485 Farhad HEMMATI 1,3 †, Judith K. PELL 1 *, H. Alastair McCARTNEY 2 and Michael L. DEADMAN 3 ‡  Department of Entomology and Nematology, IACR-Rothamsted, Harpenden, Herts AL5 2JQ, UK.  Plant Pathology Department, IACR-Rothamsted, Harpenden, Herts AL5 2JQ, UK.  Department of Agriculture and Food, University of Reading, Reading RG6 2AT, UK. E-mail ; Judith.Pellbbsrc.ac.uk Received 6 March 2000 ; accepted 22 July 2000. The temporal pattern of release and dispersal of inoculum of plant and insect pathogenic fungi play an important role in the spread of disease. Airborne concentrations of primary and secondary conidia of Erynia neoaphidis released from the rose-grain aphid Metopolophium dirhodum were monitored at the edge of two winter wheat crops on IACR-Rothamsted Experimental Farm between May and September in 1996 and 1997. Hourly average temperature and humidity were recorded at each spore trap site and daily totals of rain and sunshine hours and daily average wind speed recorded about 16 km from the monitoring sites. No airborne conidia were found in 1996, but large numbers were trapped at the two sites in 1997. They were present from mid-June until early August, reaching peak concentrations on 17–18 July. Concentrations were 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 C). Night-time conditions nearly always favoured the production of conidia. This suggests day to day variation in airborne conidium concentrations may be affected more by underlying biological factors than environmental conditions. INTRODUCTION Entomopathogenic fungi are potential biological control agents for selected crop pests. However, an understanding of the dynamics of disease epizootics in target populations is needed to develop appropriate pest management strategies. The temporal patterns of release and dispersal of the inoculum of insect pathogenic fungi play an important role in the spread of diseases. Thus, knowledge of these patterns contributes to our understanding of disease distribution, epidemiology, and management. Spore production patterns, both seasonal and diurnal, of several plant pathogenic fungi have been studied in the field for many years (e.g. Gregory 1973, Lacey 1996), but there have been few reports for entomopathogenic fungi (Steinkraus, Hollingworth & Boys 1996). The few field studies of conidium concentration patterns of entomopathogenic fungi suggest that some species release conidia early in the morning, which may be associated with periods of high humidity (Wilding 1970, Newman & Carner 1974, Harper, Herbert & Moore 1984, Steinkraus et al. 1996). Current addresses : † AREEO, Scientific & Research Bureau, PO Box 19835- 111, Tehran, Iran. ‡ Department of Agronomy, Horticulture, Entomology and Plant Pathology, Sultan Qaboos University, PO Box 34, Al Khod 123, Sultanate of Oman. * Corresponding author. Erynia neoaphidis is pathogenic on a number of agriculturally important aphid pests, and is, therefore, a potential biological control agent. However, little is known of how it spreads in the field. This paper reports a field study of the seasonal and diurnal variation in aerial concentrations of primary and secondary conidia of E. neoaphidis released from agricultural sources (Metopolophium dirhodum on wheat). Measurements of airborne concentrations of conidia were made between May and September over two years (1996 and 1997) at IACR- Rothamsted’s Experimental Farm. Temperature, humidity, rainfall, sunlight and wind speed were monitored during these experiments. MATERIALS AND METHODS Concentrations of E. neoaphidis conidia in the atmosphere were estimated using a Hirst-type, 7 d recording, automatic, volumetric spore trap (Burkard Manufacturing, Rickmans- worth), operated as described in detail elsewhere (Hirst 1952, Tilak 1982, McCartney & Lacey 1995, British Aero- biology Federation 1996, Deacon 1997). The trap collects airborne particles onto a transparent tape wrapped round a slowly rotating drum. The trace on the tape allowed both hourly and 24 h average concentrations of conidia to be estimated. After exposure for one week the tape was removed and cut into 48 mm (24 h) sections, mounted on microscope Mycol. Res. 105 (4) : 485–489 (April 2001). Printed in the United Kingdom. Airborne concentrations of conidia of Erynia neoaphidis above cereal fields