Seasonal Variations of Metapleural Secretion in the Leaf-Cutting ant Atta sexdens piriventris Santschi (Myrmicinae: Attini), and Lack of Fungicide Effect on Beauveria bassiana (Bals.) Vuillemin

Abstract

Variações Sazonais da Secreção Metapleural da Formiga Cortadeira Atta sexdens piriventrisSantschi (Myrmicinae: Attini), e Ausência de Efeito Fungicida Sobre o Entomopatógeno Beauveria bassiana (Bals.) Vuillemin RESUMO -Os mecanismos envolvidos na manutenção das colônias de insetos sociais livres de patógenos são aspectos importantes relacionados à biologia evolutiva do grupo. No caso das formigas, tem sido sugerido que a secreção das glândulas metapleurais teria importante papel na assepsia da colônia. Neste trabalho, as diversas subcastas de operárias da formiga cortadeira Atta sexdens piriventris Santschi foram comparadas quanto à presença de secreção metapleural ao longo de um ano. Simultaneamente, a atividade tópica da secreção foi testada em operárias tratadas com o fungo entomopatogênico Beauveria bassiana (Bals.) Vuillemin. De acordo com a largura média da cápsula cefálica, foram definidas seis subcastas de operárias: jardineira, mínima, média, grande, máxima e soldado. Foi encontrada uma correlação positiva entre subcasta e comprimento do reservatório metapleural. As subcastas apresentaram diferenças significativas na presença de secreção metapleural ao longo do ano exceto nos meses de abril, maio, julho e novembro. Foi observada uma correlação positiva entre as temperaturas médias sazonais e presença de secreção metapleural. Foram registradas altas freqüências de operárias de todas subcastas infectadas por B. bassiana durante os bioensaios, indicando que a secreção metapleural não tem atividade fungicida contra esse patógeno. Os resultados sugerem que a secreção metapleural não está entre os principais mecanismos de assepsia das colônias de A. sexdens piriventris.PALAVRAS-CHAVE: Insecta, formigas cultivadoras de fungo, glândula metapleural, fungo entomopatogênico, controle biológico.ABSTRACT -Mechanisms involved in maintaining colonies of social insects free of pathogens are among the main aspects of interest in the evolutionary biology of this group. For ants, it has been suggested that secretion from the metapleural glands play an important role in colony asepsis. In this study, different worker subcastes of the fungus-growing ant Atta sexdens piriventris Santschi were compared in relation to presence of metapleural secretion during a year. At the same time, the topical activity of the secretion was tested on workers treated with the entomopathogenic fungus Beauveria bassiana (Bals.) Vuillemin. Based on the mean width of the cephalic capsule, six worker subcastes were defined: gardener, minor, media, large, major and soldier. A positive correlation between worker subcaste and metapleural reservoir length was observed. Significant differences for presence of metapleural secretion were found throughout the year among subcastes, except in April, May, July and November. A positive correlation between seasonal mean temperature and presence of the metapleural secretion was observed. High frequencies of infected workers of all subcastes were observed during bioassays with inoculation of B. bassiana, indicati...

Diversity of Fungi Associated withAtta bisphaerica(Hymenoptera: Formicidae): The Activity ofAspergillus ochraceusandBeauveria bassiana

“…The potential of using fungi to control leaf-cutting ants is large, considering that several entomopathogenic species have been found in worker ants, nearby or within the nests of Psyche the ants [9][10][11][12][13] and may cause the death of the worker ants or of the fungus garden. While leaf-cutting ants are constantly in contact with a diversity of entomopathogenic fungi, they do not appear to be normally infected by them.…”

The Metapleural Secretion of Acromyrmex laticeps (Forel) does not have Fungicide Effect on the Entomopathogenic Fungus Beauveria bassiana (Bals.) Vuill

“…These insects have developed numerous defense mechanisms to deal with this situation, such as avoidance behavior, hygiene of both individuals and nest (Diehl- (Billen & Van BoVen 1987;höllDoBler & wilson 1990). The effects of antiseptics metapleural secretion have been studied more in length in Attini ants (Diehl-fleig et al 1993;Do nascimento et al 1996;Diehl & Junqueira 2001;Bot et al 2002;Baer et al 2005) and in some Solenopsis species (Pereira & stimac 1992;oi et al 1994;Bextine & thorVilson 2002).…”

“…Accordingly, they also display numerous defense mechanisms, including behavior (Diehl-fleig & lucchese 1991;Jaffé 1993), increased genetic diversity, either by polyandry or polygyny (schmiD-hemPel 1994;crozier & fJerDingstaD 2001) immunological mechanisms (schmiD-hemPel 2005), especially secretions of metapleural glands (höllDoBler & wilson 1990;schmiD-hemPel 1998;schlüns & crozier 2009). Despite these defense mechanisms, the occurrence of entomopathogenic fungi in ants is relatively common (Pereira & stimac 1992;Diehl-fleig et al 1993;oi et al 1994;Diehl & Junqueira 2001).…”

Functional role of phenylacetic acid from metapleural gland secretions in controlling fungal pathogens in evolutionarily derived leaf-cutting ants

“…Relative abundance of visible actinomycetes on ants' exoskeletons [14] and MG-grooming are key traits, but we still know rather little about the pathogen pressure on leaf-cutting ant nests in the field ( [20,28], but see [55]), seasonal variation in disease pressure and defence [56], and the possible roles of myrmecophilous arthropods in disease transmission or control [12]. Detection and cognition are also likely to be of key significance, as the smallest Atta worker castes invest more biomass in their brains relative to larger nest-mates [57,58], but it remains unknown whether they have a heightened sensitivity to cues indicating infection.…”