Lethal Concentration and Sporulation by Contact and Direct Spray of the Entomopathogenic Fungus Beauveria bassiana on Different Stages of Nezara viridula (Heteroptera: Pentatomidae)

The southern green stink bug, Nezara viridula (L.) (Heteroptera: Pentatomidae) is the most significant pest of soybean worldwide. The present study was conducted to compare the effectiveness of a Delta native strain NI8 of Beauveria bassiana by contact and direct spray on nymphs (2nd to 5th instar) and adults of N. viridula. Water control and four concentrations of B. bassiana were used to evaluate the survival, mortality, and molting percentage and to estimate median lethal concentration (LC(50)), median lethal sporulation (LS(50)), and resistance ratio (RR(50)). Direct spray at all concentrations observed the greatest reduction in survival on all life stages. Mortality and sporulation were positively correlated by concentration, while molting was highly variable with a significantly lower negative correlation on insects that were directly sprayed. Pathogenicity exhibited reduction as young stages developed and emerged to adult. The LC(50) (Contact: 612 spores/mm(2); Direct spray: 179 spores/mm(2)) and LS(50) (Contact: 1960 spores/mm(2) Spray: 3.3 × 10(6)) values showed that adults of N. viridula were highly resistant than any other life stage when exposed to either contact or direct spray. Fourth instar was the most susceptible (LC(50): Contact: 18 spores/mm(2); Direct spray: 23 spores/mm(2)) (LS(50): Contact: 53 spores/mm(2); Direct spray: 26 spores/mm(2)) followed by second, third, and fifth instars.