Isolation and evaluation of entomopathogenic fungi against the neotropical brown stink bug Euschistus heros (F.) (Hemiptera: Pentatomidae) under laboratory conditions

Abstract

ABSTRACT Although the brown stink bug, Euschistus heros (F.) is susceptible to entomopathogenic fungi, only a single formulation is currently available on the Brazilian market for its control. The objective of this work was to isolate entomopathogenic fungi with potential to control E. heros, evaluate their virulence, and determine effective conidial concentrations. Thirty six different fungal isolates were obtained from soil samples and diseased insects and pure cultures of each were established on potato-dextrose agar. Suspensions of 1 × 108 conidia mL−1 were prepared from each isolate and a 5 μL aliquot was inoculated on the dorsum of adult stink bugs (n = 8 replications of 5 bugs each). Three isolates caused 100% mortality of bugs over a 15-day observation period. These were identified by molecular techniques as belonging to the Beauveria bassiana species complex and designated UFSM-1, UFSM-2 and UFSM-26. Further bioassays determined the LC50, LC90 and cumulative mortality functions caused by these three isolates. Isolates UFSM-1 and UFSM-2 stood out as highly virulence, with an LC90 of 5 × 109 conidia mL−1 in 9 days, compared to an LC90 of 8 × 1010 conidia mL−1 for strain UFSM-26. Application of 1 × 108 conidia mL−1 of UFSM-1 and UFSM-2 isolates killed 70% of stink bugs in nine days, whereas the same concentration of UFSM-26 killed only 12%. We conclude that isolates UFSM-1 and UFSM-2 warrant field tests as novel agents for biological control of E. heros.