Biological traits and feeding capacity of Agriotes larvae (Coleoptera: Elateridae): A trial of seed coating to control larval populations with the insecticide fipronil

Abstract

Until recently, the chemical control of phytophagous larvae of the genus Agriotes was exclusively achieved through soil treatment with insecticides. Under such conditions, the larvae receive the active ingredient (a.i.) by integumental penetration whilst moving through the subsurface soil. The selectivity of such treatments is only based on the biochemical selectivity of the a.i. which is generally very low across soil invertebrates. More recent a.i.s from new chemical families such as fiprols show not only a new biochemical mode of action but also a particular mode of penetration which is restricted to the digestive pathway. This allows a new type of selectivity, based on penetration after feeding, when the a.i. is associated with food. We demonstrate that Agriotes species, which are important pests for several crops, feed almost exclusively on the seeds of plant species. This dietary selectivity is based on appetency, rather than attractivity. The appetent molecules are mostly present in the seed’s acetonic powders but there is also an effect of the small lipophilic molecules extracted by the solvent. Taking into account the meal size and the feeding behaviour of the larvae, we show that when an insecticide such as fipronil is associated with food as a seed coating, much lower amounts of a.i. are required than those necessary in a full-soil treatment. The theoretical basis of this treatment, and limits to control Agriotes populations by such seed coatings are discussed.