Entomophthora culicis, a fungus which parasitizes a variety of small adult dipteran insects, is characterized by the production of asexual spores (conidia) which are forcibly discharged. Of the four developmental possibilities available to conidia, only direct vegetative conidial germination leads to successful infection of a potential insect host. Fatty acids were found to exert profound physiological control over conidium development. In combination with chitin or chitosan, oleic acid (C18:1) consistently induced vegetative conidial germination. Palmitoleic acid (C16:1), linoleic acid (C18:2) and linolenic acid (C18:3) were toxic to conidia over a wide range of concentrations. An excess of oleic acid mitigated the toxic effects of linoleic acid. A possible role for lipid hydroperoxides in the mediation of conidial development by fatty acids is discussed.
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