Chemical causes and repercussions of colony collapse disorder in Apis mellifera

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1 Chemical causes and repercussions of colony collapse disorder in Apis mellifera Jamie Beers Abstract Honey bees use chemical cues to interact with other members of the hive to communicate and determine when they should care for young, begin foraging or take part in hive defense. These bees play a huge role in the pollination of crops and other plants, there are many stressors to them which can cause them to undergo colony collapse disorder. Pesticides sprayed to try and protect crops can have adverse effects on honey bee maturation and genomic expression, causing them to have a higher mortality rate while foraging as factors like these disrupt the chemical processes taking place in their bodies. Once these pesticides disrupt the honey bee s natural chemical processes they become more susceptible to viral parasites raising stress levels and increasing the likelihood of colony collapse. Africanized honey bees are an invasive species that fills the same ecological niche as European honey bees. They display much more aggressive behaviors than the European honey bee due to genomic differences between the species and will cause increased stress upon them and can also be so aggressive as to take over their hives. Problems in a hive compound with each other and make them more susceptible to further environmental stressors and to undergo colony collapse under the combined weight. Introduction 1

2 Honey bees (Apis mellifera) are a vital part of agriculture in the country by contributing to the pollination of many crops and helping to maintain the seed germination of various plants across the country. Many of these plant species rely on widespread pollination to complete their reproductive cycles and honey bees are very well suited for this task, being the primary pollinator of many plants. Honey bees must travel from flower to flower in a wide radius around their hive to collect enough to pollen and nectar to sustain themselves and their brood while also having enough to create stores of food in the form of honey (Seeley 1995). This process of travelling from flower to flower in such a large area makes honey bees very efficient pollinators, creating the means by which different plants are able to complete their reproductive cycles and thrive. Roughly 80% of Angiosperms require a pollinator and bees are the most active of all the pollinators (Calderone 2012). Honey bees are also an economical factor when discussed in the context of agriculture; accounting for billions of dollars in various crops worldwide. In 2009 crops that were directly dependent upon pollination were valued at $15.12 billion of which $11.68 billion is attributed to honey bees. Without honey bees acting as a pollinator for these plants there would be an 88% drop in total value; quite the dramatic loss of cash crops. Other crops are also indirectly pollinated by honey bees are valued at roughly $5.39 billion. It s apparent that honey bees are economically important in not just maintaining crops and various plants but in helping maintain the economic feasibility of growing such crops (Calderone 2012). These honey bees are undergoing what is referred to as colony collapse disorder; when a seemingly healthy colony undergoes complete failure. Not all the reasons for this happening are known and it poses a threat to our agriculture and the balance of ecosystems across the 2

3 country that rely on honey bees as pollinators (Kremen et al 2002). This sort of collapse is characterized by a disappearance of the vast majority of the adult bee population, leaving the queen and the brood left (Mullins et al 2010). This loss of the adult population means that no useful tasks can then be carried out such as nursing the brood, storing food, foraging and defense of the hive. Without these tasks being carried out by properly aged individuals the hive cannot function as it should and suffers negative consequences which has very little forgiveness in addition to various factors that increase stress on the hives ability to function such as parasites, pathogens, pesticides and invasive Africanized honey bees. Discussion Early foraging onsets higher mortality rates Foraging is the means by which a colony of bees collects pollen and nectar and is the basis of keeping a hive healthy and stable. In a single day a hive will field about a quarter of its members to forage for food in a 10 kilometer radius from the nest. The hive behaves much like a single entity in the regulation of this activity through chemical signals between individuals that help regulate when to forage, care for the brood or store incoming nectar and pollen as honey for future consumption (Seeley 1995). Queen mandibular pheromone (QMP) is the chemical that controls when an individual will be best suited to transition from nurturing the brood and performing tasks in the hive such 3

