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 reproductive potential of female survivors, egg viability, and total egg production within cohorts of adult western corn rootworm, Diabrotica virgifera virgifera, was investigated. Newly emerged female beetles were mated and then treated with a suspension of B. bassiana (5 × 107 conidia/ml) 5, 10, or 15 days later. Egg production and percentage hatch were monitored over a 6-week period. Females surviving treatment at 10 days postemergence produced on average 30% fewer eggs during the initial 2 weeks of the oviposition period compared with other treatment schedules or untreated beetles. Overall reproductive capacity (mean No. eggs/female) was significantly lower in cohorts treated with B. bassiana compared with untreated cohorts, primarily due to differential mortality. Early treatment of beetles (5 days postemergence) resulted in a greater reduction in total egg production within the cohort compared with later treatments (10 and 15 days postemergence). Egg viability 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 could potentially reduce oviposition within adult populations of D. virgifera virgifera by approximately 70%.