A Punch in the Gut: The Effect of Pesticides and Antibiotics on a Bee's Digestive Tract
One of the difficult issues affecting bees today is the use of pesticides. Pesticides have been known to have varying effects on several pollinators, ranging from disorientation to severe lethal effects. Though pesticides are not aimed at bees, bees can often become exposed if pesticides are sprayed incorrectly or even within a couple miles of a beehive.
Even worse, pesticides have been known to cause subdued lethality. In these cases, the bee does not experience many immediate side effects but exposes the rest of her hive to the chemical. In time, the hive will begin to weaken and become susceptible to several illnesses and soon progress in a downwards spiral that may end in colony collapse (see figure on the left). Though pesticides may not be the one true cause of colony collapse disorder, their presence within the environment has certainly played a role. So, while there's no doubt we could ever completely rid ourselves of pesticides, we can make sure we know how to use them wisely. Moreover, if we could better understand why pesticides can be so damaging to an entire hive, we can begin to better treat our bees if and when they were to be exposed.
Recent studies have shown that the link between pesticide use and colony collapse might be its interaction with the bee’s gut microbiome. A microbiome is the collection of all the microorganisms (i.e. bacteria) that live in a certain environment. In humans, most of these bacterial microorganisms are good bacteria located in the digestive tract that aid in food consumption and even help the immune system. The case seems to be the same for honeybees, one of the few insects that actually have a gut microbiome.
In a 2016 study, scientists performed an experiment where they tested a bee in the pupa stage for evidence of bacterial DNA. Though none was found in the pupa stage, scientists sampled a couple of newly emerged honeybees overtime and found that they acquired bacteria from their environment! The same study also found that though new bees emerge with no bacteria in their gut, by their third day in the hive they will show a gut microbiota consistent with the rest of the bees in the hive. In fact, scientists have found that the honeybee microbiota shows five core species of bacteria (shown in image to the far right) to be consistent with adult honeybee workers across the globe.
This is remarkably interesting because it is fairly similar to the method seen in humans. Like bees, humans acquire the majority of their microbiome through their surroundings. Further, a study revealed that in humans, the infant microbiome fluctuates as we encounter several new life events and then slowly starts to resemble an average adult. This is incredibly consistent with what we saw with the progression of microbial accumulation in the honeybee. This similarity between humans and bees not only means that we can begin to use the honeybee as a model organism to discover new things about our health, but we can gain some insight into bee health from what we already know of our own. And, one of the things commonly known to affect our microbiota are antibiotics.
Specifically, antibiotics can be harmful to our health because they often kill the beneficial bacteria in our system along with the harmful ones. This is the reason why your doctor may prescribe a set of probiotics to go with your antibiotics! In much the same way, a bee’s microbiome may be impacted by the very antibiotics that beekeepers apply with the intention of helping their bees. Though more research is needed to make clear conclusions, it opens up a whole world of ideas for bee medicine.
For example, a 2019 study found that the severity of a bee infection, Nosema ceranae, was linked to the presence of particular gut bacteria. The study even suggested that manipulating the microbiome could be a way to increase survival during infection. The study did, however, express that more research was needed to confirm their conclusions.
Still, understanding that honeybees need a delicate balance of bacteria can help us to find more efficient ways of treating them. One example is a study recently published in October 2019 which shows evience that using probiotic supplements might improve a bee's capability to fight infections such as American Foulbrood. This is just one of the examples that the microbiota of bees might be the key to answer our questions when it comes to bee health.