Responses of northern and western corn rootworms to semiochemical attractants in corn fields

Small plots (18 × 18 m) were treated with grids of cotton wicks that contained semiochemicals for adultDiabrotica barberi Smith and Lawrence, the northern corn rootworm (NCR). In plots treated with eugenol (350 g/hectare), NCR were attracted to point sources of the compound, but there were no significant changes in numbers of either NCR orD. virgifera virgifera LeConte, the western corn rootworm (WCR), found on plants in the plots. In plots treated with 12.5 mg/hectare of 8R-methyl-2R-decyl propanoate (2R,8R-MDP, the apparent female-produced sex pheromone of NCR and WCR), males of both species were attracted to point sources, but beetles did not congregate within treated plots. With racemic 2,8-MDP at 1.0 g/hectare, male WCR were attracted into plots, but NCR of both sexes were strongly repelled. In a separate study, capture of beetles at pheromone-baited traps declined when the surrounding area contained wicks that emitted racemic 2,8-MDP. In treated plots, male WCR were relatively inefficient at finding pheromone sources. With NCR, emigration from plots could account totally for the observed 3- to 10-fold reduction in catch at 0.01-1.0 g/hectare.