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One in four wild bee species worldwide 'haven't been seen since the 1990s'

A quarter of known bee species in the wild haven't appeared in public records since the 1990s, a concerning new study reveals. 

Argentinian researchers used a publicly available database on specimen collections and observations, complemented by citizen-science efforts. 

Despite a large increase in the number of records available, 25 per cent fewer species were reported between 2006 and 2015 than before the 1990s, they found.

While this could indicate that these species have become too rare to be found in their natural habitats, many, if not all, may be extinct. 

Bees are affected by climate change, pesticides and pathogens, low genetic diversity and habitat loss and fragmentation from intensive farming. 

Wild bee pollination is fundamental to the reproduction of thousands of wild plant species and is key to securing yields in about 85 per cent of our food crops.   

This photo shows a giant Patagonian bumblebee (Bombus dahlbomii). Four decades ago, these bees were abundant in Chile and Argentina, but now they have become an uncommon sight

'Something is happening to the bees, and something needs to be done,' said study author Eduardo Zattara at CONICET-Universidad Nacional del Comahue in Argentina.

'With citizen science and the ability to share data, records are going up exponentially, but the number of species reported in these records is going down. 

'It's not a bee cataclysm yet, but what we can say is that wild bees are not exactly thriving.' 

While there are many studies about declining bee populations, these are usually at local, regional, and country levels on different continents or focused on a specific type of bee.  

Researchers were interested in identifying more general, global trends in bee diversity. 

Bee species in the records were taken from multiple families, including apidae, of which bumblebees, honey bees, stingless bees and carpenter bees are types, among many others. 

Other bee families include megachilidae (which includes leafcutter bees) halictidae (known as sweat bees because they're often attracted to perspiration), andrenidae (commonly known as mining bees) and the rare melittidae family.  

Image shows number of species per year in GBIF records from 1946 to 2015, for six different bee families - apidae, megachilidae, halictidae, andrenidae and melittidae. Other than melittidae (pink), they're separated into short-tongued bees (red) and long-tonged bees (orange). The 1990s mark the start of a decline in sightings for several of the families 

BEES AND PESTICIDES 

Declines in recent months to honey bee numbers and health caused global concern due to the insects' critical role as a major pollinator. 

Bee health has been closely watched in recent years as nutritional sources available to honey bees have declined and contamination from pesticides has increased.  

Combined exposure to pesticide and poor nutrition decreased bee health. 

Bees use sugar to fuel flights and work inside the nest, but pesticides decrease their hemolymph ('bee blood') sugar levels and therefore cut their energy stores. 

When pesticides are combined with limited food supplies, bees lack the energy to function, causing survival rates to plummet.

'Figuring out which species are living where and how each population is doing using complex aggregated datasets can be very messy,' said Zattara. 

'We wanted to ask a simpler question – what species have been recorded, anywhere in the world, in a given period?'

Researchers looked at the Global Biodiversity Information Facility (GBIF), an international network of databases, which contains over three centuries' worth of records from museums, universities, and private citizens.

GBIF accounts for more than 20,000 known bee species from around the world.

In addition to finding that a quarter of total bee species are no longer being recorded, researchers observed that this decline is not evenly distributed among bee families. 

Records of halictid bees – the second most common family – have declined by 17 per cent since the 1990s. 

Those for melittidae – a small and much rarer family – have gone down by as much as 41 per cent. 

The team highlighted how species such as the giant Patagonian bumblebee (Bombus dahlbomii), which was abundant in Chile and Argentina four decades ago, are `now an uncommon sight. 

A booming international bee trade has involved the co-introduction of bee pathogens, which has caused the decline for the giant Patagonian bumblebee and other species. 

This photo shows a plasterer bee (Cadeguala albopilosa), one of thousands of species of wild bee that are fundamental for reproduction of wild plants and crops.

Researchers also revealed that an increasing fraction of the total global bee records is composed of the western honey bee (Apis mellifera) – the most common honey bee in the world. 

Increasing dominance by one or a few species can be observed at the regional scale, like the case of the western honeybee in the Mediterranean. 

Despite this, loss of other bee species is a blow to science.  

'It's important to remember that "bee" doesn't just mean honeybees, even though honeybees are the most cultivated species,' said Zattara. 

'Our society's footprint impacts wild bees as well, which provide ecosystem services we depend on.'

This photo shows a leafcutter bee (Megachile sp.). Leafcutting bees are important native pollinators of North America

An introduced honey bee and a smaller native sweat bee (Ruizanthedella mutabilis) share a flower in a Patagonia forest

While this study, published in the journal One Earth, provides a close look at the global status of bee diversity, it is too general an analysis to make any certain claims about the current status of individual species.

'It's not really about how certain the numbers are here. It's more about the trend,' said Zattara. 

'It's about confirming what's been shown to happen locally is going on globally, and also about the fact that much better certainty will be achieved as more data are shared with public databases.'

However, this type of certainty may not come until it is too late to reverse the decline – or may not be possible at all. 

'We cannot wait until we have absolute certainty because we rarely get there in natural sciences,' said Zattara. 

'The next step is prodding policymakers into action while we still have time. The bees cannot wait.'          

Earlier this month, researchers revealed wild bees are under greater threat from climate change than they are from destruction of habitats around the world.

Experts from Penn State University studied 14 years of data from wild bee populations in over 1,000 locations in Maryland, Delaware and Washington DC.

They found that warm winters and long hot summers are reducing the abundance and diversity of plants and flowers, putting ecosystems at risk and making it harder for wild bees to survive. 

Lead author Professor Christina Grozinger said the most critical factor influencing wild bees was the weather – particularly changes to temperature and rainfall. 

Last year, another team said bumblebees are at risk of becoming extinct due to higher global temperatures and 'climate chaos'.

Bumblebees are agricultural pollinators, meaning they carry pollen that lead to the spread and germination of human-consumed crops like tomato, squash and berries.

But they can't take the heat of rising global temperatures and are now disappearing at rates 'consistent with a mass extinction'. 

The public can help by maintaining habitats that offer shelter and let bumble bees get out of the heat – like trees, shrubs or slopes. 

DECLINING BEE POPULATIONS

Declines in recent months to honey bee numbers and health caused global concern due to the insects' critical role as a major pollinator.

Bee health has been closely watched in recent years as nutritional sources available to honey bees have declined and contamination from pesticides has increased.

In animal model studies, the researchers found that combined exposure to pesticide and poor nutrition decreased bee health.

Bees use sugar to fuel flights and work inside the nest, but pesticides decrease their hemolymph ('bee blood') sugar levels and therefore cut their energy stores.

When pesticides are combined with limited food supplies, bees lack the energy to function, causing survival rates to plummet.

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