Chronic exposure to imidacloprid or thiamethoxam neonicotinoid causes oxidative damages and alters carotenoid-retinoid levels in caged honey bees (Apis mellifera)

Abstract

Over the last decade, the persistent dwindling of the populations of honey bees has become a growing concern. While this phenomenon is partly attributed to neonicotinoids (NEOCs), chronic exposures to these insecticides at environmentally-relevant concentrations are needed to fully estimate their implications. In this study, honey bees were orally exposed for 10 days to low field-realistic concentrations of NEOCs known for their effects on the cholinergic system (imidacloprid – IMI or thiamethoxam – THM). Selected biomarkers were measured such as acetylcholinesterase (AChE) activity, lipid peroxidation (LPO), α-tocopherol as well as several forms of vitamin A (retinoids) and carotenoids. Bees exposed to IMI showed lower levels of two carotenoids (α-carotene and α-cryptoxanthin) and α-tocopherol. The THM exposure increased the oxidized vitamin A metabolites in bees conjointly with the LPO. These results could be the consequence of a pro-oxidant effect of NEOCs and were observed at levels where no effects were recorded for AChE activity. This study reveals that exposure to low levels of NEOCs alters the carotenoid-retinoid system in honey bees. This would merit further investigation as these compounds are important in various aspects of bees’ health. Overall, this study contributes to the development of biomonitoring tools for the health of bees and other pollinators.

Effects of chronic dietary thiamethoxam and prothioconazole exposure onApis melliferaworker adults and brood

“…Similar to Hatjina et al ., mean pollen paste consumption at the start of our experiment, coinciding with HPG development, was significantly ( P < 0.001) elevated, up to 3‐fold greater than overall mean consumption. Syrup consumption in our study (mean 0.023 mL bee –1 per day, SD = 0.016) was within the range reported for other chronic cage studies . Considering that HPG development may be influenced by the laboratory environment, the results of our study suggest that semi‐field exposure may be the best experimental context for evaluation of HPGs.…”

“…Syrup consumption in our study (mean 0.023 mL bee -1 per day, SD = 0.016) was within the range reported for other chronic cage studies. 46 Considering that HPG development may be influenced by the laboratory environment, 31 the results of our study suggest that semi-field exposure 26,31 may be the best experimental context for evaluation of HPGs.…”

Sublethal effects of neonicotinoids in bees: a review

“…When the study was conducted using 3 ng/bee of the insecticide, 36 regions were upregulated and 77 regions downregulated (Christen et al, 2018) This result shows that different concentrations of insecticide cause different genes to be transcribed. Gauthier et al (2018) observed a decrease in α-carotene, α-cryptoxanthin and α-tocopherol after 10 days of oral contamination with low doses of imidacloprid in A. mellifera. Carotenoids act like antioxidants and precursors of retinoic compounds on vertebrates.…”

Pollutants and Their Interaction with Diseases of Social Hymenoptera

“…In honeybees and bumblebees, sublethal neonicotinoid exposure at concentrations comparable to those found in nectar and pollen affects the immune system negatively, resulting in a reduction of hemocyte density, encapsulation response, and antimicrobial activity [9,10,198,199]. Similar to vertebrates, exposure to neonicotinoids also induces oxidative stress by alteration in retinoid metabolism [200]. The neonicotinoid thiamethoxam alone already influences expression patterns of immune related genes in bee larvae as well as adults [201,202].…”