“Sub lethal and Lethal Effects of Pesticides on Commercial Honeybees and Wild Bees”

Abstract: It is a well-known fact that the global population of bees is declining. This is a major concern because bees are the primary pollinators of the world’s crops. Commercial honeybees and wild bees both have significant impacts on the fate of the worlds produce. Without bees, produce would be an impossibility to get because there would be very little to none available. The reasons as to why this is happening have not been completely isolated yet, but scientists are testing multiple factors as to why this could be happening. One of the reasons could be pesticide and insecticide application to crops around the world.

Pesticide and insecticide application could be a major contributing factor as to why the bee population is declining. This is very unfortunate because agriculture is expanding throughout the developing and the developed world. Between 1961 and 2006 global agriculture of pollinator dependent crops has increased by 16.7% in the developed world and by 9.4% in the developing world (Brittain & Potts, 2011). With commercial agriculture comes pesticide and insecticide application. Global pesticide application is expected to more than double to 10 million metric tons by 2050 (Brittain & Potts, 2011). This could be a major issue if in fact insecticides are a leading cause of global bee population decline. Neurotoxic insecticides may pose more of a direct threat to honeybees and wild bees than other kinds of pesticides (Thompson, 2003). Bees can be exposed to the applied pesticides in two ways; one way being contact immediately after application, and another way being oral ingestion (Brittain & Potts, 2011). The application of these neurotoxic insecticides can have sub lethal impacts on the life history traits of bees such as altered behavior, foraging ability, house cleaning, and returning to the hive, as well as more serious lethal impacts. Though in many of the studies that have been conducted, lethal impacts have not been as frequently observed in adult bees. However, lethal impacts have been observed in bees in the larval stage (Wu, Anelli, & Sheppard, 2011). It is important to understand that different species of bees do not have the same sensitivity as others (Brittain & Potts, 2011), so in order to gain valuable information about what bees are sensitive too, scientists must start out testing the bees that are used with commercial agriculture. The bee that is most widely used in experiments is Apis mellifera.
The wild bee is just as important as the commercial honeybee because both provide tremendous ecosystem stability. The wild bee pollinates not only flowers and provides stability of the wild part of the spectrum, but also assist in the pollination of crops in the agricultural industry. The wild bee will generally nest around agricultural sites and stay there year round and therefore are at extreme risk of exposure to insecticides. The commercial honeybee provides the pollination of the worlds commercial agriculture crops and is managed by beekeepers. The bee populations in America have been declining with such significance that imports of bees from Australia and other countries have been implemented (Langworthy & Henein, 2009). This could pose a problem because the bees coming from Australia are coming from a different hemisphere altogether and therefore are coming from a place with a different season. These bees have to adapt to a completely different environment with different flora in a very short amount of time (Langworthy & Henein, 2009). Importing bees may be a short-term fix but it is certainly not a long-term fix.
Many of the sub-lethal effects have to do with the life-history traits of the bees. Life-history traits include: foraging behavior, interactions with other bees in the colony, mating, etc. With increased life-history issues, come increased problems for pollinating the crops. Foraging can be greatly impacted with the application of insecticides because bees navigate by sight as well as scent. When bees leave the hive and come back, generally there is a communication to the other worker bees as to the location of the food sources. However, it has been observed in many experiments that at high levels of exposure to certain insecticides, bees cannot forage with great efficiency (Brittain & Potts, 2011). When certain insecticides are applied, the scent of the crop is impacted and the bees do not visit that crop. If they do visit the crop, they have been exposed to the pesticide and may endure negative outcomes (Thompson, 2003). Another important piece of information to think about is, not only are bees helping create 30% of our food, but also, plant and pollinator are just the basis of a more complex web of interacting organisms (Brittain & Potts, 2011). Specialization occurs quite frequently among the plant and the pollinator. Some species of bees specialize in only one type of flower and some plant species specialize in having one type of pollinator such as orchids (Brittain & Potts, 2011), and without that pollinator, that species would most likely go extinct. This would ultimately result in the extinction of any other specializing species on that particular plant. It is expected that tens of thousands of plant species will go extinct by mid century (G. Allen-Wardell et al. 1998). One of the best documented examples of a pollinator dependent crop being effected by a loss of bees were the blueberry crops in New Brunswick, Canada. These crops had insecticide applications and shortly after, bees stopped returning to the crops and the crops themselves experienced declines in output (Brittain & Potts, 2011). A global loss in plant output could result in an economic cost of around $5.7 billion a year (G. Allen-Wardell et al. 1998).
