By Athayde Tonhasca
Our honey bee – more precisely, the Western or European honey bee, Apis mellifera – is the world’s most important crop pollinator. Thanks to an ancient history of domestication, farmers can count on a work force of up to 60,000 bees per hive, which can be managed and moved from place to place to pollinate flowers of many shapes and sizes. Unlike the vast majority of bee species, honey bees live in highly social, organised colonies that last for many years. They fly long distances in search of food, and are quite effective in collecting pollen and nectar. Depending on the floral abundance, season and density of colonies in the area, a single hive may consume 10 to 60 kg of pollen and 55 to 400 kg of nectar per year.
Honey bees are efficient pollinators that have been introduced to many parts of the world to improve the yield and quality of crops. But their presence can be bad news for other pollinating species.
Bees can be infected by several viruses and other pathogens such as microsporidia (fungus-like single cell parasites). Every time a bee visits a flower, it risks being contaminated by a pathogen left by a prior visitor. The transmission can go from honey bees to other bees – and even flies – or the other way around, but honey bees are the most likely source of diseases: they are known hosts of many viruses and other pathogens. Besides, large numbers and communal, crowded living arrangements are not the best conditions for keeping diseases at bay, as we humans have recently and painfully learned. Indeed, studies have confirmed pathogen transmission from honey bees to bumble bees and solitary bees. Infections in the opposite direction have been less documented.
Honey bees are good at what they do, and the figures prove it: the amount of nectar and pollen collected by a large apiary is sufficient to support 102 bumble bee colonies; during high season (June–August), a 40-hive apiary collects as much pollen as four million wild bees: that means that one hive gathers enough pollen for an average solitary bee species to produce 100,000 offspring. It is difficult to measure whether this level of industriousness has any effect on honey bees’ wild counterparts: bees are highly mobile and cover a huge area while foraging, so it is not easy to set out experiments. Despite this, we have a great deal of circumstantial evidence to suggest there is not enough food to go around when honey bees are in the neighbourhood.
Every spring, Tenerife beekeepers temporarily move up to 2,700 beehives to Teide National Park to take advantage of the seasonal bloom. A research team saw this cyclical invasion as a great opportunity to evaluate the impact of honey bees. So for three years, they monitored the area before and after beehives were brought in. They observed a clear reduction in the number of pollinator species and diversity of flower visitors when honey bees were present. In other studies in different countries, wild bees switched to less abundant and less rewarding plant species when honey bees were present. Or they became scarcer, gained less weight, and produced fewer and smaller offspring. In other instances, wild bee numbers increased once honey bee hives were removed. In Spain and another 13 countries in the Mediterranean basin, honey bees have become more abundant over the years and are gradually replacing wild bees as visitors of wild and cultivated plants. We don’t know what the consequences are for the 3,300 or so bee species in the region, but it does not bode well.
Competition between species happens when food is a limited resource, as is the case for small or isolated areas. That helps explain why native bees have become endangered after honey bees were introduced in New Caledonia (south Pacific), New Zealand, Japan and Tasmania. But competition is not a problem for islands only; it is likely to happen whenever flowers are scarce, such as at the beginning or end of bees’ foraging period, or during unusually cold or dry years.
All of this suggests it is wise to keep honey bees apart from native bees. Introducing or enhancing beekeeping in sensitive areas – that is, those already occupied by scarce or threatened bee species, of semi-natural habitats, or where flowers can be in short supply any time during the season – can put our bee fauna at risk.
The importance of beekeeping and honey bee pollination is unquestionable, but our wild bee species are important as well, as pollinators and components of our biodiversity. Despite the recent panicked reports in the media about the imminent demise of the honey bee and supposedly mankind, beekeeping around the world has increased by ∼45% during the last 50 years (numbers from America and North Europe are exceptions). Meanwhile, many wild bees have declined for many reasons, including the presence of honey bees.
There are plenty of opportunities for all bees to coexist in our planet: it’s a matter of recognising their potential, limitations, risks and proper place.
Scottish pollinators 