Volatile organic compounds, tolerant varieties and entomopathogenic fungi: Three potential methods for wireworms’ control

Wireworms are a significant threat to global agriculture as soil-dwelling insect pests. Since the recent ban of neonicotinoids, it is of prime importance to develop integrated management strategies. In the present study, we aimed at (i) evaluating potato varietal susceptibility to wireworms’ feeding behaviour and (ii) identify efficient strains of entomopathogenic fungi.
We selected three potato varieties known to experience contrasted levels of damage in the field: Monalisa (high damage), Spunta (intermediate damage), and Charlotte (low damage). Using one-choice bioassays, we confirm that wireworms express a higher feeding activity on Monalisa tubers as compared with the other two varieties. After 50 weeks of observations, we also confirm that their life cycle was accelerated on that variety compared to the Charlotte one. Since wireworms use Volatile Organic Compounds (VOCs) to locate suitable hosts, we raised the additional hypothesis that Monalisa is attractive because of the release of specific VOCs. Through dual-choice bioassays, we show that Monalisa, the most susceptible variety, was not the most attractive. Intriguingly, wireworms exhibited greater attraction to Spunta tubers when compared to Monalisa and Charlotte tubers. Subsequently, using non-destructive headspace dynamic sampling and gas chromatography, we have identified a complex blend of 63 VOCs released by tubers in the rhizosphere. No significant differences in VOCs composition were observed between the three varieties. These findings highlight that the most damaged variety in the field is not the most attractive for wireworms but the one that initiates the more foraging activity. These results suggest the involvement of other olfactory cues in varietal selection (such as CO2 and secondary metabolites).
Finally, we assessed the biocidal capacity of 11 strains of entomopathogenic fungi on wireworms. After a continuous exposure of 12 weeks, two newly identified strains showed significant effects on wireworms’ survival. Following encapsulation of these two fungi in a biodegradable matrix (facilitating field application, providing protection, and ensuring good sporulation) we have shown that one of these two strains was highly efficient in killing wireworms. All these results provide valuable insights for wireworm integrative management.