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Please use this identifier to cite or link to this item: http://hdl.handle.net/10761/4081

Issue Date: 1-Apr-2016
Authors: Vaccalluzzo, Valerio
Title: Exposure of honeybees (Apis mellifera L.) and other hymenoptera pollinators to different Bacillus thuringiensis based biopesticides in laboratory controlled trials
Abstract: Apoidea play a fundamental and strategic role in the regulation of reproductive processes of many plants, including those of agricultural interest, due to their pollination activities. In Italy, Apoidea important for agriculture include: Apis mellifera Linnaeus 1758, known eusocial species with organization into castes Osmia cornuta, Latreille 1805 and O. rufa Linnaeus 1758, two species of solitary bees that nest in gregarious form, profitable and easy to use on different crops in semi-field and open field. However, populations of many species of Apoidea are in decline, and this phenomenon seems to be also related to the increase of the use of chemicals in agricultural practices. Biopesticides are a class of natural products used in agriculture to limit the damage caused by harmful organisms and include commercial formulations. They should be less harmful for the environment compared to traditional chemical pesticides, because they are effective at very low concentrations and have a rapid inactivation; furthermore, these products have a lower risk of non-specificity, acting mainly on the larval stages of some species of pests. Bacillus thuringiensis-based biopesticides are often used in IPM and they are dispersed in the environment. Bacillus thuringiensis (Bt) B. is one of the most common microorganisms which toxicity is due to the production of parasporal crystals exhibiting a highly specific insecticidal activity during sporulation of the bacterium. These toxic crystals (Cry), consist of different protein families (insecticidal crystal proteins or ICPs) not closely related, that are released into the environment and, once arrived in the gut of the organism by via trophic, act specifically on the epithelium of the midgut. Since insects epithelial cells of midgut are involved in multiple processes such as digestion, absorption, formation of peritrophic membrane, the alteration caused by the toxins of Bt would involve a functional impairment that could end with the death of the insect, according to the mechanisms of action. However, the natural compounds are not necessarily safer than synthetic ones because their biological properties and activity are in function of the structure rather than the origin, the applied dose in certain situations, and in relation to the safety of the product utilization. Bt-based products are considered harmless for species of Apoidea so far investigated, but it is believed that they could lead to sublethal effects, thus reducing pollinator populations in the field. Despite the importance of information on this issue, investigations, are still limited. Given the crucial role played by both honeybees and solitary bees, not only for an ecological standpoint, but also for an agro-economic aspect, I thought it was interesting to undertake investigations leading to evaluation the toxic effects associated with the administration of various concentrations of three Bt-based formulations. For this purpose, I have focused my research on the effects of products at different levels: assessing the mortality of O. cornuta, O. rufa and A. mellifera, and, for the latter species, it was observed a possible behavior modification related to histological and ultrastructural impairment of the midgut epithelium of workers. Moreover, any biochemical alteration and gene expression was assessed in midgut of workers after ingestion of one of biopesticides tested. Overall, results confirm such low toxicity of the tested Bt-based biopesticides on workers of A. mellifera and O. cornuta and O.rufa, at the concentrations presumably found in field-environment conditions, confirming that the biopesticides represent a category of commercial products certainly more convenient for the environment and the human health than the other agrochemicals, although any possible long-term and chronic effects should be taking into account.
Appears in Collections:Area 07 - Scienze agrarie e veterinarie

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