Evaluation of the distribution and impacts of parasites, pathogens, and pesticides on honey bee (Apis mellifera) populations in East Africa.

Elliud Muli,Maryann Frazier,Christina Grozinger,Joseph Kilonzo,Baldwyn Torto,Fiona Mumoki,James Tumlinson,James Ng'Ang'A Kimani,James Frazier,Tracey Baumgarten,Harland Patch,Daniel Masiga,Glenn Francis Browning

doi:10.1371/journal.pone.0094459

Abstract

In East Africa, honey bees (Apis mellifera) provide critical pollination services and income for small-holder farmers and rural families. While honey bee populations in North America and Europe are in decline, little is known about the status of honey bee populations in Africa. We initiated a nationwide survey encompassing 24 locations across Kenya in 2010 to evaluate the numbers and sizes of honey bee colonies, assess the presence of parasites (Varroa mites and Nosema microsporidia) and viruses, identify and quantify pesticide contaminants in hives, and assay for levels of hygienic behavior. Varroa mites were present throughout Kenya, except in the remote north. Levels of Varroa were positively correlated with elevation, suggesting that environmental factors may play a role in honey bee host-parasite interactions. Levels of Varroa were negatively correlated with levels of hygienic behavior: however, while Varroa infestation dramatically reduces honey bee colony survival in the US and Europe, in Kenya Varroa presence alone does not appear to impact colony size. Nosema apis was found at three sites along the coast and one interior site. Only a small number of pesticides at low concentrations were found. Of the seven common US/European honey bee viruses, only three were identified but, like Varroa, were absent from northern Kenya. The number of viruses present was positively correlated with Varroa levels, but was not correlated with colony size or hygienic behavior. Our results suggest that Varroa, the three viruses, and Nosema have been relatively recently introduced into Kenya, but these factors do not yet appear to be impacting Kenyan bee populations. Thus chemical control for Varroa and Nosema are not necessary for Kenyan bees at this time. This study provides baseline data for future analyses of the possible mechanisms underlying resistance to and the long-term impacts of these factors on African bee populations.

Highlights

Pollinators are essential contributors to global nutrition and food security
Our survey suggests that several new parasites and pathogens (Varroa, Nosema, deformed wing virus (DWV), BQCV, and acute bee paralysis virus (ABPV)) have recently invaded honey bee populations in East Africa
Honey bees provide critical pollination services to agriculture and natural landscapes, and the honey and wax produced by honey bees represent a potential source of income for families in East Africa and across the world

Summary

Introduction

Pollinators are essential contributors to global nutrition and food security. An estimated three-quarters of major global food crops benefit from pollinators [1]. The productivity of many high value crops grown in the developing world, such as cacao, coffee, and cashews, is strongly tied to pollination services [3,4,5,6]. The amount of animal pollinated crops grown globally has increased significantly in the last fifty years [7], making both developed- and developing world countries increasingly dependent on pollinator populations for food security and production of economically important crops. Large-scale surveys of managed honey bee populations in the US and Europe have failed to identify a single factor that is consistently strongly correlated with colony losses, leading researchers to believe a combination of factors acts synergistically to reduce survival [21,22,23,24,25]

Methods

Results

Discussion

Conclusion