Why are bumblebees declining?
Bumblebees are protected animals in the Czech Republic – all species of bumblebee (Bombus sp.) are classified as endangered animals by Decree 395/1992 Coll. (Annex III).
Why are bumblebees declining in our country?
There is not just one cause, there are many. They influence each other and often the effect can be potentiated.
The main factors of bumblebee decline in the Czech Republic:
1) Intensive agriculture with a predominance of monocultures on large areas
2) Inappropriate use of chemicals in agriculture and gardens
3) Excessive soil eutrophication
4) Too intensive beekeeping in disproportionate proportion to the food supply
other discussed factors that have not yet been fully confirmed by studies and research
6) Insect traps – for example, poorly made bark beetle traps, the use of yellow boards with glue to non-selectively trap insects
7) Road transport
9) Loss of host-parasite balance
10) Import of subspecies of the bumblebee for the purpose of pollination of agricultural production
The highlighted points are discussed in more detail below, clicking on a point will take you directly to the desired topic.
Excerpt from the Red List of Threatened Species of the Czech Republic, 2017
Intensive agriculture with a predominance of monocultures on large areas
First of all, it is a change in land management - the transition from a mosaic landscape to the management of large areas and monocultures is one of the main causes of the decline of bumblebees, described since the 1950s. Almost nothing has changed for the better in the Czech Republic since then. The current Minister of Agriculture has announced an adjustment of the subsidy policy for farmers farming large fields, see the media report here . However, we still have to wait a while for the practical impacts. If it concerns the disruption of long, wide fields only with, for example, a narrow 2-3m strip of a temporary crop (e.g., svazenka), we probably cannot expect much of an effect. With the intensification of agriculture for decades, bumblebees have been losing both the possibility of nesting and, above all, their food sources, because monoculture provides (if at all) a food source only for a very limited time. The decrease in food supply throughout life is considered the most significant factor in the decline of bumblebees in economically intensively used landscapes. That it can be done differently and just as effectively is shown by a comparison with our southern neighbor. We deliberately chose an area that has the same favorable growing conditions in both the Czech Republic and Austria. Both states are EU member states with equal conditions for subsidy titles…
An example of different farming in the Czech Republic (monocultures) and Austria (smaller areas with species variability). The area around Mikulov and Nový Přerov was selected, where the growing conditions are the same on both sides of the border.
Inappropriate chemical use in agriculture and gardening
It seems that bumblebees are more resistant to a number of insecticides than bees. Bumblebees of the Bombus terrestris species showed high resistance to most preparations in a vial test, with the exception of a substance based on chlorpyrifos-methyl, for which high toxicity with high mortality was recorded even at low doses . These are commercial preparations Reldan 22, Daskor, Spring set for apple trees. The preparation Daskor is primarily intended for agricultural production for the treatment of potatoes, oilseed rape, mustard, poppy, cereals (wheat and rye). Reldan 22 is also used in fruit and ornamental nurseries. This preparation is also intended for gardeners for the treatment of cruciferous vegetables, cabbage, cabbage, cauliflower, kohlrabi, apple trees, sour cherries, oilseed rape, chrysanthemums, and strawberries. Other insecticides dangerous were poisons with the active ingredient spinosad (Spintor with wide use for treating the vast majority of ornamental and fruit trees, vegetables, strawberries, potatoes and ornamental plants) and indoxacarb (Avaunt 15EC preparation for treating rapeseed, Explicit plus (cucumbers, tomatoes, peppers and other vegetables, pome crops, corn), Sindoxa (rapeseed, vines), Steward (vegetables, corn, pome crops, grasslands, fruit and ornamental nurseries, public accessible areas) Stocker (vegetables, corn, pome crops)) and in the case of mixes it was a combination of the substances thiram, difenoconazole, acetamiprid (i.e. Thiram Granuflo, Score 250 EC, Mospilan 20 SP).
Although many other products do not directly kill bumblebees, their negative impact on colony development, the number of born sexual individuals and their relative representation in the nest cannot be ruled out. Research in this area is still ongoing and is at the stage of partial studies.
