The Effects of Pesticides on the Social Behavior of Bees
A 2014-2015 survey by The Bee Informed Partnership examined the number of colonies lost in a pool of 398,247 colonies. Around two thirds of the colonies experienced winter colony loss rates greater than the acceptable winter colony mortality rate of 18.7%. This study represented around 14.5% of the approximately 2.74 million managed honey bee colonies in the country. (Engelsdorp et al., 2015) The phenomenon is referred to as CCD (Colony Collapse Disorder), and it represents a significant decline in bee colony population that has been occurring since 2005 (Schwartz 2010). The cause of this issue lies in the sublethal effects bees face when subject to harmful chemicals.
Bees, an integral part of our ecosystem, are continuing to die out due to heedless usage of pesticides. The chemicals used to treat crops across the globe are quite effective at protecting the crops from pests, yet simultaneously they risk harming important pollinators in the vicinity of the area. Widely-used toxic chemicals harm the social behavior of bees by inhibiting their ability to retrace pheromones (Stromberg, 2013), damaging their homing ability, and making it more difficult to learn and communicate to other bees. Commonly used pesticides affect the social behavior of bees by hindering their ability to recall memory and sense pheromones, fuzzing their cognitive ability, and reducing their accuracy communicating information to other bees. Bees help pollinate a third of the world’s produce (Sass, J., & Various authors at the NRDC organization., 2011), and the country is only beginning to feel the repercussions to polluting the environment and inhibiting the important functions of our bees. It is important to understand the sublethal effects that our pesticides have on the social behavior of bees in order to find ways to mend the problem.
Bees are complex, curious creatures, and the structure of their social behavior is one of the most complex to understand. Though there are a plethora of types of bees, with each holding their own respective social order, it is important to recognize the differences between social structure and anatomical differences between the types. To summarize some of the common social trends in bees, we turn to two types of bees: Honeybees and Bumblebees. Bumblebees, a major species of bee native to North America, do not have a method to communicate the location of food to other bumblebees, and are less affected by pesticides than honeybees (Meyer, J. R.). These bees burrow beneath the earth, hibernate through the winter, and emerge in the spring to pollinate flowers and reproduce. Bumblebees also take the “brute force approach” (Morell, 2012) for finding flowers; the cognitive ability and memory-recalling capability is crucial in deciding the accuracy of bumblebees’ trial and error method. With this in mind, it is clear to see how reliant they are on their ability to recollect their position relative to the nest.
Honey Bees are not native to North America, but now act as a major pollinator. These bees nest above ground, creating wax hives known as honeycombs. Honeybees communicate the location of various flowers and food sources through a means of “waggle dancing”, where the bees vibrate in certain intervals that give location information. The angle at which the vibration pattern is performed indicates the direction of the food source relative to the sun, while the length of the dance tells how far away the source is relative to the hive (Vetsci.). Honeybees must maintain a clear mind to accurately communicate these locations, untampered by chemicals that may fuzz accurate dances. Another method for communication among honey bees is the secretion of certain chemical pheromones. Attractant pheromones are used to attract lost bees to the hive, and alarm pheromones are used to alarm other bees of a potentially dangerous intruder (Oecologia). Pheromone use is ubiquitous throughout bee species, and is even more critical than the accuracy of the “waggle-dancing”.
For many species of bee, the ability to recognize and understand chemical odors is instrumental to communicate socially. In a 2013 study by Poppy, Farthing, Lusebrink, Girling, & Newman at the Centre for Biological Sciences (University of Southampton, UK) in 2013, researchers created a synthetic blend made of extracts from Brassica Napus flowers. This blend was put into into a sealed glass vessel containing either ambient ‘clean’ air or air mixed with diesel exhaust (Poppy et al., 2013.) The chemically-toxic gasses inhibited the bees from recognizing the aroma of the synthetic blends and found that at environmentally relevant levels, the mono-nitrogen oxide (NOx) fraction of the exhaust gases was a key facilitator to odour degradation (Poppy et al., 2013.) This study demonstrates how diesel exhaust inhibits the ability to smell and understand pheromones.
The effect of pesticides on the homing ability in bees is a huge component in CCD. Bees that are affected by pesticides often cannot return back to the hive, and over time the colony collapses. Scientists have observed that the “homing ability of honey bees mainly depends on their spatial memory and navigation, and could be impaired by pesticides and pathogens” (Songkun, Zhiguo, Yanping, Shaowu, Shenglu, Wenfeng, Sohr 2013). The ability to return back to the hive is also affected by the foraging behavior of these bees. In a 2012 study, scientists tested the effects of neonicotinoid and pyrethroid insecticides on the individual insect-level and colony-level traits. They treated the experimental bees with a sucrose solution composed of imidacloprid dissolved in acetone every 2 to 3 days and with a spray solution composed of = λ- cyhalothrin in acetone (Raine et al., 2012). This study found that “chronic exposure of bumblebees to two pesticides (a neonicotinoid and a pyrethroid) … impairs natural foraging behaviour and increases worker mortality….”(Raine et al., 2012) But foraging behavior isn’t the only thing affecting the homing ability of these bees, there is a multitude of various sublethal effects caused by the presence of pesticides near bee populations.
The Pesticide Action Network UK describes the sublethal effects of pesticides and toxins in their article, Sub-lethal and Chronic Effects of Neonicotinoids on Bees and Other Pollinators (2012). They deduce from previous scientific journals that bees suffer a “range of behavioural disturbances” including disorientation and hindered homing ability, impaired memory and learning, and failure to communicate properly with nest mates (Pesticide Action Network UK, 2012). Neonicotinoid and pyrethroid insecticides are both commonly used to prevent insects from consuming agricultural crops, yet subsequently they both could be harming the yield of crop by inhibiting key pollinators such as bees from pollinating the crops. In a paper on the various effects of pesticides on bee behavior (Thompson, 2003), bees have demonstrated incorrect direction in waggle-dancing, a slower learning of odour mediated response, and even abnormal behavior of antennae cleaning and rubbing together of hind legs along with the other sublethal effects of neonicotinoids. As mentioned earlier, waggle-dancing is a noteworthy method for social communication among honey bees. The paper cites a 1970 study (Schricker and Stephen, 1970) which found that common organophosphorus and carbamate insecticides (Thompson, 2003) disrupt the communication between the bees by “prevent[ing] the bees from communicating the direction of an artificial food source to other bees”(Thompson, 2003) Alongside hindering of the homing ability, pheromone reception, and waggle-dance communication, there lies a profuse number of other adverse effects from chemicals.
Overuse of insecticides to treat produce results in a impairment on bees’ ability to function and survive in the wild. But how does the impact of sublethal effects of chemicals on bee social behavior affect us? Environmentally relevant levels of diesel exhaust has been shown to interfere with bees’ ability to recognize pheromones which are important to their social communication. Frequently used pesticides cloud the perception of bees and disrupt their cognitive abilities through sending various mixed signals and misinformation. And various pollutants and chemicals have been shown to throw off the accuracy of communicated information for bees subject to the substances. Harmful chemicals, consisting mostly of pesticides and pollutants, have a dramatic effect on the social behavior of bees. CCD is a growing problem in America, and we must take action against it we ever wish to recover from the damage we have inflicted upon the environment.
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