Beyond phoresy: interactions between Histiogaster arborsignis (Acari: Acaridae), ambrosia beetles and their fungal symbionts in Florida avocados

Authors: BERTO, MARIELLE - University Of Florida; CRUZ, LUISA - University Of Florida; AVERY, PASCO - University Of Florida; Cloonan, Kevin; Dunlap, Christopher; CARRILLO, DANIEL - University Of Florida

Submitted to: Symbiosis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2025
Publication Date: 6/10/2025
Citation: Berto, M.M., Cruz, L.F., Avery, P., Cloonan, K.R., Dunlap, C.A., Carrillo, D. 2025. Beyond phoresy: interactions between Histiogaster arborsignis (Acari: Acaridae), ambrosia beetles and their fungal symbionts in Florida avocados. Symbiosis. https://doi.org/10.1007/s13199-025-01063-0.
DOI: https://doi.org/10.1007/s13199-025-01063-0

Interpretive Summary: Laurel wilt is a lethal tree disease that impacts trees in the family Lauraceae which includes avocado. Fungal spores that cause laurel wilt disease are carried by several ambrosia beetle species, and ambrosia beetles inoculate trees with this fungal pathogen when they bore into a tree. Ambrosia beetles bore into host trees and make structures called galleries, or tunnels that the beetles use to cultivate symbiotic fungi that they consume for nutrition. Mites also inhabit ambrosia beetle galleries, though little is known about the biology and ecology of these mite species. Scientists at the University of Florida and the USDA-ARS conducted tests to identify mite species that inhabit the galleries constructed by ambrosia beetles that infest avocado in Florida. Two different mite species were found associated with four ambrosia beetle species that are known to transmit the fungal pathogen that causes laurel wilt disease. Additionally, studies showed that one mite species feeds on and can reproduce on nine fungal symbionts of ambrosia beetles, including the fungal species that causes laurel wilt disease. This information may facilitate the use of mites as biological control agents for ambrosia beetles that carry the fungal pathogen that causes laurel wilt disease.

Technical Abstract: Ambrosia beetles construct complex galleries in the xylem of trees to cultivate symbiotic fungi. Besides beetles and their fungi, a few groups of organisms inhabit ambrosia beetle galleries, including mites. Some of these are phoretic on the beetles, like Histiogaster arborsignis, a cosmopolitan, generalist fungivore associated with many insects in woody habitats. There is no information available on the interactions of this mite with ambrosia beetles and their galleries. In this study, we report for the first time phoretic associations of H. arborsignis with several ambrosia beetles, as well as their feeding on symbiotic fungi of beetles that infest avocados in Florida. Phoretic deutonymphs (hypopi) were found in association with adults of Xyleborinus saxesenii, Xyleborus bispinatus, X. affinis and Ambrosiodmus lecontei, all of which have been linked to the transmission of laurel wilt pathogen to avocado. Small colonies of H. arborsignis were found in an X. saxesenii brood chamber as well as in an unidentified ambrosia beetle gallery. In fungal feeding behavior bioassays, H. arborsignis fed and reproduced at least two generations on nine common important ambrosia beetle symbionts, namely Acremonium sp., Ambrosiozyma ambrosiae, Candida berthetii, Fusarium sp., Graphium sp., Raffaelea arxii, R. lauricola, R. subalba and R. subfusca, but exhibited higher reproductive rates when feeding upon Graphium sp. The mites did not perform well when feeding solely on Beauveria bassiana GHA strain and Trichoderma harzianum Rifai strain T-22 contained in fungal biopesticides. This work is the first step towards understanding the role of H. arborsignis in wood-boring pest galleries and assessing the potential of using these mites in biological control programs against ambrosia beetles and other wood-boring insects.