Last updated March 6, 2017 at 3:16 pm
Science Update is a monthly written series from Dr Paul Willis tackling some of the controversial topics in the public and aims to provide the current research behind these subjects.
There has been a lot of coverage of the decline of bee numbers over recent decades with some claims that they face imminent extinction. The decline of bees is of great concern because of the pollination services they provide to agriculture. But a more sober assessment of what is actually happening reveals that, while there are a number of threats to the health and survival of bees around the world, bee numbers are increasing overall. In fact they’re unlikely to experience severe decline in the near future provided they are given appropriate care and protection. Time to update the science behind the plight of the humble bee.
How important are bees?
The most important product of bees is not the honey they make but the pollination services that they provide. The Agriculture and Consumer Protection Department of the Food and Agriculture Organisation of the United Nations estimated that, in 2005, the global value of crops dependant on pollination by honey bees was close to $US200 billion. The UN also claim that around 70 percent of the worlds crops depend on pollination from bees.
Colony Collapse Disorder
Any discussion about the plight of bees needs to be had in the light of Colony Collapse Disorder (CCD) where most of the worker bees leave a colony abandoning a Queen. Usually they leave the hive with plenty of food and a few nurse bees who help to raise the young.
While this phenomenon has been observed throughout the history of bee keeping, in late 2006 it was given the term Colony Collapse Disorder in response to the dramatic rise in cases across North America. Around this time a similar increase in cases of CCD was observed across Europe. By 2013 it was estimated that more than 10 million hives were lost to CCD which was around twice the rate of loss measured before 2007. This increase in CCD increased the costs of agricultural production where farmers had to pay more to rent hives for pollination services.
The causes of CCD are not well understood and several agents have been implicated, including the spread of GMO technologies, the use of insecticides (particularly a new class of insecticides called neonicotinoids) and the spread of a parasitic mite called Varroa.
GMOs and Bees
There are plenty of claims online like this one that there is a direct causal link between some Genetically Modified Organisms (GMOs) and the death of bees. One internet meme concerning the death of 37 million bees following a planting of GMO crops has been shown to be unproven. To date, no direct causal link has been demonstrated between any GMO and the health of bees.
The overwhelming evidence indicates that, while there is no direct link between GMOs and bee health, there may be an indirect linkage by the increased use of some insecticides associated with some GMO crop production. So the GMOs are not affecting the bees but some farming practices associated with some GMOs may be. There are plenty of articles where these two issues are conflated.
Bees and insecticides
It probably comes as no surprise that bees and insecticides do not mix and there has long been concern about the effects on bee populations of broad-scale spraying of crops with insecticides.
In recent years there has been a focus on a class of insecticides called neonicotinoids. Neonicotinoid insecticides are used in a variety of crops worldwide and have been shown to be harmful to commercial honeybees and bumblebees. Neonicotinoids have been implicated in CCD and, in 2013, the European Union and some other countries restricted the use of some neonicotinoid insecticides. Most studies to date into the effects of neonicotinoids on bees have only tested short-term effects in experimental settings.
The use of neonicotinoid insecticides have recently been linked to the loss of wild bees in England. Researchers found that wild bees that forage on neonicotinoid-treated oilseed rape crops are three times more likely to undergo long-term population declines than bees that forage from other sources. The paper surveys 62 bee species from the United Kingdom and links population declines over a 18-year period to the escalating use of neonicotinoid pesticides.
Recently there was a case in the US where spraying to kill the mosquitos responsible for the spread of the Zika virus actually ended up wiping out bees across a wide area. This story was also covered in a recent Brew Ha Ha on Australia’s Science Channel.
A big fear for honey producers and a real impact on bee numbers globally has been the Varroa Mite. This parasitic mite has caused the loss of many hives overseas, particularly in the 1990’s and 2000’s, and there is the ever-present threat of it getting loose in Australia and causing similar problems.
The spread of the Varroa Mite into Australia has long been seen as inevitable. It was first detected in Australia earlier this year around Townsville in North Queensland and a second infestation was detected in the same area a month later. The Queensland Government placed movement control orders around the area aimed at containing the outbreak. The Queensland Government Department of Agriculture and Fisheries are deploying bee traps carried by helium balloons as part of the eradication program of the Varroa Mite outbreak.
A study collected pollen from bee hives in seven major crops to determine what types of pesticides bees are exposed to and how different pesticide blends affect bees’ susceptibility to a gut parasite. They detected 35 different pesticides in the sampled pollen and found high fungicide loads. While fungicides are typically seen as fairly safe for honey bees, this study found an increased probability of the parasite infection in bees that consumed pollen with a higher fungicide load. This study makes a strong point about the effects on non-target species (specifically bees) of the agricultural application of pesticides.
This report notes that climate change has the potential to severely impact ecosystem services such as pollination. It investigates a wide range of pollinators, including bees, and identifies a number of potential factors related to expected climate change that could adversely affect their numbers. It recommends an ecosystem-wide approach to dealing with these threats.
Crisis? What crisis?
There are claims that there is no bee crisis at all. This article from Genetic Literacy Project uses supporting data from the US Department of Agriculture to show that the number of honey-producing colonies across the US has remained pretty constant for the last couple of decades.
At a glance, this data appears to be contradicted by another graph found in a publication from the United Nations Environment Programme which also sources data from the US Department of Agriculture to show the decline over time. However, in fact, the two graphs are consistent with each other because the first graph only gives data since 1995 while the second graph goes back to 1945.
Interestingly, the Genetic Literacy Project article also provides data from the UN Food and Agriculture Organisation showing a steady increase in hive numbers globally since the beginning of the 1960’s. The dip in growth in the 1990s is attributed to the impact of the Varroa Mite.
This graph is consistent with the finding published in the journal Cell on the number of hives globally but it is worth noting that the growth in the number of hives globally does not meet the growth in demand for the pollination services that the hives provide.
It appears that, while there are a number of threats to honey bees and the pollination services they provide, we are not experiencing a beemagedon or the imminent extinction of bees around the world. The conclusions in this report from the United Nations Environment Programme are that the “currently available global data and knowledge on the decline of pollinators are not sufficiently conclusive to demonstrate that there is a worldwide pollinator and related crop production crisis”. It goes on to note that, while honey bee hives have increased globally by close to 45% over the last 50 years, declines have been reported in several locations, particularly in Europe and Northern America. It cautions that human activities and their environmental impacts may be detrimental to some species but beneficial to others with sometimes subtle and counter-intuitive causal linkages.