Effects of constant and fluctuating temperatures on sporulation and infection by the aphid-pathogenic fungus Pandora neoaphidis

Laboratory studies were performed to assess the importance of temperature on sporulation and infection by the aphid-pathogenic fungus Pandora neoaphidis (Remaudiere and Hennebert) Humber. Numbers of primary conidia discharged from mycelium formulated as alginate granules and unformulated mycelial mats were assessed, as well as infection of the potato aphid, Macrosiphum euphorbiae (Thomas) (Homoptera, Hemiptera, Aphididae), using culture plugs as inoculum sources. Sporulation from experiments at constant temperatures indicated the optimum temperature range was 10-20 degreesC for both mycelial preparations and there was no or very little sporulation at 30 degreesC. Infection of aphids kept at 15 degreesC was 34-50%, while infection at 25 degreesC was 11-44%. At 20 degreesC, 77-79% of aphids were infected. Under fluctuating temperature cycles, conidia numbers did not differ when mycelial preparations were maintained at 18-25 degreesC compared with 18-20 degreesC, but fewer conidia were recorded when preparations were exposed continuously to 18-30 degreesC. Infections of inoculated aphids kept for varying numbers of days at 18-25 degreesC varied between 24-47%, but only 3-32% of aphids were infected when exposed to a cycle of 18-30 degreesC for various times. Unformulated mycelial mats of P. neoaphidis appear to be superior to forumlated alginate granules for use in experimental greenhouse and field trials, since temperature stability is similar for both materials but mycelial mats are much easier to produce.