Brain metabolomics in an insect pollinator: impacts of CO2 and cold-induced anaesthesia alone and in combination with neonicotinoid exposure

Characterizing the effect of pesticides on pollinators is essential in the strive to protect biodiversity while maintaining efficient food production. Metabolomics offers detailed insight into the physiological response to pesticides. The impact of pre-dissection and dissection methodology on the metabolic response remains largely unknown, as does their possible effect on the measured metabolic response to pesticide exposure. Three different pre-dissection treatments were evaluated in Eristalis tenax: carbon dioxide, ice or no anaesthesia. Brain dissections were conducted at room temperature or on ice. Flies were also orally exposed to a high dose of the neonicotinoid insecticide acetamiprid (4 μg per fly) in sucrose or sucrose alone. Brains were homogenized, and metabolites extracted and analysed by gas chromatography/mass spectrometry. Pre-dissection and dissection conditions affected metabolites linked to oxidative stress, energy production and cold response. Acetamiprid exposure elicited consistent metabolic responses across all immobilization methods, including significant alterations in glutamate metabolism. Alterations in brain metabolism in response to acetamiprid were largely conserved across various pre-dissection methods, allowing for flexibility in methodology to address experimental constraints. Whether the subtle differences observed would compromise studies of lower doses of acetamiprid or other pesticides requires further validation.