Efeitos combinados de Nosema ceranae e do inseticida imidacloprido sobre abelhas Apis mellifera africanizada
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Data
2017-07-21
Autores
Soares Lima, Hellen Maria
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Universidade Estadual Paulista (Unesp)
Resumo
As abelhas Apis mellifera são importantes polinizadores de plantas nativas ou cultivadas, porém o contato com os agroecossistemas pode expor esses insetos à substâncias tóxicas, como o inseticida imidacloprido. A sistemicidade desse composto pode levar a contaminação não só das abelhas forrageiras, mas também dos outros indivíduos da colônia, inclusive, das larvas por meio do consumo de pólen e néctar contendo resíduos de imidacloprido. Assim, a primeira etapa desse trabalho determinou a toxicidade do imidacloprido para larvas e abelhas adultas do híbrido A. mellifera africanizada. Os resultados mostraram que as larvas são mais tolerantes ao imidacloprido do que as abelhas recém-emergidas e que alterações no desenvolvimento larval só foram observadas em concentração oito vezes maior do que a concentração letal média estabelecida para as abelhas adultas. Visto que não só os inseticidas, como também as parasitoses, como a nosemose, podem enfraquecer as colônias e comprometer a viabilidade destas, este trabalho visou avaliar, ainda, os efeitos da exposição de operárias de A. mellifera africanizada ao inseticida imidacloprido e/ou da infecção das abelhas por Nosema ceranae e compreender como esses fatores atuam isolados e em conjunto sobre o organismo desses insetos. A sobrevivência das abelhas diminuiu quando estas foram expostas ao inseticida e/ou infectadas pelo parasita, sendo que a combinação destes dois estressores comprometeu ainda mais a longevidade delas. Tanto a N. ceranae quanto o imidacloprido, isolados ou em combinação levaram às células do intestino médio das abelhas ao estresse, evidenciado pela imunomarcação da chaperona HSP 70 e a morte celular, provavelmente por macroautofagia, indicada pela intensa vacuolização e pela diminuição na expressão gênica da caspase-3. No intestino, a atividade tecidual da glutationa-S-transferase não foi afetada, provavelmente, devido aos danos encontrados no epitélio que afetaram as funções de metabolização e biotransformação. Uma vez com o intestino comprometido, uma maior quantidade do inseticida poderia ter atingido a hemolinfa, levando as células dos túbulos de Malpighi, órgão responsável pela excreção de substâncias tóxicas do organismo, à morte celular. No cérebro, o inseticida alterou a atividade sináptica dos corpos pedunculados, conforme demonstrado pela imunomarcação da sinapsina, causou estresse celular e aumento de células gliais, que podem indicar injúria do tecido nervoso. A ação neurotóxica do inseticida provocou, ainda, aumento da atividade tecidual das enzimas acetilcolinesterase e carboxilesterase na cabeça das abelhas. A atividade sináptica alterada e o aumento do estresse celular nos corpos pedunculados foram observados também nas abelhas infectadas apenas por N. ceranae, indicando resposta ao parasitismo. Adicionalmente, a combinação patógeno-inseticida e os estressores, quando isolados, causaram imunossupressão, diminuindo o número de hemócitos circulantes na hemolinfa e transcrição de genes relacionados a resposta imune individual e social. A partir dos resultados deste trabalho, concluiu-se que a combinação entre N. ceranae e concentrações residuais do imidacloprido afetou a sobrevivência das abelhas não só pela ação do inseticida em seu órgão alvo, o cérebro, mas, também, pelo comprometimento das funções digestórias e excretoras e pela diminuição da imunidade das abelhas.
