Becchimanzi, Andrea (2018) Exploring honeybee-mite immune interactions for developing RNAi based control technologies of Varroa destructor. [Tesi di dottorato]

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Item Type: Tesi di dottorato
Lingua: English
Title: Exploring honeybee-mite immune interactions for developing RNAi based control technologies of Varroa destructor
Date: 13 December 2018
Number of Pages: 66
Institution: Università degli Studi di Napoli Federico II
Department: Scienze Chimiche
Dottorato: Biotecnologie
Ciclo di dottorato: 31
Coordinatore del Corso di dottorato:
Pennacchio, FrancescoUNSPECIFIED
Date: 13 December 2018
Number of Pages: 66
Uncontrolled Keywords: honeybee; mite; saliva
Settori scientifico-disciplinari del MIUR: Area 07 - Scienze agrarie e veterinarie > AGR/11 - Entomologia generale e applicata
Date Deposited: 15 Jan 2019 09:18
Last Modified: 16 Jun 2020 09:26


The economic impact of beekeeping, including crop pollination, is very difficult to assess, but, according to the Italian Federation of Beekeepers (FAI), it can be estimated around 1,500 millions of euros annually, generated by about one million of hives. Honeybee colony losses have been a major problem since the beginning of modern apiculture; however, in 2006, the dramatic dimension of this phenomenon attracted the attention of the public opinion and the increasing interest of the scientific community. After a few years of intense investigation, a specific causal agent for the widespread colony losses was not found, but rather a multifactorial origin was proposed for this syndrome. It is now largely accepted that both landscape deterioration and agrochemicals can be directly or indirectly responsible for colony losses. However, several monitoring programs indicate that the large majority of losses are associated with the co-presence of the mite Varroa destructor and the Deformed Wing Virus (DWV). V. destructor is an ectoparasitic mite that creates a wound in the host’s cuticle through which it feeds on haemolymph and fat body, representing an important stress factor that weakens honeybee colonies and promotes the spreading of viral diseases. In order to facilitate feeding, V. destructor delivers a complex of factors, including proteins, through its salivary secretions. The scarcity of information about the sialome of the mite limits the functional analysis of the host regulation process and, thus, the opportunity to impair the mite’s fitness using biotechnological approaches. Here, we have used a functional genomics pipeline to identify V. destructor candidate salivary proteins, along with in situ hybridization detection to assess their expression in salivary glands. Using this approach, we identified a chitinase (Vd-CHI), specifically expressed in salivary glands, which affects mite survival and causes alterations of honeybee immune response. In particular, gene knockdown experiments revealed that Vd-CHI deficient mites tend to show a reduced survival as a likely consequence of reduced feeding capacity on honeybee pupae, due to the lack of chitinoloytic activity that favours the patency of the feeding wound. The importance of Vd-CHI for the feeding success of Varroa destructor is also supported by the upregulation of this gene during the reproductive phase of the mite, when the adult female creates large communal feeding site for her and the offspring, usually in the middle of the 2nd abdominal sternite of honeybee pupae. Vd-CHI has also an impact on honeybee’s immune response, determining the upregulation of an endogenous chitinase and the downregulation of an endocuticle structural glycoprotein, associated with wound healing and Varroa-resistance. On the other hand, infestation by Vd-CHI deficient mites led to upregulation of β-1,3-glucan binding protein and hymenoptaecin, as a likely consequence of bacterial infections, suggesting that Vd-CHI could also prevent detrimental bacterial proliferation. Collectively, these results shed light on Varroa-honeybee interaction, confirming that V. destructor sialome plays an important role in host exploitation. In particular, V. destructor feeding success on A. mellifera is mediated by the action of Vd-CHI, which probably facilitates the opening and patency of the feeding wound in the honeybee’s cuticle. Indeed, this chitinase is likely involved both in maintaining the feeding site open, by interfering with the regular healing process of cuticle, and in limiting opportunistic infections, by priming antimicrobial defenses. The present work contributes to a better knowledge of salivary repertoire of V. destructor and also demonstrates that dsRNA targeting of genes expressed in salivary glands can offer a promising new tool for controlling the mite.


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