Influence of Foliar-Applied Bacillus thuringiensis subsp. tenebrionis and an Early Potato Harvest on Abundance and Overwinter Survival of Colorado Potato Beetles (Coleoptera: Chrysomelidae) in North Carolina

The effects of Bacillus thuringiensis subsp. tenebrionis applications and early harvest of potatoes on reducing the size of overwintering Colorado potato beetle, Leptinotarsa decemlineata (Say), populations in eastern North Carolina were investigated over 3 yr. In large-plot (0.04 ha) experiments, potato beetle densities and defoliation levels in plots that were either treated with B. thuringiensis or left untreated were compared during the season. Similarly, the size of the overwintered potato beetle populations in these plots was compared the following spring. In a simulated harvest experiment, 1st-generation adults (generation that overwinters) were collected from untreated and B. thuringiensis-treated plots at various times and then placed into small Þeld cages containing tubers and dead potato vines. Survival of these beetles was determined the following spring. Additionally, the effects of early harvests of ÔAtlanticÕ and ÔSuperiorÕ potatoes on marketable tuber yields were examined. Results suggest that a single foliar application of B. thuringiensis made when the large larval populations reached1per stemreducedanddelayed thedevelopmentofpotato beetle populations and, more importantly, suppressed defoliation during the critical bloom stage. Although overwinter survival and the size of the overwintered population from plots treated with B. thuringiensis theprevious seasondidnotdifferwith those fromuntreatedplots, overwinter survival was positively correlated with an increase in the period between planting and harvest. These results suggest that beetle populations could be reduced if potatoes are harvested before many 1stgeneration adults emerge. To accomplish this while minimizing the potential for yield loss by harvesting too early, Þelds of the early-maturing variety Superior could be harvested as early as 85Ð92 d after planting.