Monitoring ambrosia beetles in ornamental nurseries: the influence of flood-stress and protective sprays

Ambrosia beetles (Coleoptera: Curculionidae: Scolytinae), particularly Xylosandrus crassiusculus, are important pests in ornamental trees grown in nurseries. Growers begin making frequent applications of insecticides in early spring to prevent or hinder ambrosia beetle attacks; applications of these protective sprays are typically made biweekly and often result in unwanted drift.
Flood-stressed trees emit ethanol, the primary cue for ambrosia beetle host selection, increasing the trees susceptibility. Our objective was to reduce the economic impact of ambrosia beetles in nurseries by improving grower irrigation practices and minimizing insecticide usage. Experiments were conducted at a research field in Raleigh, North Carolina in 2015. In order to effectively time insecticide treatments with the emergence of ambrosia beetles, ethanol baited bottle traps were deployed in early March to monitor beetle activity. There were four treatments: normally watered sprayed trees, normally watered unsprayed trees, over-watered sprayed trees and over-watered unsprayed trees. These treatments were applied to two common ornamental trees: flowering dogwood (Cornus florida) and Japanese snowbell (Styrax japonicas) with a total of 24 of each species and six replicates each. C. florida under the normal water treatment received no attacks, regardless of being sprayed or not. C. florida in the over-watered treatment that were sprayed received about half as many attacks as those that had not been sprayed. S. japonicas under the normal water treatment that had been sprayed received approximately 10 times fewer attacks than those left untreated. S. japonicas that were over-watered and treated received 3 times fewer attacks than those left untreated.