4 as food storage, to moving outside the hive for foraging activities. This pheromone effects the brain chemistry of individuals and induces behavioral changes to the associated tasks as they mature, disturbance of this pheromone could be a cause of early foraging behavior along with other stressors that hives face (Grozinger et al 2003). Loss of individual foragers in bee populations is one of the biggest causes of stressors towards the hive which leads to further problems for the hive as fewer and fewer suitable bees are then able to take part in foraging activities, decreasing food supply and heightening stress (Dussaubat et al 2013). Honey bees spend the earlier parts of their lives in the hives until they begin to reach a mature enough age to start foraging outside in the wild to collect both nectar and pollen (Seeley 1995). Those individuals that leave the hive too early and begin foraging before maturation are not as well suited for the task as others; these bees who begin foraging too early may not be as capable fliers due to a higher body mass, leaving them less capable than older bees (Vance et al 2009). These precocious foragers are not as effective as those that have started foraging in the proper amount of time. Factors such as pathogens, parasites, lack of food and pesticides can all cause honey bees to move to a state of early foraging, often done by individuals who are too heavy and not as experienced of fliers which causes these individuals to suffer a higher mortality which ends up leaving brood uncared for in the honey bee colony (Perry et al 2015). This increase in foragers can cause the honey bee hive to initially bounce back from environmental stressors as their food supply is increased, but it is unsustainable as they continue to decline due to the excess mortality of these foragers which further damages the stability of the hive and causes collapse. The adult population is better suited to carry out 4

5 these tasks and have the ability to properly forage for nectar and honey to ensure the survival of the brood and create the necessary supply of honey reserves for the winter months. Parasites and pathogens creating further stress and loss of individuals Parasites in honey bees can have very deleterious results on individuals which further compounds such problems for the hive. Varroa destructor is a parasitic mite that causes foragers to lose the ability to fly properly and orient their position to the hive (Dussaubat et al 2013). Nosema cerenae is another parasite that negatively effects the ability of honey bees for both orientation and homing. This parasite attacks a bee s immune system and gut tissue degeneration. An individual bee can fight this parasite by increasing energy uptake which seems to cause an increase in precocious foraging and those foraging activities which has been discussed to have detrimental outcomes to bee mortality and overall stress levels of the hive (Dussaubat et al 2013). Both N. cerenae and V. destructor increase the mortality rate of bees and disturb the balance between foragers and nurses, upsetting the chemical balance that controls the proper maturation of honey bees is negatively affected. This can be compounded by additional stressors to the hive as discussed throughout this paper, causing a tipping towards collapse of the hive (Dussaubat et al 2013). 5

6 Pesticides effects on hive health Honey bees aren t especially sensitive to pesticides compared to other pollinators, but due to the way in which they collect pollen and nectar for honey it helps them bypass defense toxins in various plants they forage such pollen and nectar from, however by these same means the honey they process tends to accumulate various phytochemicals at a higher concentration from pesticides (Mao et al 2011). Taking pollen and nectar from plants with toxins present and converting this to honey helps these bees avoid sustaining lethal or harmful doses by taking smaller amounts from a wider variety of plants, however this means that trace amounts of pesticides picked up from various plants tend to accrue into higher concentrations because of this same accumulation of pollen and nectar into amounts that can cause damage to normal honey bee behavior. Pyrethroid acaricides are pesticides used on crops to remove parasitic mites from hives but may be suspected to play a part in the decline of the honey bee population and factor in to colony collapse disorder (Mullin et al 2010). Exposure to pesticides is commonplace for honey bees due to their nature of being a general pollinator and visiting many different species of plants they find their way crossing the paths of many different pesticides. Not all pesticides have a negative effect on honey bees but there are many that do, a total of 118 pesticides were found to have been contained within beebread, honey, wax, pollen, adult bees and their brood. These multitude of pesticides are used to control for mites, fungi and insects. These pesticides can ultimately be lethal to honey bees and reduce the number of foragers in a cascading effect by reducing the number of healthy bees in a colony and causing these bees to forego normal times of maturation leading to precocious foraging (Mullin et al 2010). 6