The Apis mellifera honeybees are importants pollinators both for native and cultivated plants. However, the contact with the agroecosystems may expose these insects to toxic substances, such as imidacloprid insecticide. Compound systemicity may lead to the contamination not only of forager honeybees, but also of other colony individuals, including larvae, through both pollen and nectar consumption containing imidacloprid residues. Thus, the first stage of this work evaluated the imidacloprid toxicity to both larvae and adult honeybees of hybrid Africanized A. mellifera. Results showed that larvae are more tolerant to imidacloprid than newly emerged honeybees, and alterations in larvae development were only observed at concentrations eight times higher than the average lethal concentration established for adult honeybees. Since not only insecticides, but also diseases such as nosemosis may weaken colonies and compromise its viability, the second stage of this work was the evaluation of the exposure effects of Africanized A. mellifera workers to imidacloprid insecticide and/or to honeybees infection by Nosema ceranae in order to understand how these factors act both isolated and together on organism of these insects. Honeybees survival decreased when they were exposed to insecticide and/or infected by parasite, and the combinations of these two stressors further compromised their longevity. Both N. cenarae as imidacloprid, either alone or in combination, led midgut cells of honeybees to stress, evidenced by HSP 70 chaperone immunostaining, and to cell death, probably by macroautophagy, as indicated by genic expression decrease of caspase-3. In the midgut, glutathione-S-transferase tissue activity was not altered, probably due to damage found on the epithelium that may affect both metabolization and biotransformation function. Once midgut was compromised, probably more quantity of insecticide reached hemolymph, leading cells from Malpighian tubules, organ responsible for toxic substances excretion from organism, to cell death. In the brain, the insecticide altered mushroom body synaptic activity, as verified by synapsin immunostaining, and it also caused cellular stress and increased of glial cells, which may indicate nerve tissue injury. Insecticide neurotoxic action also caused an increase in the activity of acetylcholinesterase and carboxylesterase enzymes in the heads of the honeybees. Altered synaptic activity and increased cellular stress in mushroom bodies were also observed for honeybees infected only by N. ceranae, indicating response to parasitism. Additionally, pathogen-insecticide combination and the stressors, when isolated, caused immunosuppression, reducing both the hemocytes circulating number in hemolymph and transcription of genes related to individual and social immune response. Based on results from this work, we may conclude that combination between N. ceranae and residual concentrations of Imidacloprid affected honeybees survival, due to insecticide action on their target organ (brain), impairment on digestory and excretory functions and honeybees imunity decreased.
The Apis mellifera honeybees are importants pollinators both for native and cultivated plants. However, the contact with the agroecosystems may expose these insects to toxic substances, such as imidacloprid insecticide. Compound systemicity may lead to the contamination not only of forager honeybees, but also of other colony individuals, including larvae, through both pollen and nectar consumption containing imidacloprid residues. Thus, the first stage of this work evaluated the imidacloprid toxicity to both larvae and adult honeybees of hybrid Africanized A. mellifera. Results showed that larvae are more tolerant to imidacloprid than newly emerged honeybees, and alterations in larvae development were only observed at concentrations eight times higher than the average lethal concentration established for adult honeybees. Since not only insecticides, but also diseases such as nosemosis may weaken colonies and compromise its viability, the second stage of this work was the evaluation of the exposure effects of Africanized A. mellifera workers to imidacloprid insecticide and/or to honeybees infection by Nosema ceranae in order to understand how these factors act both isolated and together on organism of these insects. Honeybees survival decreased when they were exposed to insecticide and/or infected by parasite, and the combinations of these two stressors further compromised their longevity. Both N. cenarae as imidacloprid, either alone or in combination, led midgut cells of honeybees to stress, evidenced by HSP 70 chaperone immunostaining, and to cell death, probably by macroautophagy, as indicated by genic expression decrease of caspase-3. In the midgut, glutathione-S-transferase tissue activity was not altered, probably due to damage found on the epithelium that may affect both metabolization and biotransformation function. Once midgut was compromised, probably more quantity of insecticide reached hemolymph, leading cells from Malpighian tubules, organ responsible for toxic substances excretion from organism, to cell death. In the brain, the insecticide altered mushroom body synaptic activity, as verified by synapsin immunostaining, and it also caused cellular stress and increased of glial cells, which may indicate nerve tissue injury. Insecticide neurotoxic action also caused an increase in the activity of acetylcholinesterase and carboxylesterase enzymes in the heads of the honeybees. Altered synaptic activity and increased cellular stress in mushroom bodies were also observed for honeybees infected only by N. ceranae, indicating response to parasitism. Additionally, pathogen-insecticide combination and the stressors, when isolated, caused immunosuppression, reducing both the hemocytes circulating number in hemolymph and transcription of genes related to individual and social immune response. Based on results from this work, we may conclude that combination between N. ceranae and residual concentrations of Imidacloprid affected honeybees survival, due to insecticide action on their target organ (brain), impairment on digestory and excretory functions and honeybees imunity decreased.
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Palavras-chave
Concentração letal média, Sinapsina, HSP 70, Morte celular, Sistema imune, Lethal median concentration, Synapsin, Cell death, Immune system