Feeding preferences of Spodoptera exigua in response to form and concentration of selenium

Minimal information is available on the impact of various organic and inorganic forms of the ecologically and agriculturally important pollutant, selenium (Se), on insect herbivores. We conducted bioassays with artificial diet to examine the feeding responses of a generalist herbivore, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), to various forms and concentrations of Se. Two different‐aged cohorts of larvae were examined in choice tests with control diets vs. test diets incorporating lethal concentrations (LC 10 , LC 30 , LC 50 , and LC 70 ) of sodium selenate, sodium selenite, seleno‐ DL ‐cystine, and seleno‐ DL ‐methionine. Tests initiated with neonates showed larvae significantly preferred control diet over diet with sodium selenate, sodium selenite, or selenocystine, but at most concentrations showed no preference between selenomethionine and control diet. Choice tests initiated with third instars demonstrated a preference for control diet over sodium selenate treatments, and sodium selenite treatments. In contrast, no significant responses were found in tests initiated with third instars offered the choice between selenocystine or selenomethionine and untreated controls. Additionally, comparisons of consumption demonstrated that inorganic selenium compounds were antifeedants whereas the organic selenium compounds tested have little antifeedant activity. The toxicity of all of the tested forms of selenium, in combination with the lack of antifeedant activity of some compounds, has the potential to affect both the distribution and diversity of terrestrial herbivores in both agricultural and natural systems. Arch. Insect Biochem. Physiol. 42:64–73, 1999. © 1999 Wiley‐Liss, Inc.