoids (Calvert & van den Bosch, 1979;Allen, 1990;Gross, 1993).…”