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 e arly harvest of potatoes on reducing the size of overwintering Colorado pot ato beetle, Leptinotarsa decemlineata (Say), populations in eastern North C arolina were investigated over 3 yr. Tn large-plot (0.04 ha) experiments, p otato beetle densities and defoliation levels in plots that were either tre ated with B. thuringiensis or left untreated were compared during the seaso n. Similarly, the size of the overwintered potato beetle populations in the se plots was compared the following spring. In a simulated harvest experime nt, Ist-generation adults (generation that overwinters) were collected from untreated and B. th thuringiensis-treated plots at various times and then placed into small held cages containing tubers and dead potato vines. Survi val of these beetles was determined the following spring. Additionally, the effects of early harvests of 'Atlantic' and 'Superior' potatoes on marketa ble tuber yields were examined. Results suggest that a single foliar applic ation of B. thuringiensis made when the large larval populations reached 1 per stem reduced and delayed the development of potato beetle populations a nd, more importantly, suppressed defoliation during the critical bloom stag e. Although overwinter survival and the size of the overwintered population from plots treated with B. thuringiensis the previous season did not diffe r with those from untreated plots, overwinter survival was positively corre lated with an increase in the period between planting and harvest. These re sults suggest that beetle populations could be reduced if potatoes are harv ested before many 1st-generation adults emerge. To accomplish this while mi nimizing the potential for yield loss by harvesting too early, fields of th e early-maturing variety Superior could be harvested as early as 85-92 d af ter planting.