Effect of Beauveria bassiana on the fecundity of western corn rootworm, Diabrotica virgifera virgifera (Coleoptera : Chrysomelidae)

The effect of the entomopathogenic fungus, Beauveria bassiana, on the repro ductive potential of female survivors, egg viability, and total egg product ion within cohorts of adult western corn rootworm, Diabrotica virgifera vir gifera, was investigated. Newly emerged female beetles were mated and then treated with a suspension of B. bassiana (5 X 10(7) conidia/ml) 5, 10, or 1 5 days later. Egg production and percentage hatch were monitored over a 6-w eek period. Females surviving treatment at 10 days postemergence produced o n average 30% fewer eggs during the initial 2 weeks of the oviposition peri od compared with other treatment schedules or untreated beetles. Overall re productive capacity (mean No. eggs/female) was significantly lower in cohor ts treated with B. bassiana compared with untreated cohorts, primarily clue to differential mortality. Early treatment of beetles (5 days postemergenc e) resulted in a greater reduction in total egg production within the cohor t compared with later treatments (10 and 15 days postemergence). Egg viabil ity declined significantly over time for all treatments with no difference in percentage hatchability of eggs between treated and untreated females. A properly timed application of B. bassiana causing 75% beetle mortality cou ld potentially reduce oviposition within adult populations of D. virgifera virgifera by approximately 70%.