The effect of insecticide application by dropleg sprayers on pollen beetle parasitism in oilseed rape

Abstract Dropleg sprayers apply pesticides below the flower horizon of oilseed rape plants and thus reduce unwanted side effects on pollinating insects. Whether this technique benefits parasitoids seed pollen feeding insect pests has not been studied earlier. To answer question, we first assessed vertical distribution using a portable aspirator. In addition, parasitism rates beetle, Brassicogethes aeneus Fabricius (Coleoptera: Nitidulidae) , by larval parasitoid Tersilochus heterocerus Thomson (Hymenoptera: Ichneumonidae) were compared in conventional dropleg sprayed fields over four years (2016–2019), neonicotinoids thiacloprid acetamiprid. Our results show that feeders mainly found flowering canopy, while predominant location was species-specific. Among beetle parasitoids, Phradis interstitialis more abundant canopy (63% total catch), whereas T. caught (84% catch). spraying experiments, average beetles ranged between 55 82% untreated controls. spray treatments, did differ significantly from control levels, with exception application 2019. contrast, applications resulted reduction up to 37% for at least one insecticides three out years. The impact differed years, which may be explained temporal coincidence immigration into crop. We conclude exerts lower non-target main biological agent beetle.