Impact of temperature and humidity on host-pathogen interactions between Beauveria bassiana and a coccinellid

We tested the effect of 2 exposure methods and environmental factors, tempe rature and humidity, on Beauveria bassiana (Deuteromycotina: Hyphomycetes) mycosis in Hippodamia convergens Guerin-Meneville (Coleoptera: Coccinellida e). We found that the standard EPA bioassay method of exposing nontarget in sects by immersion resulted in a per-insect dose that was 5 times greater t han that from spray applications. However, this difference did not signific antly affect mycosis levels in a simulation of field applications conducted in the greenhouse, in contrast, differences in environmental conditions be tween the laboratory and greenhouse had a large effect on mycosis. Constant temperatures between 15 and 3.5 degrees C had a significant effect on both germination rate and vegetative growth of B bassiana, with the fastest ger mination occurring at 25-32 degrees C and the fastest growth occurring at 3 0 degrees C. Although temperature affected the rate of conidial germination , total germination eventually reached 97-100% at all temperatures. Contrar y to these results, levels of mycosis in lady beetles decreased as temperat ures increased over this same range, Although high levels of humidity are r equired for conidial germination, we found no well-defined threshold period of high humidity exposure required for mycosis in this insect. In other wo rds, the effects of temperature and humidity on free-living stages of the p athogen are not sufficient to explain the effect of these factors on mycosi s. We suggest that temperature and humidity also affect physiological inter actions between the host and pathogen.