PARENT SESSION
Poster Session #37: Invertebrate Ecology.
Thursday, August 9, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Oviposition, feeding preferences, and survival of Spodoptera exigua on Se-treated alfalfa: Implications for phytoremediation.

VICKERMAN, DANEL¹, TRUMBLE, JOHN¹, ¹

ABSTRACT- We examined the effect of selenium-treated alfalfa on the oviposition response, food preference, development and survival of a model insect Spodoptera exigua on alfalfa, Medicago sativa. Alfalfa was grown in sand culture under two levels of sodium selenate irrigation. Insects were fed either treated or control plants. Less than 5g/g Se (low concentration) in alfalfa did not affect percent survival to adult eclosion, but at 340g/g Se fewer insects survived compared to insects fed untreated alfalfa (Mann-Whitney U; p<0.05). High Se levels decreased the Relative Growth Rate (RGI; Mann-Whitney U; p<0.0001) and for those insects surviving, increased mean number of days to pupation (ANOVA, p<0.05). In two-choice bioassays females preferred ovipositing on plants with sub-lethal Se concentrations over non-treated plants (Wilcoxon signed rank; p<0.05), but did not discriminate between plants with lethal Se levels and non-treated plants. Fourth instar larvae did not discriminate between plants with lethal Se levels and non-treated control plants (Wilcoxon signed rank; p<0.05) and may not discriminate against lethal concentrations of Se in plants. This suggests that although females and larvae may be able to tell the difference between Se-treated and non-treated alfalfa they do not avoid plants at this lethal Se level making alfalfa with high Se-treatment levels naturally resistant to S. exigua. Se-contaminated alfalfa may serve as a "sink" with females ovipositing and few offspring surviving to reproduce.

KEY WORDS: Spodoptera exigua, selenium, phytoremediation, host-plant choice