Effect of Beauveria bassiana (strain ATCC 74040) on two leaf beetle pests of maize under laboratory conditions

In some European countries, the Western corn rootworm, Diabrotica virgifera virgifera , and the cereal leaf beetle, Oulema melanopus , are present in maize stands in high population density, occasionally causing damage of the crops. Susceptibility of adults of these species and larvae of the cereal leaf beetle to the commercially available product Naturalis® based on Beauveria bassiana strain ATCC 74040 was explored in laboratory conditions. The results of the bioassays showed that the fungal strain caused the highest corrected mortality on O. melanopus larvae with average values above 95% for all conidia concentrations (from 2.3 × 10 2 to 2.3 × 10 7 conidia/ml) tested. For the adults of the two pests, the average mortality increased positively with concentration of conidia and the values ranges from 9.5% to 94.2% for O. melanopus (concentrations from 2.3 × 10 2 to 2.3 × 10 7 conidia/ml) and from 19.3% to 92.4% for D. v. virgifera (concentrations from 2.3 × 10 3 to 2.3 × 10 7 conidia/ml). Accordingly, the LC 50 values for O. melanopus larvae and adults and D. v. virgifera adults were determined as 4.6, 8.3 × 10 4 and 4.3 × 10 5 conidia/ml, respectively. Further studies to confirm the susceptibility of the larvae of the cereal leaf beetle to Naturalis® under field conditions should be conducted.