A new study in which the Desertification Research Center (CIDE), a joint center of the Spanish Research Council (CSIC), the University of Valencia and the Valencian Government, participates, report a previously unexplored route of insect exposure to neonicotinoid insecticides. The work, which is published in the Proceedings of the National Academy of Sciences (PNAS), concludes that the neonicotinoid insecticides present in the honeydew of treated plants can collaterally damage beneficial insects that feed on this contaminated honeydew.
Neonicotinoids are among the most widely used insecticides and their harmful effects on beneficial insects that feed on nectar and pollen were already known.
The study led by Miguel Calvo-Agudo, and with the participation of the CIDE researcher Yolanda Picó, in collaboration with researchers from the Valencian Institute of Advanced Studies (IVIA), the University of Wageningen, and other centers of the University de València focuses on the study of the routes of exposure of beneficial parasitic insects in agriculture, such as siphids and parasitoid wasps, to neonicotinoids.
Neonicotinoids are among the most commonly used insecticides and can harm beneficial insects that feed on contaminated nectar and pollen. The study authors examined whether beneficial insects could also be exposed to neonicotinoids through contaminated honeydew.
Honeydew is a sugar-rich substance excreted by phloem-feeding insects that is an important nutrient source for many beneficial insects such as pollinators and natural enemies of insect pests.
The authors collected honeydew produced by citrus mealybugs (Planococcus citri) that fed on citrus trees treated with either water or the neonicotinoids thiamethoxam and imidacloprid, applied either via the soil or as a foliar spray. The honeydew was fed to two beneficial insect species: a hoverfly (Sphaerophoria rueppellii) and a parasitic wasp (Anagyrus pseudococci). A majority of hoverflies and wasps that fed on mealybug-produced honeydew from thiamethoxam-treated trees died within three days, as did approximately half of the hoverflies that fed on honeydew from foliar imidacloprid-treated trees, compared with 6-15% of both beneficial insects fed on control honeydew.
Honeydew from a significant fraction of insecticide-treated trees contained detectable levels of neonicotinoids. No neonicotinoids were detected in honeydew from control trees.
The results suggest that beneficial insects could be exposed to neonicotinoids via contaminated honeydew, which is likely to affect a wider range of insects than contaminated nectar, according to the authors.
Scientific reference:
Miguel Calvo-Agudo, Joel González-Cabrera, Yolanda Picó, Pau Calatayud-Vernich, Alberto Urbaneja, Marcel Dick, and Alejandro Tena. 2019. Neonicotinoids in excretion product of phloem-feeding insects kill beneficial insects. PNAS DOI: 10.1073/pnas.1904298116
