2.3. Bioassays

The efficacy of individual B. bassiana strains was tested on CPB adults collected in an organic potato field in Malonty, South Bohemia, Czech Republic. The beetles were individually immersed in the suspension of conidiospores of the fungus (1 × 10⁷ spores per mL) for 30 s (dip-test). All specimens in a control group were immersed in a sterile solution of 0.05% Tween^® 80 only. The beetles were then placed into polystyrene Petri dishes (vented, inner diameter 90 mm, height 15 mm, Gosselin™, Borre, France) lined with moist filter paper KA 0 (Papírna Perštejn Ltd., Pernštejn, Czech Republic) and kept under constant conditions (25 ± 1 °C and 16L:8D photoperiod). Fresh leaves from potted potato plants (cv. Magda) grown under greenhouse conditions were added daily to provide food for beetles. The filter paper was also daily moistened with distilled water to maintain optimal humidity inside the Petri dishes and replaced with a new one once a week. The insects were monitored daily for 21 days to record insect mortality and development of mycosis on cadavers. Only mycosis verified by microscopic examination of sporulating fungus as B. bassiana was considered. The bioassays were repeated twice; each replication tested 30 insect individuals.