Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 23, 2013
Publication Date: August 6, 2013
Citation: Castrillo, L., Griggs, M., Vandenberg, J.D. 2013. Granulate ambrosia beetle, Xylosandrus crassiusculus (Coleoptera: Curculionidae), survival and brood production following exposure to entomopathogenic and mycoparasitic fungi. Biological Control. 67:220-226. Interpretive Summary: The granulate ambrosia beetle, Xylosandrus crassiusculus, is one of the most important exotic pests of orchards and nurseries in the U.S. The beetle has a wide host range, including some of the most popular and valuable trees in nurseries, and is difficult to control using conventional insecticides because of its cryptic habits. We evaluated beetle susceptibility to three commercially available strains of microbial control agents. These include two strains of Beauveria bassiana and one of Metarhizium brunneum. Females exposed to beech stems treated with these fungi produced offspring and had low survival after 5 days. Beetles exposed to Trichoderma harzianum, a fungus that parasitizes other fungi, produced galleries with limited growth of the beetle’s fungal symbiont and with fewer offspring. Our results demonstrate the potential of these fungi to act directly, by killing beetles, or indirectly, by limiting symbiont growth. Further testing in the field is planned.
Technical Abstract: The granulate ambrosia beetle, Xylosandrus crassiusculus, is one of the most important exotic pests in orchards and nurseries in the U.S. The beetle has a wide host range, including some of the most popular and valuable trees in nurseries, and is difficult to control using chemical insecticides because of its cryptic habits. In this study we evaluated the susceptibility of X. crassiusculus to three commercial strains of entomopathogenic fungi and also examined gallery formation and brood production among females exposed to these biocontrol agents and a mycoparasitic fungus, Trichoderma harzianum. All three entomopathogens were virulent to X. crassiusculus: Beauveria bassiana strains GHA and Naturalis and Metarhizium brunneum F52 produced mortality among treated adult females at the highest dose (600 conidia per square millimeter) 5 days after inoculation. Females exposed to beech stems treated with entomopathogenic fungi at the highest dose had lower survival rates and produced fewer galleries. All doses tested, however, resulted in females with fewer offspring compared to control. Those exposed to T. harzianum produced galleries with sparse, patchy, or no symbiont growth, many of which had no or few brood present. Some of the females exposed to either B. bassiana or M. brunneum also had galleries with sparse mycelial growth. These results show the potential of entomopathogenic or mycoparasitic fungi in controlling X. crassiusculus, either directly by killing adult females and preventing or reducing brood production or indirectly by suppressing growth or establishment of their fungal symbiont in galleries.