title: Parasitism rates and sex ratios of a parasitoid wasp: effects of herbivore and plant quality.
abstract: We studied interactions among collards, Brassica oleracea var. acephala, the diamondback moth (DBM), Plutella xylostella (Lepidoptera: Yponomeutidae) and its parasitoid Diadegma insulare (Hymenoptera: Ichneumonidae) by manipulating plant nitrogen (N) concentrations in field and laboratory experiments. Parasitoid abundance strongly reflected DBM abundance and was related to total leaf N. Parasitism rates were high (70.7%) and density-independent. Wasp sex ratios varied markedly (3-93% female) in response to the herbivores, the plants, or both. Higher proportions of female wasps emerged from DBM larvae on plants with high leaf N than on unfertilized plants. More female wasps also emerged from larvae parasitized as larger instars. We suggest that wasps have the potential to control DBM populations through long-term numerical responses mediated by variable sex ratios.
authors.affiliation: Department of Biology, University of California, 95064, Santa Cruz, CA, USA.
authors.forename: Laurel R
authors.initials: LR
authors.lastname: Fox
authors.affiliation: Environmental Studies Board, University of California, 95064, Santa Cruz, CA, USA.
authors.forename: Deborah K
authors.initials: DK
authors.lastname: Letourneau
authors.affiliation: Department of Biology, University of California, 95064, Santa Cruz, CA, USA.
authors.forename: Jamin
authors.initials: J
authors.lastname: Eisenbach
authors.affiliation: Department of Biology, University of California, 95064, Santa Cruz, CA, USA.
authors.forename: Saskya
authors.initials: S
authors.lastname: Van Nouhuys
keywords: Brassica oleracea var. acephala; Diadegma insulare; Host-parasitoid interactions; Nitrogen; Plutella xylostella; Sex ratio