Laboratory toxicity of three insecticides and effects to physiological biochemistry of Phenacoccus solenopsis Tinsley

Phenacoccus solenopsis Tinsley is an important invasive pest, whose control mainly depends on chemical insecticides. This study aimed to select highly effective insecticides for the control of P. solenopsis and to clarify their effects on its physiological biochemistry.

Three different chemical types of insecticides (acetamiprid, beta-cypermethrin and methomyl), which are effective in controlling sucking mouthparts, were selected and analyzed the toxicity of these insecticides against third-instar nymphs of P. solenopsis with the leaf-dipping method under laboratory conditions. Moreover, we assessed the detoxification enzymes activity [glutathione-S-transferases (GSTs) and carboxylesterase (CarE)], and the energy substances content (soluble proteins, triglycerides and trehalose) of P. solenopsis at LC₅₀, LC₃₀ and LC₁₀.

The results showed that acetamiprid had the lowest median lethal concentration (22.97 mg/L). The activity of GSTs was significantly increased when exposed to LC₅₀ of all three insecticides. However, the activity of CarE was inhibited by beta-cypermethrin and methomyl stresses. The lowest activity of CarE was observed in methomyl LC₃₀ treatment (48.14 U/g). The contents of trehalose of P. solenopsis were significantly decreased in all the concentrations when exposed to the three candidates. The lowest content of trehalose was observed in acetamiprid LC₃₀ treatment (16.60 mg/g). However, soluble protein content was significantly decreased only in the exposure of beta-cypermethrin and methomyl. At the same lethal concentration, the soluble protein content after acetamiprid treatment was significantly higher than that of beta-cypermethrin and methomyl treatment. The triglyceride content in P. solenopsis was significantly increased only under methomyl LC₁₀ stress (31.11 mg/g) and significantly decreased under beta-cypermethrin LC₅₀ treatment (11.93 mg/g).

It indicated that P. solenopsis was more sensitive to acetamiprid and consumed a large amount of energy to survive when exposed to insecticides, and GSTs may play an important role in the detoxification process of P. solenopsis. Our results provide a theoretical basis for the rational selection of insecticides and the study of resistance mechanism in the integrated pest management of P. solenopsis.