SEMIOCHEMICAL-BASED TOXIC BAITS FOR DIABROTICA-VIRGIFERA-VIRGIFERA (COLEOPTERA, CHRYSOMELIDAE) - EFFECTS OF PARTICLE-SIZE, LOCATION, AND ATTRACTANT CONTENT

Survival of adult Diabrotica virgifera virgifera LeConte was monitored in field cages that contained maize plants, Zea mays L., treated with semiochemical-based toxic baits. Baits consisted of starch granules that contained a feeding stimulant (cucurbitacins) and an insecticide (0.5% carbaryl); they were sprinkled by hand over plants at a rate of 5 kg/ha. In cages of silking maize, granules of bait that were 2-4 mm in diameter were significantly less effective (27% of beetles survived 48 h) than granules from three smaller size categories (13-18% survival). In another test, however, granule size appeared to influence efficacy of baits in cages of dent-stage maize but not in cages of silking plants. Efficacy did not differ significantly among baits that were formulated to contain 0, 0.5, 2, or 8% of the "TIC" attractant (a 1:1:1 mixture of 1,2,4-trimethoxybenzene, indole, and trans-cinnamaldehyde). Granules containing TIC attracted large numbers of D. v. virgifera in open cornfields when placed in traps constructed from 59-ml pill vials. In laboratory assays, TIC initially reduced the proportion of beetles that consumed a lethal dose of bait, but the effect was not evident after granules were exposed to open air for 24 h. Starch-granule bait and a similar cereal-based bait produced 87-94% mortality of D. v. virgifera when applied carefully to leaves of maize plants, but did not measurably affect survival when an equal amount was distributed on the soil surface. The distribution of bait particles within a maize field will profoundly affect efficacy and must be considered when developing formulations and application methodology. Adding moderate amounts of TIC to a bait will probably not affect mortality of beetles that are present in treated portions of fields.