To many, bees are deemed a pesky nuisance to be avoided at all costs. They buzz and they sting, which is often met by swatting hands and ducking for cover. Yet, bees are vitally important to many flowering plants for their work as pollinators. Honey bees are an important pollinator of food crops across the world and their value to agriculture is estimated to be worth $14 billion in the United States alone. So, despite the reaction of many of us to say “Ew! Gross! Bugs! No!”, we depend on bees to pollinate the food we eat.
Perhaps, you’re now thinking “I guess bees aren’t so bad, maybe we can come to some sort of mutual understanding”. However, your new found friendship faces a roadblock because our insect friends are vanishing at an alarming rate. In 2006 and 2007, U.S. beekeepers started to notice a startling number of colony losses. What was peculiar about these losses was the absence of adult bees. The hives were usually empty aside from a few immature bees and the queen. Subsequently, this unusual phenomenon was termed colony collapse disorder (CCD).
So what’s causing the disappearances seen in colony collapse disorder? The answer is not so clear. Honey bees are hosts for a variety of pathogens, from viruses to bacteria, to mites and parasites. However, none of these factors alone are enough to explain the widespread losses seen in CCD. Recent research is implicating, instead, a group of pesticides called neonicotinoids that could explain the recent decline. Neonicotinoids are the newest family of insecticides introduced to the market. Therefore it was only within the last decade that scientists began to question whether these chemicals had something to do with honey bee decline and CCD.
Neonicotinoids have been considered a safer alternative to other pesticides because they selectively target the invertebrate central nervous system. They can be applied to crops without posing serious risk to ourselves and other mammals. However, their selectivity among insects is limited because beneficial pollinators, like honey bees, are still susceptible to neonicotinoid toxicity. These chemicals irreversibly bind to insect nicotinic acetylcholine receptors and in high enough exposure lead to paralysis and death.
Honey bees are consistently exposed to neonicotinoids in the field, especially during the sowing season in which seeds are planted using seed drilling machines. Seeds are often coated with neonicotinoids in order to provide pest protection for each plant from the moment it is put into the ground as a seed. However, the process of seed drilling has an unexpected consequence as a route to neonicotinoid exposure for bees. In the machine, the seed coating fragments and turns into a fine dust that is forced out into the surrounding area. Honey bees are subsequently forced to fly through the chemical plume during their foraging from hive to plant.
Another route of neonicotinoid exposure is caused by the systemic characteristics of neonicotinoids. Systemic insecticides are absorbed into all of the plant’s tissues and therefore confer insect protection to the entirety of the plant. This, however, is problematic for our tiny friends. When a honey bee goes to collect pollen or nectar from a treated plant, it is either ingesting the chemical directly or bringing it back to the hive to expose the rest of the colony. Neonicotinoids have been found in non-target areas surrounding agricultural fields. The chemicals were found in the soil (despite no treatment for two seasons), in collected pollen, and in all dead and dying bees.
It is clear that bees have ample opportunity to come into contact with neonicotinoids, but what happens to them when they do? To answer this question researchers expose their tiny test subjects to various dosages of neonicotinoids and observe the effects. In one experiment bees were exposed to the neonicotinoid clothianidin at a field concentration that was determined as the highest concentration recommended for crop treatment. All of the bees died within three hours. Likewise the other neonicotinoid used, thiamethoxam, killed all bees in six hours, even at 200 times less than the field concentration.
In some cases, however, hazardous effects of neonicotinoids on honey bees are not so blatant as to cause quick death. Neonicotinoids induce abnormal foraging behavior in bees. This means that exposure to these chemicals can disrupt the normal ability of bees to travel far from the hive and find their way back. In one study bees that ingested imidacloprid took a significantly longer time to return to their hive from a feeding site. The travel time of unexposed bees is fairly consistent, but with each increased dosage of imidacloprid the bees took longer to return to the hive. Some bees were never seen again.
It was unclear what actually happened to these bees, however, because the tracking was based solely on first person observation. However, one group of researchers took foraging observation one step further by using radio frequency tracking devices. The devices were attached to the bees as well as in the entrance of their hives. After being treated with sub-lethal doses of thiamethoxam, bees had a significantly reduced rate of being able to return to the hive. These findings seem to offer some insight to the absence of adult bees found in colony collapse disorder. There are no bodies because the bees never make it back to the hive from the field.
Although the future health of our tiny friends may be unclear, the research on the harmful effects of neonicotinoids has not gone unnoticed. In 2013 the European Commission of the European Food Safety Authority implemented a ban on the most widely used and harmful neonicotinoids including: imidacloprid, thiamethoxam, and clothianidin. Only time and future research wilI reveal the full extent to which neonicotinoids are impacting honey bee health. However, it remains apparent that the staggering decline of honey bees due to colony collapse disorder is in some way linked to neonicotinoid exposure.