Selection of Beauveria spp. isolates for control of the termite Heterotermes tenuis (Hagen, 1858)

Heterotermes tenuis is an important pest in sugarcane in Brazil, where alternative control methods are necessary due to cancellations of chemical pesticide registrations. Experiments were conducted to determine the pathogenicity, virulence and mass production yields of Beauveria spp. isolates as potential microbial control candidates for H. tenuis. Results demonstrated that the average virulence of the B. brongniartii isolates was comparable to that of B. bassiana isolates. Isolates obtained from soil were as effective as microbial control agents as those obtained directly from insect hosts. However, no B. brongniartii or soil isolate was among those best isolates selected, which included two of the three termite isolates tested. LT50 for 15 selected isolates varied between 2.91 and 4.91 days, and termite mortalities caused by these isolates were between 78.7 and 98.7% after 8 days. Significant differences were observed among these selected isolates. Conidial productions on artificial media (PDA and cooked rice) correlated well for the selected isolates. However, spore production on the termite cadavers did not correlate with production on these artificial media. The most productive isolate on cadavers (634) was 21% more productive than the second best isolate (447), and was also a good conidial producer on artificial media with 25% lower conidial yield than the best producer (756). The least productive isolate on cadavers or artificial medium (760) produced only 3% of production by isolate 756 on cooked rice and 45% of production on termite cadavers. Because high conidial production on cadavers is a desirable characteristic to facilitate transmission of the disease in the nest, isolate 634 was selected for further development as microbial agent for H. tenuis control.