Feeding response of the cotton aphid, Aphis gossypii, to sublethal rates of flonicamid and imidacloprid

The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is an important sap-sucking pest of many plants, including melons and peppers. This study was conducted to determine the effects of sublethal exposure to flonicamid and imidacloprid and the mechanisms by which these insecticides affect the feeding behavior of A.gossypii. The median lethal concentrations (LC50) of flonicamid and imidacloprid for adult A.gossypii were 2.40 and 1.92mgl(-1), respectively. The lower lethal concentrations of flonicamid were 1.01mgl(-1) (LC30) and 0.29mgl(-1) (LC10), and those of imidacloprid were 0.82mgl(-1) (LC30) and 0.24mgl(-1) (LC10). The developmental period of A.gossypii nymphs at LC30 was 3.6days for both insecticides, which was shorter than that of the untreated controls (4.2days). Longevity and total fecundity of A.gossypii adults were decreased at the sublethal concentrations of both insecticides. The lowest net reproductive rate was observed in A.gossypii treated with the LC30 of flonicamid. Feeding behavior analyses using an electrical penetration graph showed that sublethal concentrations of flonicamid and imidacloprid had significant effects on the duration of phloem ingestion. Higher doses of flonicamid induced starvation by inhibiting phloem ingestion, whereas imidacloprid acted as a contact toxin rather than an inhibitor of feeding behavior.