Flood stress as a technicque to assess preventive insecticide and fungicide treatments for protecting trees against ambrosia beetles

Authors: Ranger, Christopher; SCHULTZ, PETER - Virginia Polytechnic Institution & State University; Reding, Michael - Mike; FRANK, STEVEN - North Carolina State University

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2016
Publication Date: 8/16/2016
Publication URL: http://handle.nal.usda.gov/10113/63345
Citation: Ranger, C.M., Schultz, P.B., Reding, M.E., Frank, S.D. 2016. Flood stress as a technicque to assess preventive insecticide and fungicide treatments for protecting trees against ambrosia beetles. Insects. 7(3) 40; doi:10.3390/insects7030040.

Interpretive Summary: Ambrosia beetles tunnel into the heartwood of trees where they cultivate and feed upon a symbiotic fungus. We assessed the effectiveness of flood stress as a tactic for making trees attractive and vulnerable to attack as part of insecticide and fungicide efficacy trials conducted under field conditions in Ohio and Virginia. Since females will not begin laying eggs until their symbiotic fungus is established within the host, we also assessed treatment of flooded and non-flooded trees with an insecticide (permethrin) and fungicide (azoxystrobin and potassium phosphite) on attacks, fungal establishment, and the presence of eggs, larvae, pupae, and foundress adults. Permethrin, but not azoxystrobin or potassium phosphite, reduced attacks on flooded trees deployed in Ohio and Virginia. Permethrin and azoxystrobin reduced the number of galleries within flooded trees deployed in Ohio containing the white conidial form of the symbiotic fungus and foundress’ eggs. All of the flooded and untreated trees deployed in Ohio and Virginia were attacked, but none of non-flooded trees. While pre-treatment with permethrin and azoxystrobin can reduce attacks, fungal establishment, and/or oviposition, maintaining tree health continues to be the most effective management strategy

Technical Abstract: The exotic ambrosia beetles Xylosandrus germanus, Xylosandrus crassiusculus, and Xylosandrus compactus tunnel into the heartwood of trees where they cultivate and feed upon a symbiotic fungus. We assessed the effectiveness of flood stress as a tactic for making trees attractive and vulnerable to attack as part of insecticide and fungicide efficacy trials conducted under field conditions in Ohio and Virginia. Since females will not begin ovipositing until their symbiotic fungus is established within the host, we also assessed pre-treatment of flooded and non-flooded trees with permethrin, azoxystrobin, and potassium phosphite on attacks, fungal establishment, and the presence of eggs, larvae, pupae, and foundress adults. Permethrin, but not azoxystrobin or potassium phosphite, reduced attacks on flooded trees deployed in Ohio and Virginia. Permethrin and azoxystrobin reduced the number of galleries within flooded trees deployed in Ohio containing the white conidial form of the symbiotic fungus and foundress’ eggs. All of the flooded and untreated trees deployed in Ohio and Virginia were attacked, but none of non-flooded trees. While pre-treatment with permethrin and azoxystrobin can reduce attacks, fungal establishment, and/or oviposition, maintaining tree health continues to be the most effective management strategy.