FIELD RELEASE OF AN ISRAELISTRAIN OF THE FUNGUS ZOOPHTHORA RADICANS (BREFELD) BATKO FOR BIOLOGICAL CONTROL OF THERIOAPHIS TRIFOLII (MONELL) f. MACULATA

An exotic pathogen, Zoophthora radicans was released into lucerne crops for the biological control of Therioaphis trifoli f. maculata. At one site an epizootic was initiated, with up to 88% infection being recorded within 3 m of the point of release. No rain was recorded during the epizootic and disease transmission could be correlated with prolonged periods of high humidity at night. Data from 4 other sites are summarised. The disease did not occur on other aphids but has persisted, probably as resting spores, at one site for many months in the apparent absence of the host. Initial levels of field infection have been usually low despite the use of a high humidity field cage. A method which is expected to improve this initial infection rate is described.