Today we have another photo-and-text essay from Athayde Tonhasca Júnior, featuring another introduced insect from Japan. Athayde’s captions are indented, and you can enlarge his photos by clicking on them.
AND. . .special kudos for Athayde, for he noted this:
If I’m correct, this will be my 100th contribution to WEIT. As we all make a fuss about 100 (is it because it marks the boiling point of water?), I thought it would be worth mentioning it.
That’s a lot of education he’s given us over the years, so thank you, Athayde!
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Menacing tenants
In an apple orchard somewhere in the American state of Pennsylvania, an adult Japanese horn-faced bee (Osmia cornifrons) has just emerged from its nest and makes its way into the big wide world. The apple grower has high hopes for that bee; in fact, he bought many of them when they were still inside their cocoons. The Japanese horn-faced bee was introduced from Japan in the 1970s, and since then it has been widely used in the Eastern United States to improve the pollination of apples and other fruit trees such as peaches, pears and cherries.
A female Japanese horn-faced bee © Chelsey Ritner, Exotic Bee ID:
In their natural habitats, the Japanese horn-faced bee and similar species nest inside cavities such as hollowed reeds, tree holes and cracks in stones. Females use a range of materials, especially mud and pebbles, to build individual nest cells in which they lay an egg. When bees are done, they seal off the nest entrance with mud – so they are known as mason bees. Fruit growers offer bees nesting alternatives such as drilled blocks of wood or bunches of cardboard tubes tightly packed together.
Two types of mason bee nests used in orchards: cardboard tubes (a) and wood blocks (b) © Kline et al., 2023:
The future seemed promising for that Japanese horn-faced bee in Pennsylvania. But opportunists were on standby, ready to pounce when an unsuspecting bee leaves its nest. In the blink of an eye, a gang of hypopi (singular hypopus) jumps on the bee, holding on for dear life as their ride flies away.
Hypopi, also known as hypopodes, are a special nymphal stage found in some mites. In this case, the hairy-footed pollen mite (Chaetodactylus krombeini). Hypopi have no head or mouthparts, but are armed with special structures for hanging on; either powerful claws or a sucker plate to glue themselves to their host. These adaptations greatly facilitate phoresis, which is when an organism attaches itself to another for the purpose of transportation. Phoresis is typically found in small and poorly mobile organisms such as nematodes and mites. But curiously, the hypopus stage is usually facultative for mites; it occurs only when conditions deteriorate (food scarcity, overcrowding, dry climate, etc.), so that skedaddling increases the likelihood of survival.
A hypopus, the stage adapted for phoresis © Reynolds et al., 2014:
The departing bee has no chance of avoiding the lurking hitchhikers who react instantaneously to the slightest touch to their dorsal setae (bristles) or to air movement caused by a passing body. And the feats of some of these mites defy credulity; the tiny Histiostoma laboratorium (formally known as H. genetica), a scourge of vinegar fly (Drosophila melanogaster) laboratory colonies, lurches into the air to grab fruit flies flying above them (Hall, 1959. J. Kansas Entomological Society 32: 45-46). Some species that have hummingbirds as hosts rush to the birds’ nostrils at a rate of 12 body-lengths per second, which is a speed proportional to a cheetah’s (Colwell, 1985)
Hypopi attached to their host © D.E. Walter, Invasive Mite Identification, Colorado State University and USDA/APHIS/PPQ Center for Plant Health Science and Technology:
After being mobbed by hypopi, the bee carries on with its life. If it’s a female, she will mate and start a nest of her own. When her brood cells are ready, her unwanted companions come out of their lethargic state, jump off and resume their development, maturing and reproducing quickly, all the while feeding on the pollen and nectar gathered by the bee. When their numbers reach certain levels, they may feed on the bee’s eggs and larvae (details are sketchy). In a few months the mites may reach thousands and overrun the brood cell, leaving space for nothing else.
Hairy-footed pollen mites inside a mason bee nest cell © Pavel Klimov, Wikimedia Commons.
