Location: Application Technology ResearchTitle: Residue age and tree attractiveness influence efficacy of insecticide treatments against ambrosia beetles (Coleoptera: Curculionidae)
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2017
Publication Date: 12/19/2017
Citation: Reding, M.E., Ranger, C.M. 2017. Residue age and tree attractiveness influence efficacy of insecticide treatments against ambrosia beetles (Coleoptera: Curculionidae). Journal of Economic Entomology. 111:269-276.
Interpretive Summary: Attacks by exotic ambrosia beetles often lead to wilting, stem dieback, or death of nursery trees. The pyrethroids bifenthrin and permethrin are the most effective materials for managing ambrosia beetles in ornamental tree nurseries, but their efficacy is inconsistent. Assessing residual activity of bifenthrin and permethrin is important for gauging the duration that trees are protected by these materials. Ambrosia beetles are attracted to trees that emit stress-induced ethanol, and attraction increases as ethanol emission increases. Field observations indicate efficacy of insecticides against ambrosia beetles might decline as attractiveness of trees increases. The objectives of the current research were to: 1) determine the residual efficacy of bifenthrin and permethrin against ambrosia beetles, on ornamental trees; and 2) examine the relationship between host attractiveness and efficacy of insecticides at preventing ambrosia beetle attacks. Results from our study provide insight into the duration for which trees can be protected, such that the residual efficacy of permethrin was longer than bifenthrin for reducing attacks. In particular, permethrin prevented attacks from occurring for at least 4 weeks, while bifenthrin was more inconsistent and only lasted about 10 days. However, our current study indicates that the degree of host attractiveness can influence efficacy and that trees emitting comparatively high levels of stress-induced ethanol are unlikely to be well protected. Management of ambrosia beetles will therefore benefit from cultural practices that reduce the potential for tree injury and stress-induced ethanol emissions.
Technical Abstract: Management of ambrosia beetles in ornamental nurseries relies, in part, on treatments of insecticides to prevent beetles from boring into trees emitting stress-induced ethanol. However, data on residual efficacy of commonly used pyrethroid insecticides is warranted to gauge the duration that trees are protected during peak beetle pressure. Furthermore, field observations suggest that efficacy of insecticide treatments against ambrosia beetles may be influenced by attractivity of trees, but research is lacking. Residual efficacy of bifenthrin and permethrin was examined in field trials using trees injected with 10% ethanol to ensure host attractiveness. Permethrin consistently reduced attacks by Xylosandrus germanus (Blandford) and other ambrosia beetles for at least 4 wks, while efficacy of bifenthrin was inconsistent and only lasted 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 the level of host attractiveness. Preventive treatments with bifenthrin reduced ambrosia beetle attacks at all concentrations of injected ethanol compared to non-sprayed controls. There was no interaction between level of host attractiveness and insecticide treatment on total attacks or attacks by X. germanus. However, increasing host attractiveness 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 host attractiveness increases. Cultural practices should therefore maximize host vigor and minimize host attractiveness associated with stress-induced ethanol emissions.