Feeding behaviour as a limiting step in insecticide absorption for the wireworm Agriotes sp. (Coleoptera: Elateridae)

The fipronil control of wireworms field populations (larval Agriotes sp., Coleoptera: Elateridae) is difficult because of the low integumental penetration rates of this insecticide into the target larval body. The main way of insecticide absorption being associated with food, analysis of the larval feeding behaviour is of key importance for designing a strategy of dietary chemical control of those subterranean pests. In this purpose, a standard method for assessing the long-term survival of field specimens in the laboratory was developed together with experimental designs for investigating food searching and choosing by larvae. Larval biological performances under those laboratory conditions were checked monthly. Three criteria were taken into account for measures: the duration of individual survival, the gain in average body weight, and the moulting rhythm. Experimentation revealed that seed flour was highly desired by larvae and that larval feeding choice was affected over short distances only. This suggests the involvement of dietary preference rather than attractivity in the larval feeding behaviour. This implies that, at the operational step, insecticide had better be associated to food, either as a coating on the seeds, or inside preferred baits.