Abstract:

The insecticide sensitivity of larvae of the red imported fire ant (Solenopsis invicta Buren) was evaluated by the analysis of the contact toxicity of 17 insecticides of various types against the fourth instars reproductive larvae. It was found that the toxicities of the tested insecticides were relatively low with LC50 from 639.28 μg/mL to 1028.03 μg/mL, amongst the LC50 of 88.24% insecticides were higher than 1000 μg/mL. It was indicated that the larvae were insensitive to insecticides. In comparison of the activities of carboxyl esterases, phosphorases, and glutathione-S-transferases of the reproductive larval ants with those of worker ants, it was found that the specific activities of the measured metabolic enzymes in larvae were significantly higher than those in worker ants, especially the activity of phosphorases at folds of above 100, suggesting that strong activity of metabolic enzymes was an important factor for the insensitivity of larval ants to insecticides.