Biopesticide spinosad induces transcriptional alterations in genes associated with energy production in honey bees (Apis mellifera) at sublethal concentrations.

Bees experience substantial colony losses, which are often associated with pesticides. Besides synthetic insecticides biological compounds such as spinosad are used in agriculture and organic farming against insect pests. However, potential adverse effect at sublethal concentrations to pollinators are poorly known. Here we aim to determine potential adverse outcome pathways of spinosad and to identify molecular effects by investigating transcriptional alterations in the brain of honey bees. We experimentally exposed bees to three sublethal concentrations of 0.05, 0.5 and 5 ng spinosad/bee, and assessed transcriptional alterations of target genes. Additionally, we evaluated whether spinosad-induced transcriptional alterations were influenced by the time of the year. In April, alterations were most pronounced after 24 h exposure, while in June alterations occurred mostly after 48 h. In July, expressional alterations were often lower but the pattern was more similar to that in June than that in April. Down-regulation of genes encoding acetylcholine receptors, enzymes involved in oxidative phosphorylation (cox5a, ndufb7 and cox17), cytochrome P450 dependent monooxygenases (cyp9q1, cyp9q2 and cyp9q3) and insulin-like peptide-1 were among the most significant transcriptional alterations. This suggests adverse effects of spinosad to energy production and metabolism and thus negative consequences on foraging. Together, our study indicates that spinosad causes adverse effects at environmentally realistic concentrations, which may pose a risk to bee populations.

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