Abstract
Leaf-cutting ants, whose name comes from the habit of cutting leaves and other parts of plants, are dominant herbivores in the Americas, attacking different crops to keep symbiotic fungi (their main food source) in the colony. These ants are soil inhabitants, an environment rich in microorganisms, many of which are considered entomopathogenic. In order to describe a kind of microbial biological control of these ants through histological techniques, we used the fungus Beauveria bassiana (Bals.- Criv.) Vuill. Larvae and adult workers of Atta sexdens (Linnaeus, 1758) were exposed to a fungal suspension with the concentration of 106/conidia/mL. The specimens were adequately prepared to describe the behavior of the fungus on the integument at 24, 48 and 72 hours after initial exposure. Some specimens were used to represent these periods, being properly processed for scanning electron microscopy, which was applied to document the fungus development on the surface of the insect integument. To better understand the dynamics of the fungal infection, from the conidial adhesion to the potential colonization of the insides of the insect, the histological technique with HE staining was applied. The results showed that, in immature individuals, the hyphal penetration of B. bassiana fungi into the insect integument occurred in 48 h.
Highlights
The leafcutter ants of the genus Atta, popularly known as saúvas, are considered important agriculture pests, defoliating crops and causing losses to livestock breeding and silviculture (Della Lucia & Vilela, 1993, p. 262)
For exposure of individuals to the suspension of conidia, the fungus B. bassiana replicated in petri dishes each 15 days were removed from its culture PDA+ malt agar (2%), as previously described and adjusted to 106 conidia/mL in order to standardize the exposure of individuals isolated in 250 ml plastic containers or Petri dishes, in the larvae case, which were removed in different time periods of 24, 48 and 72 hours, and fixed in paraformaldehyde (4%) for monitoring with the use of different ultramorphological techniques Scanning Electron Microscopy (SEM) and hematoxylin and eosin (HE) as described in the sequence
The results of the present study show the dynamics of adhesion, germination and penetration of the fungus B. bassiana in the integument of A. sexdens larvae and workers in different developmental stages
Summary
The leafcutter ants of the genus Atta, popularly known as saúvas, are considered important agriculture pests, defoliating crops and causing losses to livestock breeding and silviculture (Della Lucia & Vilela, 1993, p. 262). There are several strategies and control methods in the literature (Zanetti et al, 2014), chemical bait granules are currently the most widely used (Britto et al, 2016). This method, despite being practical and efficient, presents inconveniences, such as the contamination of the environment and the release of toxic agents that can directly affect human health when misapplied (Boaretto & Forti, 1997; Loureiro & Monteiro, 2005). The pathogenic potential of many species of fungus Beauveria bassiana and Metarhizium anisopliae Metsch have caused death when applied on workers and soldiers of Atta sexdens and Atta bisphaerica Forel, 1908 ants to foster a biological control (Alves & Sosa-Gómes, 1983; Castilho et al, 2010; Travaglini et al, 2016)
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