Can the exposure of Apis mellifera (Hymenoptera, Apiadae) larvae to a field concentration of thiamethoxam affect newly emerged bees?

Abstract

The use of insecticides on crops can affect non-target insects, such as bees. In addition to the adult bees, larvae can be exposed to the insecticide through contaminated floral resources. Therefore, this study aimed to investigate the possible effects of the exposure of A. mellifera larvae to a field concentration of thiamethoxam (0.001 ng/μL thiamethoxam) on larval and pupal survival and on the percentage of adult emergence. Additionally, its cytotoxic effects on the digestive cells of midgut, Malpighian tubules cells and Kenyon cells of the brain of newly emerged A. mellifera bees were analyzed. The results showed that larval exposure to this concentration of thiamethoxam did not influence larval and pupal survival or the percentage of adult bee emergence. However, this exposure caused ultra-structural alterations in the target and non-target organs of newly emerged bees. The digestive cell of bees that were exposed to the insecticide exhibited a basal labyrinth without long and thin channels and compromised mitochondria. In Malpighian tubules cells, disorganized basal labyrinth, dilated mitochondria with a deformed shape and a loss of cristae, and disorganized microvilli were observed. The results showed that the exposed bees presented Kenyon cells with alterations in the nucleus and mitochondria. These alterations indicate possible tissue degeneration, demonstrating the cytotoxicity of thiamethoxam in the target and non-target organs of newly emerged bees. Such results suggest cellular organelle impairment that can compromise cellular function of the midgut cells, Malpighian tubules cells and Kenyon cells, and, consequently, can compromise the longevity of the bees of the whole colony.

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

“…Our findings contrast with those of Grillone et al ., who found significant, dose‐responsive decreases in survival of larvae fed diets containing THI from 2 to 0.2 mg L –1 THI . Significantly decreased Africanized A. mellifera adult emergence has been reported in larvae acutely exposed to 0.001 mg L –1 THI, but other studies refuted this finding . One reason for the disagreement between our work and that of Grillone et al .…”

“…51 Significantly decreased Africanized A. mellifera adult emergence has been reported in larvae acutely exposed to 0.001 mg L -1 THI, 49 but other studies refuted this finding. 53 One reason for the disagreement between our work and that of Grillone et al 51 could be that Grillone et al 51 used the in vitro larval rearing methods of Aupinel et al 54,55 with 5 days of THI exposure (corresponding to days 2-6), whereas we used the Schmehl et al 30 protocol with 4 days of THI exposure (days 3-6), resulting in a 6.6% lower total dose per larva in our study for the same test concentration of THI. Nevertheless, our lack of effect at 0.1 mg L -1 THI on larval survival is consistent with the no adverse effect concentration established by Dai et al 35 of 0.1 mg L -1 for worker larvae fed CLO, a metabolite of THI.…”

Acute and chronic toxicity of acetamiprid, carbaryl, cypermethrin and deltamethrin to Apis mellifera larvae reared in vitro

“…Adult honey bees will bring pollen and nectar contaminated with insecticides back into the comb during their foraging activities, and acaricides used by beekeepers to control varroosis by beekeepers are also disseminated in‐hive . Honey bee larvae may be exposed directly or indirectly to these insecticides.…”

“…There is clear evidence that bee larvae reared in treatment combs containing insecticide residues experience delayed development . Reduced survival and weight loss are the main indicators of the effects of insecticides on bee larvae in the literature . Several studies have even confirmed that insecticide toxicity occurs at lower exposure rates to larvae compared to adult bees …”

“…24 Reduced survival and weight loss are the main indicators of the effects of insecticides on bee larvae in the literature. [25][26][27][28] Several studies have even confirmed that insecticide toxicity occurs at lower exposure rates to larvae compared to adult bees. 29 Neonicotinoids are insecticides that interact with the nicotinic acetylcholine receptors (nAChRs) of the insect central nervous system, resulting in abnormal behavior, inactivity and death of insects.…”