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 efficiently 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, 17-37 degrees 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) insecticides was evaluated against adult D. citri. The toxicity of both organophosphates showed a positive temperature correlation within the 17-37 degrees C range. Similarly, carbaryl (carbamate) and abamectin (avermectin) exhibited increased toxicity with increasing temperature from 17 to 37 degrees 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 degrees 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 degrees 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 temperature-dependent toxicity correlations against D. citri adults over the temperature range tested. These data will enable citrus growers to choose the most effective insecticides for D. citri control from the various classes currently available depending on the prevailing temperature conditions.