Comparative Efficacy of <i>Beauveria</i> and <i>Metarhizium</i> Against Immature and Adult Stages of the Stink Bugs <i>Euschistus heros</i> and <i>Diceraeus melacanthus</i>

ABSTRACT Biopesticides based on entomopathogenic fungi are considered a potential alternative for controlling stink bug populations in soybean and maize crops. We investigated the susceptibility of immature stages of Euschistus heros (Fabricius, 1974) and Diceraeus melacanthus (Dallas, 1851) (Pentatomidae, Carpocorini) to infections by 30 strains of Beauveria bassiana and Metarhizium spp. In general, Metarhizium spp. strains exhibited a greater capacity to reduce egg hatching and infect nymphs of both E. heros and D. melacanthus compared to B. bassiana . Bioassays with two selected strains, one of each fungal species ( M . anisopliae CG1127 and B. bassiana CG1105), demonstrated a 10%–30% reduction in egg hatching compared to untreated eggs of both stink bugs, regardless of egg age (1, 2, or 3 days old). Second‐instar E. heros nymphs demonstrated higher susceptibility to M. anisopliae CG1127 infections than fourth‐instar nymphs, with ST 50 of 5.1 and 5.7, respectively. Furthermore, co‐infection assays showed that M . anisopliae CG1127 was more prevalent than B. bassiana CG1105, and no synergistic effect was observed against either E. heros or D. melacanthus nymphs. Adult survival of both E. heros and D. melacanthus after treatment with both strains consistently remained &gt; 80%. Additionally, the number of eggs produced by E. heros females treated with fungal conidia did not differ significantly from the control. Our findings suggest that applications of selected fungal strains should primarily target the immature stages of both stink bug species to optimize biopesticide performance in field conditions.