Both for domesticated honey bees, who appear to be suffering from a combination of negative effects with a main combatant being the Varroa destructor mite slowly wearing down hives and destroying them, and wild bees, who appear to be instead suffering from a combination of urbanization effects that are removing their habitat spaces.
Today’s topic, however, is not on issues like colony collapse disorder (CCD), but on an upcoming bee threat that may prove even more hazardous to honey bee populations.
The Emerging Threat
Tropilaelaps mercedesae is likely not a scientific name you’ve heard of before and you’d be forgiven for not knowing it. Thus far, it is a species that has been restricted in its range and none of that is felt in Western countries. These mites are a terror in the places that they do live.
Let’s start at the beginning. T. mercedesae are a species of mite that infect bee hives as their hosts. They were first documented in the Philippines in 1961 by members of the Chicago Field Museum, one of whom the species in question was named after, Mercedes D. Delfinado.
They are a vicious little species with a lot of similarities to the Varroa mite, but worse. T. mercedesae reproduce far faster than Varroa, likely due to them having shorter lifespans than their brethren, but this means they can easily outnumber their competitor 25:1 in a short period of time.
The Gross Part
They produce their young within the sealed brood cells of bee larvae. Once hatched, the developing mites feed on the blood of their developing bee hosts, often with 20 or more mites within a single brood cell. They are able to move about the hive and even hitch rides on adult bees to other colonies if necessary.
T. mercedesae in particular cause heavy brood mortality, especially in comparison to Varroa mites, and also severely weaken any bees that survive to adulthood due to the blood loss and stricken development. In the worst possible cases of infestation, an entire generation of bees can have 50% of their offspring killed before adulthood, more or less dooming the hive as a whole.
This usually results in the adult bees abandoning the hive and seeking out new colonies to join or claim. Often with them unknowingly carrying little passengers on their flight to a new home.
Spread and Research
In the 40-50 years since their discovery, the range of T. mercedesae has expanded tremendously, moving beyond the Philippines to all of the southeast Asian countries and recently into southern China, India, and South Korea. With globalized industry as it is, that puts many other places around the world at risk of contracting the mites from an improperly inspected shipping container, especially shipping of bee hives and queens to other countries.
Due to this evolving threat, researchers have been looking into the species over the past few years to truly determine what beekeepers might be facing. In 2009, a study on the mites was able to confirm that T. mercedesae are also able to cause deformed wing virus infections, much like their Varroa cousins. But, with their higher reproduction and spread, that means it is far easier for them to infect more bees with the condition.
And now we come to the research happening today. In a collaboration between Liverpool University in the UK and its separate branch in China, Jiaotong-Liverpool University, researchers have been able to sequence the genome of T. mercedesae to learn more about it.
It Doesn’t Look Good
For the most part, what they learned doesn’t look good. The mites appear to have evolved to have a close parasitic relationship on bees, with a specialized life cycle that relies on honey bees being available and a hive being stable enough to have a constant brooding system going. Since without brood larvae to drink dry, the mites will die off themselves.
However, because of this reliance, the mites are quite different from other mites species that live in more free habitats. The common mite function of sensing particular chemicals in order to modulate and determine their behavior is non-existent in T. mercedesae. This means that control methods for other mites related to sending them interfering chemical signals won’t work on these mites.
In addition, their bodies appear full of detoxifying enzymes, meaning any miticide (anti-mite pesticides) used against them won’t be effective for long, as they will quickly develop resistance to it.
Some Small Hope
The only potential positive that was found from the genetic sequencing was the symbiotic host bacteria inside the mites. Practically all arthropods have them and the genus Wolbachia is the most common one to find in these sorts of species. But, instead of Wolbachia, the scientists found Rickettsiella grylli related bacteria, a strange discovery.
Even more strange, there was evidence of horizontal gene transfer between the bacteria and their mite hosts. But it wasn’t Rickettsiella grylli DNA being transferred, but Wolbachia DNA, even though no Wolbachia were present. This perhaps indicates that the T. mercedesae mites were originally hosting Wolbachia bacteria that did transfer DNA to them, but these bacteria were later forced out by an influx of Rickettsiella grylli related bacteria as the mites evolved.
This is made even more weird by this being the first case of horizontal gene transfer between bacteria and mites yet found. Though that’s likely due to a lack of study, since 33% of other arthropod species studied have been found to have such transferred DNA in their genomes.
Keep Your Fingers Crossed
Anyways, what this means is that these Rickettsiella grylli bacteria may be the in that scientists need to control and kill off the mites. Research of this sort is already ongoing for Wolbachia bacteria in other species, so this different bacteria just needs to be added to the list.
It is hoped that that research will come up with some sort of solution. Because, otherwise, the future of bees is looking rather bleak.
If T. mercedesae continues to spread and even leaps to Europe or the Americas, bee populations will be in trouble and we won’t have very many options to fight back against it.
Photo CCs: CSIRO ScienceImage 7018 Asian bee mites Tropilaelaps sp on European honey bees and a deformed bee top left from Wikimedia Commons