Fitness costs associated with thiamethoxam and imidacloprid resistance in three field populations ofDiaphorina citri(Hemiptera: Liviidae) from Florida

Insecticide resistance is an increasing problem in citrus production. The Asian citrus psyllid,Diaphornia citriKuwayama, is recognized as one of the most important citrus pests worldwide and it has developed resistance in areas where insecticides have been overused. The development of insecticide resistance is often associated with fitness costs that only become apparent in the absence of selection pressure. Here, the fitness costs associated with resistance to thiamethoxam and imidacloprid were investigated in three agricultural populations ofD. citrias compared with susceptible laboratory colonies. Results showed that all field populations had greater resistance than laboratory susceptible colonies. For both thiamethoxam and imidacloprid, aCandidatusLiberibacter asiaticus-positive (CLas(+)) colony was more susceptible than theCLas(-)colony. Resistance ratios ranged from 7.65-16.11 for imidacloprid and 26.79-49.09 for thiamethoxam in field populations as compared with a susceptible,CLas(-)laboratory strain. Among three resistant field populations, a significantly reduced net reproductive rate and finite rate of population increase were observed in a population from Lake Wales, FL as compared to both susceptible strains. The fecundity of field populations from Lake Wales, FL was statistically lower than both laboratory susceptible populations. Certain changes in morphological characteristics were observed among resistant, as compared, with susceptible strains. Our data suggest fitness disadvantages associated with insecticide resistance inD. citriare related to both development and reproduction. The lower fitness ofD. citripopulations that exhibit resistance to neonicotinoid insecticides should promote recovery of sensitivity when those populations are no longer exposed to thiamethoxam and/or imidacloprid in the field. The results are congruent with a strategy of insecticide rotation for resistance management.