Readers’ wildlife photos

Athayde Tonhasca Júnior has returned with another text+photos story, this time about bees. His text is indented, and you can enlarge his photos by clicking on them:

Dubious helpers

by Athayde Tonhasca Júnior

Eikyu Matsuyama, an apple grower from Aomori (the northernmost prefecture on Japan’s main island), noticed mason bees building nests inside holes in utility poles and wooden walls near his orchard. As this species of bee (Osmia cornifrons) was a keen visitor of apple flowers, Mr Matsuyama pondered whether he could attract more bees to his orchard by supplying them with pieces of reed as extra nesting sites. This was the 1930s, when apple pollination in Japan was mostly done by hand – a labour-intensive, costly operation. Sometimes the military was recruited to help pollinate apple flowers during the two-week blooming period. Aomori was—and still is—the leading apple-producing region in Japan, accounting for nearly half of the country’s harvest. So any extra help from bees would be much appreciated by the growers.

An apple blossom in the Aomori prefecture with Mount Iwaki in the background © 岩浪陸, Wikimedia Commons:

Mr. Matsuyama’s experiment was a huge success; soon the numbers of mame-ko bachi (the bee’s Japanese name) expanded dramatically, with a corresponding improvement in apple production. Other growers quickly followed suit, and Mr Matsuyama went on to lecture about mason bees at several Japanese universities (Mader et al., 2010).

In the 1960s, apple growers in the Aomori Prefecture began to use the Western or European honey bee (Apis mellifera) as an alternative pollinator, while researchers improved propagation and management methods for the mame-ko bachi, named the Japanese hornfaced bee in English-speaking countries. Nowadays Aomori growers of apple, pears, peaches and plums are likely to use commercially available Japanese hornfaced bees instead of honey bees because the former are considerably more efficient. The hornfaced bee visits about 15 flowers per minute (4050/day) and carries ~267,000 grains of pollen on its scopa (pollen-carrying bristles), while the honey bee visits about 6 flowers per minute (720/day) and transports ~100,000 grains of pollen. Equally important, the Japanese hornfaced bee, like other species in the group, is a bit sloppy in transferring pollen to her nest; about 10% of it remains on her body (Matsumoto et al., 2009). This residual pollen, viable for up to 12 days, has a good chance of ending up on a receptive apple flower and pollinating it.

A Japanese hornfaced bee leaving its nest © Beatriz Moisset, Wikimedia Commons:

The Aomori Prefecture’s achievements with the Japanese hornfaced bee didn’t go unnoticed. In the 1960s, the American Agricultural Research Service (Department of Agriculture) introduced this species to the United States to improve pollination of fruit crops such as apple and blueberry. Since then, the Japanese hornfaced bee has spread through the eastern and mid-west states. And in 2002, another Asian mason bee was found doing its bit for pollination in America: the taurus mason bee (Osmia taurus). Nobody knows how or when this species entered the country: it probably was introduced accidentally at the time of Japanese hornfaced bee importation. These two species look alike superficially, so an unintentional introduction is plausible.

Female Japanese hornfaced bee (L) © Chelsey Ritner, and taurus mason bee © Chelsey Ritner, Exotic Bee ID:

Bees are overwhelmingly valued by the public, so the addition of two new species to the local fauna, even if inadvertently in one case, must be a good thing. Indeed, introduced bees may increase the local pollinating force. But these newcomers may also be harmful to native species, most likely because of competition. This happens when two or more species need a common resource – food, water, a place to live – that is in short supply. In the case of bees, competition for food (nectar and pollen) or nesting sites are the most likely problems.

Assessing competition: Diet analyses from carbon (δ13C) and nitrogen (δ15N) isotopes indicate a considerable overlap of food taken by the invasive American mink (Neovison vison) and the native, critically endangered European mink (Mustela lutreola) in Spain; these results suggest a substantial competitive pressure imposed by the American mink on the European mink © García et al., 2020:

The Japanese hornfaced bee and the taurus mason bee found America to be very much to their liking; their populations have increased dramatically since their arrival – reaching growth rates of three to five times per year. This is not good news for the blue orchard bee (Osmia lignaria), a reliable orchard pollinator and a native species that has much in common with the intruders: they all emerge more or less at the same time, take pollen from similar plants, and have similar nesting habits. This overlapping of resource needs inevitably raises the possibility that the blue orchard bee would get the short end of the stick in these species interactions.

