Chemical defenses of the fire ant, Solenopsis invicta Buren, against infection by the fungus, Beauveria bassiana (Balsamo) Vuill

Solenopsis invicta venom alkaloids and cuticular hydrocarbons were evaluated for antimycotic activity against Beauveria bassiana. Cuticular hydrocarbons were noninhibitory in both liquid and solid media assays. Hydrocarbons supported conidial germination and subsequent fungal development when present as the sole carbon source on agarose. Alkaloid concentrations {dollar}>{dollar}20 ug per cm{dollar}sp2{dollar} caused {dollar}>{dollar}80% inhibition of conidial germination in both solid and liquid media assays for 24 hours post-treatment. Percent germination increased within 48 hours, indicating a fungistatic effect of venom alkaloids. The developmental sequence of the fungus also was modified by the alkaloids, resulting in induction of the hyphal body phase.; Release of venom alkaloids into sand by 50 fire ant workers was quantified by gas chromatographic analysis of methanol extracts of sand taken from laboratory assay units. Alkaloid levels were significantly higher in B. bassiana inoculated sand than in noninoculated sand at 7 and 14 days post-treatment. However, alkaloid levels in the sand were below those defined as fungistatic in vitro. Infection of fire ants in inoculated sand was less than 40%.; Both inoculated and noninoculated sand from fire ant assay units used in the alkaloid release studies caused almost 90% mortality of Artipus floridanus larvae in bioassays. However, infection of the larvae by B. bassiana was expressed in only 20% of the cadavers from inoculated assay unit sand compared to over 80% infection of A. floridanus in inoculated non-ant sand. Sterilizing assay unit sand removed the fungicidal and insecticidal activities of the sand. Venom alkaloid spiked sand was neither insecticidal to a. floridanus larvae nor inhibitory to the infection of the larvae by B. bassiana.