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Effect of avocadofurans on larval survival, growth, and food preference of the generalist herbivore, Spodoptera exigua

Rodriguez-Saona, C.R., Trumble, J.T.
Entomologia experimentalis et applicata 1999 v.90 no.2 pp. 131-140
food intake, antifeedants, Spodoptera exigua, Persea americana, plant fats and oils, furans, feeding preferences, cells, sublethal effects, biological development, mortality, larvae
We examined the effect of two avocadofurans, 2-(pentadecyl)furan and 2-(heptadecyl)furan, from avocado idioblast oil cells on maturation and larval feeding behavior of a generalist insect herbivore, Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae). Experiments were conducted using two larval sizes: early-stadium larvae refer to those larvae from experiments initiated with neonates while late-stadium larvae refer to those larvae from experiments initiated with third instars. In order to use selected sublethal doses for developmental and behavioral studies on early- and late-stadium larvae, log-dose probit lines were determined using diet incorporation bioassays. Both avocadofurans had similar toxicities to early-stadium larvae [LC(50) = 2.2 and 1.9 micromoles/g of diet for 2-(pentadecyl) furan and 2-(heptadecyl)furan, respectively] and late-stadium larvae (LC(50) = 3.0 and 3.4 micromoles/g of diet, respectively). In diet bioassays extending from egg hatch to adult emergence, the avocadofurans significantly prolonged larval developmental times and reduced S. exigua pupal weights. In 7 d no-choice bioassays initiated with cohorts of newly-molted third instars, the avocadofurans significantly reduced larval weights at various sublethal concentrations (below LC(50) values). To test larval feeding deterrence effects of these avocadofurans, choice tests were conducted using early and older instar larvae. A significantly higher proportion of early-stadium larvae preferred control diet over diet treated with either avocadofuran at several sublethal concentrations. Similarly, choice tests with late-stadium larvae showed greater proportions of larvae on control diet than treated diet even at concentrations below the LC(50), Moreover, late-stadium larvae consumed significantly more of the control diet than the treated diet. Thus, the avocadofurans may act as feeding deterrents as well as toxicants in plant protection against non-adapted insect herbivores.