A salivary chitinase of Varroa destructor influences host immunity and mite’s survival

Abstract

Varroa destructor is an ectoparasite of honey bees and an active disease vector, which represents one of the most severe threats for the beekeeping industry. This parasitic mite feeds on the host’s body fluids through a wound in the cuticle, which allows food uptake by the mother mite and its progeny, offering a potential route of entrance for infecting microorganisms. Mite feeding is associated with saliva injection, whose role is still largely unknown. Here we try to fill this gap by identifying putative host regulation factors present in the saliva of V. destructor and performing a functional analysis for one of them, a chitinase (Vd-CHIsal) phylogenetically related to chitinases present in parasitic and predatory arthropods, which shows a specific and very high level of expression in the mite’s salivary glands. Vd-CHIsal is essential for effective mite feeding and survival, since it is apparently involved both in maintaining the feeding wound open and in preventing host infection by opportunistic pathogens. Our results show the important role in the modulation of mite-honey bee interactions exerted by a host regulation factor shared by different evolutionary lineages of parasitic arthropods. We predict that the functional characterization of Varroa sialome will provide new background knowledge on parasitism evolution in arthropods and the opportunity to develop new bioinspired strategies for mite control based on the disruption of their complex interactions with a living food source.

Changing the Recipe: Pathogen Directed Changes in Tick Saliva Components

“…Herein, we will discuss how sialostatin L and L2 enhance the transmission of A. phagocytophilum, TBEV, and B. burgdorferi. Additionally, salivation has also been associated with pathogen transmission in non-vertebrate vector-host systems such as Varroa destructor and Apis mellifera, where salivation alters hemocyte behavior as well as in plant diseases caused by whiteflies, aphids, mites, and psyllids, where vector salivation plays a role in altering host plant defenses [26][27][28][29][30][31][32][33].…”

Varroa destructor from the Laboratory to the Field: Control, Biocontrol and IPM Perspectives—A Review

“…New borns feed from the hole (100 μm) pierced by the mother’s chelicerae in the pupa [ 42 , 43 ]. The feeding pit on bee pupae stands open due to anticoagulants from the ecto-parasite saliva and suppression of healing processes [ 37 , 44 , 45 ]. The first born is always a male (haploid) while the following eggs laid are females (diploid).…”

Standard Methods for Dissection of Varroa destructor Females

“…The latter can be very useful as low temperatures allow the conservation of organs. Several fixation methods are described in the literature using wax, glue, or double-sided tape [11,16,31,32]. In this guide, we used cyanoacrylate gel glue as we found liquid glue less practical to precisely fix the mite.…”

“…For genes expression or transcriptomic projects, organs can be kept in RNA later provided sample tubes are then stocked at −80 • C [13,19]. Alternatively, the dissected organs can be directly transferred in extraction buffer or Trizol reagent and stored at −80 • C [11,12,28]. Thanks to the constant improvement in proteomic and metabolomic methods, storage in PBS 1X at −80 • C is now possible for such analyses although flash freezing in liquid nitrogen is recommended.…”

“…However, only a few have focused on the V. destructor anatomy or on an organ in particular, the reproductive organs being the main exception [11][12][13][14][15][16][17][18]. Dissection and extraction of specific organs, as it is often performed on honey bees, allows more subtle investigations of the host-parasite interactions [11][12][13][19][20][21][22][23][24]. The reproductive status and fertility of mites can indeed be precisely assessed by microscopy once the genitalia are extracted [14,16].…”