Field evaluation of Beauveria bassiana: its persistence and effects on the pea aphid and a non-target coccinellid in alfalfa.
Several strains of the entomopathogenic fungus Beauveria bassiana have been considered for use as microbial insecticides. Experimental sprays were conducted in an alfalfa [lucerne] field in Oregon, USA, with an aphid-derived strain of B. bassiana to determine its persistence and its effects on pea aphids, Acyrthosiphon pisum, and a non-target aphid predator, the coccinellid Hippodamia convergens. B. bassiana conidia persisted in the field for at least 28 days, when approximately 10% of the original inoculum was still present. In the lower canopy, more conidia were present than on other plant parts and they persisted longer on the leaves in this location. However, conidia were still abundant in the upper canopy, where 97.9% of the aphids and 95.5% of H. convergens larvae were found. Thus, both insect species were exposed to the fungus for at least 1 month. However, pea aphid populations were not affected by the fungus. The predator's incidence was reduced by 75-93% (depending on application rate) early in the season, but was not affected later in the season. Insect life history patterns and weather conditions are likely causes for the differences seen in field effects.