Toxicity and residual effectiveness of insecticides on insecticide-treatedspheres for controlling females of Rhagoletis pomonella (Diptera : Tephritidae)

This study evaluated the toxicity of five technical-grade insecticides of f our different classes to apple maggot females, Rhagoletis pomonella (Walsh) ,following a 10-min exposure period in insecticide-coated glass jars, with or without a feeding stimulant (sucrose) present. According to LC90 values for toxicity by ingestion and tarsal contact, imidacloprid was 1.5 times mo re toxic than dimethoate or abamectin, diazinon was less toxic, and phloxin e B (a phototoxic dye) least toxic. Based on LC50 values for tarsal contact alone, dimethoate was 2.3, 4.0, and 18.4 times more toxic than imidaclopri d, abamectin, and diazinon, respectively. Contact alone with phloxine B cau sed no mortality. When exposure was assessed using spheres coated with a la tex paint mixture containing sucrose and formulated dimethoate (Digon 400 E C) or imidacloprid (Provado 1.6 F) at concentrations ranging from 5 to 70 g (AI)/cm(2), both insecticides showed reduced effectiveness compared with t oxicities from glass jar tests, with Digon two times more toxic than Provad o. After exposure to artificial rainfall and retreatment with sucrose, Digo n- and Provado-treated spheres exhibited greatest residual effectiveness, w ith diazinon-treated spheres less effective. Spheres treated with formulate d abamectin (Agri-Mek 0.15 EC) at 1.0% (AI) performed only slightly better than phloxine B-treated spheres, which completely lost effectiveness after exposure to rainfall. Spheres treated with formulated imidacloprid (Merit 7 5 WP) at 1.5% (AI) showed equal or better residual efficacy in killing appl e maggot flies (>80% mortality, shelter lethal duration of feeding) over a 12-wk exposure period to outdoor weather than spheres treated with Digon at 1.0% (AI) after both types were retreated with sucrose. Our results indica te that imidacloprid is a promising safe substitute for dimethoate as a fly killing agent on lure-kill spheres. Imidacloprid formulated as Merit 75 WP had greater residual efficacy than imidacloprid formulated as Provado 1.6 F.