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Conidia of the entomogenous fungus Erynia variabilis germinate vegetatively on the cuticular surface of adults of the lesser housefly, Fannia canicularis, and on a basal agar growth medium in which cuticular lipid extracts of adult flies have been incorporated. Formation and discharge of secondary spores occur on puparial cuticles and on media in which puparial cuticle lipid extracts have been included. Relative free fatty acid compositions of puparial and adult cuticle lipid extracts are nearly identical, but adults average ca. five times the concentration of free fatty acids on their cuticle surface as that found on puparia. A regulatory role for esterified fatty acids in conidial germination is suggested. Limitation of E. variabilis to adult dipteran hosts is postulated to be due in part to characteristics of the fatty acids of this order of insects: the presence of sufficient oleic acid to induce germination; high levels of palmitoleic acid to enhance mycelial growth; and low levels of linoleic and linolenic acids, which have deleterious effects on spore germination and mycelial proliferation.
James L. Kerwin (Wed,) studied this question.