We examined the effect of selenium (Se) in plants transferred through an insect herbivore on the development and survival of a parasitoid wasp, Cotesia marginiventris (Hymenoptera: Braconidae). Alfalfa, Medicago sativa, was grown in sand culture under two levels of sodium selenate irrigation. Neonate host larvae, Spodoptera exigua (Lepidoptera: Noctuidae), were exposed to the parasioids for 24h on control plants, then fed on control (< 5mg/g Se) or Se-treated alfalfa (> 300 mg/g Se) until parasitoid emergence from the third instar host larva. Treated plants at this Se concentration significantly reduce S. exigua survival through the adult stage. We recorded parasitoid pupal emergence, pupal weight and days to adult emergence. There was no reduction in the number of parasitoids in the treatment groups as would be expected if Se treatment reduced parasitoid survival. However, parasitoids reared from hosts grown on control plants emerged sooner and pupae weighed more than those from hosts fed Se-treated plants. Thus, although mortality is not directly affected, the increase in parasitoid generation time and the decrease in weight (a variable generally related to oviposition capacity in insects) will impact the population dynamics of this parasitoid-herbivore system. Behavioral experiments examining parasitoid preference are currently underway.
Species 1: Braconidae Hymenoptera Cotesia marginiventris
Species 2: Lepidoptera Noctuidae Spodoptera exigua (beet armyworm)
Keywords: selenium, biomagnification
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