Post-fire effect of savannah vegetation on the establishment of new colonies of Atta sexdens rubropilosa (Hymenoptera: Formicidae)
Keywords:
female, initial nest, nuptial flight, leaf-cutting ant, fireAbstract
Establishing their initial colony is probably the most critical moment in the life of leaf-cutting ants. The non-establishment is connected to abiotic and biotic factors, and the high mortality rates of initial colonies are possibly associated with entomopathogenic or antagonistic microorganisms to the symbiotic fungus present in the soil, hosted by these ants. Fire in the vegetation, depending on the intensity, is known to cause significant changes to the soil physical, chemical, and microbiological properties. The impact of a fire in savannah vegetation (Cerrado) on the establishment of early colonies of Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae) was evaluated. For this end, two areas were selected, one where there had been an accidental fire, and a contiguous one with the same size and vegetation characteristics without burning. In these areas and in soil collected in the same areas and stored in the laboratory, females recently fertilized in the nuptial flight were placed to excavate the soil and establish their colonies. Post-fire changes in the soil chemical and microbiological properties were quantified and correlated successfully in the establishment of new colonies of this leaf-cutting ant. Under field conditions, the females of A. sexdens rubropilosa did not show preference for which areas to excavate: the ones that had been burned or the ones that were unburned; under this condition, no colony survived according to the evaluation performed 120 d after the nuptial flight. Under laboratory conditions, the majority of the females excavated the soil, whether it had been burned or not. However, the establishment of initial colonies was significantly higher in soils collected far from the surface and in areas that had not directly been affected by the fire, showing a negative effect of fire on colony establishment under laboratory conditions.
Resumo
Estabelecer sua colônia inicial provavelmente seja o momento mais crítico da vida das formigas-cortadeiras. O não-estabelecimento está ligado a fatores abióticos e bióticos e, possivelmente, as altas taxas de mortalidade de colônias iniciais estejam associadas aos microrganismos entomopatogênicos ou antagônicos ao fungo simbionte cultivado por essas formigas presentes no solo. Sabe-se que o fogo na vegetação, dependendo de sua intensidade, provoca alterações significativas nas propriedades físicas, químicas e microbiológicas do solo. Assim, neste trabalho avaliou-se o impacto de um incêndio em vegetação de savana (cerradão) no estabelecimento de colônias iniciais de Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae). Para isso, foram selecionadas áreas onde ocorreu uma queima acidental e outra, de mesmo tamanho, com mesmas características vegetacionais e contígua sem queima. Nessas áreas e em solo coletados nessas mesmas áreas e acondicionados em laboratório foram colocadas fêmeas recém copuladas no dia da revoada para perfurarem o solo e fundarem suas colônias. Alterações nas propriedades químicas e microbiológicas do solo pós-fogo foram quantificadas e correlacionadas com sucesso no estabelecimento de novas colônias dessa formiga-cortadeira. Em condições de campo, as fêmeas de A. sexdens rubropilosa não apresentaram preferência para perfurar o solo de áreas queimadas ou não e, nessa condição, nenhuma colônia sobreviveu, em avaliação realizada 120 dias depois da revoada. Em condições de laboratório, a maioria das fêmeas perfurou o solo, independentemente de o solo onde elas foram acondicionadas ter sido queimado ou não. Entretanto, o estabelecimento inicial de colônias foi significativamente maior em solos coletados distantes da superfície e em areas que não sofreram ação direta do fogo, o que mostrou efeito negativo do fogo no estabelecimento de colônias no laboratório.
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