Effect of the fungus, Beauveria bassiana (Balsamo) Vuillemin, on the beet armyworm, Spodoptera exigua (Hubner) 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 (Hubner) (Lepidoptera: Noctuidae) larvae reared on artificial diet. Seven successive increased conidiospore concentrations (2 x 10(1), 2 x 10(2), 2 x 10(3), 2 x 10(4), 2 x 10(5), 2 x 10(6), and 2 x 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 LC50 for L-3 and L-4 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 x 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.