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

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.