Abstract
The aim of the study was to test the effects of various concentrations of zinc sulfate (ZnSO4) on the radial growth of Trichoderma harzianum and Leucoagaricus gongylophorus in Petri dishes. In addition, we investigated the acceptance of baits containing live propagules of the encapsulated T. harzianum fungus and baits containing ZnSO4 by foraging leafcutter worker ants, A. sexdens, as well as their effects on the colonies of these ants. For the in vitro test, the design was completely randomized using ten replicates of a 2 × 7 factorial scheme: two species of fungi (T. harzianum and L. gongylophorus) and seven concentrations of ZnSO4. For bait acceptance tests, four treatments were used: baits without the mycelium and ZnSO4 (T1, control), baits containing encapsulated T. harzianum mycelium (T2), baits containing ZnSO4 (T3), and baits containing zinc sulfate and the encapsulated T. harzianum (T4). Each treatment was tested in duplicates using eight colonies. In the in vitro test, a ZnSO4 concentration of 0.25 g/L was sufficient to completely inhibit the development of L. gongylophorus without affecting the development of T. harzianum. In the bait acceptance test, the workers accepted ~55% of the bait combination of ZnSO4 and T. harzianum. This suggests the potential of treatment T4 in controlling leafcutter ants. Moreover, treatment T4 is environmentally friendly.
Highlights
Leafcutter ants of the genus Atta (Hymenoptera: Formicidae) are a problematic pest in Brazilian forests
The plant materials are carried into an underground nest and used as a substrate for the development of the symbiotic fungus L. gongylophorus that is cultivated by the ants (Della Lucia, 2011)
Leucoagaricus gongylophorus degrades the foliar polysaccharides and converts them into glycogen for easy nutrient assimilation; the glycogen is stored in reserve structures called gongylidia, which are used as a source of food by the ants (Aylward et al, 2012)
Summary
Leafcutter ants of the genus Atta (Hymenoptera: Formicidae) are a problematic pest in Brazilian forests. Ants may attack plants at any stage of development. The plant materials are carried into an underground nest and used as a substrate for the development of the symbiotic fungus L. gongylophorus that is cultivated by the ants (Della Lucia, 2011). Leucoagaricus gongylophorus degrades the foliar polysaccharides (i.e., pectin, starch, and cellulose) and converts them into glycogen for easy nutrient assimilation; the glycogen is stored in reserve structures called gongylidia, which are used as a source of food by the ants (Aylward et al, 2012). In the symbiotic ant-fungus relationship, both the species are favored: the fungus is used in the diet of the ants, which in turn, provide substrates for fungus development, protection against their parasites and competitors, and ensures their propagation (Fine Licht et al, 2014; Lange and Grell, 2014)
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