Intensively Cultivated Landscape and Varroa Mite Infestation Are Associated with Reduced Honey Bee Nutritional State.

Adam G Dolezal,W Allen Miller,Jimena Carrillo-Tripp,Amy L Toth,Bryony C Bonning,Raul Narciso Carvalho Guedes

doi:10.1371/journal.pone.0153531

Abstract

As key pollinators, honey bees are crucial to many natural and agricultural ecosystems. An important factor in the health of honey bees is the availability of diverse floral resources. However, in many parts of the world, high-intensity agriculture could result in a reduction in honey bee forage. Previous studies have investigated how the landscape surrounding honey bee hives affects some aspects of honey bee health, but to our knowledge there have been no investigations of the effects of intensively cultivated landscapes on indicators of individual bee health such as nutritional physiology and pathogen loads. Furthermore, agricultural landscapes in different regions vary greatly in forage and land management, indicating a need for additional information on the relationship between honey bee health and landscape cultivation. Here, we add to this growing body of information by investigating differences in nutritional physiology between honey bees kept in areas of comparatively low and high cultivation in an area generally high agricultural intensity in the Midwestern United States. We focused on bees collected directly before winter, because overwintering stress poses one of the most serious problems for honey bees in temperate climates. We found that honey bees kept in areas of lower cultivation exhibited higher lipid levels than those kept in areas of high cultivation, but this effect was observed only in colonies that were free of Varroa mites. Furthermore, we found that the presence of mites was associated with lower lipid levels and higher titers of deformed wing virus (DWV), as well as a non-significant trend towards higher overwinter losses. Overall, these results show that mite infestation interacts with landscape, obscuring the effects of landscape alone and suggesting that the benefits of improved foraging landscape could be lost without adequate control of mite infestations.

Highlights

Honey bees are economically-important managed pollinators, contributing billions of dollars in added yields to a variety of crops worldwide [1]
The goals of the study were to test the following hypotheses: 1) due to reduction in floral forage availability, intensively cultivated landscapes are associated with poor bee pre-overwintering nutritional physiology, 2) because poor pollen nutrition is associated with decreased immune response [18] and pathogen replication [8], intensively cultivated landscapes are associated with higher virus loads, 3) the presence of parasitic Varroa mites is associated with poor bee nutrition, and 4) the presence of Varroa mites is associated with higher virus loads
The effects of heavily managed agricultural landscapes on honey bee health have been of increasing interest in recent years [16]

Summary

Introduction

Honey bees are economically-important managed pollinators, contributing billions of dollars in added yields to a variety of crops worldwide [1]. Significant efforts devoted to identifying the causes of these honey bee losses have led to the consensus that multiple environmental factors interact to stress honey bee colonies. These factors include exposure to a variety of pesticides, incidence of new and more widespread pathogens, increasing pressure from Varroa destructor mite infestations, and changes in landscape use that affect the floral resources available to honey bee foragers [4]. The replacement of native and weedy plant resources due to agricultural intensification has dramatically changed the bee foraging landscape [12, 15]

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