Storing dry Beauveria bassiana mycelium.

The insect fungi (Deuteromycotina: Hyphomycetes) that commonly infect rice insects such as brown planthopper (BPH) Nilaparvata lugens (Stal) can be isolated on artificial media and mass-produced. Mycelium and conidia of the fungi conventionally are produced by solid fermentation (mycelium growth and sporulation occur on solid substrates) or by diphasic fermentation (the mycelium is produced in liquid media and later sporulates on solid substrates). A method was used to produce dry mycelium particles (the marcescent process). Fungi are grown in fermenters in liquid media and the mycelium dried and ground into small particles (0.5-0.7 mm diam). The mycelium can be applied in the field, where it sporulates on the rice plant. Conidia produced in the field infect pest insects. Storage of dried mycelium can be a problem. The optimum storage conditions were tested for mycelium of a Beauveria bassiana (Bals.) Vuill. strain originating from BPH in China. Mycelium was produced in 15-liter bubbler-type airlift fermentors in a saccharose (3%)- yeast extract (1%) medium. After 3 d growth, mycelium was harvested by filtration and dried to 7-10% moisture content, using forced air and the desiccant calcium oxide. Four storage temperatures (-20, 5, 25, and 35 deg C) and 7 storage times (0, 1, 2, 4, 8, 16, and 32 wk) were tested in 3 replications. Each replication was a small air tight tube holding 300 mg mycelium particles. To evaluate regeneration, mycelia were incubated for 3 d on moist filter paper in small petri dishes; conidia were harvested in a Tween 80(R) 0.02% solution, counted with standard hemocytometer techniques and number of conidia produced per mg mycelium calculated. With 5 deg C treatment, sporulation at 2, 4, 8 and 32 wk differed from initial sporulation. At 32 wk, about 75% of the original amount of conidia was produced. At 25 deg C, significantly fewer conidia were produced after 2 wk; after 8 wk, all mycelia were dead. At 35 deg C, virtually no viable mycelia were left 1 wk.