WATER POTENTIAL, TEMPERATURE, AND CLAY-COATING OF BEAUVERIA-BASSIANA CONIDIA - EFFECT ON SPODOPTERA-EXIGUA PUPAL MORTALITY IN 2 SOIL TYPES

When Spodoptera exigua pupae were buried for 10 days at 24°C in nonsterile soil inoculated with Beauveria bassiana conidia, 1 × 107 conidia/cm3 of soil was the lowest conidial density to produce disease in pupae and adults. At water potentials of -37 and -200 bars (24°C), adult emergence was reduced when 3.2 × 107 or 1 × 108 conidia/cm3 was used in Yolo fine sandy loam (YFSL) and Staten peaty muck (peat). In these dry soils, adult emergence was as low as 6% at 1 × 108 conidia/cm3. At water potentials of -0.3, -2, and -15 bars, a concentration of 1 × 108 conidia/cm3 was necessary to reduce adult emergence. In these treatments, 18 to 62% of the pupae eclosed to the adult stage. Thus, adult emergence was greater at water potentials from -0.3 to -15 bars that at -37 and -200 bars. Also at -0.3 and -2 bars, adult emergence was greater in peat than in YFSL. Uninoculated control soils had 85-94% adult emergence. Adult emergence increased as the temperature decreased from 25° to 8°C. At 8°C, adult emergence was the same in inoculated and uninoculated soil. Clay-coating of conidia, to increase conidial longevity, did not influence S. exigua mortality. © 1990.