Phoretic mites associated with ambrosia beetles in Florida avocados

Authors: BERTO, MARIELLE - University Of Florida; Kendra, Paul; CARRILLO, DANIEL - University Of Florida

Submitted to: Acarology International Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/31/2022
Publication Date: 12/1/2022
Citation: Berto, M.M., Kendra, P.E., Carrillo, D. 2022. Phoretic mites associated with ambrosia beetles in Florida avocados. In Zhang, Z.-Q., Fan, Q.-H., Heath, A.C.G., and Minor, M.A. (Eds.). Acarological Frontiers: Proceedings of the XVI International Congress of Acarology. (1-5 Dec 2022, Auckland, New Zealand). Magnolia Press, Auckland, 328 pp. https://doi.org/10.11646/zoosymposia.22.1.42.
DOI: https://doi.org/10.11646/zoosymposia.22.1.42

Interpretive Summary:

Technical Abstract: Ambrosia beetles are wood borers that spend most of their life concealed inside galleries within host trees. They use the xylem as a substrate for farming symbiotic fungi, carried in specialized sac-like structures called mycangia. Most of their symbionts offer no threat to plants. However, some of these symbionts are phytopathogens that infect avocado (Persea americana) and other plants in the family Lauraceae. Raffaelea lauricola is a fungal pathogen vectored by several species of ambrosia beetles in the United States. It is the causal agent of laurel wilt, a deadly disease affecting avocado and forest ecosystems in Florida. The cryptic living habits of the ambrosia beetles make their management challenging. Conventional insecticide and fungicide applications have not been successful so far. This system requires novel IPM strategies. A few other organisms inhabit ambrosia beetle galleries, such as nematodes and phoretic mites. Little is known about the ecology of phoretic mites and their potential application in IPM. As a first step to understand the association between ambrosia beetles and phoretic mites, a survey was conducted in eight avocado orchards and swampbay (Persea palustris) stands in Florida. Ambrosia beetles were obtained by three methods: (1) field capture of in-flight females using modified Lindgren traps, (2) collection of beetles as they emerged from infested logs held in lab chambers, and (3) physical excavation of beetles from infested logs. Nine mite species in five families were collected from nine beetle hosts, including Asca sp. (Ascidae), Proctolaelaps bickleyi and Proctolaelaps sp. (Melicharidae), Acarothorectes curculionium, Elattoma sp., Brazilopsis floridensis, and Pediculaster sp. (Pygmephoridae), Tarsonemus sp. (Tarsonemidae), and Histiogaster arborsignis (Acaridae). The mite family Pygmephoridae was the most abundant group. Acarothorectes curculionium and Elattoma sp. were the most common phoretic mite species, and B. floridensis is a new mite species found in this study. The phoretic associations were not specific to a particular ambrosia beetle species. Histiogaster arborsignis is a cosmopolitan phoretic mite commonly associated with wood-boring insects. This fungivorous mite can be easily mass-reared and could potentially transport fungal spores into the beetle galleries. The fungal feeding plasticity of H. arborsignis has been assessed through no-choice assays offering R. lauricola, Fusarium sp., six non-pathogenic ambrosia beetle fungal symbionts, and two commercially available beneficial fungi. The ability of H. arborsignis to carry and inoculate Beauveria bassiana and Trichoderma harzianum into ambrosia beetle colonies has also been assessed. H. arborsignis developed and reproduced for two generations on all beetle symbionts, particularly more on Graphium sp. No reproduction on T. harzianum or B. bassiana was observed. The mites transferred beneficial fungi to X. bispinatus galleries in avocado sawdust rearing media, affecting the beetles’ survivability and reproduction. Histiogaster arborsignis has consistently shown a close association with the beetle fungal symbionts and the potential to be incorporated into innovative IPM practices for managing wood boring pests. This research is the first step towards understanding complex symbiotic associations between phoretic mites, ambrosia beetles and ambrosia fungi. Future studies will evaluate the potential of phoretic mites to be incorporated into innovative IPM practices for managing ambrosia beetles and other wood-boring pests.