بیماریزایی Fusarium solani جداشده از شب‌پره زنبور مانند چوبخوار،(Lep.: Sesiidae) Paranthrene diaphana روی مرحله لاروی آفت در شرایط آزمیشگاهی

The clearwing moth, Paranthrene diaphana, Dalla Torre & Strand is one of the most important xylophage pests that has caused significant damage to landscape and forestry in recent years due to its wide host range. In the present study, the pathogenicity of the isolate which recently isolated from larvae extracted from the branches of the weeping willow trees located in the green space of Shahed University, Tehran has been investigated. The isolate were first isolated from the larvae and cultured on SDA and PDA media then the cultivated fungus was treated on the larvae of the pest and thus its pathogenicity was proved. After isolation and purification and study of morphological and molecular characteristics, the isolation of the fungus was identified as Fusarium solani (Mart.) Appel & Wollen W. emend. Snyder & Hansen. To determinate LC50 value, the pathogenicity test of the isolate on last instar larvae of the pest was performed as completely randomized design with three replicates by immersion method at 25±1 °C and 65±5 % RH under laboratory conditions. For this purpose, after conducting preliminary experiments, seven concentrations including 0.5× 101, 1× 101, 1× 103, 1× 104, 1× 106, 1×107 and 1× 108 spore/ml of sterile distilled water containing 0.02% Tween®80, was prepared and the larvae were immersed in spore suspension. Sterile distilled water containing 0.02% Tween®80 was used for the control. Cumulative mortality of larvae was recorded daily for two weeks. The results of the pathogenicity test (data processing using logarithm-probit method) indicated that the fungal isolate was pathogenic on the studied larvae and increasing in concentration of fungal suspension led to increasing of the larvae mortality rate. The highest average mortality rate (100%) was obtained to 1× 107 spores/ml or higher concentrations and the lowest average mortality rate (22%) was obtained to 5 spores/ml (P<0.05). The LC50 and LC90 values were 102.836 and 1.586×105 spores/ml, respectively. Values LT50 and LT90 at a lethal concentration of 50% were 2.83 and 36.99 days, respectively. As the results showed, this isolation caused such mortality pest even at very low concentrations on the larvae and showed high pathogenicity potential. Therefore, it is necessary to investigate its pathogenicity on other insect pests as well as its pathogenicity on sensitive plant species.