Stylops ater

Strepisptera is an order of parasitic insects with some very unique characteristics.They are also known as twisted wing parasites, based on the twisted hindwings on the male parasite. They infect many different orders of insects, but mostly target wasps and bees where they up take up residency in the host's abdomen. If you know what to look for, you can immediately spot their presence. In fact, there's even a special term for describing bees and wasps that are parasitised - they get "stylopized".

Top: A male Stylops ater (indicated by red arrow) attempting to mate with a female in a bee's abdomen.
Bottom left: Female Stylops ater adult (indicated by red arrow) in a bee's abdomen,
Bottom right: Male Stylops ater pupa casing (indicated by red arrow) in a bee's abdomen. 
From Fig. 1 of the paper

And it's not just the hindwings of stresipterans that are a bit twisted, these insects have extreme sexual dimorphism, so much so that if you didn't know any better, you'd think the females and males are completely different types of animals. The female stresipteran looks like a grub, and she spends her entire life inside the abdomen of the host, with just her head partially poking out from between the segments of the host's abdomen.

In contrast, the males have a pair of giant compound eyes, prominent branched antennae and the "twisted wings" that give this group of insects its name. They have a short and frantic adulthood - after emerging from the host, he only lives for a few hours and his sole mission in life is to find and mate with an elusive female strepisteran, hidden away in the abdomen of a host insect. And he does the deed with an appendage that entomologist Tom Houslay once vividly called a "stabby cock dagger". The technical term for this form of mating is "hypodermic insemination" - where the male basically stabs and inject his sperm into the female, and the sperm somehow find their way to the eggs. Strespiterans are not alone in having this type of appendage, male bed bugs also have a stabby cock dagger - but that's another story.

The study being featured in this post focuses on Stylops ater, a species which parasitises Andrena vaga, the grey-backed mining bee. Unlike the honeybees that most people are familiar with, these are solitary bees, with no castes. And while they do gather into an aggregation to nest, each bee just builds and looks after their own nest. The researchers examined a population of these bees in Lower Saxony, Germany. They sampled over two periods, during late winter, when all 508 bees they looked at were stylopized, and late spring, when they only managed to find two stylopized bees out of a total of 150.

Almost two-third of the stylopized bees were female, but these parasites seem to prefer hosts that are of the same sex as themselves. Since female bees live longer and can provide more nutrients than male bees, this works out well for the life history of female Stylops as it gives them more time and nutrients to grow her brood. After mating, the female Stylops can release up to 7000 offspring, which crawl off to find other bees. While each larva is merely 0.2 millimetre long, they can traverse long distances by hitching a ride on the hair, pollen sacks, or even the crop of bees, to end up in a new bee nest, filled with fresh hosts.

While most bees only hosted a single parasite, some had two or three, and the researchers did find one very unlucky bee that was harbouring four Stylops in its abdomen. But even a single Stylops can take a severe toll on its host. In fact, this parasite is so demanding that it wouldn't grow as big if it had to share its host with another Stylops. As a result, bees infected with Stylops are unable to develop eggs or only produce poorly developed eggs.

But aside from effectively sterilising the bee, Stylops also tinkers its host's biological clock, making it emerge out of hibernation a few weeks earlier than uninfected bees - hence why the researchers found so many stylopized bees in late winter. Making the bees such early risers ensures that there will be plenty of female Stylops around for the male Stylops to find, which will be emerging at that time to live out their extremely short lives. It also gives the female Stylops' larvae more time to develop, so they will be able to crawl off in time to find new hosts in the bee's brood cells. This type of behaviour manipulation is comparable to what's found in Sphaerularia vespae, a nematode that alters the seasonal biological clock of hornet queens.

In order to make these changes to the bee's internal clock, Stylops would have to manipulate the host's hormones, but this also results in some side effects on the bee's body. Female bees that get stylopized tend to have a hairier back, skinnier legs, and the hairs on said legs become shorter and more sparse. In short, they take on characteristics that are more similar to that of regular male bees.

So next time you are out and about, keep an eye out for a bee that looks a bit different from the rest. It might be flying under the influence of a parasite tucked away in its abdomen, looking to make a rendezvous with her short-lived partner.

