Using a conditioned place preference assay in fruit flies to examine effects of insecticidal compounds on contextual memory

Insecticides are vital for safeguarding agricultural crops against pests, albeit many lack selectivity towards pest species and are poorly bio-degradable. This leads to targeting of beneficial organisms like pollinators and widespread environmental contamination of soil and water. Exposure to insecticides such as neonicotinoids causes insect paralysis and mortality at higher doses, while sublethal doses can disrupt other functions that are crucial for survival such as learning and memory performance. Potent and selective arachnid venom peptides affecting a variety of molecular targets are being explored as bioinsecticide candidates. However, their effect on insect learning is poorly understood. We therefore established a sucrose-induced conditioned place preference (CPP) assay using Drosophila melanogaster fruit flies to provide a means of evaluating how various classes of insecticidal compounds interact with insect memory to assess their broader ecological consequences. Our results confirmed the adverse effect of a sublethal dose of the neonicotinoid insecticide imidacloprid (20 pg/fly) on fly CPP formation upon daily injection during the conditioning phase. However, imidacloprid did not affect CPP retrieval when applied after the conditioning phase. Sublethal doses of the two insecticidal spider venom peptides μ-DGTX-Dc1a (Dc1a; 70 pg/fly) and U1-AGTX-Ta1a (Ta1a; 125 pg/fly) had no effect on either CPP formation or retrieval, underlining their potential as novel and safe bioinsecticide candidates.