Toxicity effect of five insecticides on the development and enzyme activities of Trichogramma ostriniae

As an egg parasitoid, Trichogramma ostriniae (T. ostriniae) exhibits a broad host range and plays a crucial role in controlling various lepidopteran agricultural pests. However, the application of chemical pesticides negatively impacts its development and survival. Therefore, it is essential to assess the toxicity of commonly used insecticides against T. ostriniae and evaluate their compatibility. This study aims to to determine the toxic effects of five common insecticides (dinotefuran, abamectin, imidacloprid, beta-cypermethrin, and chlorantraniliprole) on the development, reproduction, and enzymatic activity of Trichogramma ostriniae. The contact, lethal, and developmental toxicities were evaluated. Activities of detoxification enzymes, including cytochrome P450 (CYP450), carboxylesterase (CarE), and glutathione S-transferase (GST), and protective enzymes, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) as well as malondialdehyde (MDA) and reactive oxygen species (ROS), mitochondrial respiratory chain complex I (MRCC I), adenosine triphosphate (ATP) of T. ostriniae were examined after being treated with the five insecticides. The results showed that the order of lethal toxicity in adult T. ostriniae was beta-cypermethrin > dinotefuran > imidacloprid > abamectin > chlorantraniliprole. The emergence rates of adult T. ostriniae exposed to insecticides during the egg and larval stages were higher than those exposed to insecticides during the prepupal and pupal stages. The activities of CYP450, GST, and SOD were increased, but CarE activity and ROS content were decreased in T. ostriniae treated with the five insecticides compared with the control. Beta-cypermethrin increased the POD and CAT activities. Chlorantraniliprole decreased CAT activity and increased MDA content. The MRCCI of T. ostriniae was not significantly affected by any of the five insecticides tested. The ATP content of T. ostriniae was not significantly affected by chlorantraniliprole but was significantly decreased by the other four insecticides. In conclusion, the toxicities of the five insecticides to T. ostriniae were different, among which imidacloprid, dinotefuran, abamectin, and beta-cypermethrin had a high risk of toxicity to T. ostriniae, and chlorantraniliprole had a low risk to T. ostriniae.

Methods
Corcyra cephalonica (Stainton) (C. cephalonica) were used as hosts to establish a stable population of T. ostriniae by breeding multiple generations. The feeding conditions were 25°C, 75% relative humidity, and a 15 L: 9D photoperiod.
The diluted insecticide was evenly distributed on the inner wall of a glass tube (54.6 cm2) to construct the insecticide membrane. For the contact test, a total of 100 ± 10 adult T. ostriniae that had emerged for 6 h were put into each tube containing the insecticide membrane after all the acetone was volatilized and fed with 10% honey water. After being sealed with a black cloth, the tubes were placed for 8 h. The number of dead and surviving adult T. ostriniae in the tube was counted.
The safety evaluation of pesticides on T. ostriniae can be divided into four levels according to the safety factor: low risk, moderate risk, high risk, extreme high risk. Safety factor = LR50/recommended dose in the field.
Egg parasitism was achieved by exposing T. ostriniae to host C. cephalonica eggs at a 1:20 ratio (insects: eggs) for 4 h. After removing T. ostriniae, the parasitic eggs were developed for 8 h (egg stage), 48 h (larval stage), 92 h (prepupal stage) and 144 h (pupal stage), respectively. Parasitoids at different developmental stages on host egg cards were immersed in LC50 concentrations of insecticide solution for 5 s and then sealed in glass tubes. After emergence, the number of parasitic and emergence eggs was counted under a dissecting microscope to calculate the emergence rate. 
A total of 200±10 adult T. ostriniae that had emerged for 6 h were put into each tube containing the LC50 concentrations of insecticide membrane after all the acetone was volatilized and fed with 10% honey water. After sealing the tube with a black cloth, the T. ostriniae were cultured at 25 ± 1°C, 75 ± 5% humidity, and 15 L: 9D photoperiod for 8 h. The surviving T. ostriniae were collected. Activities of detoxification enzymes, including cytochrome P450 (CYP450), carboxylesterase (CarE), and glutathione S-transferase (GST), and protective enzymes, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) as well as malondialdehyde (MDA) and reactive oxygen species (ROS), mitochondrial respiratory chain complex I (MRCC I), adenosine triphosphate (ATP) of T. ostriniae were examined.