Potential of Two Metarhizium anisopliae (Clavicipitaceae) Isolates for Biological Control of Diatraea saccharalis (Lepidoptera: Crambidae) Eggs

Abstract

Chemical pesticides tend to accumulate in soil, resulting in human and environmental health risks. Hence, alternative methodologies involving chemical pesticides are beneficial for the control of agricultural pests. Metarhizium anisopliae is an entomopathogenic fungus that acts on different developmental stages of pest insects such as Diatraea saccharalis , a holometabolic lepidopteran with high potential for infestation in sugarcane crops. The present study evaluated the biocontrol effect of M. anisopliae isolates MT and E9 on D. saccharalis eggs at different ages by investigating the external and internal morphological alterations in treated eggs. Conidial suspensions of M. anisopliae isolated from MT and E9 at concentrations of 107 conidia/mL were applied to eggs of D. saccharalis aged 0, 24, 48, 72, 96 and 120 h. The eggs were observed every 24 h during development (0 h to 144 h). Samples were collected for observational, histological, and ultrastructural analyses. We found that the MT isolate caused 100% inviability of eggs aged 0 - 72 h, 144 h after the bioassays, while the effect of the E9 isolate varied between 49.40% and 93.75%. Melanization was observed on the periphery of the eggs 24 h after the bioassays. Fungal hyphae developed 48 h after bioassays, crossed the egg chorion, and dispersed through the yolk region, inhibiting embryonic development. After 72 h, hyphae and conidiophores were observed on the eggs, which persisted for 144 h. In sum, M. anisopliae MT isolate can be used as a biological controller for D. saccharalis eggs.