The role of Varroa and viral pathogens in the collapse of honeybee colonies: a modelling approach

Abstract

Summary1. The ecto-parasitic mite Varroa destructor is a serious world-wide pest of the honeybee Apis mellifera and has being linked with the death of millions of colonies, although its role in colony death has remained elusive. 2. A simulation model was developed to explain the link between the mite and collapse of the host bee colony, given that colony death does not always occur. We investigated the effects of two pathogens, deformed wing virus (DWV) and acute paralysis virus (APV), vectored by the mite, on the host colony. 3. Two previously published simulation models, a bee and a mite, were combined and adapted for use in temperate climates with a variety of bee diseases. The model was constructed using Modelmaker® software, which allows the progression of a disease in the host colony to be followed daily. 4. The population dynamics generated by the model were similar to those observed in a natural honeybee colony. When DWV-or APV-transmitting mites were introduced into the colony, its adult worker bee population collapsed either during winter or spring for DWV, or autumn to spring for APV. This corresponds well with field observations of colony death in Europe. 5. The model revealed that DWV initially had little effect on the colony but during late summer, as the population of DWV-transmitting mites increased, the virus caused a reduction in the number of healthy young bees entering the overwintering population. This imbalance in the age structure of the overwintering bees resulted in the eventual death of the colony during the winter or spring. As few as 2000-3600 mites in autumn could kill a colony. 6. In contrast, APV transmitted by Varroa was only able to kill the honeybee colony if a large (10 000+) mite population was already present when an overt APV infection occurred. It was difficult for APV to become established within the bee population due to it causing rapid host death. 7. The model predicts that the less virulent DWV will become more widely established than the highly virulent APV, and that mite control measures need to be taken prior to the production of overwintering bees.

Horizontal transmission of deformed wing virus: pathological consequences in adult bees (Apis mellifera) depend on the transmission route

“…Such vertically transmitted infections are mainly if not exclusively covert, which might present a mechanism for long-term persistence in the honeybee population as has also been described for other insect viruses (Bonsall et al, 2005;Burden et al, 2003;de Miranda & Genersch, 2010;Hails et al, 2008). Only in association with the ectoparasitic mite V. destructor have overt outbreaks of DWV infection, characterized by deformed wings as the most prominent symptom, been recorded (Ball, 1989;Ball & Allen, 1988;Bowen-Walker et al, 1999;Martin, 2001). However, a direct causal link between the virus and the symptom 'wing deformity' had not been established.…”

“…DWV normally causes covert infections in honeybees (de Miranda & Fries, 2008;Hails et al, 2008;Yue et al, 2007). Overt DWV infections characterized by the occurrence of visible disease symptoms (deformed wings, bloated and shortened abdomen, and miscolouring) are associated with V. destructor infestation (Ball & Allen, 1988;Bowen-Walker et al, 1999;Martin, 2001;Martin et al, 1998; Santillán-Galicia et al, 2010;Tentcheva et al, 2006;Yue & Genersch, 2005). However, the exact role of the mite in the pathogenesis of DWV is still not fully understood and a direct causal link between the virus and the symptom 'wing deformity' has not been established yet (de Miranda & Genersch, 2010).…”

Evidence of Varroa-mediated deformed wing virus spillover in Hawaii

“…In fact, the presence of V. destructor in honey bee colonies has been linked to increased viral loads, virulence, and prevalence of DWV in honey bee populations (Martin et al, 2012). Additionally, Varroa has also been associated with other viral diseases in honeybees including AKI, KBV, BQCV, and SBV (Francis et al, 2013;Martin, 2001;Shen et al, 2005).…”

Seasonal prevalence of pathogens and parasites in the savannah honeybee (Apis mellifera scutellata)

“…The health of honeybees has been one of the most important topics in apicultural research in recent years (Genersch, 2010). This is primarily due to the recent emergence of high honeybee colony losses in many parts of the world (Le Conte et al, 2010;Neumann and Carreck, 2010;Stokstad, 2007;vanEngelsdorp et al, 2008) and the vulnerability of honeybees to parasitic mites, fungi, viruses and bacteria (Bailey and Ball, 1991;Chen et al, 2006;Dietemann et al, 2012;Genersch, 2010;Genersch et al, 2010;Martin, 2001;Ribière et al, 2010;Sammataro et al, 2000). These pathogens and parasites can have harmful effects on honeybee health and the services they offer, which in turn can lead to severe economic losses (Genersch, 2010;Morse and Calderone, 2000;Shen et al, 2005).…”