Growth response to squalene, a tick allomonal component, by fungi commonly associated with the american dog tick, dermacentor variabilis (say)

Squalene, a bloodmeal component secreted by ticks for defense (allomone), was tested for antifungal activity against naturally occurring antagonistic molds isolated from the American dog tick, Dermacentor variabilis (Say). Temperature-growth profiles separated Aspergillus niger van Tieghem, Penicillium glabrum (Wehmer) Westling and the entomopathogen Metarhizium anisopliae (Metsch.) from slower developing Cladosporium cladosporioides (Fresenius) de Vries and Scopulariopsis brevicaulis (Sacc.) Bainier and demonstrated peak growth at 24°C-34°C. In contrast to fast growing fungi, C. cladosporioides and S. brevicaulis showed heightened growth on blood agar but suppressed growth on media supplemented with squalene. Squalene had no effect on the growth of other fungi, indicating its release has minimal significance as a surface antimycotic. Scopulariopsis brevicaulis is endosymbiotic in D. variabilis, and depleting tick secretory (squalene) reserves by leg pinching promoted susceptibility to increasing levels of S. brevicaulis by creating a fungal bloom that killed the tick. We conclude that mycostatic ability of squalene to regulate growth of S. brevicaulis within the tick is more important than its ability to deter fungi from penetrating internally.