Bumblebees (and bees) collect nectar and pollen.  Pollen is a vital food, used in the various stages of a bumblebee’s life. In Spring, newly emerged queens feed on pollen, then it is used to feed its their sister workers. The workers, in turn, take over the feeding of the colony (the larvae and future queens). If not enough pollen is collected, then the colony will not thrive, which can have significant long term effects.  Bumblebees are already facing many threats (from habitat fragmentation, agrochemicals and disease). The collection of pollen is a demanding process, and bumblebees will forage over a wide area.  They start their pollen collecting activities earlier than many insects as they can warm themselves up by ‘shivering’, that is, rapid muscle contractions which generate heat, warming the insects up ready for flight.  Bumblebees can fly in colder conditions and at higher elevations than many other insects. However, research at North Carolina State University has shown that the North American bumblebee (Bombus impatiens) can overheat when exposed to high temperatures (circa 42oC plus).  So,  if a bee is carrying a significant load of pollen and it is a hot day, its muscles have to work harder and the bee is at risk of overheating. A bumblebee loaded with pollen may be 2oC hotter than an unladen bee; it may be reaching its ‘thermal limit’ - a temperature at which its organs are damaged.  Climate change means that many parts of the world are now experiencing extreme weather events, when temperatures can reach into the forties. [caption id="attachment_39978" align="aligncenter" width="675"] Bumblee leaving foxglove[/caption] Increasing temperatures could affect the foraging activities of bumblebees in a significant way - affecting how much pollen is collected and how much pollination takes place.  If pollen collection is reduced then colony development is affected and so population numbers will be affected.  Bumblebees are key pollinators in natural and agricultural systems, and if their numbers decline there will be ecological and agricultural consequences.  

The decline in many insect populations across the globe is worrying, threatening economies and ecosystems.  A German study in 2017 indicated that the mass of flying insects (in various natural areas) had fallen by some 70%+.  The decline in insect populations has been associated with habitat fragmentation, the spread of agriculture and the use of pesticides, with the neonicotinoids being particularly associated with damage to bee and bumblebee populations. Recent work at the University of Konstanz suggests that when bumblebee colonies are exposed to limited resources of nectar and exposure to the herbicide - glyphosate,  then their colonies may fail.  Bumblebee colonies need a good supply of nectar as a ‘fuel’ in order to maintain a constant brood temperature (of approximately 32oC).  Only at this sort of temperature does the eggs & larvae develop quickly from egg to adult, and the colony grow from a single queen to several hundred bees.  If the temperature is not maintained, then the brood develops slowly or not at all.  The loss of wild flowers (and their nectar) plus the use of the herbicide (in agricultural areas) looks to be a problem for the bumblebees. Just as bumblebees are facing problems, so are honey bees.  The bees have faced infections with a variety of viruses, such as the deformed wing virus.  This virus affects wing development so that the wings are 'stubby' and useless, plus they may be deformities of the abdomen and leg paralysis;  the insect cannot function and dies.  The virus is transmitted by the Varroa mite - a parasite (that also feeds on the bees’ tissues).  The virus was originally identified in Japan in 1980’s and is referred to as DWV-A.  However, a new form of the virus (DWV-B) was identified in the Netherlands in 2001 and it is spreading across Europe, and to other continents.  Sadly, this variant of the virus kills bees faster and is more easily transmitted (according to research at the Martin Luther University).

The woodlands blog has previously reported on the worrying decline in insect numbers, but there has been yet another report detailing significant falls in the populations of (flying) insects.  This survey was run by Buglife and the Kent Wildlife Trust  (KWT) using a smart phone app - “Bugs Matter”. The survey suggest that between 2004 and 2021 the number of flying insects (in Kent) has fallen by some 70%.  This finding is not dissimilar to that carried out in rural Denmark which found an 80% decline in insect numbers between 1997 and 2017. Insects are vital to the functioning of ecosystems.  They help maintain: A healthy environment Contribute to the recycling of organic matter Act as pollinating agents Help control pests Without insects the ‘web of life’ begins to fall apart.  The loss of insects and other forms of wildlife can be helped by: Creating larger areas of natural habitats (many have been lost to roads, agriculture, urban expansion) Creating wildlife corridors to link up similiar habitats / ecosystems throughout the landscape Creating wild flower ‘meadows’ by road sides, verges etc Reducing the use of pesticides and other chemicals which have significant effects on wildlife The Buglife survey makes use of a simple technique to estimate insect abundance - the ‘splatometer’.  This involves counting the number of ‘squashed’ insects on car registration plates.  The Danish survey used a similar method but looked at insects found on car windscreens.   This summer Buglife is hoping that people will again contribute to another survey using the splatometer technique.  The survey will run from June 1st to August 31st.   To contribute to the survey you will need :- The “Bugs matter” app (free) and a smart phone. To create an account to send in your results Clean the car number plate before the start of any journey in your vehicle At the end of your journey, count the number of squashed insects on the number plate (using the splatometer grid - which will be sent to you) and take a photo. This enables Buglife to calculate the ‘splat rate’, that is the number of insects recorded per mile.  NB.  Journeys on wet days are not recorded as rain might wash off any insects from the number plate.   The more journeys and counts that you can carry out the better, and zero counts of squashed insects are just as important as those with an actual number of squashed insects. Note : The app includes a tutorial and some safety advice. It is available for android or apple phones.

