Estudos comportamentais e mecanismos de contaminação em colônias da formiga cortadeira Atta sexdens (Hymenoptera, Formicidae)
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2020-12-18
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Universidade Estadual Paulista (Unesp)
Resumo
As formigas cortadeiras cortam e transportam para o ninho uma grande quantidade de plantas que são incorporadas ao fungo simbionte, do qual se alimentam. Para evitar a contaminação da colônia, esse material vegetal passa por um processo de assepsia e o mesmo ocorre quando carregam as iscas formicidas; porém, ainda se questiona como ocorre a contaminação, se pelo contato direto das operárias durante o processamento do substrato, ou por “allogrooming” e “self-grooming”, ou ainda por trofalaxia. Deste modo, o objetivo foi estudar os mecanismos de contaminação com operárias de formiga cortadeira, Atta sexdens, por meio de estudos comportamentais, buscando esclarecer como ocorre a dispersão e a contaminação com diferentes ingredientes ativos na colônia, e elucidar se a contaminação das operárias pode ocorrer via trofalaxia oral. Assim, foram analisados e registrados os atos e frequências comportamentais realizados pelas operárias durante o processamento dos pellets utilizando um corante traçador lipossolúvel, e registrando a quantidade de operárias coradas, após o cultivo do fungo. O comportamento mais frequente foi o “allogrooming”, que correspondeu a 45,87% do processo de contaminação das operárias, seguido de segurar, lamber e repicar os pellets, que responderam a 40,22% do processo. Após o processamento dos pellets, as operárias apresentaram as estruturas morfológicas externas e internas marcadas pelo corante traçador, 93,75% e 79,25%, respectivamente. Os resultados confirmaram que os comportamentos realizados durante o cultivo do fungo contribuem para a dispersão de substâncias, como os inseticidas, causando a contaminação das operárias. Adicionalmente, verificou-se como os fragmentos das iscas são dispersados e se o modo de ação do ingrediente ativo, que bloqueia os canais de sódio e interrompe a produção de ATP na mitocôndria, interfere na distribuição dos fragmentos no interior do ninho. Para isso, avaliou a dispersão dos fragmentos de pellets durante o cultivo do fungo pelas operárias, referenciando espacialmente o fragmento no jardim do fungo. Os fragmentos de pellets foram distribuídos aleatoriamente, mas a quantidade dos fragmentos foi influenciada pelo modo que o ingrediente ativo atua na colônia. E por fim, se o comportamento de forrageamento líquido está relacionado às taxas de trofalaxia em formigas cortadeiras. Para estudar se a ocorrência de trofalaxia está relacionada com a ingestão de substâncias líquidas, avaliou se há forrageamento líquido e troca de alimento líquido em colônias de laboratório de formigas cortadeiras. Os resultados revelaram que as forrageiras comumente ingerem líquido quando fornecido com uma fonte líquida. Dentro do ninho, as operárias forrageiras realizaram diversos comportamentos, mas nenhuma troca alimentar (trofalaxia oral) ocorreu durante todo o período de oito horas em que as operárias foram observadas. Nas condições experimentais, o forrageamento líquido não teve relação com a trofalaxia oral entre operárias dentro do ninho. Assim, a coleta de líquidos atende às necessidades individuais das operárias e não se destina à trofalaxia entre elas, uma vez que esse comportamento é para alimentar a colônia, dependendo principalmente do hábito alimentar e do papo desenvolvido para transportar alimento líquido. Portanto, o presente estudo concluiu que a contaminação das operárias pelos ingredientes ativos presentes nas iscas formicidas ocorre pelo processamento das iscas para incorporação no jardim de fungo, bem como o contato indireto (“allogrooming” e “self-grooming”). O modo de ação dos ingredientes ativos, sulfluramida e indoxarcarbe, influencia a quantidade de fragmentos incorporados no jardim de fungo. E o forrageamento líquido realizado pelas operárias não implica na ocorrência de trofalaxia oral.
