Penetration of 14c-insecticides (imidacloprid, thiacloprid, thiamethoxam and indoxacarb) in apples to optimize insecticide performance in fruit pest management

Many of the new reduced-risk insecticides including neonicotinoids, IGRs, and oxidiazines hold promise for replacing older pesticides, fruit growers, however, are concerned about their high cost and unique performance characteristics. Understanding the insecticides’ penetrative characteristics will help describe and expand their pest management capabilities for apple IPM. The objective of this study was to determine the penetration of ^14C-insecticides (^14C- thiamethoxam, ^14C-thiacloprid, ^14C-clothianidin and ^14C-indoxacarb) in apples. Cores consisting of the apple cuticle, and flesh from a low wax cuticle apple variety (Golden delicious) and a high wax cuticle variety (Red delicious) were placed in Petri dishes. 14C -insecticides were mixed with formulated compounds dissolved with distillated water. Cores were exposed to the insecticides for 1, 6, and 24 h. After this time the surface cuticle of the fruit was washed, and the core were partitioned into different sections. All sections were dried at 70 oC and processed in a biological oxidizer, and the resulting 14CO2 were trapped in a scintillation vial with cocktail and counted. A profile of spatial insecticide distribution and penetration were performed. In addition, an autoradiography was taken from the cuticle. As the time progressed the insecticides accumulated more in the skin of the fruit. Varying minor amounts were found to penetrate into the flesh of the fruit, depending on the compound, cultivar and time of exposure.