Persistence of imidacloprid in trunk injected horse chestnut and its impact on Cameraria ohridella (Lepidoptera: Gracillariidae)

Abstract

Trunk injection with imidacloprid is used to reduce the infestation rate of trees by pests. However, further research is needed to determine the insecticide persistence in trees. Here, we present a case study in which we evaluated horse chestnut trees for imidacloprid residues and the invasive leaf miner Cameraria ohridella (Lepidoptera: Gracillariidae) infestation 14 years after a single injection (5 mL of pesticide per tree). We detected residues of imidacloprid (on average 0.648 μg/kg in leaves) and its metabolites: imidacloprid-guanidine in leaves and inflorescences and imidacloprid-urea in the leaves of treated trees. In addition, imidacloprid residues in inflorescences were at much lower concentrations (on average 0.07 μg/kg) compared to those found in leaves. Tree infestation by leaf miners was significantly lower in injected trees (0.035 mines/cm²) than in control trees (0.091 mines/cm²). Our research thus indicates for the first time that, once applied, imidacloprid may affect the target and non-target species for a long time owing to its persistence in plant tissues.