Soil eutrophication
Plants rely primarily on biological processes to obtain nutrients for successful growth. As human activity has increased the nutrient content in precipitation, natural ecosystems are gradually becoming eutrophic – forests and meadows are becoming more nutritious. This, among other things, leads to a decrease in their overall biodiversity. Agriculture has long ceased to rely solely on organic fertilizers (manure, fallow farming). The massive application of mineral fertilizers (nitrogen, phosphorus, potassium) increased agricultural yields during the 20th century. The reckless supply of nutrients causes eutrophication and acidification of soils and surface waters, where these fertilizers are washed away during rains.
The maps show the concentrations of the main eutrophic parameters (nitrogen and phosphorus) in surface waters in our territory. It is clear that, especially in the agricultural areas of South Moravia and the Elbe region, the concentrations are above the legislative limits for drinking water (50 mg NO3/l and 0.15 mg P/l) and above the limits for environmental quality (24 mg NO3/l and 0.05 mg P/l). (taken from Klimaticzazmena.cz)
Nitrate concentration in surface waters.
source – Climate change.cz
Concentration of total phosphorus in surface waters
source Climate change.cz
Climate change
The effects of global warming are not yet so noticeable in the Czech Republic. However, the average increase in temperatures can change the timing of life cycles and shift the distribution boundaries of individual species. The bumblebee is a representative of insects adapted to a colder climate. Unlike many other pollinators, it has the ability to be active even in cold or bad weather.
To what extent climate affects bumblebees, this was the subject of a study published in Science in 2015 (Kerr et al., Science 349, 177–180, 2015). The authors tried to find out how bumblebees in Europe and North America are affected by climate. They used more than 400,000 data on the distribution of 67 European and North American bumblebee species between 1901 and 2010 for the analyses. The data show that in both Europe and North America, bumblebees are declining strongly, mainly in the southern parts of their range. Since 1974, the loss of their historical territory has reached up to 300 km from south to north. This means that bumblebees are rapidly declining mainly in the warmest parts of their range. This change is very consistent with phylogeny - related bumblebee species usually show a similar trend in range loss. Compared to other insect groups, bumblebees have hardly spread further north. This is true on both continents. Species that live more in southern regions occupy higher altitudes. Since 1974, they have risen by an average of 300 m.
P. Rasmont and colleagues in the study Climatic risk and distribution atlas of European bumblebees. ( BioRisk 10, 1–236, 2015. ) evaluated the current range of bumblebees and used climate models to estimate their distribution in the years 2050–2100. The prospects are not optimistic. Of the 80 European species, only 3 species would benefit from climate change models.
In connection with climate change, bumblebees in our country are currently threatened by the accompanying extreme weather fluctuations. Sudden intense rainfall accompanied by floods leads to the destruction of many nests.
Other factors are being considered, but convincing data supported by high-quality studies is still lacking:
1.) Warm autumns and mild winters can disrupt the life cycle and lead to increased mortality of young mothers.
2.) Spring weather fluctuations. Bumblebee queens don't mind gradual temperature changes, but sudden changes between summer days and frosty days exhaust them, and many nests can disappear in the early stages.
3.) Hot and dry summers or, conversely, long rainy periods result in a decrease in food resources, which is further exacerbated by the overall change in the landscape. It can be assumed that nests weakened in this way will not produce a sufficient number of queens.
The other factors mentioned are at the level of assumptions and hypotheses. We do not have enough convincing evidence/studies for them in the Czech Republic.
However, we also include them because we would welcome the help of experts in verifying them (or pointing to published work that addresses the risks mentioned).
Inbreeding
The loss of natural nesting areas in monoculture landscapes results in a reduction in the living space for bumblebees and the places where bumblebees have the opportunity to establish and maintain their offspring. In a smaller area, together with the decrease in the total population, inbreeding occurs more frequently than in a mosaic-managed landscape. Inbreeding results in a change in the composition of individual representatives of the bumblebee colony, as proven by experiments in laboratory breeding. Half of the eggs laid by the queen hatch into diploid drones instead of females: workers or queens. As a result, the nest is weakened, dies prematurely and does not produce a sufficient number of new queens.
