Effect of temperature and relative humidity on the virulence of the entomopathogenic fungus, Verticillium lecanii, toward the oat‐bird berry aphid, Rhopalosiphum padi (Hom., Aphididae)

The effect of temperature and relative humidity on the infectivity of Verticillium lecanii in Rhopalosiphum padi was investigated. The fecundity of untreated and treated aphids at the temperatures between 8 to 37 °C and relative humidity regimes was also recorded. No reproduction or mortality was found in control or infected apterous aphids when placed at 8 °C for 14 days. Aphids placed at 37 °C, whether treated or not treated, died in one day. At 15 °C, 100% mortality in infected aphids was observed at day 4. The percent mortality for the control aphids at 15 °C was 39.7% after 7 days of observation. At 21 °C and 27 °C, 100% mortality in the infected aphids was observed at day 3. At 21 °C and 27 °C, 11.4% and 46.8% mortality was observed in the control group after 7 days of observation, respectively. The average fecundity in infected and control aphids also differed significantly. The average fecundity of infected aphids at 15 °C, 21 °C, and 27 °C was 7.9, 9.2, and 5.8 individuals per aphid, and in the control the corresponding fecundity was 17.8, 42.0, and 27.3 individuals per aphid.