Potential pesticides for control of a recently introduced ambrosia beetle (Euwallacea sp.) in southern California

Abstract

Polyphagous shot hole borer (PSHB) has recently invaded southern California. This beetle attacks more than 200 host tree species, including avocado (Persea americana Mill.) and many important native, urban landscape and nursery stock trees including sycamore (Platanus racemosa Nutt.), and box elder (Acer negundo L.). The beetle, along with its associated fungi, causes branch dieback and tree mortality in a large variety of tree species. Due to the severity of the impact of PSHB, short-term management tools must include chemical control options for the industry and private landowners to protect trees. We assessed the effectiveness of systemic and contact insecticides for control of PSHB in laboratory tests using fresh-cut castor bean (Ricinus communis L.) branches. Castor bean was chosen because, as a weedy species, it is widely available, and it is a preferred host for the beetles. We conducted field tests using mature, weedy, infested field-grown castor bean. We also surveyed infested coral trees (Erythrina corallodendron L.) in an established residential landscape. For field-grown infested castor bean, beetle activity was lowest for plants treated with bifenthrin, imidacloprid and dinotefuran. Bifenthrin was the most effective insecticide for reducing beetle attacks and gallery formation in castor bean branches in laboratory experiments with cut branches. Dinotefuran was more variable in effectiveness in laboratory trials. Fenpropathrin, clothianidin and orange oil extracts did not differ from untreated controls in beetle attacks and gallery formation. Based on these results, bifenthrin and imidacloprid were selected for further testing in combination with fungicides for control of PSHB.