Enhancing Field‐Acquired Infection of Euschistus heros (Hemiptera, Pentatomidae) Populations by Targeting Early Immature Stages With Metarhizium anisopliae

ABSTRACT

The Neotropical brown stink bug Euschistus heros is one of the major pests in soybean. In this study, we aimed to evaluate the susceptibility of second‐ and fifth‐instar E. heros nymphs to a virulent M. anisopliae strain, under both laboratory and field conditions. In the laboratory, concentrations ≥ 2.5 × 10 ⁷ conidia/mL drastically reduced the survival of second‐instar nymphs and resulted in mycosis of nearly 80%. Fungal treatment had a severe impact on the pest's population dynamics. Although the control group showed a population growth potential of up to 65‐fold per generation, the application of M. anisopliae (≥ 1.6 × 10 ⁶ conidia/mL) restricted this increase to less than tenfold. In field, insects exposed to the fungus were recovered 48 h after spraying and maintained in laboratory until mortality was recorded. Field experiments showed that the fungus's efficacy was dose‐dependent. Doses between 1–2 × 10 ¹² conidia/ha resulted in 55%–60% mortality, whereas a dose of 5 × 10 ¹² conidia/ha yielded 85% mortality. In contrast, higher doses (≥ 8 × 10 ¹² conidia/ha) provided only a slight increment in efficacy, with total mortality of second‐instar nymphs reaching up to 89% at 8 days post‐spraying. Furthermore, notably less promising results were obtained for fifth‐instar nymphs in both laboratory and field trials. Mortality of fifth‐instar nymphs at doses ranging from 5 × 10 ¹² to 8 × 10 ¹² conidia/ha was only 17%–50% in field. The results presented here suggest that control strategies for E. heros using entomopathogenic fungi should target early‐instar nymphs and utilize doses not lower than 5 × 10 ¹² conidia/ha for the M. anisopliae strain evaluated in this study.