Toxicidade de inseticidas organofosforados para as abelhas sem ferrão Scaptotrigona bipunctata e Tetragonisca fiebrigi

• Ano de defesa: 2015
• Autor(a) principal: Dorneles, Andressa Linhares
• Orientador(a): Blochtein, Betina
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Pontifícia Universidade Católica do Rio Grande do Sul
• Programa de Pós-Graduação: Programa de Pós-Graduação em Zoologia
• Departamento: Faculdade de Biociências
• País: Brasil
• Palavras-chave em Português: ZOOLOGIA; ABELHAS; PESTICIDAS; INSETICIDAS; POLINIZAÇÃO
• Área do conhecimento CNPq: CIENCIAS BIOLOGICAS::ZOOLOGIA
• Link de acesso: http://tede2.pucrs.br/tede2/handle/tede/6407

The current bee populations decline has been mainly attributed to the excessive use of pesticides. The most of researches about risks of pesticides to bees are focused on honeybee Apis mellifera. However, due to the wide diversity of stingless bees in Brazil, studies evaluating the risks to native species become necessary and relevant. In Brazil, the importance of pollination services provided by bees is recognized in economic interest crops such as apple, coffee, cotton, orange, and soybeans. In these crops, many insecticides are used for pest control, especially organophosphates such as chlorpyrifos (Lorsban®) and phosmet (Imidan®). Due to the large use of pesticides on crops that offer attractive flowers for bees in Brazil, the aim of this study was to determine the lethal concentration (LC50), via oral exposure, and the lethal dose (LD50) for topically applied of these insecticides to stingless bees Scaptotrigona bipunctata e Tetragonisca fiebrigi.In acute oral toxicity tests, five concentrations dilute in sucrose solution were offered to the bees through the food. In acute topical toxicity tests, 1μL of each one of the five doses diluted in acetone were applied topically on bees. After 48 hours of exposure, the number of dead bees was recorded. In the oral assay, the LC50 values of chlorpyrifos was 0,0112 μg a.i./μL diet to S. bipunctata and 0,0018 μg a.i./μL diet to T. fiebrigi. The LC50 values of phosmet was 0,0245 μg a.i./μL diet to S. bipunctata and 0,0236 μg a.i./μL diet to T. fiebrigi. In the topic application assay, the LD50 of chlorpyrifos was 0,0110 μg a.i./bee to S. bipunctata and 0,0033 μg a.i./bee to T. fiebrigi. The LD50 of phosmet was 0,0087 μg a.i./bee to S. bipunctata and 0,0083 μg a.i./bee to T. fiebrigi. According to the results, there was significant difference in susceptibility between the stingless bees species tested, indicating that forager workers of S. bipunctata were more tolerant to the insecticide chlorpyrifos than T. fiebrigi, in both assays. These differences in susceptibility may be related to the body weight of the bees, i.e., S. bipunctata species with the highest weight (18.28 mg) would be more tolerant than T. fiebrigi, with the lowest weight (4.36 mg). In addition, characteristics genetically determined, as the chemical composition of the cuticle, may facilitate penetration of the insecticide into the bee's body, increasing the susceptibility of each species. Another point is related to detoxification capacity of the bees, by the action of detoxifying enzymes present in its digestive system. In contrast, the susceptibility between the two stingless bees species showed no significant differences regarding the insecticide phosmet, an event that could be associated with the ability of these bees metabolize and remove this product. Comparing the LD50 values obtained in this study with literature data established for A. mellifera (chlorpyrifos 0.11 μg/bee; phosmet 1.13 μg/bee), we concluded that native bees are more sensitive to the insecticides chlorpyrifos and phosmet. This evidence emphasizes the importance of including other species of bees in toxicity assays required for the authorization of the use of pesticides, in order to ensure the protection of native bees. Our results indicate that the insecticides chlorpyrifos (Lorsban®) and phosmet (Imidan®) are potentially dangerous to S. bipunctata and T. fiebrigi species, both topically and by ingestion. Thus, it is essential to propose measures to minimize the impact on pollinators. This study is the first evaluation of the lethal effects of the insecticides chlorpyrifos and phosmet to S. bipunctata and T. fiebrigi, providing important subsidies for future studies on pesticide toxicity in stingless bees.