Abstract
Fungal endophytes can protect plants against herbivory and be used to control leaf-cutting ants. In this study, we aimed to evaluate the potential of endophytic colonization of Eucalyptus urophylla by three filamentous fungal species and their influence on the plant development and foraging behavior of Atta sexdens. The study design was completely randomized and comprised a factorial scheme of 4 × 3, three antagonistic fungal species (Escovopsis sp., Metarhizium anisopliae, and Trichoderma strigosellum) of the leaf-cutting ant, and one control and three inoculation methods (conidial suspension via foliar spray [FS] and soil drench [SD] inoculation, and seedlings inoculated with mycelium [SWM]). The SWM method allowed T. strigosellum to colonize all plant organs, and these plants exhibited higher height, leaf number, shoot dry mass, and total dry mass than the ones subjected to the other inoculation methods. The SWM method increased the plant height than the control plants and those inoculated with Escovopsis sp. and M. anisopliae. Trichoderma strigosellum, previously isolated from soil, colonized E. urophylla plants and positively influenced their development, as demonstrated by the SWM method. Trichoderma strigosellum promoted the increase in E. urophylla height compared with when the FS and SD methods were used (by 19.62% and 18.52%, respectively). Our results reveal that A. sexdens workers preferentially began cutting the leaves from plants not previously colonized by T. strigosellum. This behavior can be explained by modifications in the phenotypic traits of the eucalyptus leaves.
Highlights
In the seedlings with mycelium (SWM) method, this fungus was detected in 90% of the roots, 70% of the stems, and 60% of the leaves of the treated plants
Using the soil drench (SD) method, T. strigosellum was detected in 50% of the roots and 60% of the stems of the treated plants
Escovopsis sp. and M. anisopliae were not detected in E. urophylla plants, regardless of the inoculation method (Table 1, Figure 2)
Summary
Leaf-cutting ants are considered the main insect pests in these cultivated forests [2]. Eucalyptus urophylla is one of the main species cultivated in Brazil [4], and several studies have demonstrated the susceptibility of E. urophylla to attack by different leaf-cutting ant species [5,6]. Damage caused by leaf-cutting ants in cultivated forests results from the constant cutting of fresh plant material, which is used as a substrate by the symbiotic fungus of the leaf-cutting ants Leucoagaricus gongylophorus. This mutualistic symbiotic fungus is used by leaf-cutting ants as food for their larvae and queen
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