Influences of impatiens pollen and exposure to Beauveria bassiana on bionomics of western flower thrips Frankliniella occidentalis

Adult female western flower thrips, Frankliniella occidentalis, were exposed for 24 h to impatiens leaf disks treated with Beauveria bassiana at low and high application rates (ca. 100 and 1000 viable conidia/mm2) and subsequently maintained on impatiens leaf disks supplemented or not supplemented with impatiens pollen. Offspring production and mortality of insects were monitored daily. Exposure to B. bassiana at the low and high rates significantly reduced thrips longevity by 3.9 and 4.0 days, reduced the ovipositional period by 3.4 and 3.0 days, and reduced lifetime fecundity by 22 and 46% at the low and high rates, respectively. Infection by B. bassiana resulted in a sublethal (pre-mortem) effect on offspring production, decreasing offspring production on the day before death by 1.2 offspring/female. Pollen supplements had no effect on adult female thrips longevity, yet did significantly increase both daily (2.3 and 3.8 times) and lifetime fecundity (2.1 and 3.6 times) compared to control insects in tests at the low and high rates, respectively. No significant Beauveria x pollen interactions were detected at the low rate; however, a marginally significant pollen x B. bassiana interaction was present in tests of both daily and lifetime fecundity. There was a significant effect of B. bassiana on lifetime offspring production in the presence of pollen, but the effect was not detectable in the no pollen treatment. The increase in both daily and lifetime offspring production in the presence of pollen and the slow action of B. bassiana suggest that if B. bassiana is to be used successfully as a thrips management tool in impatiens crops, it must be applied before pollen becomes present and targeted against thrips immature stages to kill the insects before they reach reproductive maturity.