Pathogenicity of Beauveria bassiana and Isaria farinosae on Hyphantria cunea (Lep.: Arctiidae)

Hyphantria cunea Drury (fall webworm moth) is an important forest pest in Guilan province. Larval damage of the insect sometimes leads to severe host tree defoliation which in turn calls for drastic control measures. The objective of this study was to determine pathogenicity of four isolates of Beauveria bassiana and one isolate of Isaria farinosae on 4th larvae (2-days-old) of Hyphantria cunea. Susceptibility of different instars of this insect was also studied against the isolate having the highest percent mortality. Bioassay tests were conducted in the form of factorial and completely randomized design with 30 treatments and four replications. Ten larvae were topically infected with fungus spores. The control larvae were treated with distilled water plus Tween 80 0.03%. Results showed that Fashand isolate caused the highest percent mortality (39%), whereas 1872c was second in importance. LD50s of the above three isolates were 0.2×103(6.6×103-6.9×104), 9.5×105(0.3×105-4.9×106) and 7.8×106(1.5×106-0.2×107) conidia/ml., respectively. Susceptibility of different larval instars was varied too. Second and third instars had the most mortality rate (57 and 51%) respectively. In 108 concentrations Fashand caused the 85% mortality.