Relative Toxicity of Six Insecticides to Cycloneda sanguinea and Harmonia axyridis (Coleoptera: Coccinellidae)

Abstract

Two ladybeetles, Cycloneda sanguinea (L.) and Harmonia axyridis Pallas, were exposed to leaf residues and topical applications of six insecticide formulations commonly used in citrus production in Florida. Exposure of larvae to leaf residues of chlorpyrifos corresponding to 1/100th the recommended field rate caused 55 and 73 percent mortality to larvae of C. sanguinea and H. axyridis, respectively. Cycloneda sanguinea was more sensitive than H. axyridis to all other materials tested. Both fenpropathrin and ethion plus petroleum oil caused significant mortality of larvae of both species as a leaf residue at the field rate and of C. sanguinea larvae at 1/10th the field rate. Sublethal doses of ethion delayed larval development in both species. Imidacloprid was toxic to larvae of both species as a leaf residue at the recommended rate and at 1/10th the recommended rate following topical application. Topical application of imidacloprid at the recommended rate killed 84.6% of adult C. sanguinea, whereas H. axyridis adults were unaffected. Adult beetles survived topical applications of chlorpyrifos, ethion + petroleum oil, and fenpropathrin at concentrations that were lethal to larvae. Esteem® (Valent USA Corp., Walnut Creek, CA) and Spinosad® (Dow Agrosciences, Indianapolis, IN) were relatively benign but did cause 38% and 28% mortality, respectively, of C. sanguinea larvae in topical assays. Fenpropathrin and Spinosad demonstrated repellency to adults of C. sanguinea, but not to adults of H. axyridis. The generally greater sensitivity of C. sanguinea to insecticides may represent a selective disadvantage for this native species in the citrus ecosystem relative the introduced H. axyridis.