Thiamethoxam exposure deregulates short ORF gene expression in the honey bee and compromises immune response to bacteria

Abstract

Maximizing crop yields relies on the use of agrochemicals to control insect pests. One of the most widely used classes of insecticides are neonicotinoids that interfere with signalling of the neurotransmitter acetylcholine, but these can also disrupt crop-pollination services provided by bees. Here, we analysed whether chronic low dose long-term exposure to the neonicotinoid thiamethoxam alters gene expression and alternative splicing in brains of Africanized honey bees, Apis mellifera, as adaptation to altered neuronal signalling. We find differentially regulated genes that show concentration-dependent responses to thiamethoxam, but no changes in alternative splicing. Most differentially expressed genes have no annotated function but encode short Open Reading Frames, a characteristic feature of anti-microbial peptides. As this suggested that immune responses may be compromised by thiamethoxam exposure, we tested the impact of thiamethoxam on bee immunity by injecting bacteria. We show that intrinsically sub-lethal thiamethoxam exposure makes bees more vulnerable to normally non-pathogenic bacteria. Our findings imply a synergistic mechanism for the observed bee population declines that concern agriculturists, conservation ecologists and the public.

Memory consolidation in honey bees is enhanced by down-regulation of Down syndrome cell adhesion molecule and changes its alternative splicing

“…It is thus surprising that Dscam alternative splicing changed substantially, such that significant changes could be detected in central brains. It will be of interest to follow up which neurons exactly change splicing upon learning, which might be possible with the development of long-read sequencing technology for single cell analysis to overcome current limitations in alternative splicing analysis ( Zaharieva et al, 2012 ; Decio et al, 2019 ; Decio et al, 2021 ).…”

Memory consolidation in honey bees is enhanced by down-regulation ofDown Syndrome Cell Adhesion Moleculeand changes its alternative splicing

“…It is thus surprising that Dscam alternative splicing changed substantially, such that significant changes could be detected in central brains. It will be of interest to follow up which neurons exactly change splicing upon learning, which might be possible with the development of long-read sequencing technology for single cell analysis to overcome current limitations in alternative splicing analysis (Decio et al, 2021, Decio et al, 2019, Zaharieva et al, 2012).…”

Acute toxicity of the fungicide captan to honey bees and mixed evidence for synergism with the insecticide thiamethoxam

“…Thiamethoxam's action as a neurotoxin can lead to paralysis and death of adult bees by binding to nicotinic acetylcholine receptors, and at sublethal exposure levels, can affect the ability of bees to perform important tasks inside and outside of the hive [28, [30][31][32]. Exposure of larvae to thiamethoxam is also known to affect survival and physiology of the honey bee postembryonic stages [33][34][35].…”