ARS | Publication request: Susceptibility of adult alfalfa leafcutting bees and honey bees to a microbial control agent, Beauveria bassiana

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 5, 2012
Publication Date: N/A

Interpretive Summary: Bee pollination is required for alfalfa seed production, with the alfalfa leafcutting bee and the honey bee being most commonly used, although the alkali bee is also used in some areas. Lygus bugs are common pests in alfalfa seed, and work is being done to develop the fungus Beauveria bassiana as a biological control of lygus bugs, for both alfalfa and cotton. We conducted laboratory bioassays to determine the susceptibility of the alfalfa leafcutting and honey bees to three different strains of this fungus, B. bassiana. Virulence (how quickly the pathogen kills) and pathogenicity (the percentage of bees infected) differed among the fungal strains, but none were highly pathogenic to either bee, although the alfalfa leafcutting bee tended to be more susceptible to all strains than did the honey bee. One strain, 17-41, had very low pathogenicity towards the bees. Thus, it is possible to find fungi that are highly pathogenic to the pest insect, yet have little or no pathogenicity towards bees, such as strain 17-41.

Technical Abstract: Bee pollination is required for alfalfa seed production, with the alfalfa leafcutting bee (Megachile rotundata, Hymenoptera: Megachilidae) and the honey bee (Apis mellifera, Hymenoptera: Apidae) being most commonly used, although the alkali bee (Nomia melanderi, Hymemoptera: Halictidae) is also used in some areas. Lygus spp. (Heteroptera: Miridae) are common pests in alfalfa seed, and the fungus Beauveria bassiana (Balsamo) Vuillemin has been proposed as a microbial control for these pests. We conducted laboratory bioassays to assess the susceptibility of the alfalfa leafcutting and honey bees to three different strains of B. bassiana. Virulence and pathogenicity varied significantly among the fungal strains tested, but none showed high pathogenicity at moderate spore dosages to either bee, although the alfalfa leafcutting bee tended to be more susceptible to all strains than did the honey bee. One strain, 17-41, had very low pathogenicity towards the bees. Thus, it is possible to find fungi that are highly pathogenic to the pest insect, yet have little or no pathogenicity towards bees, such as strain 17-41.