The exotic ambrosia beetles Xylosandrus crassiusculus (Motschulsky) and Xylosandrus germanus (Blandford) (Coleoptera: Curculionidae: Scolytinae) are

Wood-boring ambrosia beetles (Coleoptera: Curculionidae: Scolytinae), including Xylosandrus spp., are key pests in ornamental nurseries. Knowledge of their acti

Xylosandrus germanus (Blandford) and Xylosandrus crassiusculus (Motschulsky) (Coleoptera: Curculionidae: Scolytinae) are two of the most damaging nonnative ambrosia beetle pests in ornamental plant nurseries. Adult females tunnel into the stems and branches of host plants to create galleries with brood chambers. Hosts are infected with symbiotic Ambrosiella spp. fungi that serve as food for the larvae and adults. Plants can also become infected with secondary opportunistic pathogens, including Fusarium spp. Both X. germanus and X. crassiusculus have broad host ranges, and infestations can result in “toothpicks” of extruded chewed wood and sap flow associated with gallery entrances, canopy dieback, stem and trunk cankers, and plant death. Beetles efficiently locate and preferentially attack living, weakened plants, especially those physiologically stressed by flooding, inadequate drainage, frost injury, or winter injury and low temperature. Maintaining plant health is the foundation of a management plan. Vulnerable hosts can be partially protected with preventive pyrethroid applications in the spring before peak flight and attack, which are monitored using ethanol-based trapping tactics.

Exotic ambrosia beetles are damaging pests in ornamental tree nurseries in North America. The species Xylosandrus crassiusculus (Motshulsky) and Xylosandrus ger

Ambrosia beetles tunnel into the heartwood of trees where they cultivate and feed upon a symbiotic fungus. We assessed the effectiveness of flood stress for making Cercis canadensis L. and Cornus florida L. trees attractive to attack as part of insecticide and fungicide efficacy trials conducted in Ohio and Virginia. Since female ambrosia beetles will not begin ovipositing until their symbiotic fungus is established within the host, we also assessed pre-treatment of trees with permethrin, azoxystrobin, and potassium phosphite on fungal establishment and beetle colonization success. Permethrin reduced attacks on flooded trees, yet no attacks occurred on any of the non-flooded trees. Fewer galleries created within flooded trees pre-treated with permethrin, azoxystrobin, and potassium phosphite contained the purported symbiotic fungus; foundress’ eggs were only detected in flooded but untreated trees. While pre-treatment with permethrin, azoxystrobin, and potassium phosphite can disrupt colonization success, maintaining tree health continues to be the most effective and sustainable management strategy.

Management of ambrosia beetles in ornamental nurseries relies, in part, on insecticide treatments to prevent beetles from boring into trees. However, data on residual efficacy of commonly used pyrethroid insecticides is needed to gauge the duration that trees are protected during spring when peak beetle pressure occurs. Residual efficacy of bifenthrin and permethrin trunk sprays was examined in field trials which used trees injected with 10% ethanol to ensure host attack pressure. Permethrin consistently reduced attacks by Xylosandrus germanus (Blandford; Coleoptera: Curculionidae) and other ambrosia beetles for at least 4 wk, while efficacy of bifenthrin was inconsistent and lasted only about 10 d. Since previous studies demonstrated attacks are positively correlated with host ethanol emissions, we injected trees with 2.5, 5, and 10% ethanol to determine if residual efficacy was affected by attack pressure. Preventive treatments with bifenthrin reduced ambrosia beetle attacks at all concentrations of injected ethanol compared to non-sprayed controls. There was no interaction between attack pressure and insecticide treatment with respect to total attacks or attacks by X. germanus. However, increasing attack pressure did increase the probability of attacks on insecticide treated trees by X. germanus and other Scolytinae. Results from our current study will improve the ability of growers to make decisions on frequency of protective sprays, but residual efficacy of insecticide treatments may decline as attack pressure increases. Cultural practices should therefore maximize host vigor and minimize attack pressure associated with stress-induced ethanol emissions.