Conidial discharge in the aphid pathogen Erynia neoaphidis

The patterns of conidial discharge of Erynia neoaphidis were measured from three species of aphids: nettle aphid (Microlophium carnosum), grain aphid (Sitobion avenae) and pea aphid (Acyrthosiphon pisum). The effects of relea se height, morph of aphid and temperature on the horizontal and vertical di scharge of conidia were studied. Numbers of conidia deposited in the dorsal and lateral directions were distributed with distance in truncated bell sh aped patterns. Discharge distances ranged from 2 to 11 mm and half the coni dia caught travelled further than 5 mm. There was little difference in the horizontal dispersal patterns of conidia when ejected from cadavers of diff erent morphs of the same species, or from different species. The weight of infected aphids showed little correlation with discharge patterns. Values o f maximum discharge distance, D-m, were generally between 6 and 9 mm. Tempe rature had a significant effect on conidia discharged from the dorsal surfa ce of apterous A. pisum cadavers. D-m was greater at 18 degreesC than at 10 or 25 degrees. Vertical discharge distances for conidia released from A. p isum cadavers ranged between about 2 and 8 mm. The maximum height to which conidia were projected vertically was not affected by temperature. However, the average height tended to be greater at 18 degrees. Half of the conidia reached heights of about 3.5 mm while the maximum heights reached were abo ut 8 mm. The initial speeds of conidia were estimated from measured dischar ge distances. The results suggest that conidia of E. neoaphidis may be ejec ted at speeds of about 8 ms(-1).