You might have heard that bee numbers are declining …
In this guide, we outline the the causes of bee population loss and decline when it happens.
Summary – Causes Of Bee Population Loss & Decline
There’s various potential causes of bee population loss and decline – we’ve listed an array of potential causes below
Each individual species of bee in each geographic location needs to be studied to confirm the exact causes that affect them
Sometimes the tools available to local agencies to study bee population decline are not as good as they could be, and can be deficient in some ways
Firstly, Are Bee Population Numbers Actually Declining?
Yes, and no.
Causes Of Bee Population Loss & Decline
It really depends on the region and bee species we are talking about when talking about causes of bee population loss and decline.
For example, the threats facing the Hawaiian yellow faced bees might be different threats facing US honey bees.
Causes Of Hawaiian Yellow Faced Bee Population Loss & Decline
[Hawaiian Yellow Face bee populations face] a wide variety of threats, including habitat destruction because of urbanization or non-native animals, the introduction of nonnative plant species, wildfires, nonnative predators and natural events such as hurricanes, tsunamis and drought.
Causes Of US Honey Bee Population Loss & Decline
US honey bee population numbers temporarily dipped for a few years during the Colony Collapse Disorder trend (for roughly 3-5 years, with the first signs appearing in 2006 in California).
But, since then they have been increasing, and have been steady overall throughout history.
There is no one single factor that causes bee numbers to drop (when they do), but rather a combination of factors (sierraclub.org).
In general, the threats and factors that cause US Honey Bee population numbers to drop when they do are thought to be:
Varrora mites that feast on bees, and the viruses these mites carry … they bring roughly a dozen different diseases into beehives, and the widely prevalent gut fungus, Nosema ceranae (acsh.org). They also bring a virus that deforms bees’ wings (sierraclub.org)
Poor nutrition in the bees’ diet … they don’t eat enough of a variety of nutritious food sources. They tend to get nutrition from one crop such as almonds which is farmed in a monoculture, and sugar water or corn syrup that beekeepers feed them) (acsh.org).
They don’t get a variety of pollen that stimulates resistance to disease (sierraclub.org).
The end result is that bees are weakened, and more susceptible to illness, disease and death from the other factors and causes.
Pesticides … synthetic insecticides called neonicotinoids used to spray crop seeds – bees come into contact with these chemicals during pollination and carry it back to the hive. These types of pesticides have sometimes shown to short-circuit bees’ memory and navigation (sierraclub.org)
Insecticides used to kill varrora mites (also usually synthetic)
Winter causing bee numbers to drop naturally compared to summer numbers
Colony collapse disorder (a short multi year period where US honey bee numbers decreased due to various factors)
Habitat loss of lower meadows because of urban development
Inexperienced amateur beekeepers having a higher bee loss rate than bigger or more professional beekeepers with more experience and resources
Acarina mites and hive beetles
Bee diseases such as foulbrood and chalkbrood (which are made higher risk by bees having a poor diet)
Climate change and a changing global average temperature (although this is more a ‘maybe cause than a definite cause) – changing temperatures can push bees’ physiological limits, change hive behavior, can change their eating and feeding patterns, and can force them to go find new habitats where it’s more mild in temperature
sierraclub.org describes the temporary honey bee decline this way:
It’s likely that it’s [the loss of bees] not GMOs, cellphones, ultraviolet lights, electromagnetic radiation
It more likely to be a combination of factors that include parasites, pathogens, pesticides, poor nutrition, and habitat loss
beeinformed.org describes a 44% decline in 2015/16 as:
… many factors are contributing to colony losses. A clear culprit is the varroa mite, a lethal parasite that can easily spread between colonies.
Pesticides and malnutrition caused by changing land use patterns are also likely taking a toll, especially among commercial beekeepers
Varroa is a particularly challenging problem among backyard beekeepers (defined as those who manage fewer than 50 colonies).
In regards to some people claiming pesticides are the main cause of honey bee deaths, agdaily.com writes this:
… despite over a decade of study, it’s still yet to be proven that they’re [pesticides] playing a significant role in honeybee deaths
beelab.umn.edu express how important bee health and nutrition is to fighting off other causes of bee sickness and death:
… pollen and nectar [is] collected from flowering plants [and contains] nutrients necessary for growth and survival. Honey bees with access to better and more complete nutrition exhibit improved immune system function and behavioral defenses for fighting off effects of pathogens and pesticides
Bee colonies are chronically exposed to parasitic mites, viruses, diseases, miticides, pesticides, and poor nutrition, which weaken and make innate defenses insufficient at overcoming these combined stressors
Colonies that are chronically weakened can be even more susceptible to infections and levels of pesticide exposure that might otherwise be innocuous, further promoting a downward spiral of health.
Sick and weakened bees diminish the colony’s resiliency, ultimately leading to a breakdown in the social structure, production, efficiency, immunity, and reproduction of the colony, and eventual or sudden colony death
beelab.umn.edu also express how it can be difficult to pin point what the main causes of bee decline might be in a particular area over a multi year period:
… mechanisms for reporting colony losses and identifying the source of contamination are deficient and variable based on state and local government agencies