Dormant-Season Sprays Affect the Mortality of Peach Twig Borer (Lepidoptera: Gelechiidae) and Its Parasitoids

Abstract

The effectiveness of a dormant-season oil spray with or without an organo-phosphate insecticide for control of the peach twig borer, Anarsia lineatella Zeller, was investigated. Results from experimental field plots indicated that an application of a dormant oil alone resulted in poor control of peach twig borer inside the hibernaculum. Limb crotches containing live peach twig borer in hibernacula were field-collected and treated in the laboratory with either organophosphate (diazinon) and oil insecticides or varying concentrations of a dormant oil alone. Significantly greater larval mortality was found in the organophosphate treatment, whereas mortality in the oil treatments was not significantly different from the control. Overwintering larvae from an insectary colony that were exposed to two rates of an oil had significantly greater mortality than larvae in a control sprayed with water, indicating that peach twig borer inside the hibernaculum may be protected from the insecticidal activity of the oil. To determine the effect of dormant sprays on parasite species composition and numbers, peach twig borer were field-collected and reared through to adult moths or parasitoids. Parasitoid activity was low, with only 0.79% of peach twig borer parasitized (n = 3,032). Macrocentrus ancylivorus Rowher, Spilochalcis n.sp. aff torvina (Cresson), Paralitomastix pyralidis (Ashmead), Erynnia tortricis (Coquillett), Euderus cushmani Crawford, and an unidentified braconid species were reared from 2,528 peach twig borer collected in orchards that did not receive an organophosphate insecticide. A single parasitoid, M. ancylivorus , was reared from 504 peach twig borer collected in orchards treated with an organophosphate insecticide. The virtual absence of peach twig borer parasitoids in fields treated with an organophosphate may be a reflection of the low number of moth pests collected at those sites.