Such massive numbers of kleptoparasites (organisms that steal food from another one) spell serious trouble for Japanese horn-faced bees; their eggs and larvae die or develop poorly for lack of food or direct attack from mites. Some adult bees may not even have a chance to start a new family; they are so burdened by mites that they cannot fly. They fall to the ground and become easy pickings for ants and other predators.
A mason bee loaded with pollen mites © GeeBee60, Wikimedia Commons:
Several mason bee species are susceptible to the hairy-footed pollen mite, but managed Japanese horn-faced bees have been hit particularly hard, with losses reaching up to 50% of the population. It’s not difficult to understand why. The same way crowded slums make people more vulnerable to all sorts of diseases, jam-packed nests increase the chances of mites passing from one bee to another. And the hairy-footed pollen mite does not even depend on phoresis: adults can walk from one nest to another nearby, getting inside through holes in the sealing mud made by parasitic wasps. To make the situation worse, this mite can turn into a dormant stage that survives several years inside an empty nest, rousing back to activity as soon as new tenants arrive.
The effects of the hairy-footed pollen mite on the Japanese horn-faced bee are a reminder of the unintended consequences of well-intentioned actions. Bee houses or bee ‘hotels’ have been promoted as enhancers of wild bee populations, but there’s no indication of such effects. They do however increase the risk of pathogens and parasites: not only mites, but a range of fungi, parasitic flies and wasps bedevil mason bees (Groulx & Forrest, 2017).
A bee hotel: not such a great idea © Colin Smith, Wikimedia Commons:
American fruit growers do their best to keep mites under control by replacing the nesting tubes yearly, sterilising wood blocks, or removing and storing bee cocoons during the winter. If you have a bee house but don’t have the resources, time or inclination to do the same, you should follow Colin Purrington‘s advice: buy a garden gnome instead.
Great milestone! This series is a delight to read and see.
Another way to interpret 100 could be either 1 or 4 in binary (little or big endian). Otherwise, 100 has one more digit than 99 and more is better!… even though 1 is less that 9…. hmmmm…
Really interesting, as always. I did not know that people could buy living, potentially invasive non-native insects. I am frankly rooting for the hypopi. Of course the normal honeybee is also non-native and is an important pollinator for many crops. But sometimes I secretly root for their parasites as well… I think they must have a huge effect on the native bee populations, because they are so efficient at finding nectar sources and mobilizing their harvest (see https://naturalareas.org/docs/16-067_02_Overview-of-the-Potential-Impacts-of-Honey-Bees_web.pdf for a review)
OMG. I wonder if those mites attach to other organisms as well, say, people! This is an interesting example of how introducing new species to solve one problem often leads to another problem that itself demands solution. (And so on.) if I’m not mistaken, Apis mellifera was itself introduced to North America.*
*Oops. I posted this before seeing that Lou Jost beat me to it.
Another great one! I did not know about the issue surrounding those bundles of wood tubes to encourage solitary bees will also encourage their parasites. It of course makes perfect sense.
Horse racing: and broken legs suffering. The horses are raced too young. Somewhat comparable to 10-12 year-old humans running marathons. Horses are supposed to be 3 years old to race – if I understand it correctly. But depending on their true DOB, they can be closer to 2 years old. The only reason for such stress when so young is human greed, the desire to get the horses out making money ASAP. If the horse race crowd cared, had an equal desire for humane treatment of animals, they would refrain from competing horses for at least another year. It could make a big difference in the number of broken legs and euthanasia. There are other causes for such of course.
No horse racing expertise at all claimed here but running fillies and colts seems cruel and needless.
The horse racing industry cares as much about protecting horses as does the Tennessee Walking horse crowd. The don’t.
Athayde, thanks for your many interesting, instructive contributions to WEIT!
Looking forward to more of your fascinating posts.
This is a really interesting post.
Thanks so much!
Fascinating. One of the more interesting reader posts for some time. I’m not a biologist, just interested (How could one not be?), but my initial reaction to the story of hypopi was an enormous “Yuk”. Fascinating evolved behavior, tho.