Diet-mediated effects of cadmium on fitness-related traits and detoxification and antioxidative enzymes in the oriental armyworm, Mythimna separata

Abstract

Cadmium (Cd) is a heavy metal that is of great concern in the agroecosystem, because of its toxicity to plants and herbivores. Previous research has suggested that populations of herbivorous insects can be affected by Cd, via disrupting tri-trophic interactions comprising plants, herbivores, and predators. However, there is less understanding of the direct effects of dietary Cd on the life history traits and the detoxification or antioxidant enzyme systems of insects. Here we show that the life history traits of the herbivorous oriental armyworm, Mythimna separata (Walker), can be impacted by Cd. The body mass of larvae was decreased under an artificial diet containing a low (0.15 mg kg -1 ) Cd concentration, but was increased by intermediate (0.30 mg kg -1 ) and high (0.60 mg kg -1 ) concentrations of Cd. In contrast, pupal weight declined under intermediate and high concentrations of Cd compared to either low Cd concentration or the control. When Cd concentrations increased, larvae survival rate and fecundity decreased and the pupation rate and pupal deformity rate increased. Low and intermediate concentrations of Cd extended the length of the larval stage while high concentrations of Cd shortened the larval period. Dietary Cd inhibited the activity of antioxidant enzyme polyphenol oxidase (PPO), but increased acetylcholinesterase (AChE) activity and the activities of detoxifying enzymes carboxylesterase (CarE) and glutathione S -transferase (GST) of third-instar larvae. Overall, our results indicate that for Cd concentration there is a physiological trade-off between its adverse effects on life history traits and elevated detoxification, acetylcholinesterase sensitivity and antioxidation of M. separata , thus representing a potential adaptation strategy.