Beauveria bassiana and Paecilomyces fumosoroseus are two naturally occurring fungi that are known to infect the Russian wheat aphid and that are being commercially developed for insect control. A newly-developed standardized laboratory bioassay was used to test the relative virulence of several isolates of each of these two fungi against Russian wheat aphid. This assay includes estimates of spore inoculum viability (ability to germinate and grow) in addition to the more typical growth and sporulation parameters used in other assays.
Aphids were much less susceptible to B. bassiana than to P. fumosoroseus in standardized screening assays. There was a relatively narrow range of potency for the 23 isolates of B. bassiana and the 14 isolates of P. fumosoroseus tested. However, the Russian wheat aphid is readily susceptible at doses that are logistically and economically achievable in the field. This assay method is quite sensitive compared with other assays, so it is being used in additional studies on factors that may affect aphid susceptibility to these fungi, such as temperature, relative humidity, host plant variety, and insect age. Field research on effective control of this aphid is also under way.
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