The ambrosia beetles Xylosandrus crassiusculus and X. germanus are among the most important invasive pests of orchards and nurseries in the US. Both have a wide host range and are difficult to control because of their cryptic habits. We conducted studies on the use of biocontrol fungi and results showed their potential in targeting both foundresses and their brood inside tree galleries. We observed that both species were susceptible to entomopathogenic fungi Beauveria bassiana and Metarhizium brunneum, resulting in early death of foundresses and reduction in brood produced. Cadavers of infected foundresses also generated fungal inocula that infected their brood, which further reduced viable brood number. Although most of the studies targeted first generation foundresses that emerged in spring, additional studies with next generation foundresses showed that these could be targeted as well using a “rescue spray” strategy. Antagonistic interactions between B. bassiana or M. brunneum and beetle symbionts could also enhance the impact of these biocontrol fungi on beetle populations since the beetles depend on their symbionts for food. Another strategy tested was to target the symbionts directly by use of mycoparasitic fungi like Trichoderma spp. Our studies showed that exposure of both species to T. harzianum-treated logs resulted in beetle galleries with sparse or no symbiont growth, many of which had few or no progeny present. These results demonstrated the potential of entomopathogenic or mycoparasitic fungi against ambrosia beetles and/or their symbionts and indicated ways by which these fungi can be used for beetle management.
