Effect of the fungus, Beauveria bassiana (Balsamo) Vuillemin, on the beet armyworm, Spodoptera exigua (Hübner) larvae (Lepidoptera: Noctuidae), under laboratory and open field conditions

A local isolate of the fungus Beauveria bassiana was tested against the beet armyworm Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) larvae reared on artificial diet. Seven successive increased conidiospore concentrations (2 × 10 1 , 2 × 10 2 , 2 × 10 3 , 2 × 10 4 , 2 × 10 5 , 2 × 10 6 , and 2 × 10 7 spores/ml) were tested against larvae of L 3 and L 4 . Larval mortality increased by increasing the conidiospore concentrations. The larvae of L 3 were more susceptible to the treatment with B. bassiana conidiospores than larvae of L 4 . The infected larvae survived the tested low concentrations more than 5 days and died later in the fifth larval instar. The LC 50 for L 3 and L 4 was 18,463 (slope 0.414) and 35,990 (slope 0.387) spores/ml, while the LC 90 was 37,806 (slope 0.345) and 74,391 (slope 0.387) for the two larval instars, respectively. Applying B. bassiana (6 × 10 7 conidiospore/ml) for controlling the beet worm, S. exigua , in sugar beet fields in Fayoum Governorate, Egypt, resulted to a suppression in its larval populations through 5 applications by 54.5–70% in season 2016/2017 and 66.6–80% in season 2017/2018.