The Environmental Impacts of Honey Bee Colonies
The short answer is yes, for the majority of the new world (Americas/Australasia), honey bees are invasive. HOWEVER! there is a distinction between “invasive” and “introduced”; A species is introduced when humans transport it outside its native range. It is considered invasive when/if it causes significant harm (ecological or economic) in its new environment. A species like the European honey bee, Apis mellifera, is native to the European continent, whereas the Asian Honey bee, Apis cerana, is endemic to Eastern & Southern Asia.
With the distinction above, it’s wrong to say that the (managed) introduction of these two species outside their native ranges makes them an “invasive alien species”. A. mellifera is the beekeeping species introduced in Australia. A. cerana on the other hand is treated as a biosecurity threat after its accidental introduction to Northern Queensland.
This article discusses the impacts of introduced honey bees to economies and ecosystems outside of their native habitat. It compares the invasive Apis species against the the lifecycle of native bees. Native bees tend to be wild pollinators that are often solitary in nature, and the competitive pressures exhibited by introduced species like A. mellifera challenge their survival.
Where do Honey Bees Come From?
The European honey bees that were first classified by Linnaeus are now known as Apis mellifera mellifera. Three theories exist for the origin of honey bees, and are based around the split from other cavity-nesting bees (Fan et al., 2012). One theory models it as emerging from the middle east or north Africa (Ruttner et al., 1978), in the middle east alone (Garnery et al., 1992) and from Africa, based on genomic analysis (Whitfield et al., 2006).
Regardless of the evolutionary model, A. mellifera migrated to Northern Europe at the end of the the last Ice Age, approximately 12,000 years ago. This subspecies is commonly known as the “European Dark Bee”; research suggests that honey bees originated from Africa over a million years ago . For simplicity, references to A. mellifera will refer to their most recent common ancestor, which migrated to Europe after that Ice Age.
On these grounds, one can argue that A. mellifera are also an invasive species in Europe. However, their presence within the European continent has been far longer than the Americas or Australia, suggesting that they are more established in the European ecosystem. As colonies continue expanding, honey bee subspecies began to emerge, each having slight adaptions which make them better suited to their locality. Example traits include improved cold tolerance or more defensive colony behaviour.
How Honey Bees Spread
Swarming is the natural reproductive behaviour of colonies. Feral honey bees also use this as a means of dispersal, and a more detailed description of this process is covered in raising bee queens.
The ability of honey bees to forage long distances (up to 10 km from the hive), combined with their highly adaptable nature means that the newly-swarmed colonies are able to rapidly establish themselves in their environment, enabling them to successfully spread across continents. The illustration below demonstrates the approximate origin of several subspecies of honey bees, despite the geographic proximity.
Solitary Bee Life Cycle
When the term “native bees” is brought up, the immediate image is that of solitary bees, as the majority of “native” bees do not live in social colonies. Like honey bees, their lifecycle is driven by a single female that lays eggs within burrows in autumn, with the new bees generally emerging in spring and summer.
The basic life cycle is similar across species, and is as follows:
The male and female bees emerge in the spring and summer. Like the honey bee drones, solitary bee males mate with the females and die soon after.
The now-mated females search for suitable nesting sites.
In urban environments, nesting sites can be encouraged by using bee hotels.
Once a nest is located (mainly in small ground or wood cavities), some species will exhibit similar behaviours to honey bees, such as constructing brood cells from mud or leaves (Persson et al., 2018).
In the constructed cells, eggs are laid along with pollen and nectar for the larvae to consume upon hatching. The nest entrance is sealed with mud or plant material until the young bee(s) emerge.
Depending on the species and environmental conditions, the larval stage can last from weeks to months. Once the larva is fully grown, it spins itself a cocoon and enters the pupation phase.
In the cocoon, metamorphoses into an adult bee takes place. Like the larval period, this can take from weeks to months depending on the species.
Many insects like the solitary bee species exhibit “diapause”, in which the growth of an organism is arrested for a set period of time until favourable conditions are met. In most species, this is to overwinter and emerge in the spring or summer, starting start this cycle anew (Gullan & Cranston, the Insects, 2nd edition).
How Many Generations of Solitary Bees are there per Year?
Some species, like the Leafcutter and Mason bees, have one generation per year. Others, like several species of the Sweat and Mining bees, can have multiple generations of bees in a year if the weather and foraging conditions are favourable.
A general trend is as follows: solitary bee species living in warmer climates with more abundant floral resources are more likely to have multiple generations compared to those in colder or more limited floral environments.