Reference:

Hoffmann, M., Gardein, H., Greil, H., & Erler, S. (2023). Anatomical, phenological and genetic aspects of the host–parasite relationship between Andrena vaga (Hymenoptera) and Stylops ater (Strepsiptera). Parasitology 150: 744-753

Ascosphaera apis

This is the second post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2013. This particular post was written by Karen McDonald on a paper published in 2008 on how bees use resin to protect their hive against fungal parasites (you can read the previous post about toxic birds and their lice here).

Animals have evolved many different strategies to fight parasite infections; from eating tough or poisonous leaves (which would normally never be chosen as part of their diet), dirt bathing, grooming themselves with plants that contain chemicals that kill parasites, living in hostile environments that parasites can't tolerate, to drinking toxic substances like alcohol to kill internal parasites. Animals in general are individuals and care only for their own personal well-being and so the parasite-ridding strategies animals use really only affect their own health and well-being. But bees, on the other hand, are different.

SEM photo of Ascosphaera apis sporeball from here

Bees are communal animals and each bee is an important part of the hive community. The article I am going to talk about today shows that bees don't act on a self-motivated level where they are only concerned with their own well-being, instead bees work only to improve and support the whole hive community. Wild bees always smother the inside of their nests with sticky plant resin and the reason for this was never really understood. Domesticated bees don't use much, if any resin at all. They have been selectively bred to not use it because the sticky resin makes opening the hive and removing the honey and combs very difficult. But domestic bees are also plagued by many, often destructive, parasites.

In 2008 researchers decided to document whether the amount of plant resin that domestic bees use in their hives has an effect on fungal parasite levels in that hive. Two groups of hives were set up; the first group of 12 had the inside of each box painted with thick resin to replicate the nests of wild bees, the second group of 11 boxes were only painted with the type and quantity of resin used by commercial apiaries. Bees from both groups were fed with pollen infected with Chalkbrood, which they ate and/or carried back to their hives.

Photo of chalkbrood-infect larvae from here

Chalkbrood (Ascosphaera apis) is a fungal infection of bee larvae, causing them to die and mummify in the nest (see photo on the right). Adult bees are not affected by the parasite but they do carry it in their bodies and drop spores throughout the nest infecting young bees. Normally, as mentioned above, infected animals are usually only concerned with their own well-being and so the researchers were interested in seeing whether the adults would react to the threat to the larvae or ignore the parasite menace because it did not affect them personally.

Within days, the bees immediately began collecting more resin for their nests. Normally, there are only a few bees in each hive that forage for resin, the majority forage for pollen or nectar. Bees do not eat resin; its only function is to line the nest, so not much energy is used by the hive community to collect it. But when the hive is under threat from a parasite like Chalkbrood, more bees begin to forage for resin and a lot of energy is used to find it.  The nests painted with resin, although infected at the same level, also had a reduced level of infection compared to the commercial standard nests, but the level of infection in all nests dropped as the amount of resin in the nest increased. The bees were using the resin as a form of  social immunity rather than self-immunity.

References:
Simone-Finstrom M.D., Spivak M., (2012) Increased Resin Collection after Parasite Challenge: A Case of Self-Medication in Honey Bees? PloS One, 7(3): e34601. Doi: 10.1371/journal.pone.0034601

This post was written by Karen McDonald

Apocephalus borealis

Many of you have heard of the very scary phenomenon called "Colony Collapse Disorder" - and if you haven't, you should, because it could be a major threat to the food we eat. CCD is when the worker honey bees abandon their hives and die, which, if widespread, can mean drastic decreases in pollination of crops. This phenomenon was first reported in the U.S. in 2006 and ever since that time, scientists have struggled to uncover what was responsible. Everything from cell phone radiation to genetically modified crops to a variety of parasites of honey bees were suggested to be the cause. Then, today, a new paper in PLoS One showed data suggesting that another kind of parasite is linked to CCD. Apocephalus borealis is a parasitoid fly that was known to attack bumblebees and paper wasps, but now has been demonstrated to also attack honeybees in the U.S. - in fact, 77% of the colonies sampled near San Francisco were parasitized by A. borealis. The authors used DNA barcoding to confirm that the flies in the honey bees were genetically indistinguishable from those parasitizing bumble bees.

