Resistance to carbaryl in populations of the parasite Aphytis melinus debach (Hymenoptera: Aphelinidae): Implications for california citrus IPM

Abstract

Abstract Populations of Aphytis melinus DeBach collected from Valencia orange groves in McFarland and Springville, California, during 1989 were as tolerant to residues of carbaryl as a laboratory-selected (R) strain of the parasite. Bioassays using carbaryl-treated plastic cups were conducted on adult A. melinus collected from the McFarland and Springville orchards prior to and after releases of the R strain into the orchards. Survival of the prerelease colonies collected from both orchards was comparable to that of the laboratory-selected R strain, which suggested that endemic populations of A. melinus in these orchards had developed resistance to carbaryl. Given the high carbaryl tolerance of the endemic A. melinus populations, the establishment and recovery of the R strain could not be confirmed in either orchard. A survey of 11 A. melinus populations collected from citrus orchards during 1990–1991 indicated that resistance had developed in at least one area of California. Four of six colonies collected from the San Joaquin Valley showed high tolerances to carbaryl using the standard bioassay. The four resistant colonies originated from Tulare County, and the two susceptible colonies were from Kern and Fresno counties. Colonies collected outside the San Joaquin Valley in Ventura (n = 1), San Bernadino (n = 1), and Riverside (n = 3) counties showed no evidence of resistance. Concentration/mortality tests using carbaryl-treated plastic cups conducted on populations of A. melinus obtained from two commercial insectaries indicated that both parasite colonies were susceptible. Commercial insectaries mass rear and release the laboratory-selected strain of A. melinus in citrus orchards throughout California. Management strategies for implementing the R strain in citrus pest management systems are discussed.