Population growth of Varroa destructor (Acari: Varroidae) in honey bee colonies is affected by the number of foragers with mites

Gloria Degrandi-Hoffman,Geoffrey Hidalgo,Victor Zazueta,Fabiana Ahumada,Mona Chambers,Emily Watkins Dejong

doi:10.1007/s10493-016-0022-9

Gloria Degrandi-Hoffman, Geoffrey Hidalgo + Show 4 more

Open Access

https://doi.org/10.1007/s10493-016-0022-9

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Abstract

Varroa mites are a serious pest of honey bees and the leading cause of colony losses. Varroa have relatively low reproductive rates, so populations should not increase rapidly, but often they do. Other factors might contribute to the growth of varroa populations including mite migration into colonies on foragers from other hives. We measured the proportion of foragers carrying mites on their bodies while entering and leaving hives, and determined its relationship to the growth of varroa populations in those hives at two apiary sites. We also compared the estimates of mite population growth with predictions from a varroa population dynamics model that generates estimates of mite population growth based on mite reproduction. Samples of capped brood and adult bees indicated that the proportion of brood cells infested with mites and adult bees with phoretic mites was low through the summer but increased sharply in the fall especially at site 1. The frequency of capturing foragers with mites on their bodies while entering or leaving hives also increased in the fall. The growth of varroa populations at both sites was not significantly related to our colony estimates of successful mite reproduction, but instead to the total number of foragers with mites (entering and leaving the colony). There were more foragers with mites at site 1 than site 2, and mite populations at site 1 were larger especially in the fall. The model accurately estimated phoretic mite populations and infested brood cells until November when predictions were much lower than those measured in colonies. The rapid growth of mite populations particularly in the fall being a product of mite migration rather than mite reproduction only is discussed.

Highlights

The parasitic varroa mite, Varroa destructor Anderson & Trueman, is a serious pest to honey bees and a major cause of colony losses worldwide (Genersch et al 2010; GuzmanNovoa et al 2010; van Dooremalen et al 2012)
We compared the estimates of mite population growth with predictions from a varroa population dynamics model that generates estimates of mite population growth based on mite reproduction
As at site 1, predicted and actual colony sizes did not differ in October and November. The proportion of both adult workers with phoretic mites and infested brood cells was correlated with the frequency of foragers with mites (FWM) entering and leaving the hive

Summary

Introduction

The parasitic varroa mite, Varroa destructor Anderson & Trueman, is a serious pest to honey bees and a major cause of colony losses worldwide (Genersch et al 2010; GuzmanNovoa et al 2010; van Dooremalen et al 2012). Varroa can devastate colonies that are highly infested due to effects from parasitism and transmission of viruses. If colonies are established with low varroa populations, it should take more than a year before they become highly infested even if untreated (DeGrandi-Hoffman and Curry 2004; Genersch 2010). Mite populations in the late fall can be unexpectedly large even if miticides are applied in late summer (Le Conte et al 2010; DeGrandi-Hoffman et al 2014). This suggests that factors other than reproduction might be contributing to the growth of the mite population

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