| Abstract: | Studies on the blastospore production of Metarhizium anisopliae var. anisopliae were conducted in Adamek's medium used as a standard, enriched with lecithin, collagen, lactic acid or polyethylene glycol 200 (PEG 200) to increase spore yield and suppress mycelial pellet formation. The addition of 5% lecithin resulted in a significant 10-fold increase in spore yield up to 1.9 108 blastospores/ml compared with 1.9 107 spores/ml in the standard medium. Collagen (3%) increased the number of blastospores 3.7-fold, and lactic acid (1.5%) two-fold. A reduction of mycelial pellet formation in favour of spore production was noted with each additive. The viability of blastospores at 40IC from media with lecithin, collagen and lactic acid suspended in 25% Ringer's solution was comparable to that of spores produced in the standard medium. Striking differences were noticed in the viability of spores produced with 5% PEG 200 in standard medium. The half-life of blastospores produced in standard medium suspended in sunflower oil was 33.6 h and that of 5% PEG 200 spores only 25.2 h. In bioassays, the virulence of spores produced in standard medium to which 3% lecithin, 3% collagen, 1.5% lactic acid or 5% PEG 200 had been added was tested against third-instar nymphs of Locusta migratoria migratorioides (R. & F.). The median lethal time and the mortality of L. migratoria achieved with blastospores produced with 3% lecithin (5.7 days, 99%) was comparable to that of blastospores from standard medium (5.1 days, 98%). The virulence of blastospores from all other media with additives was significantly reduced. |
