Intercropping-induced leaf metabolic changes increase plant resistance to herbivory

Intercropping-induced plant resistance to herbivorous pests is explained by different factors such as pest deterrence, attraction of natural enemies, microclimate, soil fertility, and soil microbial communities. The role of plant chemistry in this context has received less attention. Here, we investigated the impacts of intercropping-induced changes in leaf chemistry on the growth and physiological performance of lepidopteran insect pests.

Insect populations were monitored through two field seasons in three cropping systems: peanut monocropping, maize monocropping, and peanut/maize intercropping. Laboratory experiments were carried out to determine the influence of cropping system on leaf metabolic profiles and to link cropping system-induced leaf chemistry changes with the growth and physiological performance of Spodoptera litura larvae.

In the field, cropping system influences the distribution and feeding preferences of lepidopteran insects, with peanut plants in monocropping more attractive to these insects. Under laboratory settings, S. litura grow better on the leaves of peanuts grown under monocropping than on the leaves of peanuts grown in maize/peanut intercropping. The observed insect growth effects were accompanied by higher lipase activity, and lower activity of detoxification enzymes in larvae fed on peanut plants grown in intercropping. Untargeted metabolomics revealed clear differences in the metabolic profiles of peanuts from different cropping systems. Amino acid metabolism, carbohydrate metabolism, and nicotinate and nicotinamide metabolism were particularly impacted. Based on the artificial diet supplementation experiments, we show that leaf nicotinamide and isomaltose may explain the observed intercropping-induced resistance to lepidopteran pests.

Intercropping-induced changes in leaf chemistry mediate plant resistance to agricultural pests.