Effect of nitrogen on resistance of sweet potato to sweetpotato weevil (Coleoptera: Curculionidae) and on storage root chemistry.

The effects of nitrogen fertilizer on sweet potato, Ipomoea batatas (L.) Poir., resistance to the sweetpotato weevil, Cylas formicarius elegantulus (Summers), was studied. Adult weevil feeding and oviposition preference, larval survival, and pupal weight were used as measures of sweet potato resistance. Sweet potato resin glycosides and caffeic acid concentrations in the periderm tissue of storage roots also were measured. Sweet potato genotypes (Beauregard, Excel, W-244, W-250, and Sumor) with varying levels of resistance to sweetpotato weevil were grown in the field under three nitrogen regimes (0, 45, and 135 kg N/ha). Harvested storage roots were evaluated in the laboratory for feeding and oviposition activity of sweetpotato weevil female adults under no-choice and choice test conditions. Larval survival rate and pupal weight were determined by rearing the insects individually on storage root sections. Nitrogen level had a significant effect on the number of eggs deposited, but not on the number of feeding punctures. Sweetpotato weevils laid fewer eggs on plants with the highest level of nitrogen. Nitrogen levels did not significantly affect larval survival and pupal weight. Genotype had a significant effect on feeding, oviposition, and larval survival. Beauregard had higher levels of feeding, oviposition, and larval survival compared with the other genotypes. No interaction effects between nitrogen and genotype were significant. Resin glycosides and caffeic acid concentrations were significantly different among genotypes and between years. Nitrogen levels significantly affected the concentrations of caffeic acid in 1997.

Sex pheromone components of the buck moth Hemileuca maia.

The sex attractant pheromone blend of Hemileuca maia (Lepidoptera: Saturniidae) from the vicinity of Baton Rouge, Louisiana, has been identified. The major component of the blend is (E10,Z12)-hexadeca-10,12-dienal (E10,Z12-16:Ald), in combination with the minor components (E10,Z12)-hexadeca-10,12-dien-1-ol (E10,Z 12-16:OH), and (E10,Z12)-hexadeca-10,12dien-1-yl acetate (E10,Z12-16:Ac). Ratios of the compounds in extracts of female pheromone glands varied around a mean of 100:7.4:6.3. None of the three components were attractive to male moths when tested as single components. Several other compounds were tentatively identified from female pheromone gland extracts, including E10,E12-16:Ald, E10,E12-16:OH, and E10,E12-16:Ac, but addition of these components, either alone or in combination, at biologically relevant rates, did not significantly increase the attractiveness of lures. The saturated analogs, hexadecanal, hexadecanol, and hexadecyl acetate, also were identified in gland extracts, but had no apparent effect as pheromone components.

Looplure efficacy and electrophysiological responses in three plusiinae species.

Source concentration differences of (Z)-7-dodecen-1-ol acetate, or looplure, were evaluated for field trapping efficiency and electrophysiological responses with malePseudoplusia includens (Walker),Trichoplusia ni (Hubner) andRachiplusia ou (Guenné) (Lepidoptera: Noctuidae). Sticky traps baited with 1000 µg of the lure captured a significantly greater (P < 0.05) number of maleP. includens andT. ni than any other concentration;R. ou males were caught at a greater rate in traps baited with 100 µg of looplure, significantly more (P < 0.05) than with 1000 µg. Electroantennogram (EAG) studies demonstrated that antennae of maleP. includens have a lower response threshold to looplure than eitherT. ni orR. ou antennae, the latter demonstrating the highest significant threshold of response. No differences in the stimulus-response functions of the three species were detected.