Effects of a granulosis virus,andBacillus thuringiensis on life-table parameters of the potato tubermoth,Phthorimaea operculella

Experiments were conducted to evaluate the effect of 3 different concentrations of a granulosis virus (GV), and a standard application ofBacillus thuringiensis Berliner, on the life table parameters of the potato tubermothPhthorimaea operculella (Zeller) in the laboratory. Survival from egg to adult emergence was lowest (0.4%) and no reproduction occurred when larvae were fed on tubers treated withB. thuringiensis (i.e. 200 mg Thiricide/kg potatoes). Survival was 0.8, and 11.1% on tubers treated with 2.0, and 0.2 larval equivalents/kg potatoes (LE) of the GV, respectively, and was significantly (p<0.05) reduced compared to that for the lowest GV concentration (0.002 LE), and the control, i.e. 34.7, and 32.5% survival, respectively. However, generation time was not affected by the GV and fecundity was reduced only at the highest concentration. As a result, the intrinsic rate of increase (r_m) was significantly reduced at the highest, slightly reduced at the intermediate, and was not different for the lowest GV concentration as compared to the control, i.e. 0.0004, 0.0071, and 0.0100 compared to 0.0105, respectively. The implications for a potential biological control of the potato tubermoth in rustic potato stores are discussed.