Thiamethoxam toxicity on the stingless bee Friesiomelitta varia: LC50, survival time, and enzymatic biomarkers assessment.

Bees play a crucial role as pollinating insects in both natural and cultivated areas. However, the use of pesticides, such as thiamethoxam, has been identified as a contributing factor compromising bee health. The current risk assessment primarily relies on the model species Apis mellifera, raising concerns about the applicability of these assessments to other bee groups, including stingless bees. In this study, we investigated the acute toxicity of thiamethoxam on the stingless bee Frieseomelitta varia by determining the average lethal concentration (LC50) and mean lethal time (LT50). Additionally, we evaluated the enzymatic profile of Acetylcholinesterase (AChE), Carboxylesterase-3 (CaE-3), and Glutathione S-Transferase (GST), in the heads and abdomens of F. varia after exposure to thiamethoxam (LC50/10). The LC50 of thiamethoxam was determined to be 0.68 ng ai/µL, and the LT50 values were 37 days for the control group, 25 days at LC50/10, and 27 days at LC50/100. The thiamethoxam significantly decreased the survival time of F. varia. Furthermore, the enzymatic profile exhibited differences in CaE3 activity within one day in the heads and ten days in the abdomen. GST activity showed differences in the abdomen after one and five days of thiamethoxam exposure. These findings suggests that the abdomen is more affected than the head after oral exposure to thiamethoxam. Our study provides evidence of the toxicity of thiamethoxam at both the cellular and organismal levels, reinforcing the need to include non-Apis species in pollinator risk assessments. and provide solid arguments for bee protection.

Transcriptomic analysis of Malpighian tubules from the stingless bee Melipona scutellaris reveals thiamethoxam-induced damages.

The concern about pesticide exposure to neotropical bees has been increasing in the last few years, and knowledge gaps have been identified. Although stingless bees, (e.g.: Melipona scutellaris), are more diverse than honeybees and they stand out in the pollination of several valuable economical crops, toxicity assessments with stingless bees are still scarce. Nowadays new approaches in ecotoxicological studies, such as omic analysis, were pointed out as a strategy to reveal mechanisms of how bees deal with these stressors. To date, no molecular techniques have been applied for the evaluation of target and/or non-target organs in stingless bees, such as the Malpighian tubules (Mt). Therefore, in the present study, we evaluated the differentially expressed genes (DEGs) in the Mt of M. scutellaris after one and eight days of exposure to LC50/100 (0.000543 ng a.i./µL) of thiamethoxam (TMX). Through functional annotation analysis of four transcriptome libraries, the time course line approach revealed 237 DEGs (nine clusters) associated with carbon/energy metabolism and cellular processes (lysosomes, autophagy, and glycan degradation). The expression profiles of Mt were altered by TMX in processes, such as detoxification, excretion, tissue regeneration, oxidative stress, apoptosis, and DNA repair. Transcriptome analysis showed that cell metabolism in Mt was mainly affected after 8 days of exposure. Nine genes were selected from different clusters and validated by RT-qPCR. According to our findings, TMX promotes several types of damage in Mt cells at the molecular level. Therefore, interference of different cellular processes directly affects the health of M. scutellaris by compromising the function of Mt.