War in the darkness: Association of semiochemicals and entomopathogens to control wireworms

Wireworms (Coleoptera: Elateridae) are generalist insect pests attacking a wide range of plants, causing significant damages in agriculture. They feed on seeds, roots or crown and are particularly impactful on young seedlings. Wireworms locate their hosts using different cues including Volatiles Organic Compounds (VOCs) released in the rhizosphere and guiding the larvae to an appropriate host. In this study, we aimed at developing an Attract-and-kill strategy by setting up two distinct objectives : (1) comparing the attraction potential of different semiochemicals and (2) identify strains of entomopathogenic fungi and nematodes that are efficient in killing wireworms.
Plant natural extracts were encapsulated in alginate beads and were shown to attract up to 76% of the tested wireworms, during behavioral assays performed in two-way olfactometers. We then performed volatile collection on these alginate beads and revealed that beads released a blend of eight VOCs, of which acetoin was the one released in higher quantity. Finally, the virulence of twelve strains of entomopathogenic fungi and eleven strains of entomopathogenic nematodes was evaluated. Two species of Metarhizium and one species of Ophiocordyceps were the most virulent against wireworms, leading to mortality levels of 39%, 50% and 57%, respectively. Three entomopathogenic nematodes strains of species Heterorhabditis bacteriophora were highly effective in killing wireworms (88 %, 53 %, and 53 % of mortality).
The encapsulation of natural extracts in alginate beads appears to be a promising lure to manipulate wireworms behavior, while the co-encapsulation with entomopathogenic fungi and nematodes remains the major challenge for the development of a new Attract-and-kill strategy