Toxicities and Cross-Resistance of Imidacloprid, Acetamiprid, Emamectin Benzoate, Spirotetramat, and Indoxacarb in Field Populations of Culex quinquefasciatus (Diptera: Culicidae)

Simple Summary Culex quinquefasciatus is a major vector of several human and animal diseases. This species' ability to develop resistance to synthetic insecticides can lead to failure to control it. Therefore, we conducted toxicity bioassays of imidacloprid, acetamiprid, emamectin benzoate, spirotetramat, and indoxacarb on five field populations of Cx. Quinquefasciatus from Pakistan. These five populations showed susceptibility to high resistance against imidacloprid, susceptibility to moderate resistance against acetamiprid, susceptibility to emamectin benzoate, susceptibility to spirotetramat, and low-high resistance against indoxacarb. Correlation analyses revealed a significant positive correlation between imidacloprid, acetamiprid, and spirotetramat median lethal concentration values, indicating the possibility of cross-resistance. Meanwhile, there were no significant correlations among the median lethal concentration values of other tested insecticides, indicating the possible absence of cross-resistance. Our findings provide a useful background for the public health authorities, medical entomologists, and pest managers to control Cx. quinquefasciatus. Culex quinquefasciatus is a major vector of several pathogens and is capable of breeding in various aquatic habitats. The extensive and injudicious use of synthetic chemicals against the mosquito species has led to the problem of insecticide resistance. To explore this resistance in detail, toxicity bioassays of imidacloprid, acetamiprid, emamectin benzoate, spirotetramat, and indoxacarb were performed on five Cx. quinquefasciatus field populations from Pakistan in addition to a laboratory susceptible strain. Compared with the susceptible strain, results for the five Cx. quinquefasciatus field populations were as follows: susceptibility to high resistance against imidacloprid (resistance ratio (RR): 0.09-11.18), susceptibility to moderate resistance against acetamiprid (RR: 0.39-8.00), susceptibility to emamectin benzoate (RR: 0.002-0.020), susceptibility to spirotetramat (RR: 0.01-0.07), and low to high resistance against indoxacarb (RR: 3.00-118.00). Correlation analyses revealed a significant positive correlation between imidacloprid, acetamiprid, and spirotetramat median lethal concentration (LC50) values, indicating the possibility of cross-resistance. In contrast, there were no significant correlations between the LC50 values of other tested insecticides, indicating the possible absence of cross-resistance. These results can assist public health authorities, medical entomologists, and pest managers to manage the insecticide resistance of Cx. quinquefasciatus as well as the associated pollution and human health issues.

Automated summary

Culex quinquefasciatus is a major vector of several human and animal diseases. The development of resistance to synthetic insecticides in this species can lead to control failure. This study conducted toxicity bioassays on five Cx. Quinquefasciatus populations and found the possibility of cross-resistance.