Farming systems for pest control, based on the stimulo-deterrent diversionary strategy or push-pull system, have become an important target for sustainable intensification of food production. A prominent example is push-pull developed in sub-Saharan Africa using a combination of companion plants delivering semiochemicals, as plant secondary metabolites, for smallholder farming cereal production, initially against lepidopterous stem borers. Opportunities are being developed for other regions and farming ecosystems. New semiochemical tools and delivery systems, including GM, are being incorporated to exploit further opportunities for mainstream arable farming systems. By delivering the push and pull effects as secondary metabolites, for example, (E)-4,8-dimethyl-1,3,7-nonatriene repelling pests and attracting beneficial insects, problems of high volatility and instability are overcome and compounds are produced when and where required.

Summary: The mediation of volatile secondary metabolites in signalling between plants and other organisms has long been seen as presenting opportunities for sustainable crop protection. Initially, exploitation of interactions between plants and other organisms, particularly insect pests, foundered because of difficulties in delivering, sustainably, the signal systems for crop protection. We now have mounting and, in some cases, clear practical evidence for successful delivery by companion cropping or next‐generation genetic modification (GM). At the same time, the type of plant signalling being exploited has expanded to signalling from plants to organisms antagonistic to pests, and to plant stress‐induced, or primed, plant‐to‐plant signalling for defence and growth stimulation. Contents Summary 856 I. Introduction 856 II. Plant volatile‐mediated host signalling 857 III. Plant volatile‐mediated nonhost signalling 858 IV. Plant volatile‐mediated signalling between plants via air 859 V. Plant volatile‐mediated signalling between plants through soil 860 VI. Plant volatile‐mediated signal transduction 862 VII. Success and lessons from exploiting plant volatile‐mediated signalling by companion cropping: push–pull 863 VIII. Exploitation of plant volatile‐mediated signalling in agriculture by GM 864 IX. Conclusions 866 Acknowledgements 866 References 866

Significance: An old enigma in insect toxicology, the mode of action (MoA) of selective chitin biosynthesis inhibitors in arthropods, is resolved. Benzoylureas, buprofezin, and etoxazole share a MoA by directly interacting with chitin synthase 1. The finding that a single mutation confers striking levels of insecticide resistance against three putative different MoAs has important ramifications on resistance management strategies and rational use of insecticides against major agricultural pestsand vectors of human diseases. Our results also show that CRISPR/Cas9-mediated gain-of-function mutations in single-copy genes of highly conserved target sites in arthropods provide opportunities for comprehensive insecticide resistance investigations across species boundaries and against several insecticide classes.

Insect pheromones offer potential for managing pests of crop plants. Volatility and instability are problems for deployment in agriculture but could be solved by expressing genes for the biosynthesis of pheromones in the crop plants. This has now been achieved by genetically engineering a hexaploid variety of wheat to release (E)-β-farnesene (Eβf), the alarm pheromone for many pest aphids, using a synthetic gene based on a sequence from peppermint with a plastid targeting amino acid sequence, with or without a gene for biosynthesis of the precursor farnesyl diphosphate. Pure Eβf was produced in stably transformed wheat lines with no other detectable phenotype but requiring targeting of the gene produced to the plastid. In laboratory behavioural assays, three species of cereal aphids were repelled and foraging was increased for a parasitic natural enemy. Although these studies show considerable potential for aphid control, field trials employing the single and double constructs showed no reduction in aphids or increase in parasitism. Insect numbers were low and climatic conditions erratic suggesting the need for further trials or a closer imitation, in the plant, of alarm pheromone release.

Significance: In vector-borne disease systems, there is mounting evidence that vertebrate hosts become more attractive to disease vectors during infection, yet in human malaria, the underlying mechanism has not been studied. We identified compounds, including aldehydes, that are produced in relatively greater amounts in the skin odor of individuals with malaria, thus demonstrating a basis for this phenomenon in the cues used during mosquito host location. By establishing the attractiveness of these compounds to malaria mosquito vectors in laboratory bioassays, we characterize a process by whichPlasmodiuminfection of humans could lead to increased mosquito biting. These compounds may serve as biomarkers of malaria or be used to enhance the efficacy of chemical lures used to trap mosquitoes.