Susceptibility of different castes of the red imported fire ant(Solenopsis invicta Buren) to insecticides
Author of the article:GUO Wen-Ju** LIU Jia-Li CUI Ru-Kun ZENG Xin-Nian***
Author's Workplace：Key Laboratory of Natural and Chemical Biology of the Ministry of Education, South China Agricultural University
Key Words：Solenopsis invicta Buren, fipronil, beta-cypermethrin, indoxacarb, toxicity
Abstract： [Objectives] Different castes of the red imported fire ant (Solenopsis invicta Buren) play different roles in the colony. However, the susceptibility of different castes of this ant to insecticides is still not clear. [Methods] In this study, the contact toxicities of three insecticides, fipronil, beta-cypermethrin and indoxacarb, to different castes of the red imported fire ant were measured by topical application. [Results] There were significant differences in the susceptibility of ants to the different insecticides; ants were highly sensitive to fipronil, then to the beta-cypermethrin, and least sensitive to indoxacarb. The susceptibility of different castes to these insecticides also varied. Winged adults and queens were highly susceptible and, with the exception of beta-cypermethrin, soldiers were less susceptible than winged ants and queens. Workers were less sensitive than soldiers. Fourth-instar larvae were the least susceptible to the three insecticides tested; the LD50 values of which were 428.77 mg/kg、699.77 mg/kg and 1 159.95 mg/kg, respectively. Regression analysis shows that susceptibility to different insecticides differed significantly among individuals in same caste. This was especially true for soldier and worker ants. For example, with respect to fipronil, the slope values for these castes were 1.1 and 1.8, respectively. [Conclusion] However, individuals showed little variation in their susceptibility to indoxacarb, with slope values > 4.7 and reaching 7.8 in worker ants. Though we didn’t observe a general pattern in susceptibility to different insecticides among individuals of the same caste, individual differences were basically low, especially in fourth-instar larvae, winged male ants and queens, all of which had slope values > 4.0. These results provide theoretical guidance for the use of insecticides to control fire ants in the field.