Production of Escovopsis conidia and the potential use of this parasitic fungus as a biological control agent of leaf-cutting ant fungus gardens.

Abstract

This study was carried out to investigate the use of different substrates for the production of Escovopsis conidia and verify the virulence of four different isolates cultured on four types of substrates using a novel bioassay. Escovopsis isolates were molecularly identified, based on Internal Transcribed Spacer (ITS) nucleotide sequences. To evaluate conidial production, suspensions (1 × 106 conidia mL-1) of each Escovopsis isolate were inoculated onto four substrates (parboiled rice, white rice, rolled oats, and corn grits). After 14days, conidial yields were assessed. The virulence of each isolate cultured on the four substrates was tested against Leucoagaricus fungus garden fragments, by directly applying 500µL of each conidial suspension (1 × 107 conidia mL-1), and the development of the parasite was monitored daily until it completely colonized the fungus garden. It was observed that rolled oats were the best substrate for conidial production, with a yield of1.7 × 107 to 2.0 × 108 conidia mL-1. Furthermore, isolate AT-01 produced the highest number of conidia when compared with the other isolates. Regardless of the substrate used to produce AT-01 conidia, this isolate completely colonized the fungus garden 6days post inoculation (dpi), followed by AT-02, AC-01, and AC-2. High levels of both conidial production and virulence against the leaf-cutting ant fungus garden were observed here.