A female blue orchard bee © Chelsey Ritner, Exotic Bee ID:

LeCroy et al. (2020) set out to assess just that. They examined trap catches of the two introduced bees, the blue orchard bee and five other native mason bees from four eastern American states from 2003 to 2017 (5,901 records). Their results: all native species declined between 76 and 91% since 2003, while the exotic species were doing just fine; populations of Japanese hornfaced bee were stable, while taurus mason bee numbers increased by 800% since 2003. This latecomer represented 22% of captures in the years 2003–2009, raising to over 43% of all captures from 2010 to 2017, making it the most common mason bee species in the region.

We don’t know the consequences of such dramatic population shifts. The two exotic species may take up the pollination work from the bees they displaced, although a complete, seamless substitution is improbable: the dynamics between plants and pollinators are bound to become different, although we can’t say how. Native and alien bees may adapt and co-exist; in the worst case scenario, native species may become threatened.

The not so sweet side of honey bees

Our honey bee—the European honey bee—is the world’s most important crop pollinator. Thanks to an ancient history of domestication, farmers can count on a work force of up to 60,000 bees per hive, which can be managed and moved from place to place to pollinate flowers of many shapes and sizes. Unlike the vast majority of bee species, honey bees live in highly social, organised colonies that last for many years. They fly long distances in search of food, and are quite effective in collecting pollen and nectar. Depending on the floral abundance, the season and density of colonies in the area, a single hive may consume 10 to 60 kg of pollen and 55 to 400 kg of nectar per year.

A honey bee displaying its skills in pollen gathering. ©Phonon.b, Wikimedia Commons:

Honey bees are efficient pollinators that have been introduced to many parts of the world to improve the yield and quality of crops. But their presence can be bad news for other pollinating species.

Bees can be infected by several viruses and other pathogens such as microsporidia (fungus-like single cell parasites). Every time a bee visits a flower, it risks being contaminated by a pathogen left by a prior visitor. The transmission can go from honey bees to other bees – and even flies – or the other way around, but honey bees are the most likely source: they are known hosts of many diseases and pathogens. Besides, large numbers and crowded communal living arrangements are not the best conditions for keeping diseases at bay, as we humans have recently and painfully learned. Indeed, many studies have confirmed pathogen transmission from honey bees to bumble bees and solitary bees. Infections in the opposite direction have been less documented.

Honey bees are good at what they do, and the figures prove it: the amount of nectar and pollen collected by a large apiary is sufficient to support over 100 bumble bee colonies; during high season (June–August), a 40-hive apiary collects as much pollen as four million wild bees. It is difficult to measure whether this level of industriousness has any effect on wild bees: these are highly mobile creatures that cover a huge area while foraging, so they are not easy subjects for experiments. Despite this, we have a great deal of circumstantial evidence to suggest there is not enough food to go around when honey bees are in the neighbourhood, especially in small or isolated areas. That helps explain why native bees have become endangered after honey bees were introduced in New Caledonia (south Pacific), New Zealand, Japan and Tasmania. Or Tenerife.

Every spring, Tenerife beekeepers temporarily move up to 2,700 beehives to Teide National Park to take advantage of the seasonal bloom. Valido et al. (2019) saw this cyclical invasion as a great opportunity to evaluate the impact of honey bees. So for three years, they monitored the area before and after beehives were brought in. They observed a clear reduction in the number of pollinator species and diversity of flower visitors when honey bees were present.

Teide National Park, a natural habitat altered by honey bees. © Mike Peel, Wikimedia Commons:

Competition is not a problem for islands alone; it is likely to happen whenever flowers are scarce, such as at the beginning or end of bees’ foraging period, or during unusually cold or dry years. Studies from different countries revealed that wild bees switched to less abundant and less rewarding plant species when honey bees were present. Or they became scarcer, gained less weight, and produced fewer and smaller offspring. In other instances, wild bee numbers increased once honey bee hives were removed. In 14 countries in the Mediterranean basin, honey bees have become more abundant over the years and are gradually replacing wild bees as visitors of wild and cultivated plants. We don’t know the consequences for the 3,300 or so bee species in the region, but it does not bode well.

