Post-Fire Effect of Savannah Vegetation on the Establishment of New Colonies ofAtta sexdens rubropilosa(Hymenoptera: Formicidae)

Abstract

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. ResumoEstabelecer sua colonia inicial provavelmente seja o momento mais critico da vida das formigas-cortadeiras. O nao-estabelecimento esta ligado a fatores abioticos e bioticos e, possivelmente, as altas taxas de mortalidade de colonias iniciais estejam associadas aos microrganismos entomopatogenicos ou antagonicos ao fungo simbionte cultivado por essas formigas presentes no solo. Sabe-se que o fogo na vegetacao, dependendo de sua intensidade, provoca alteracoes significativas nas propriedades fisicas, quimicas e microbiologicas do solo. Assim, neste trabalho avaliou-se o impacto de um incendio em vegetacao de savana (cerradao) no estabelecimento de colonias iniciais de Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae). Para isso, foram selecionadas areas onde ocorreu uma queima acidental e outra, de mesmo tamanho, com mesmas caracteristicas vegetacionais e contigua sem queima. Nessas areas e em solo coletados nessas mesmas areas e acondicionados em laboratorio foram colocadas femeas recem copuladas no dia da revoada para perfurarem o solo e fundarem suas colonias. Alteracoes nas propriedades quimicas e microbiologicas do solo pos-fogo foram quantificadas e correlacionadas com sucesso no estabelecimento de novas colonias dessa formiga-cortadeira. Em condicoes de campo, as femeas de A. sexdens rubropilosa nao apresentaram preferencia para perfurar o solo de areas queimadas ou nao e, nessa condicao, nenhuma colonia sobreviveu, em avaliacao realizada 120 dias depois da revoada. Em condicoes de laboratorio, a maioria das femeas perfurou o solo, independentemente de o solo onde elas foram acondicionadas ter sido queimado ou nao. Entretanto, o estabelecimento inicial de colonias foi significativamente maior em solos coletados distantes da superficie e em areas que nao sofreram acao direta do fogo, o que mostrou efeito negativo do fogo no estabelecimento de colonias no laboratorio. View this article in BioOne