Genetics of tolerance in honeybees to the neonicotinoid clothianidin

Authors: TSVETKOV, NADEJDA - York University; BAHIA, SIMRAN - York University; Calla, Bernarda; BERENBAUM, MAY - University Of Illinois; ZAYED, AMRO - York University

Submitted to: iScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2023
Publication Date: 3/17/2023
Citation: Tsvetkov, N., Bahia, S., Calla, B., Berenbaum, M.R., Zayed, A. 2023. Genetics of tolerance in honeybees to the neonicotinoid clothianidin. iScience. 26(3). Article 106084. https://doi.org/10.1016/j.isci.2023.106084.
DOI: https://doi.org/10.1016/j.isci.2023.106084

Interpretive Summary: Neonicotinoid insecticides appear to negatively impact native pollinators but studies on managed honey bees have been mixed. Understanding the cause of these inconsistencies is critical for developing evidence-based policy on the use of these types of insecticides. In this work, we carried out experiments to study the genetic and molecular basis of neonicotinoid tolerance in honey bees. We discovered that worker survival post exposure to an acute oral dose of clothianidin (a neonicotinoid insecticide) is heritable and likely not associated with differences in expression of detoxification enzymes. Instead, genetic variation in the primary neonicotinoid detoxification genes CYP9Q1 and CYP9Q3 were strongly associated with worker survival. In some instances, the strong association between CYP9Q haplotypes and worker survival was associated with the protein’s predicted binding affinity to clothianidin. In light of our findings, we recommend that pesticide risk assessments account for genetic variation within and between pollinator populations.

Technical Abstract: The relationship between neonicotinoid insecticides (NNIs) and honey bee health is intensely debated, there is some evidence that suggest that honey bee genotypes vary in their tolerance to NNIs. We exposed individual worker bees from two colonies to the average LD50 dose of clothianidin, and recorded whether bees survived or died after 24 hours of exposure. We genotyped the workers from this experiment at many microstallite loci and assigned them into patriline families. This framework allowed us to estimate the heritability of NNI tolerance, here defined as the proportion of a patriline that survived the clothianidin treatment at 24h. To better understand the molecular mechansims underlying NNI tolorance in honey bees, we carried out a second experiment on the same colonies, where we exposed individual workers to a sublethal dose of clothiandin. After genotyping and assignment to patrilines, we carried out transcriptional profiling to identify differentially expressed genes between patrilines with high or low tolerance to NNIs, as determined by the lethal dose experiment. Here we targeted three tissues where NNI detoxicfciation enzymes are known to be expressed: the brain, the ventriculus (i.e. mid-gut) and the Malpighian tubules. We then sequenced CYP9Q1, CYP9Q2 and CYP9Q3 genes from high and low survival patrilines and asked if mutations in these genes segregated with the propencity of a patrline to survive the lethal dose at 24h. We then preformed a molecular modeling analysis of some CYP9Q1 and CYP9Q3 haplotypes assoicated with survival in our expierment. Our analyses shed new isnights on the genetics and mechanisms underlying NNI suspeitablity in honey bees.