Résumé
The viburnum leaf beetle Pyrrhalta viburni (Coleoptera: Chrysomelidae) is a specialist Viburnum leaf-feeder that is native to Eurasia and invasive in North America. Eggs of P. viburni are laid in round cavities excavated by the ovipositing female beetle and covered with a protective secretion. We document in this paper the mite fauna associated with P. viburni egg masses on Viburnum tinus in southern France. We then report the results of experiments investigating the seasonal patterns of mite infestation and the effects of the most common mite found within egg masses, Trichoribates trimaculatus (Oribatida: Ceratozetidae), on P. viburni egg survivorship. A diverse mite fauna of 18 species was found on V. tinus twigs, often living within P. viburni egg masses, including predaceous, phytophagous, and detritivorous species. Mite abundance and diversity were higher on Viburnum twigs containing at least one intact egg mass and were positively correlated with the number of intact egg masses per twig. Detritivorous mites were more abundant on twigs nine months after oviposition than one and four months after oviposition. Finally, we found no evidence that T. trimaculatus impacts P. viburni egg survivorship and overwintering success. These findings show that P. viburni egg masses and their associated cavities form a microhabitat favorable for the establishment of several mite species. It seems likely that these associations are cases of commensalism where mites benefit from the presence of food and shelter in these protected cavities, with no direct negative impact on P. viburni eggs.