There are many different experiments being done by scientists around the globe to try and determine what exactly is going on with the bees. One experiment done by Wu, Anelli, & Sheppard, (2011) showed what happened when bee larvae was raised in an environment either with or without pesticides present. Experimental brood combs of honeybees were assembled. The “brood comb” has the purpose of raising the larval bees and providing a home while they pollinate the surrounding plants and make honey. The USDA-ARS honeybee laboratory in Beltsville, MD provided the frames for the treatment combs for the experiment (Wu et al. 2011). There were also control brood combs in which pesticides were not present. The frames were then cut into smaller pieces for experimental purposes. The goal of this experiment was to determine whether or not pesticides had a direct sub-lethal effect on the honeybees being raised in these circumstances. The experiment in total took about a month, (Wu et al. 2011). It was replicated 28 times as to provide more accurate results. There were measurements taken before and after the experiment was done to show which combs contained specific pesticides. The queens were separated from the colony very early in the procedure as to avoid any further mating and birthing of any more bees. Measurements of mortality and developmental delays were taken periodically throughout the experiment on different days, (Wu et al. 2011). In the data provided, at days 4 and 8, there were noticeable developmental delays in the bees that were being brooded in the treatment combs (Wu et al. 2011). Some of the bees at day 4 had not hatched and the bees at day 8 were experiencing larval developmental delays. Alongside the sub-lethal effects, the mortality rates were also measured. The data showed that the mortality rates in the bees raised in the treatment combs were not statistically higher than the mortality rates in bees raised in the control combs (Wu et al. 2011).
This was a great experiment in that the results seemed to relate to many other scientists experiments with different levels of insecticide. This paper takes a closer look at some other experiments that have exposed various levels of insecticide to honey bees. However, one issue at hand with this experiment was that over the course of the 28 replications, bees that were supposed to be a part of the control were being exposed to insecticides because of the fact that the same frames of the brood combs were being used repeatedly and not necessarily with the same groups (Wu et al. 2011). This could pose a problem with the overall accuracy of any of the replications of the experiment. It was shown that bees that were not exposed to pesticides in the control of the first experiment had been exposed to pesticides in the following experiments (Wu et al. 2011). Though this had little effect on the overall results, frames of bee combs should be cleaned or replaced with each replication of the experiment.
Sub-lethal effects of insecticides on commercial honeybees have also been noted in many other experiments done by scientists. Notably in a paper written by Thompson (2003), there are many different types of sub lethal effects that insecticides can have on bees. Thompson, (2003), This paper focuses on the effects of insecticides on bees over a longer period of time at a lower exposure which is generally the situation the bees are in. Many experiments put bees at an unusually high exposure level and expect accurate results, when in actuality bees are exposed to much less of the insecticides at one time (Thompson, 2003). There is a wide range of insecticides that have been studied which are frequently used in the field. The types of honeybees that are studied in this paper are the species Apis mellifera and the species Bombus terrestris (the commercial honeybee and the bumblebee), which are of prime importance around the globe. There are different sub lethal effects that these insecticides can have on the bees. A few of these things in the bee A. mellifera include, different foraging behavior, failure to return to the colony, as well as increased self-cleaning and decreased movement (Thompson, 2003). The effects on B. terrestris were slightly different in that the insecticides seemed to affect the larval stage of the bees rather than the adult stage, for example there was larval mortality, decreased brood production, and less larvae overall (Thompson, 2003). In the comb, the bees preform different tasks such as cleaning. Much like cleaning your own house, the bees make sure nothing is going to ruin their house. For example, many different insects would try and feed on the honeybee’s nectar and honey if it weren’t for the house cleaning routine. The bees will clean and preform daily duties to prevent this. When exposed to the insecticides, the bees showed to do less house cleaning overall. This in turn resulted in extensive moth damage to the hive (Thompson, 2003).
