Integumental penetration of the pea aphid, Acyrthosiphon pisum, by Conidiobolus obscurus (Entomophthoracease)

Conidiospores of Conidiobolus obscurus adhered to and germinated on the surface of the pea aphid cuticle. Conidial germination was manifested by the formation of either a secondary conidium or one or more germ tubes. The germ tubes manifested two types of behavior: direct penetration or errant growth. Penetration was restricted to the thorax and abdomen, with a low number of penetrating hyphae (< 10% of germinating conidia). Penetrating hyphae gave no evidence of appressoria. Perforation of the cuticle was achieved by mechanical and apparent enzymatic means.