Solitary & Honey Bee Interactions
Why Competition Favours Honey Bees
Where honey and solitary bees interact (e.g. overlapping nesting sites or foraging sources), it is the honey bee populations that prosper. Social and solitary species can coexist, yet the generalist foraging nature of honey bees gives them an advantage in areas with limited forage. The large size of honey bee colonies means they’ll deplete the local floral resources, making it difficult for the solitary bees. This is evident in urban and agricultural areas, where there tends to be a scarce food supply from native plants.
The introduction of managed honey bee hives can displace many native bees, further increasing the competitive pressures. Wild bees are forced to forage further from their nests, or utilise less-favourable floral sources, potentially resulting in negative impacts on their population size and reproductive success.
The solitary species that are unaffected by this are those with specialist foraging behaviour, such as Chelostoma florisomne (large scissor bee) who specialises in the buttercup family or Hoplitis adunca who Feeds exclusively on Viper’s Buglos (and is aptly named the “Viper’s Bugloss Mason Bee”).
Honey Bees as Disease Vectors
Research from Ravoet et al (2014) showed that honey bees can transmit diseases (but not mites) to other bee species. The study sampled solitary bees near an apiary that had known occurrences of parasites and diseases, finding solitary bees infected with:
- The Apis mellifera filamentous virus, a weak pathogen which cripples infected bees, making them gather around the hive entrance.
- Bees with severe infections display a milky-white haemolymph (blood) colouring due to the breakdown of body tissue (as opposed to the normal clear, or pale-straw colour).
- The Varroa mite-borne bee “Macula-like Virus”, a pathogen whose impact is not completely understood in honey bees, and is known to be transmitted by the varroa mite.
- This virus is in the same family as the Deformed Wing virus & Sacbrood virus.
- Interestingly, there is no evidence that varroa & its viruses are able to infect the stingless bees of the Tetragonula genus, a species of social bees native to Australia.
- One species, the grey-backed mining bee, was found to be infected with a microsporidium fungus that resembles Nosema thomsoni, a pathogen responsible for Nosema disease, which leads to impaired nutrient absorption in the gut of adult bees, and subsequent “honey bee diarrhoea”.
Can Invasive (or Managed) and Native Species Live Together?
Native species can coexist alongside honey bees if enough food and natural resources are available to reduce the impacts of competition. This can be achieved by increasing the diversity of flowering plants in the urban and agricultural landscapes, providing suitable nesting and foraging spaces for these wild species.
I wager that it is survival of the fittest. Honey bees can compete with native pollinators for floral resources and this would negatively impact species in resource-limited environments. However, such competitive outcomes depend on local ecology and floral availability; it is not true in all landscapes and seasons, and simple examples include bumble bees being able to forager in colder weather than honey bees on account of their superior musculature/self-heating capabilities (Karbassioon et al., 2023).
The Invasive Bumble Bees & Asian Honey Bees in Australia
The Asian honey bee, A. cerana is another competitor to both native pollinator species and Apis mellifera. A. cerana is particularity effective in restricting wild nesting sites, as a single colony may swarm up to six times a year. Currently, their introduction is isolated near the Cairns region and is actively monitored by the the biosecurity personnel to prevent further spread. Go read the scientific name of bees article for further comparisons of the two.
Bumble Bees in Tasmania
Wild colonies of the European bumble bees Bombus terrestiris were accidentally introduced to Tasmania in the early 1990s, and have since spread across the entire island. They have not been established on the Australian mainland… yet.
Like A. cerana, the main issue with bumble bees is competition for foraging with other bees. Bumble bees perform buzz pollination– rapidly vibrating their bodies to release pollen from flowers. This provides them with a competitive advantage over other species in foraging, making them better pollinators of foodcrops like tomatoes and blueberries.
Over time, the ongoing exposure to buzz pollination could lead to adaptions in plants to favour this process, shifting in the plant-pollinator dynamics and disrupting how wild bees and other insects obtain their pollen and nectar. Some solitary species, like the Blue-Banded bee, also perform buzz pollination (Hogendoorn et al., 2007). however their population numbers and specialist foraging behaviour pale in comparison to the bumble bee.
Are Honey Bees an Invasive Species?
This article agrees that honey bees are invasive species in most parts of the world. Such a conclusion is supported by broad examples such as the comparison of native bee lifecycles and behaviours, as well as through more specific examples of other invasive alien species, such as the introduction of the Asian honey bees & bumble bees to Australia.
All that being said, there are many ways to help native bees which are far less intensive than honey bee management.
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