Soil actinobacteria inhibit antagonistic fungi of leafcutter ant colonies.

Founder females of the leaf-cutting ant species Atta sexdens experience high mortality during the founding and establishment of their colonies. The foundation site is crucial for the success of a new colony. In this study, we isolated and identified actinobacteria from fungus garden chambers of A. sexdens colony growth in soils from (1) forested areas without leafcutter ant nests and (2) open ground areas close to leafcutter ant nests. The inhibitory effect of these isolates on pathogenic fungi and the mutualistic fungus cultivated by leafcutter ants was evaluated. The 16S rRNA gene sequences were employed to identify nine selected actinobacteria species found in the soil: Streptomyces (6), Nocardia (2), and Kitasatospora (1). One Streptomyces and one Kitasatospora isolate inhibited all the tested fungi. Since there is no evidence of actinobacteria cultivation in the workers' cuticle of the Atta genus, our results corroborate the hypothesis that these workers may establish temporary adaptive symbiosis with soil microorganisms that produce antibiotic substances, living in some parts of their nest, or even inside their bodies. Pathogenic fungi are a risk factor that can be controlled by actinobacteria metabolites from soils, with minimal energy cost to the colony.

Immune Defense Strategies of Queens of the Social Parasite Ant Acromyrmex ameliae and Queens of Its Natural Hosts.

Social parasitism is well known in ants, but many aspects of this social phenomenon remain mysterious and unexplored. In some cases, parasite queens, who are able to mate very rarely end up producing brood and, thus, depend virtually on the labor of host ants. In this work, we sought to test the occurrence of grooming by host workers of Acromyrmex subterraneus subterraneus Forel, to their own queens and queens of the parasite Acromyrmex ameliae De Souza, Soares and Della Lucia and to compare the immune defense responses of parasite queens and queens of A. subterraneus subterraneus and Acromyrmex subterraneus brunneus Forel, the natural hosts. Duration and frequency of behavioral acts were recorded. The relative size of the bulla and the encapsulation response to a standardized antigen were analyzed. Regarding behavioral acts, self-grooming (duration and frequency) and allogrooming (duration) were statistically different between the species; the first is more frequent and lasted longer in parasite queens, while the second act lasted longer in host ants than in parasite ants. The bulla of A. ameliae was approximately 50% wider than those of its hosts. Parasite queens exhibited a stronger immune response than host queens. The results of this work contribute to elucidate potential mechanisms involved in the parasitism capacity of A. ameliae queens such as their strategies of immune defense.

Deleterious action of azadirachtin against the mutualistic fungus of leaf-cutting ants.

Leaf-cutting ants have a beneficial and obligatory relationship with the fungus that they grow. This mutualism allowed the evolutionary success of these ants. The great defoliation capacity of these insects, which often exceeds the level of tolerable economic damage, includes them as severe pests in many cultures. However, given the close relationship between these two agents of mutualism, it is expected that an impact on the fungus will reflect on the performance of the colony as a whole. Therefore, the effect of azadirachtin on the development, and the macronutrient composition of Leucoagaricus gongylophorus was evaluated. Azadirachtin reduced the final fungal mass at the end of treatment at all concentrations tested, but did not reduce the final growth area. A reduction in the amount of hyphae produced with increasing azadirachtin concentration was also observed. Regarding macronutrients, the compound did not affect their total amount in the fungus. Thus, it is observed that azadirachtin did not alter the composition of L. gongylophorus macronutrients, but inhibited its growth by reducing the number of hyphae produced. This reduction reflects directly on the amount of nutrients offered to the workers and the queen and may improve the management of these insects.

Effect of azadirachtin on mortality and immune response of leaf-cutting ants.

Leaf-cutting ants are difficult pests to control because they have numerous defense strategies and are highly selective in their plant harvesting choices. The search for effective pest control methods that have minimal negative effects on the environment has been continuous. Azadirachtin, a compound extracted from the neem tree (Azadirachta indica), is a promising alternative for the control of various pests, as it is toxic to some insects but readily degrades in the environment. In this study, we evaluated the effects of azadirachtin on the mortality, through topical exposure to the compound, and immune response, by introducing an artificial antigen into leaf-cutting ants Atta sexdens and Acromyrmex subterraneus subterraneus. Azadirachtin caused death to minor and major workers of both species in a concentration-dependent manner. Topical application of the compound did not diminish the immune response of ants in a microfilament encapsulation assay. Azadirachtin showed no effect on the immune response of workers but increased worker mortality, which indicates its potential as an ant control agent.

Comparative reproductive biology of the social parasite Acromyrmex ameliae de Souza, Soares & Della Lucia and of its host Acromyrmex subterraneus subterraneus Forel (Hymenoptera: Formicidae).

Social parasites exhibit several characteristics that allow them to exploit their host species efficiently. The smaller size of parasite species is a trait commonly found in ants. In this work, we investigated several aspects of the reproductive biology of Acromyrmex ameliae De Souza, Soares & Della Lucia, a recently discovered parasite of Acromyrmex subterraneus subterraneus Forel. Sexuals of A. ameliae are substantially smaller than those from host species. Parasite queens laid significantly less worker eggs than host queens and inhibit sexual production of the host. The sex ratio of parasite species is highly female biased. Interestingly, we have observed parasite coupling on the laboratory, inside the nests and in the ground, opening the possibility to use controlled mating to study genetic approaches of parasitism in the ants.

Blochmannia endosymbionts improve colony growth and immune defence in the ant Camponotus fellah.

BACKGROUND: Microorganisms are a large and diverse form of life. Many of them live in association with large multicellular organisms, developing symbiotic relations with the host and some have even evolved to form obligate endosymbiosis. All Carpenter ants (genus Camponotus) studied hitherto harbour primary endosymbiotic bacteria of the Blochmannia genus. The role of these bacteria in ant nutrition has been demonstrated but the omnivorous diet of these ants lead us to hypothesize that the bacteria might provide additional advantages to their host. In this study, we establish links between Blochmannia, growth of starting new colonies and the host immune response. RESULTS: We manipulated the number of bacterial endosymbionts in incipient laboratory-reared colonies of Camponotus fellah by administrating doses of an antibiotic (Rifampin) mixed in honey-solution. Efficiency of the treatment was estimated by quantitative polymerase chain reaction and Fluorescent in situ hybridization (FISH), using Blochmannia specific primers (qPCR) and two fluorescent probes (one for all Eubacterial and other specific for Blochmannia). Very few or no bacteria could be detected in treated ants. Incipient Rifampin treated colonies had significantly lower numbers of brood and adult workers than control colonies. The immune response of ants from control and treated colonies was estimated by inserting nylon filaments in the gaster and removing it after 24 h. In the control colonies, the encapsulation response was positively correlated to the bacterial amount, while no correlation was observed in treated colonies. Indeed, antibiotic treatment increased the encapsulation response of the workers, probably due to stress conditions. CONCLUSION: The increased growth rate observed in non-treated colonies confirms the importance of Blochmannia in this phase of colony development. This would provide an important selective advantage during colony founding, where the colonies are faced with severe inter and intraspecific competition. Furthermore, the bacteria improve the workers encapsulation response. Thus, these ants are likely to be less susceptible to various pathogen attacks, such as the Phoridae fly parasitoids, normally found in the vicinity of Camponotus nests. These advantages might explain the remarkable ecological success of this ant genus, comprising more than 1000 species.