Loss of balance in the parasite-host relationship
Bumblebees have a number of pests and although clear scientific evidence in this area is lacking, it can be assumed that the disruption of natural diversity also affects this area. People often contribute unknowingly through their conservation activities. Uncleaned birdhouses become a safe wintering ground for the feared bumblebee pest – the parasitic wasp (Aphomia sociella). Partial works point to the possible negative impact of insect hotels and the possibility of expansive spread of parasites from them. The very usefulness of houses for solitary bees in this context is contradicted by the latest work from Germany – read here. We also discuss, for example, Melittobia acasta, which primarily attacks the nest cavities of solitary bees but also bumblebee hives. You can find a work warning about the possible risks of the spread of wasps from such houses here.
Import of subspecies of the bumblebee for the purpose of pollination of agricultural production
Introduction of non-native subspecies, especially of the bumblebee (Bombus terrestris terrestris and Bombus terrestris dalmatinus) for the purpose of pollinating greenhouses and gardens.
Example of importing bumblebees from large-scale farms intended for greenhouse pollination
The nests of these bumblebees tend to be very strong, they can produce many queens that are larger and stronger than those from our natural nests, which gives them a competitive advantage. The native population, otherwise best adapted to our conditions, can therefore come under selection pressure and may ultimately be replaced by these non-native subspecies.
In connection with the import of these breeds from abroad, the risk of introducing diseases or parasites cannot be completely ruled out.
Bumblebee breeders
Bumblebee breeders can also contribute in a rather negative way. Inexpert collection of searching queens from the wild, escalating to hunting, can ultimately reduce the population in a location.
Likewise, settling in hives that are completely unsuitable in terms of construction, or leaving hives without further care, results in the destruction of the bumblebee colony established in this way before it has time to produce a sufficient number of new sexual individuals for the next year.
Such a breeder often becomes a breeder of bumblebee parasites, which also threaten natural nests in the area.
In the afternoon queue are also breeders who simply want to have bumblebees at any cost. The only option to buy a ground bumblebee with demonstrably Czech origin is the Czech Bumblebee Research Institute of Forage Research, Ltd., where nests are usually reserved within a few hours of the offer being launched, and so some interested in breeding prefer to order nests from a seller importing them from abroad, thereby threatening natural diversity, as we mentioned above. We strongly warn against this purchase, because sellers with the hope of profit calculate with people's ignorance and often pass off imports as "help" for bumblebees. Until the final assessment is made by the Ministry of the Environment and the Ministry of Agriculture, it is necessary to consider the release or escape of these bumblebees into the wild as a serious risk and a factor in the threat to the original species of bumblebees in our nature.
In addition to the factors we mentioned, you can also read why the Czech bumblebee here.
A sample of a nest being sold to bumblebee breeders. These are bumblebees intended for pollination of greenhouses.
A totally eaten nest of a keeper who neglected to protect the entrance.
Aphomia sociella caterpillars had pupated behind a plastic hive inserted into a wooden body.
Many people (like us 🙂 ) are addicted to bumblebees, Ondra even made a diagnosis for it (it is not yet internationally recognized in the ICD) and has a number of hives in his garden, and depending on the tolerance of the closest surroundings, even dozens of them. Here too, it is necessary to emphasize the possible negative risks of such breeding:
- transmission of parasites or diseases from hive to hive due to loss of distance barrier
- possible competition for food resources if they are scarce
If a breeder of a large number of bumblebees becomes fond of or specializes in only one species, which is stronger and more competitive than other species (e.g. ground bumblebee and rock bumblebee), then his breeding may ultimately be rather harmful because it is necessary to consider:
- risks of inbreeding and competition between mothers in the spring for nesting space in the area (many young mothers like to return to the original nest sites in the spring and look for suitable conditions for establishing a nest there)
- possible selective pressure mentioned in the point above also on other natural bumblebee populations in the area
If you are interested in breeding and respect the principle of First Do No Harm, please read our treatise here
how to choose the right hive here
Author of the text KK
In the video below you can see what it looks like for a breeder who has his rock bumblebee sisters returning "home"