Investigating hoverfly responses to chemical cues and honeydew in agro-ecosystem

Predatory insects play a pivotal role in regulating pest populations within agricultural crops. Among these, aphidophagous hoverflies are key insect vectors for controlling aphids in wheat crops. The initial attraction of hoverflies is facilitated by the honeydew secreted by aphid pests. Notably, certain bacteria present in aphid honeydew, such as Staphylococcus sciuri, generate chemically enticing compounds that effectively draw in aphidophagous hoverflies. Additionally, incorporating flower strips as intercrops enhances aphid regulation by attracting a greater number of natural enemies to control insect pests. To assess the predatory potential of aphidophagous insects, the oviposition behavior of the Episyrphus balteatus hoverfly was examined in a flight tunnel under various conditions. These conditions included fresh honeydew from Acyrthosiphon pisum and Aphis fabae, a filtered solution of S. sciuri bacteria, and a combination of chemical compounds—specifically, 3-methyl-2-butenal and 3-dimethyl-3,3 acrylic acid—released by S. sciuri. Field experiments involved applying this chemical compound mixture to experimental plots of camelina (Camelina sativa (L.)) and buckwheat (Fagopyrum esculentum Moench) sown in a wheat field at Gembloux (Wallonia, Belgium) to gauge the attraction of aphidophagous hoverflies. Results indicated no significant difference from negative controls, both in laboratory and field settings, with regard to the filtered bacterial solution and the specified chemical compounds. However, the oviposition behavior of E. balteatus hoverflies was observed to be stimulated by both types of honeydew tested. Consequently, exploring alternative methods for pest control through natural predators may diminish the reliance on widespread pesticide application in cultivated fields, potentially aiding in the conservation of biodiversity increasingly impacted by human activities.