Effects of Exogenous Melatonin on Life History Traits and Cold Tolerance of Leguminivora glycinivorella (Lepidoptera: Tortricidae)

The chemical control of Leguminivora glycinivorella (Mats.) (Lepidoptera: Tortricidae) has been a major threat to the soybean industry in China over the years. Therefore, we need to develop green, safe, and environmentally friendly alternatives for pest control. Amine hormones, such as melatonin, represent an adjunct strategy for the green control of L. glycinivorella. We aimed to investigate the effects of exogenous melatonin on the development, survival, reproduction, nutrient accumulation, and cold tolerance of L. glycinivorella and to provide insights into the role of melatonin in insect adaptive regulation. Newly hatched L. glycinivorella larvae were fed on soybean pods immersed in solutions with different concentrations of exogenous melatonin. The developmental duration of larvae and pupae, survival rate, pupation rate, adult eclosion rate, body weight and length of larvae and pupae, nutrient composition of mature larvae, adult reproductive parameters, and supercooling and freezing points were measured. With increasing melatonin concentrations, the developmental durations of larvae and pupae were significantly prolonged, while the larval survival rate, pupation rate, and adult eclosion rate significantly decreased. The body weight and length of both larvae and pupae declined with increasing melatonin concentrations, reaching the lowest values in the 200 mg/L group. Melatonin treatment significantly reduced protein and lipid contents in mature larvae but significantly increased glycogen content. Reproductive parameters, including pre-oviposition period, oviposition period, fecundity, and female adult longevity, all decreased significantly with increasing melatonin concentrations. Additionally, melatonin treatment significantly lowered the supercooling point and freezing point of mature larvae. Exogenous melatonin significantly inhibits the growth, development, survival, reproduction, and nutrient metabolism of L. glycinivorella, yet enhances its low-temperature tolerance, suggesting that melatonin may serve as a potential tool for population management of L. glycinivorella through its dual regulatory role in insect physiology.