Monitoring the insecticide susceptibility of a newly introduced invasive species, Tuta absoluta (Meyrick), in China

The South American tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is a newly introduced invasive destructive pest that poses a major threat to tomato production in China. Chemical control is a predominantly measure for controlling this pest. Monitoring of insecticide efficacy is the basic tool for proactive evidence-based resistance management. As a new invasive species, the insecticide susceptibility of T. absoluta to main insecticides has been uncertainty so far in China. Here, we investigated the insecticide susceptibilities of seven populations (Yunnan, Guizhou, Sichuan, Gansu, Inner Mongolia, Shanxi and Xinjiang) of T. absoluta across China. The response of these populations was evaluated through laboratory bioassays with the main insecticides used for T. absoluta control: chlorantraniliprole, chlorpyrifos, indoxacarb, emamectin benzoate, spinosad and Bacillus thuringiensis. Analysis of the results showed the largest LC₅₀ values for chlorpyriphos were generated in populations from Shanxi and Yunnan, resulting in 22.59-fold and 11-fold differences, respectively, compared with the values generated in the most susceptible population (Inner Mongolia). The LC₅₀ values observed for chlorantraniliprole in Shanxi and Gansu were 24.66-fold and 20.83-fold greater, respectively, than the LC₅₀ value observed in the most susceptible population (Guizhou). However, almost all populations of T. absoluta presented low resistance levels to indoxacarb, emamectin benzoate, spinosad and B. thuringiensis. Our study sheds light on most insecticides can provide sufficient control of T. absoluta in China, however, scientific selection and use of insecticides, such as rotational use of insecticides of different modes of action classes, also need to adopt as soon as possible, because a moderate level of resistance has already been observed somewhere on chlorantraniliprole and chlorpyrifos.