We know that insects (especially, bumblebees, bees, hover flies) are the world’s top pollinators, and we also know from many reports that many insect species are in decline.  Crops such as tomatoes, blueberries, peppers, cocoa, coffee, almonds and cherries are dependent on these pollinators.  Climate change, increasing temperatures and extreme weather events are affecting plants and animals across the world, and it seems that social insects, like bumblebees, are particularly impacted. Research with bumblebee colonies (at Stockholm University) has indicated that if the colonies are exposed to higher temperatures (than normal) then the workers in the colonies were smaller.  This decrease in body size could affect their foraging behaviour and the collection of pollen,  which would mean less food brought back to the colony and reduced pollination of plants. Studies in the United States looked at some 20,000 bees  (bumblebees, leafcutter bees, mason bees etc) along the Rocky Mountains, a region which is vulnerable to climate change.  It was found that the larger bees (particularly bumblebees) and those that built nests with combs were affected most by increases in temperature.  On the plus side, smaller (soil nesting) bees fared better.  Bumblebees would seem to have a lower heat tolerance.  The loss of bigger bees, which generally can fly and forage further may again mean reduction in long distance pollination (which promotes outbreeding in plant populations). One reason why hot or hotter weather affects bumblebees is that it influences the nectar that the bumblebees collect.  The balance of the various micro-organisms (bacteria and yeasts) in the nectar changes.  Whilst bumblebees are attracted to nectar with some microbes in it, a small change in temperature can speed up the metabolism / growth of the microbes so that they use up more of the sugar - with the result that it is less palatable / less nutritious for the bees.  Experiments conducted at the University of California have shown that bees did not ‘like’ the nectar rich in microbes, nor a sterile one - with no microbes at all. There seems to be a 'happy medium' in terms of the composition of the nectar. There seems to be a growing consensus that climate change, increasing temperatures and extreme events are pushing bumblebees (in particular) beyond their physiological limits. [caption id="attachment_38081" align="aligncenter" width="650"] Bumblebee visiting foxglove[/caption]

Climate change is affecting all parts of the world, from the melting of the ice caps in Antarctica, to droughts in Australia and California.  On a more local level, we may see changes in our rainfall pattern.  Certainly for many parts of the UK, it has been a very dry start to the Spring, coupled with some very cold nights. Cold and dry weather affects plant growth in significant ways.  Warmth is needed for a plant’s enzymes (catalysts) to work, speeding up reactions and allowing growth.  Similarly, if water is in short supply, growth is stunted; plants do not realise their full ‘potential’. They are smaller overall as is the number and size of flowers that they produce.  Flowers attract visitors by colour, size and scent; or combinations thereof.   Smaller and fewer flowers, in turn, have ‘knock-on effects’ for their pollinators - bees, bumble bees, hoverflies etc. The effects of drought on pollination has been recently investigated by researchers at Ulm University in Germany.  They studied the effect of drought on field mustard (aka Charlock) : Sinapsis arvensis.  This is an annual plant that is to be found in fields, waysides and field margins across Europe.  It has bright yellow flowers, with four petals.  It is visited by many different pollinators (it cannot self-pollinate).   The researchers compared the number of visits by bumblebees (Bombus terrestris) to drought-stressed plants to well-watered ones.  The data showed that as the number and size of the flowers decreased so did the number of pollinator visits.  [caption id="attachment_21589" align="aligncenter" width="600"] Bumblebees also favour the teasels[/caption] The ‘attractiveness’ of the plants / flowers to pollinators was reduced, and it is possible that the smaller flowers were more difficult for relatively large pollinators (like the bumblebees) to ‘deal with’.  If pollen movement is reduced, then fewer fruits / seeds will be set and (insect pollinated) plant populations could decline.  The effects of reduced rainfall and water stress need to be considered alongside the declining number of pollinators.  The reduction in pollen movement has lead some to speculate that it might lead to a selective pressure for self-pollination / self-fertilisation, with plants dispensing with the need for visiting insects.  Other Woodlands blogs have reported on the falling numbers of insects / pollinators. Featured image : garlic mustard.

The science journal Nature has published the results of another insect survey, specifically of pollinating insects.   The UK pollinator monitoring scheme looked at some 353 species of bees, bumblebees and hoverflies.  The survey analysed 700,000+ sightings of pollinating insects over thirty years or more (1980 to 2013).  The survey yielded information about the changes in the range of these different pollinators - that is the different parts of the countryside that these insects were found in.  The survey did not attempt to determine actual numbers of bees etc in an area.   There were “winners and losers’ in the survey but the overall picture was somewhat depressing. Read more...