Selection pressure by specialist and generalist insect herbivores leads to optimal constitutive plant defense. A mathematical model

Identification of attractants for adult Spodoptera litura based on the interaction between odorant-binding protein 34 and host volatiles

Odorant-binding proteins (OBPs) play key roles in host plant location by insects, and can accordingly serve as important targets for the development of attractants. In this study, we detected the high expression of SlitOBP34 in male antennae of Spodoptera litura. Subsequently, the fluorescence competitive binding experiments displayed that the SlitOBP34 protein has binding affinity for different ligands. Then, protein-ligand interaction analyses found the presence of six amino acid residues may serve as key recognition sites. Further electroantennographic and biobehavioral assessments revealed that the electrophysiological responses of male antennae were evoked in response to stimulation with the six identified host volatiles, and that these volatiles attracted male moths to varying extents. Notably, low concentrations of benzaldehyde, 1-hexanol, and cis-3-hexenyl acetate were found to have significant attractant effects on male moths, thereby identifying these three host volatiles as potential candidates for the development of male attractants. These findings advance our current understanding of the olfactory-encoded mechanisms of host plants selection in S. litura and have enabled us to develop novel adult attractants for controlling the pest in the future.

How Plant Toxins Cause Early Larval Mortality in Herbivorous Insects: An Explanation by Modeling the Net Energy Curve

Plants store chemical defenses that act as toxins against herbivores, such as toxic isothiocyanates (ITCs) in Brassica plants, hydrolyzed from glucosinolate (GLS) precursors. The fitness of herbivorous larvae can be strongly affected by these toxins, causing immature death. We modeled this phenomenon using a set of ordinary differential equations and established a direct relationship between feeding, toxin exposure, and the net energy of a larva, where the fitness of an organism is proportional to its net energy according to optimal foraging theory. Optimal foraging theory is widely used in ecology to model the feeding and searching behavior of organisms. Although feeding provides energy gain, plant toxins and foraging cause energy loss for the larvae. Our equations explain that toxin exposure and foraging can sharply reduce larval net energy to zero at an instar. Since herbivory needs energy, the only choice left for a larva is to stop feeding at that time point. If that is significantly earlier than the end of the last instar stage, the larva dies without food. Thus, we show that plant toxins can cause immature death in larvae from the perspective of optimal foraging theory.