Leaf-cutting ants cut and transport a large number of plants to their nest which are incorporated into symbiotic fungus, on which they feed. Although plants undergo an asepsis process even they carry toxics baits to avoid the colony’s contamination, it may be asked how contamination occurs, or rather, whether it occurs by direct contact of the workers during substrate processing or by allogrooming and self-grooming, or even by trophallaxis. Current analysis studies the mechanisms of contamination in the workers of the leaf-cutting ant, Atta sexdens, through behavioral studies and clarifies how dispersion and contamination with different active ingredients in colony occur and also verifies whether contamination of workers occurs via oral trophallaxis. Behavioral acts and their frequencies performed by workers during the pellet processing were analyzed and recorded by means of a liposoluble tracer dye, whereas the number of stained workers was recorded after the cultivation of the fungus. Allogrooming, reaching 45.87% of the contamination process of the worker ants was the most frequent behavior, followed by holding, licking and pellet cutting, which accounted to 40.22% of the process. After pellets processing, the workers had their external and internal morphological structures marked by the tracer dye, 93.75% and 79.25%, respectively. Results proved that behaviors performed during fungus cultivation contribute towards the dispersion of substances, such as insecticides, which contaminate workers. Further, it has also been verified how bait fragments are dispersed and whether the mode of action of the active ingredient, which blocks sodium channels and interrupts of ATP production in the mitochondria, interferes with the distribution of fragments in nest. For this, it evaluated the dispersion of the fragments of pellets during the cultivation of the fungus by the workers, spatially referencing the fragment in the fungus garden. Although pellet fragments were randomly distributed, the amount of pellet fragments was affected by the manner the active ingredient works in the colony. It has also been analyzed whether liquid foraging is related to rates of trophallaxis in leaf-cutting ants. The investigation on the occurrence of trophallaxis as related to the ingestion of liquid substances has been carried out by evaluating liquid foraging and exchange of liquid food in laboratory colonies of leaf-cutting ants. Results revealed that foragers commonly ingest liquid when provided with a liquid source. Foragers workers performed several behaviors inside the nest, but no food exchange (oral trophallaxis) occurred during a period of eight hours they were observed. In experimental conditions, liquid foraging was not related to oral trophallaxis among workers inside the nest. Thus, liquid foraging meets the workers individual needs and it is not meant for trophallaxis among them, once this behavior is to feed the colony and mainly depends on feeding habits and the existence of a well-developed crop, and the resulting mode of transporting liquid food. Thus, present study revealed that the contamination of workers by active ingredients present in the toxic baits occurs through the bait processing for incorporation in fungus garden and through indirect contact, such as allogrooming and self-grooming. The mode of action of active ingredients, sulfluramid and indoxarcarb, influences the number of fragments incorporated in fungus garden. Moreover, liquid foraging carried out by workers does not imply the occurrence of oral trophallaxis.
Leaf-cutting ants cut and transport a large number of plants to their nest which are incorporated into symbiotic fungus, on which they feed. Although plants undergo an asepsis process even they carry toxics baits to avoid the colony’s contamination, it may be asked how contamination occurs, or rather, whether it occurs by direct contact of the workers during substrate processing or by allogrooming and self-grooming, or even by trophallaxis. Current analysis studies the mechanisms of contamination in the workers of the leaf-cutting ant, Atta sexdens, through behavioral studies and clarifies how dispersion and contamination with different active ingredients in colony occur and also verifies whether contamination of workers occurs via oral trophallaxis. Behavioral acts and their frequencies performed by workers during the pellet processing were analyzed and recorded by means of a liposoluble tracer dye, whereas the number of stained workers was recorded after the cultivation of the fungus. Allogrooming, reaching 45.87% of the contamination process of the worker ants was the most frequent behavior, followed by holding, licking and pellet cutting, which accounted to 40.22% of the process. After pellets processing, the workers had their external and internal morphological structures marked by the tracer dye, 93.75% and 79.25%, respectively. Results proved that behaviors performed during fungus cultivation contribute towards the dispersion of substances, such as insecticides, which contaminate workers. Further, it has also been verified how bait fragments are dispersed and whether the mode of action of the active ingredient, which blocks sodium channels and interrupts of ATP production in the mitochondria, interferes with the distribution of fragments in nest. For this, it evaluated the dispersion of the fragments of pellets during the cultivation of the fungus by the workers, spatially referencing the fragment in the fungus garden. Although pellet fragments were randomly distributed, the amount of pellet fragments was affected by the manner the active ingredient works in the colony. It has also been analyzed whether liquid foraging is related to rates of trophallaxis in leaf-cutting ants. The investigation on the occurrence of trophallaxis as related to the ingestion of liquid substances has been carried out by evaluating liquid foraging and exchange of liquid food in laboratory colonies of leaf-cutting ants. Results revealed that foragers commonly ingest liquid when provided with a liquid source. Foragers workers performed several behaviors inside the nest, but no food exchange (oral trophallaxis) occurred during a period of eight hours they were observed. In experimental conditions, liquid foraging was not related to oral trophallaxis among workers inside the nest. Thus, liquid foraging meets the workers individual needs and it is not meant for trophallaxis among them, once this behavior is to feed the colony and mainly depends on feeding habits and the existence of a well-developed crop, and the resulting mode of transporting liquid food. Thus, present study revealed that the contamination of workers by active ingredients present in the toxic baits occurs through the bait processing for incorporation in fungus garden and through indirect contact, such as allogrooming and self-grooming. The mode of action of active ingredients, sulfluramid and indoxarcarb, influences the number of fragments incorporated in fungus garden. Moreover, liquid foraging carried out by workers does not imply the occurrence of oral trophallaxis.
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Atos comportamentais, Cultivo do fungo simbionte, Dispersão de ingrediente ativo, Ingestão de líquidos, Trofalaxia, Behavioral acts, Cultivation of symbiotic fungus, Dispersion of active ingredient, Fluid intake, Trophallaxis