In an experiment done by Bortolotti, et al (2003), an experiment was set up to determine the sub-lethal effects of imidacloprid on the homing rate and foraging activity of honey bees. Many beekeepers across the world have noticed that the bee populations of their hives have declined significantly (Bortolotti, et al 2003). This experiement aimed to target the insecticide that has been being blamed most frequently in the case of the dissapearing bees, imidacloprid.
This experiment used one colony of healthy A. mellifera bees with one queen. A hive was set up about 500 meters away from a feeding location. There were four different doses of imidacloprid used in this experiment. One was the control which contained 0 ppb (parts per billion) of imidaclorpid. There were also solutions containing 100 ppb of imidacloprid, 500 ppb, and 1000 ppb, respectively. There were multiple trials done of this experiment. The first step in the experimental process was training the bees to feed off of the provided solution. In order to accomplish this, the food was set up close to the hive and moved away until approximately 500 meters. The flying distance from the hive to the food was very linear and training the bees was fairly simple (Bortolotti, et al 2003). The bees feeding on the certain solutions were captured and tagged accordingly. After the bees had been feeding on their designated food solution, they were transported to a flying cage for 2-24 hours and then released to return back to the hive (Bortolotti, et al 2003). There were three different times that the bees were released out of the flying cages to go back to the hive or the food source; 2 hours, 5 hours, and 24 hours. The results concluded that with the control group, the bees generally returned to the hive fairly quickly (within 2 hours), whilst the bees that were exposed to the 100 ppb had noticable effects in their homing and foraging ability so the numbers that returned to the hive were somewhat smaller than in the control. The bees exposed to 100 ppb had 3/4 of their numbers return to the hive within 2 hours and the other ¼ within 24 hours. In the 500 and 1000 ppb, no bees returned to the hive which suggested that the bees probably got lost and died somewhere (Bortolotti, et al 2003). The number of bees that returned to the food source in the control group was again, somewhat higher than the bees that were exposed to the 100 ppb (Bortolotti, et al 2003). The bees in the control group returned to the feeder mostly either within 2 hours or 5 hours, and a small amount within 24 hours. The bees that were exposed to the 100 ppb took much longer to return to the feeder in that most only returned within 24 hours (Bortolotti, et al 2003).
An important note about this experiment was that it was observed that the insecticide, imidacloprid, did not itself cause mortality in the bees. At the high dosage it caused orientation difficulties. It was observed that the bees exposed to the 1000 ppb took much longer to leave the flying cage and when they did, they often fell to the ground and their flight pattern seemed to be affected negatively. If they got lost in the field and couldn’t find their way back, this was just the mental effect that imidacloprid had on the bees. This experiment showed that honey bees are suseptible to extremely high concentrations of insecticides, but are they as suseptiple to the smaller amounts actually found on the plants? This experiment represented an extremely high amount of insecticide being exposed to the bees. As stated previously, this is how bees are generally tested to try and understand the effects of the pesticides (Thompson, 2003). However, in the field, bees will almost never come across plants with over 10 ppb of most insecticides indicating that the amount of insecticides in this experiment were not valuble in determining realistic effects.
