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 × 101, 2 × 102, 2 × 103, 2 × 104, 2 × 105, 2 × 106, and 2 × 107 spores/ml) were tested against larvae of L3 and L4. Larval mortality increased by increasing the conidiospore concentrations. The larvae of L3 were more susceptible to the treatment with B. bassiana conidiospores than larvae of L4. The infected larvae survived the tested low concentrations more than 5 days and died later in the fifth larval instar. The LC50 for L3 and L4 was 18,463 (slope 0.414) and 35,990 (slope 0.387) spores/ml, while the LC90 was 37,806 (slope 0.345) and 74,391 (slope 0.387) for the two larval instars, respectively. Applying B. bassiana (6 × 107 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.