Association Between Bagrada hilaris Density and Feeding Damage in Broccoli: Implications for Pest Management

Bagrada hilaris (Burmeister) (Hemiptera:Pentatomidae) has become a serious economic pest of brassica crops in Arizona and southern California. Feeding damage on broccoli can result in excessive seedling mortality and, on established plants, in malformed plants which are not commercially marketable. Although management tactics have been developed for this new pest, a reliable sampling technique for estimating adult density is lacking. Here, we analyzed data from 18 insecticide trials conducted from 2011 to 2014 in plots planted to broccoli to determine if estimates of fresh feeding damage on broccoli plants can be used to forecast B. hilaris densities. The proportion of plants with fresh feeding damage in a plot was significantly affected by year, trial nested within year, number of insecticides applied, and time after insecticide application. Average density of B. hilaris adults per plant in a plot was significantly affected by year, trial nested within year, and number of insecticides applied, while time after insecticide application had a marginal effect on population density. Across plots and years, the proportion of plants with fresh feeding damage was strongly and positively associated with the average number of B. hilaris adults per plant. Our results suggest that sampling young plants for signs of fresh feeding damage will provide a reliable and accurate sampling technique for monitoring B. hilaris in broccoli fields. We recommend that growers and pest control advisers focus their monitoring efforts on sampling broccoli plants for the presence of fresh feeding damage, rather than adults alone, when making pest management decisions.