One of the most important aspects of our agriculture is the wild bee. They provide pollination on top of what the commercial honeybees provide. Many studies have focused mainly on the commercial honeybee. However with the rapid decline of honeybee populations throughout the globe, the wild bee is going to take on a whole new meaning in the agriculture industry. These bees can be used for the same crop pollination as the honeybees in the event that the numbers of honeybees drop so low we have no other choice (Abbott, et al 2008). Wild bees tend to forage around the existing crops as well as nest around those crops. The main issue at hand is that these bees are at risk for greater exposure to the insecticides because they cannot be moved while the pesticides are being applied (Abbott, et al 2008). Wild bees are generally smaller than the commercial honeybee and this can pose a threat because they show greater suseptability to the pesticides. If the honeybee population falls to a dangerous level, than these bees will have to take over the important job in pollinating the worlds crops. If they are not studied and we do not find out just how suseptible they are, than all of the bee populations could be in trouble (Abbott, et al 2008).
In the experiment done by V. A. Abbott, Nadeau J. L., Higo H. A., and Winston M. L. (2008), there were two different experiments done on two different species of bee. The first experiment was done on the bee Osmia lignaria. Considered a wild bee because they are collected from natural parts of the environment, they were used in the experiment to test pesticides on wild bees. The field experiments were done in high bush blueberry fields in Canada from April to June (Abbott, et al 2008). There were nest blocks set up to face southeast next to the blueberry fields. There were three different doses of the insecticide imidacloprid used on the bees. There was a low dose (3 parts per billion), an intermediate dose (30 ppb), and a high dose (300 ppb). The high dose is very unlikely to be found in the field, but was important to be tested to identify whether or not this amount of insecticide would have a significant effect on O. lignaria. The low dose was more likely to be found in the field (Abbott, et al 2008). There was also a control group in which the insecticide level was at 0 ppb (Abbott, et al 2008). This test aimed to find the effects of the imidacloprid on the whole life cycle of the bees. The treated pollen was injected into the pollen provisions (where the larvae develop), and then the development was observed. Multiple aspects of the life-history traits of the bees were tested such as time to reach the last larval stage, darkening and spinning of the cocoon, and time until emergence (Abbott, et al 2008). There were effects on the time it took to reach the last larval stage. In general with both the males and the females, the higher levels of the insecticide caused longer development time. In the case of spinning the cocoon, only the males showed a difference in spinning time with the higher levels of insecticides. The females showed no difference in spinning. In the test of the darkening of the cocoon both the males and the females showed differences in the time it took with the higher insecticide levels (Abbott, et al 2008). These all effect the life-history traits of the bees which put them into the category of sub-lethal effects. No lethal effects were observed in the bee O. lignaria (Abbott, et al 2008).
The bee Megachile Rotunda, also known as the alfalfa leaf cutting bee, was also tested. The pesticide Clothianidin was used in this experiment. This experiment was set up in a wild dutch clover field in Delta, BC during 2005 (Abbott, et al 2008). There were east facing hives set up in the field. There were four different doses of clothianidin used in the experiment. The first dose, 0 ppb was used as the control. The other three doeses were 6 ppb, likely to be found in the normal field; 30 ppb, an intermediate dose that the bees would most likely not run into; and 300 ppb which was the unusually high dose. In order to determine how much solution the scientists should be putting into the pollen provisions, they first have to take the weight of the bees (Abbott, et al 2008). This helps determine what would be too much solution for the bees to handle. The results concluded that the bees exposed to clothiandin did not show any significant sub lethal effects as the bees in the first experiment did. The only effect was the lengthened time it took for the female M. Rotunda to spin her coccoon and this only occurred on two days (Abbott, et al 2008).
This experiment had many good aspects. For example, the fact that the experimenters decided to use insecticides that these bees would most likely come across in their hunt for plants was a great idea because as stated previously, bees do not have the same sensitivity across species (Brittain & Potts, 2011). Also the fact that the level of insecticides used were closely related to what could be found in the field. This experiment was conducted in a manner that was great for studying bees in their field locations. However, the laboratory experiment had the problem that the sample sizes of the bees were not as large as in the field and the space in which the bees could preform their activities was not that close to what is available in the field and therefore observations could be affected (Abbott, et al 2008). Overall, this was a good experiment with acurate results.
