Effect of herbicides on the redox metabolism and longevity of Lema praeusta (Fab.) (Coleoptera: Chrysomelidae): a biological control agent of Commelinaceae weeds

Conserving insects as biological control agents of weeds is a critical part of weed management strategy as it employs target specific organisms to control the economic losses caused by weeds in crop fields. Lema praeusta (Fab.) (Coleoptera: Chrysomelidae) is an important biocontrol agent of two Commelinaceae weeds, Commelina benghalensis L. and Murdannia nudiflora (L.) Brenan growing in rice fields. Growers apply 2,4-dichlorophenoxyacetic acid (2,4-D) and metribuzin to control these weeds. Indiscriminate use of herbicides is not safe for the environment and non-target organisms. So, we have evaluated the effects of recommended field doses of 2,4-D (3.33 mg/ml) and metribuzin (0.8 mg/ml), which are applied to control these weeds, in redox metabolism and survival of L. praeusta young virgin females. Exposure to recommended field doses of 2,4-D and metribuzin in young virgin females resulted increase of total reactive oxygen species and hydrogen peroxide in herbicide exposed insects than control insects, and these parameters were higher in metribuzin exposed insects than 2,4-D exposed insects. Activity of catalase, superoxide dismutase, glutathione-S-transferase and malondialdehyde content were higher in metribuzin exposed insects than 2,4-D exposed insects. Six-days old females lived up to 26 and 18 days when exposed to 2,4-D and metribuzin, respectively, while control females lived up to 107 days on C. benghalensis . The above observations suggested that both herbicides are harmful for the biocontrol agent, L. praeusta , and between two herbicides, metribuzin is more harmful. Therefore, it is necessary to re-evaluate herbicide usage practices to safeguard non-target organisms and promote sustainable agriculture management.