Airborne concentrations of conidia of Erynia neoaphidis above cereal fields

The temporal pat-fern of release and dispersal of inoculum of plant and ins ect pathogenic fungi play an important role in the spread of disease. Airbo rne concentrations of primary and secondary conidia of Erynia neoaphidis re leased from the rose-grain aphid Metopolophium dirhodum were monitored at t he edge of two winter wheat crops on IACR-Rothamsted Experimental Farm betw een May and September in 1996 and 1997. Hourly average temperature and humi dity were recorded at each spore trap site and daily totals of rain and sun shine hours and daily average wind speed recorded about 1.6 km from the mon itoring sites. No airborne conidia were found in 1996, but large numbers we re trapped at the two sites in 1997. They were present from mid-June until early August, reaching peak concentrations on 17-18 July. Concentrations we re usually highest during the night and in the early morning (01:00-07:00 h GMT) and were generally low during the day. On the 3 days when significant numbers of conidia were caught in the afternoon. daytime relative humidity was high (about 89%) and day-time temperature low (about 16 degreesC). Nig ht-time conditions nearly always favoured the production of conidia. This s uggests day to day variation in airborne conidium concentrations may be aff ected more by underlying biological factors than environmental conditions.