The Role of Larval Nutrition in Shaping Pheromone Composition in Fall Armyworm

The fall armyworm (FAW), Spodoptera frugiperda (JE Smith), is polyphagous that enables it to develop on different hosts, likely has a host-induced impact on its developmental biology as well as pheromone composition and production. While the effect of geographic variation on the components of FAW pheromone has been extensively studied, fewer studies have explored the influence of larval diet on the FAW pheromone composition. We conducted a laboratory study that examined the pheromone composition and production of FAW reared on horticultural plants, both known and potential hosts, in Australia. FAW larvae were raised on sweetcorn leaves/kernel, bean leaves/pod, okra leaves/fruits, strawberry leaves, capsicum fruits/leaves, and artificial diet. The headspace and pheromone gland compounds were collected from female FAW from each diet and analysed by gas chromatography-mass spectrometry (GC-MS). FAW female produced four pheromonal compounds (Z)-7-dodecenyl acetate (Z7C12Ac), (Z)-9-dodecenyl acetate (Z9C12Ac), (Z)-9-tetradecenyl acetate (Z9C14Ac), and (Z)-11-hexadecenyl acetate (Z11C16Ac). FAW reared on capsicum and okra exhibited higher release levels of these pheromonal compounds, whereas those fed on sweetcorn, beans, strawberry, and artificial diet released lower amounts. Notably, analysis of pheromones extracted from the pheromone gland showed that larval diets had no effect on the female FAW pheromone components, except for Z11C16Ac which vary significantly. While these findings improve our understanding of FAW pheromone production physiology mediated by larval diets, this knowledge could potentially be utilized to improve or optimise pheromone lure to enhance their effectiveness in early detection, monitoring and management of FAW populations across diverse cropping systems.