HORTICULTURAL ENTOMOLOGY Influence of Posttreatment Temperature on the Toxicity of Insecticides Against Diaphorina citri (Hemiptera: Psyllidae)

The psyllid Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is one of the most important pests of citrus worldwide because it efÞciently vectors three bacteria in the genus Candidatus Liberibacter that cause the devastating citrus greening disease (huanglongbing). Current management practices for this insect pest rely on multiple sprays of foliar insecticides and one or two applications of soil systemic insecticides per season. Effective psyllid and disease management in Florida requires insecticide applications throughout the entire season over wide ranging temperature and environmental conditions. Using a petri dish bioassay technique, the effect of posttreatment temperature (range, 17Ð37 C) on the toxicity of selected organophosphate (chlorpyrifos and dimethoate), carbamate (carbaryl), avermectin (abamectin), pyrethroid (bifenthrin, zeta-cypermethrin, fenpropathrin, and lambda-cyhalothrin), and neonicotinoid (acetamiprid, imidacloprid, and thiamethoxam) insecticideswas evaluatedagainst adultD. citri. The toxicityof bothorganophosphates showed a positive temperature correlation within the 17Ð37 C range. Similarly, carbaryl (carbamate) andabamectin (avermectin) exhibited increased toxicitywith increasing temperature from17 to 37 C, with abamectin showing higher overall temperature-dependent toxicity against D. citri adults than carbaryl. With the exception of bifenthrin, which showed a positive temperature-dependent toxicity correlation between 27 and 37 C, all other pyrethroids tested exhibited a negative correlation over the temperature range examined. The toxicity of fenpropathrin and lambda-cyhalothrin dramatically decreased with increasing temperature from 17 to 37 C. The neonicotinoids imidacloprid and thiamethoxam exhibited a mixed response to increasing temperature, whereas acetamiprid showed a positive temperature correlation. However, all three neonicotinoids showed positive temperaturedependent toxicity correlations against D. citri adults over the temperature range tested. These data will enable citrus growers to choose themost effective insecticides forD. citri control from the various classes currently available depending on the prevailing temperature conditions.