Additive effects of a local diatomaceous earth formulation and indigenous entomopathogenic fungi on mortality and F₁ progeny suppression of Sitophilus oryzae (Linnaeus, 1763) (Coleoptera: Curculionidae) in stored wheat

Abstract

ABSTRACT Diatomaceous earth (DE) and entomopathogenic fungi (EPF) are promising residue-free alternatives to synthetic insecticides for stored-product protection. This study evaluated the individual and combined additive effects of a local Turkish DE formulation, Diaterra®, and two indigenous EPF isolates, Beauveria bassiana and Metarhizium anisopliae, against Sitophilus oryzae adults on stored wheat. Treatments included DE at 100, 200, and 400 ppm, fungal suspensions at 1 × 10⁶, 1 × 10⁷, and 1 × 108 conidia mL−1, and their binary combinations. Adult mortality was assessed at 7, 14, and 21 days after treatment, while F₁ progeny production was evaluated after 56 days. DE alone showed a clear dose-dependent effect, with 100 ppm causing 72.87% mortality at day 21, whereas 200 and 400 ppm achieved ≥97.43% mortality within 7 days and complete mortality by days 14–21. EPF sprays alone produced moderate mortality (<48%). Binary mixtures accelerated mortality, particularly at higher DE rates; combinations of 400 ppm DE with fungal isolates caused 87.09–95.01% mortality at day 7 and 98.66–100% mortality by days 14–21. Immersion bioassays confirmed higher direct virulence of B. bassiana than M. anisopliae, reaching 92.49% and 36.59% mortality at day 7 and 97.92% and 77.09% at day 21, respectively. Reproductive suppression was strongest with DE treatments, with 200 and 400 ppm reducing F₁ emergence by 97.8% and 99.4%, respectively. Binary mixtures improved progeny suppression mainly at the lowest DE rate. Overall, Diaterra® provided rapid adult mortality and strong reproductive suppression, while DE–EPF combinations showed additive benefits under stored-wheat conditions.