The authors of the new study also found that bees that were found flying around at night (something honey bees don't normally do) were significantly more likely to be parasitized by the fly and furthermore, the sick bees also seemed disoriented. It is not currently known whether or not the tendency for the parasitized bees to fly at night away from their colonies is another example of manipulation of the host by a parasite or whether this might be an act of altruism by the bee, carrying its parasite away from its colony and thus protecting the others.

Although these new results are very exciting, many questions remain to be answered about the history and impact of A. borealis. First, when did the switch into honey bees occur? Honey bees are not native to the U.S., but since they are so well monitored and studied, the authors believe that the switch must have happened recently - otherwise it would have been noticed by apiculturists. Second, could these flies also be serving as vectors for other bee pathogens? Two known bee pathogens, Deformed Wing Virus and Nosema ceranae, a microsporidian were found in the A. borealis flies. And finally, could the invasion of honey bees by this parasite mean that CCD is going to increase? The natural hosts of A. borealis are bumble bees, which live in small colonies where only the queen herself survives the winter, but honey bee colonies have thousands of bees and their activity maintains some amount of heat, even in colder winter months. This increase in host resources and more generations per year could spell a population explosion of A. borealis...and that won't be good for those of us who depend on pollination - like all of us.

The image is from the paper. Look closely at the abdomen of the bee - that's a little parasitic fly laying eggs into it. Soon the larvae will emerge from the dead host. (You can see a photo of this in the original paper as well.)

Source: Core A, Runckel C, Ivers J, Quock C, Siapno T, et al. (2012) A New Threat to Honey Bees, the Parasitic Phorid Fly Apocephalus borealis. PLoS ONE 7(1): e29639. doi:10.1371/journal.pone.0029639.

November 9 - Meloe franciscanus

Today's parasite is the larval stage of the blister beetle Meloe franciscanus. The beetle larvae are brood parasites that feed on eggs and the young of the solitary bee Habropoda pallida. The problem is, how do they get into the nest of a female bee on the first place? Well they do it by imitating the real thing. They gather into a swarm and climb to the tip of a grass stem. Once there, they clump together to form a small brown blob. While it might not look like much to you, but beetles give off a smell and produce vibrations that fool a male bee into thinking that the blob is one fine hottie. For the beetle larvae, it's a collective effort - the more of them there are in the blob, the more attractive they appear to a male bee. As soon as the bee comes into range expecting to get lucky, all the beetle larvae jump onboard. The experience leaves the bee slightly shaken, but unstirred, and he continue on his quest to find a female bee. However, once he does find a real female, he also ends up passing on his sticky hitch-hikers as a sexually transmitted infection. Once the beetles are all onboard the poor female, they cling on for dear life, eventually disembarking at her nest where they will be surrounded by all the food they'll ever need to grow up.

Photo credit: SFSU

Contributed by Tommy Leung.

February 8 - Coelioxys coturnix

A female Coelioxys (Allocoelioxys) coturnix Pérez bee dashes into the nest of another bee species, Megachile minutissima Radoszkowski, and lays an egg on top of her host’s. She has waited—loitering outside the nest while assessing the whereabouts of the other female —for the other’s moment of weakness: leaving the nest to collect the last bit of material to close the brood chamber containing her egg and the pollen and nectar provisions for the larva that will emerge from the egg. Coelioxys coturnix is a cleptoparasitic (sometimes spelled “kleptoparasitic”) bee, an entomological version of the cuckoo bird, that does not collect food or nesting material for her offspring but uses the nests and, in bees, larval provisions of other species. Depending on the species of parasitic bee, its newly hatched larva might have disproportionately large, fang-like jaws to kill the host’s brood, might feed on the host’s egg, or might (in one very unusual species from Florida currently being described) wait until it is almost too late, during its last larval stage, to do away with the competition. Cleptoparasitism has evolved many times among bees using different pathways, according to Jerry Rozen, a Curator at the American Museum of Natural History for nearly 50 years, who has studied these bee species for much of his career.

Contributed by Kristin Phillips.
Photography by Rollin Coville.

January 10 - Varroa destructor

Many people have heard of grave concerns about the loss of honey bees, key pollinators of our crops and other important plants. One of the reasons for their trouble is the ectoparasitic mite, Varroa destructor. These tiny little arachnids climb onto bees and suck out their hemolymph - insect blood - and can also transmit dangerous viruses from bee to bee.