Ambrosia beetles are wood boring insects that construct galleries and farm symbiotic fungi in the xylem of their host plants. Some of these symbionts are plant pathogens that infect avocado trees in South Florida, such as Raffaelea lauricola and Fusarium sp. Histiogaster arborsignis is a cosmopolitan mite that inhabits ambrosia and bark beetle galleries. This mite feeds on fungi and decaying organic matter and uses adult beetles for phoresy. The fungal feeding plasticity of H. arborsignis was assessed through no-choice feeding assays offering R. lauricola, Fusarium sp., several non-pathogenic ambrosia beetle fungal symbionts, and two commercially available beneficial fungal species. Their ability to feed on dead and alive eggs, larvae and adults of Xyleborus bispinatus was also assessed. Histiogaster arborsignis was able to feed and reproduce for at least two generations on the beetle symbionts, showing a strong preference for Graphium sp. By contrast, the mites did not reproduce when offered Trichoderma harzianum or Beauveria bassiana. The mites showed no predation activity on live brood stages of Xyleborus bispinatus. However, the mites fed on remains of dead eggs and larvae, as well as on dead adults. This study confirmed the generalist fungal feeding and scavenger behavior of H. arborsignis and revealed their potential use of ambrosia fungi as food sources inside bark and ambrosia beetles’ galleries.
