Evaluation on the lethal effect of Beauveria bassiana strains delta native NI8 and commercial GHA against the tarnished plant bug in cotton

Isolates of Beauveria bassiana including the commercial strain GHA and the Mississippi Delta native NI8 strain were evaluated in the field for pathogenicity and infectivity against tarnished plant bug (TPB), Lygus lineolaris (Palisot de Beauvois).  Thirty 2-d old TPB adults from a laboratory colony were placed in cages located on top and bottom parts of cotton plants in the field prior to spraying with B. bassiana. A total of 240 cage were used in the 40 plots (20 plots per concentration) (0.068 acre each)  sprayed with four concentrations (spores / acre) and a control with each B. bassiana strain (4 plots / concentration, 6 cages / plot, 2 cages/ cotton plant).  Concentrations sprayed (spores / acre) were 4.0x10¹⁰, 4.0x10¹¹, 4.0x10¹², 4.0x10¹³ of B. bassiana strain NI8 and 4.1x10¹⁰, 4.1x10¹¹, 4.1x10¹², 4.1x10¹³ of B. bassiana commercial strain GHA.  All sprays included 1.5 ml of Tween-80 per gallon of spray. Differences of mortality and sporulation on day 3, 5 and 10 were significant among concentrations for both isolates and locations. Results indicated that B. bassiana strain NI8 was superior to the commercially-available isolate suggesting that a 50% reduction of adult populations of L. lineolaris may occur 10 days after spray using a spray concentration about 73 – fold lower than that of the commercial GHA strain.