Generalist and specialist host-parasitoid associations respond differently to wild parsnip (Pastinaca sativa) defensive chemistry

Abstract

1. Plant defensive chemistry is predicted to have a more negative effect on generalist herbivores and their parasitoids than on specialist herbivores and their parasitoids.2. This prediction was examined by comparing the effects of the wild parsnip (Pastinaca sativa L.) toxin, xanthotoxin, on a generalist herbivore-parasitoid association [the cabbage looper, Trichoplusia ni Hübner, and its polyembryonic parasitoid, Copidosoma floridanum (Ashmead)] and a specialist herbivore-parasitoid association [the parsnip webworm, Depressaria pastinacella (Duponchel), and its polyembryonic parasitoid, Copidosoma sosares (Walker)].3. Copidosoma floridanum brood sizes were smaller and experienced lower survivorship when reared in a host feeding on an artificial diet containing a low concentration of xanthotoxin. No T. ni hosts, parasitised or unparasitised, survived on a diet high in xanthotoxin. In contrast, C. sosares brood size and survivorship were unaffected by the presence of low levels of xanthotoxin in the host diet. Copidosoma sosares experienced reduced brood size and survivorship only when its host consumed a diet containing 15 times the level of xanthotoxin as the diet adversely affecting its congener.4. The differences in response to xanthotoxin exhibited by C. floridanum and C. sosares are explained partly by a differential reduction in host quality and partly by differential exposure to xanthotoxin in host haemolymph. Unlike D. pastinacella, T. ni experienced reduced pupal weight and survivorship and prolonged developmental time on a low-xanthotoxin diet. More xanthotoxin passed unmetabolised into the haemolymph of T. ni than into the haemolymph of D. pastinacella.

Endophyte-mediated tritrophic interactions between a grass-feeding caterpillar and two parasitoid species with different life histories

“…Other Copidosoma species have shown reduced fitness when developing within hosts feeding on chemically defended plants other than grasses (Orr and Boethel 1985;Beach and Todd 1986;Reitz and Trumble 1996;Lampert et al 2011). In our study, cutworms were developmentally stunted when feeding on E?…”

Impact of <I>Rag1</I> Aphid Resistant Soybeans on <I>Binodoxys communis</I> (Hymenoptera: Braconidae), a Parasitoid of Soybean Aphid (Hemiptera: Aphididae)

“…Body size was measured from the anterior tip of the frons to the posterior tip of the abdomen. Body size and hind metatibiae are often used for determination of parasitoid Þtness, including fecundity and male mating ability (Ode and Strand 1995, Sagarra et al 2001, Lampert et al 2011.…”

Integration of Plant Defense Traits with Biological Control of Arthropod Pests: Challenges and Opportunities

“…Far less documentation exists regarding the consequences for parasitoids of developing in generalist vs. specialist herbivores because few studies have documented the levels of unmetabolized plant toxins in the hemolymph of herbivores with different diet breadths. In one study, significantly more xanthotoxin was passed unmetabolized into the hemolymph of the cabbage looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), a generalist herbivore, than was passed in the hemolymph of the parsnip specialist Depressaria pastinacella (Geeze) (Lepidoptera: Oecophoridae) (Lampert et al, 2011b). In turn, Copidosoma floridanum Ashmead (Hymenoptera: Encyrtidae) (a parasitoid of T. ni ) suffered increased mortality and reduced clutch sizes relative to Copidosoma sosares (Walker) (Hymenoptera: Encyrtidae) (a specialist parasitoid of D. pastinacella ) even though both herbivore-parasitoid combinations were reared on the same artificial diets (Lampert et al, 2011b).…”

“…In one study, significantly more xanthotoxin was passed unmetabolized into the hemolymph of the cabbage looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), a generalist herbivore, than was passed in the hemolymph of the parsnip specialist Depressaria pastinacella (Geeze) (Lepidoptera: Oecophoridae) (Lampert et al, 2011b). In turn, Copidosoma floridanum Ashmead (Hymenoptera: Encyrtidae) (a parasitoid of T. ni ) suffered increased mortality and reduced clutch sizes relative to Copidosoma sosares (Walker) (Hymenoptera: Encyrtidae) (a specialist parasitoid of D. pastinacella ) even though both herbivore-parasitoid combinations were reared on the same artificial diets (Lampert et al, 2011b). Other studies have documented similar patterns (e.g., Barbosa et al, 1986, 1991).…”