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 release height, morph of aphid and temperature on the horizontal and vertical discharge of conidia were studied. Numbers of conidia deposited in the dorsal and lateral directions were distributed with distance in truncated bell shaped patterns. Discharge distances ranged from 2 to 11 mm and half the conidia caught travelled further than 5 mm. There was little difference in the horizontal dispersal patterns of conidia when ejected from cadavers of different morphs of the same species, or from different species. The weight of infected aphids showed little correlation with discharge patterns. Values of maximum discharge distance, D_m′ were generally between 6 and 9 mm. Temperature had a significant effect on conidia discharged from the dorsal surface of apterous A. pisum cadavers. D_m was greater at 18°C than at 10 or 25°. Vertical discharge distances for conidia released from A. pisum 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°. Half of the conidia reached heights of about 3.5 mm while the maximum heights reached were about 8 mm. The initial speeds of conidia were estimated from measured discharge distances. The results suggest that conidia of E. neoaphidis may be ejected at speeds of about 8 ms^-1.