Viability of Entomopathogenic Fungi in Oil Suspensions and Their Effectiveness against the Agave Pest <i>Scyphophorus acupunctatus</i> under Laboratory Conditions

Abstract

Oaxaca, Mexico, is home to over 30 species of the genus Agave, and its cultivation is of great economic and social importance for the mezcal industry, which depends on its production. The incidence of the pest Scyphophorus acupunctatus causes severe losses and damage. Agrochemicals are used for its control, but a viable alternative is microbial control. The objectives of this study were to determine the natural occurrence of the entomopathogenic fungi (EPF) Beauveria bassiana and Metarhizium anisopliae, isolated from S. acupunctatus in agave crops, and to evaluate the effect of vegetable oil in water emulsions containing conidia from the native fungi against adults of S. acupunctatus under laboratory conditions. Viability of the fungal isolates was determined at a concentration of ×108 conidia/mL in avocado (Persea americana), mamey (Mammea americana), chia (Salvia hispanica), or olive (Olea europaea) oil in water emulsions at two concentrations, 20% and 40%. The most effective oil emulsion on S. acupunctatus adults was determined under laboratory conditions. Naturally occurring fungi in 900 field collected insects was 2.21%. Ninety-six hours after preparing a 20% emulsion in P. americana oil, B. bassiana and M. anisopliae had a viability of 75% and 66.5%, respectively, while the control conidia suspended in distilled water remained viable for only 48 h. Twenty-four hours after applying M. anisopliae conidia in a 40% P. americana oil emulsion, effectiveness was 100% on S. acupunctatus, followed by M. anisopliae in 20% P. americana oil emulsion with 75% effectiveness. At 72 h post-application, all fungus in oil emulsions achieved an accumulated insect mortality of 100%, while the control showed no effect on adult S. acupunctatus. The most promising combination was 40% P. americana oil emulsion, which achieved 50% viable B. bassiana or M. anisopliae conidia up to 96 h after preparation, and its accumulated effectiveness on S. acupunctatus adults was 87.5% after 24 h.

Keywords

• weevil
• conidia
• natural occurrence
• oil in water formulation