Effect of Temperature and Humidity on Formation, Germination, and Infectivity of Conidia of Neozygites fresenii (Zygomycetes: Neozygitaceae) from Aphis gossypii (Homoptera: Aphididae)

The temporal pattern of sporulation, conidial discharge, and formation of capilliconidia of Neozygites fresenii (Zygomycetes: Neozygitaceae) from Aphis gossypii (Homoptera: Aphididae) cadavers was determined. Conidial discharge from aphid cadavers began approximately 1 hr after rehydration and was substantially complete within 5 hr. At 35°C or at 85% RH or less, infected aphid cadavers did not sporulate. Within 6 hr of discharge 93% of primary conidia held at 25°C and 100% RH germinated to form capilliconidia. Primary conidia were negatively affected by short exposure to low humidities; after 1-min exposure to 75% RH only 29.4% formed capilliconidia when subsequently exposed to 100% RH, whereas 76.2% formed capilliconidia when exposed continuously to 100% RH. When primary conidia were exposed to constant temperatures and relative humidities, approximately 90% formed capilliconidia at 95 or 100% RH at 20, 25, and 30°C, whereas at 89% RH at 20 or 25°C only 40.4 and 19.3% formed capilliconidia, respectively. Capilliconidia survived longer at lower humidities than primary conidia. Capilliconidia remained infective for 14 days at 75 or 100% RH at 20 and 25°C, infecting 34.1, 37.8, 16.0, and 7.9% of treated cotton aphids, respectively. Even when stored for 7 days at 56% RH and 20°C capilliconidia were able to infect 19.9% of treated aphids. Capilliconidia (87.7%) held at 100% RH for 11 days germinated to form tertiary capilliconidia.