Toxicity of insecticides to Aphytis melinus, 2011

A laboratory test was conducted to determine the impact of insecticides on adult Aphytis melinus, a key parasitoid wasp of the California red scale, Aonidiella aurantii (Maskell). A 28-yr-old ‘Washington’ navel orange Citrus sinensis (L.) Osbeck orchard at the Lindcove Research and Extension Center, Exeter, CA, was treated using pesticide rates and water volumes for control of citricola scale, Coccus pseudomagnoliarum (Kuwana). Foliar treatments were applied in 500 gpa of water on 4–5 Aug 2011 to individual trees in an RCB using a Bean hand-sprayer at 300 psi. One citrus twig approximately 25 cm long with 5–10 leaves was cut from each of 6 treatment or untreated check trees and placed separately in 1 gal glass jars at approximately weekly intervals. Aphytis melinus adults were immobilized with CO₂ for 1.5 min, and 50 wasps were placed into each jar. Twenty-four hours after exposure to the leaves and twigs, the dead A. melinus were counted. The mean percentage survival of A. melinus was arcsine (square root (x)) transformed to normalize variances and then analyzed using a 1-way ANOVA followed by Fisher’s Protected Least Significant Difference test (P = 0.05) to separate means.

All insecticides tested, applied at rates, and water volumes for C. pseudomagnoliarum control were highly toxic to A. melinus for more than 7 wk (Table 1). More than 90% survival of A. melinus did not occur until 8 WAT for Bexar and Volium Flexi, 9 WAT for Agri-Flex, and 10 WAT for Lorsban Advanced (Table 1). Actara never allowed more than 77.7% survival during testing.¹

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