One of the most important life-history traits of bees is learning. Bees must learn the location of their food, what it looks like, and what it smells like. In one other experiment Decourtye et al (2003), tested two different insecticides for one specific reason and that was to see the effects they had on the associative learning in honey bees. The two different insecticides tested were imidacloprid and deltamethrin. Imidacloprid is often seed dressed on sunfowers and bees ingest it when they ingest the pollen (Decourtye et al 2003). There were 4000 A. Mellifera bees purchased from a laboratory in France for this experiment. There were three different feeding stations set up for this experiment for each pesticide. Two of the feeding stations contained a sucrose solution and one of the stations contained the pesticide solution. The amount of the pesticide solution that was used was the amount either found in the field or the lowest dose previously shown to have sublethal or lethal effects on the bees. The food solution was monitered and filled daily except on weekends (Decourtye et al 2003). The bees were given the option of going to either an unscented food source with no reward or a scented food source with a reward. Dead bees were collected everyday and counted except on the weekends (Decourtye et al 2003). After the initial trial period was over, the scientists tested what the bees has learned about going for the food with the odor and getting a sucrose reward. The results of this experiment showed many things. As stated previously, the amount of bees that were dying daily were collected and recorded (Decourtye et al 2003). The pesticide imacloprid showed no significant mortality rates. However the insecticide deltamethrin did show a significantly higher number of dead bees that imidacloprid, suggesting that this insecticide may be one of the few that does cause mortality (Decourtye et al 2003). Not only did the detramethrin cause mortality but also cause much more intense reactions from the bees such as paralysis (Decourtye et al 2003). This experiment also revealed that foraging activity declines with each of the insecticides. After the introduction of the detramethrin, there was a second introduction of the sucrose solution. When this was introduced, bees started returning to hive with noticably greater numbers (Decourtye et al 2003). However, with the reintroduction of the sucrose solution after the imidacloprid, there was still a significantly low number of foragers (Decourtye et al 2003). At the beginning of the experiment, bees were given a choice of a solution with an odor or without an odor. Bees generally learned to go to the food solution with the odor. After the introduction of the insecticides, the bees were tested to see if they had learned to go to a food source with a certain odor (Decourtye et al 2003). Laboratory experiments confirmed that after the introduction of imidacloprid, when bees were given the option of a solution with an odor, many did not show a significant response to the odor indidcating that they did not sucessfully learn the odor and the insecticide imidacloprid had an effect on the learning preformance of the bees (Decourtye et al 2003). The bees that were exposed to the detramethrin, however, did not show any decreased associative learning in the scent experiment. The same amount of foragers that responded to the odor in the first part of the experiment, responded to the odor introduced to them in the second part of the experiment (Decourtye et al 2003). This experiment only had one issue that I could identify. That issue being that the “control” wasn’t all that legitamite because the there was no group of bees just being exposed to a control group. The groups of bees in this experiment were all being exposed to sucrose solutions and insecticides (Decourtye et al 2003). I feel that this could affect the results in minor ways. In order to improve this experiment, the scientists should have had a strict control group of bees.
Many experiments have been conducted by scientists around the globe to determine why bee populations are declining. With the decline of bees comes the decline of pollinator dependent crops such as fruits and veggies. Without these, a good portion of our food would no longer be avaiable to us. In many experiments involving honey bees and wild bees, scientists set up nest combs and feed the bees a solution containing various amounts of whatever insecticide is being tested. In order for these experiments to be highly accurate, scientists test out in the field and with levels of the insecticide that would be found on the crops. In many of the studies preformed, doses of insecticides that matched the levels out in the field generally did not have any highly significant effect on bees. Only the high levels had significant effects. At the end of the day however, bee populations are still declining and scientists should be conducting more tests on what insecticides if any are safer on bees. Eventually, if current insecticides keep being used, bee populations could fall to a dangerous level and our worlds produce could be in trouble.

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