The importance of beekeeping and honey bee pollination is unquestionable, but our wild bee species are important too, as pollinators and components of our biodiversity. Despite the recent panicked reports in the media about the imminent demise of the honey bee and supposedly mankind, beekeeping around the world has increased by ∼45% during the last 50 years (numbers from America and North Europe are exceptions). Meanwhile, many wild bees have declined for many reasons, including honey bees.

From adorable fuzzballs to menacing rascals

In 2005, the buff-tailed bumble bee (Bombus terrestris) came out first in a poll to elect UK’s favourite insect. This wasn’t surprising: the buff-tailed is one of the most common bumble bees in the country. It is relatively large, easily recognisable and one the first bees to be seen in spring. So you could say this species is an ambassador for all those lovable and cherished bees: ‘surely, everyone knows the great furry bumble bee, that gentle giant of the blossoms, that somehow awkward, slow, bumbling bear of a bee’ (Brian L. Griffin). Beatrix Potter probably had the buff-tailed bumble bee in mind when creating Babbity Bumble.

Beatrix Potter’s Babbity Bumble, from The Tale of Mrs Tittlemouse, 1910. Wikimedia Commons:

This bee is an excellent pollinator of a variety of crops and wildflowers, especially because of its ability to buzz-pollinate and extract pollen that is firmly packed into the flowers of plants such as tomatoes, blueberries and aubergines. The buff-tailed is resourceful and adaptable: it forages over long distances, is resilient to bad weather and not picky about habitats. These characteristics help explain why their numbers remain strong and their populations seem to be expanding, while some bumble bee species have declined.

A buff-tailed bumble bee © US Geological Survey Bee Inventory and Monitoring Lab:

In the 1980s, Belgian and Dutch companies developed techniques to rear bumble bee colonies on large scales, and an industry worth millions of pounds was born. Mass-produced bumble bees, mostly the buff-tailed, replaced labour-intensive mechanical methods of pollination, and today virtually every supermarket tomato in Europe was pollinated by a captive-bred bumble bee. Commercial bumble bees made their way to farmers in the Americas, Japan, Australia and other countries to pollinate greenhouse crops such as tomatoes and peppers. And then trouble began.

The qualities that make the buff-tailed so well suited in its native habitat are the same that make it an invasive species elsewhere. When imported buff-tailed bees escape from greenhouses – and insects always escape – they become established and outperform native pollinators in the search for nest sites and food. They also carry novel diseases that are transmitted to the local fauna.

The impact of these man-made invasions has been demonstrated nowhere better than in South America. The buff-tailed was introduced to Chile in 1998, and thanks to a dispersal rate of up to 200 km per year, it rapidly invaded Argentina, spreading out through most of the country. It is expected soon to cross into Uruguay and Brazil.

Wherever the buff-tail arrived, the native Patagonian bumble bee (Bombus dahlbomii) declined sharply or disappeared altogether, whether because of competition or infection by a parasitic protozoan brought in by the buff-tailed. Nobody knows for sure. As a result, the Patagonian bumble bee, the world’s largest, in now on the list of globally threatened species. The ecological damage caused by the buff-tailed goes further: this interloper pollinates and possibly helps the spread of invasive plant species, and reduces the volume of nectar available to hummingbirds.

A Patagonian bumble bee © US Geological Survey Bee Inventory and Monitoring Lab:

Similar scenarios have played out in the USA and Japan, so today many countries prohibit the importation of buff-tailed and other exotic bumble bees. Mass-produced bumble bees have an undeniable economical value, but they are also an emerging threat to their wild counterparts.

The yellow star-thistle (Centaurea solstitialis), a Mediterranean native, has been spreading through 41 of the 48 contiguous American states thanks in part to pollination by the non-native European honey bee © J.smith, Wikimedia Commons:

Many people would not be happy to watch their native bees pushed aside by intruders, no matter how benign or useful they may be. But there’s little they can do about it. Once alien species become established, it’s extremely difficult and expensive to get rid of them. The Japanese hornfaced bee, taurus mason bee, buff-tailed bumble bee and honey bee are Dr Jekyll and Mr Hyde tales of the unintended consequences of species introductions; you are never sure how the story will end.

Pandora trying unsuccessfully to make amends for releasing humanity’s evils. Art by Frederick S. Church (1842–1924), Wikimedia Commons: