Effects of cold-acclimation, pathogen infection, and varying temperatures on insecticide susceptibility, feeding, and detoxifying enzyme levels in Diaphorina citri (Hemiptera: Liviidae)

摘要

Infection of Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), with ‘Candidatus’ Liberibacter asiaticus (Las), the causal pathogen of citrus greening disease or huanglongbing, increases psyllid susceptibility to insecticides. Diaphorina citri populations in citrus occur year-round in tropical and sub-tropical habitats, and thus insecticide applications for managing this plant disease vector occur over a wide temperature range (10–40 °C). During the winter season, D. citri is occasionally exposed to periods of freezing temperatures, when temperatures fall below ?6.5 °C. In this investigation, we compared insecticide susceptibility of uninfected and Las-infected D. citri at various temperatures (20–37 °C). Cold-acclimated (6 ± 1 °C) D. citri adults were less susceptible to neonicotinoid insecticides as compared with non-acclimated controls, but this trend was not observed for other insecticides tested. A positive correlation between temperature and percentage mortality caused by chlorpyriphos, imidacloprid, spinetoram, and thiamethoxam was found irrespective of infection status when evaluated at temperatures ranging between 20 and 37 °C. In contrast, a negative correlation between temperature and percentage mortality was observed for fenpropathrin for both infected and uninfected psyllids. Glutathione S-transferase levels were negatively correlated with temperature, whereas levels of cytochrome P450 and general esterase were not correlated with temperature fluctuations. These results indicate that altered insecticide susceptibility due to temperature may not be related to glutathione S-transferase, cytochrome P450, and general esterase levels. Diaphorina citri adults that carried the Las bacterium had reduced CYP4 transcript and protein levels, and ingested less than uninfected counterparts, as measured by the production of honeydew. Diaphorina citri adult feeding was greatest at 32 °C within the temperature range tested. Overall, annual temperature fluctuation does not appear to be a major factor impacting management of D. citri.?ResumenLa infección del psílido asiático de los cítricos, Diaphorina citri Kuwayama (Hemiptera: Liviidae), con ‘Candidatus’ Liberibacter asiaticus (Las), el patógeno que causa Huanglongbing, aumenta la susceptibilidad del psílido a los insecticidas. Poblaciones de D. citri en cítricos se producen durante todo el a?o en los hábitats tropicales y subtropicales, de ahi que las aplicaciones de insecticida para el manejo de este vector de enfermedades de las plantas ocurren en un amplio rango de temperaturas (10–40 °C). Durante la temporada de invierno, D. citri ocasionalmente se expone a períodos de congelación, cuando las temperaturas caen por debajo de ?6.5 °C. En esta investigación, se comparó la susceptibilidad a insecticidas de D. citri infectados y no infectados de Las a diversas temperaturas (20–37 °C). Los adultos de D. citri aclimatadas al frío (6 ± 1 °C) fueron menos susceptibles a los insecticidas neonicotinoides, en comparación con los controles no aclimatados, pero esta tendencia no se observó para otros insecticidas probados. Se encontró una correlación positiva entre la temperatura y el porcentaje de mortalidad a clorpirifos, imidacloprid, spinetoram y tiametoxam independente del estado de la infección cuando se evalúa a 20–37 °C. En contraste, se observó una correlación negativa entre la temperatura y el porcentaje de mortalidad para fenpropatrin tanto en los psílidos infectados y no infectados. Los niveles de glutatión S- transferasa se correlacionaron negativamente con la temperatura, mientras que los niveles de citocromo P450 y esterasa en general no se correlacionaron con los cambios de temperatura. Estos resultados indican que la susceptibilidad a los insecticidas alterados debido a la temperatura puede no estar relacionada con la glutatión S-transferasa, citocromo P450, y los niveles de esterasa generales. Los adultos de D. citri que llevan la bacteria Las tenian