7 Neonicotinoid insecticides have been used in agricultural applications but are seeing restrictions as their use has been shown to have harmful effects including loss of homing abilities and increases the likelihood they will succumb to other factors including pathogens (Di Prisco et al 2013). Studies show that neonicotinoid insecticides do indeed accumulate within honey bees, their food and their hive at both lethal and sub-lethal levels. Loss of individuals due to lethal doses can already tip a colony in the wrong direction towards collapse, but this is also compounded by the effects that sub-lethal doses can have in disturbing steady reproduction rates which may have be even more dire to the colony than the loss of foragers. Individual honey bees behavior also seems to be effected by neonicotinoids as it interferes with their ability to collect food and even disrupts simple motor functions making it near impossible to complete most tasks and tend to the needs of the hive (Blacquiere et al 2012). Overreaching uses of pesticides seem to further compound the effects of other biotic and abiotic stressors that honey bees must deal with and make them more vulnerable to such. Taking care in the use and application of pesticides with regards to the well-being of honey bees should be of the utmost importance considering their impact on both agriculture and our environment. Restrictions on those pesticides that cause harm to honey bees should be considered to help stave off the growing problem of colony collapse disorder. Influence of Africanized honey bees on European honey bees Africanized honey bees are noted for their heightened levels of aggression and defense cues to protect their hive. They are a notable invasive species and have spread across parts of the 7

8 country. Normal honey bees react to attacks on the hive by spreading pheromones which signal to other honey bees to help defend the hive to varying degrees of intensity, however Africanized honey bees seem to bypass these escalating levels of territorial defense and immediately move into a state of heavy hive defense which has been known to cause deaths in humans (Alaux et al 2009). These more aggressive Africanized bees are genetically predisposed to be such and indeed they release so much of the alarm pheromone for defense the individual bee will have trouble distinguishing between two targets and know only to attempt to sting (Millor et al 1999). African honey bees tend to swarm much more often than the European honey bee. This swarming activity involves leaving their nest and seeking a new place to nest at, these bees are incredibly defensive when they are swarming and do so at a much higher frequency. Africanized honey bees sometimes also usurp the hives of European honey bees, sometimes by force and sometimes by integrating themselves into the nest but removing the European honey bee queen (Ellis, Ellis 2008). Conclusion Honey bee colonies reflect a difficult to maintain homeostasis within the hive with caring for their brood, defense of the hive and the storing and collection of food. These activities are regulated by various chemical cues such as pheromones and those taking place within the body of individuals. Outside chemicals such as pesticides can build up within their hive and food source causing the improper expression of behavior within the honey bee colony, leading to foraging at an immature age. This leads to the heightened mortality of these underdeveloped 8

9 foragers, causing a shortage of food and further stress put upon the hive. As it can be seen the honey bee hive is regulated at a delicate balance with one environmental stressor likely pushing the hive in the path of another, and another. If we are not careful the increasing loss of honey bee colonies could become an all too pervasive problem and likely lead to a wide-scale loss of pollinators that could damage the agricultural industry and upset the balance of ecosystems across the country and the possibility of the honey bee population not being capable of recovering from such widespread losses. References Alaux, C., Sinha, S., Hasadsri, L., Hunt, G. J., Guzmán-Novoa, E., DeGrandi-Hoffman, G., Robinson, G. E. (2009). Honey bee aggression supports a link between gene regulation and behavioral evolution. Proceedings of the National Academy of Sciences of the United States of America, 106(36), doi: /pnas Di Prisco, G., Cavaliere, V., Annoscia, D., Varricchio, P., Caprio, E., Nazzi, F., Pennacchio, F. (2013). Neonicotinoid clothianidin adversely affects insect immunity and promotes replication of a viral pathogen in honey bees. Proceedings of the National Academy of Sciences of the United States of America, 110(46), doi: /pnas Dussaubat, C., Maisonnasse, A., Crauser, D., Beslay, D., Costagliola, G., Soubeyrand, S., Le Conte, Y. (2013). Flight behavior and pheromone changes associated to Nosema ceranae infection of honey bee workers (Apis mellifera) in field conditions. Journal of Invertebrate Pathology, 113(1), doi: /j.jip Grozinger, C. M., Sharabash, N. M., Whitfield, C. W., & Robinson, G. E. (2003). Pheromonemediated gene expression in the honey bee brain. Proceedings of the National Academy of Sciences of the United States of America, 100 Suppl (90002), doi: /pnas Millor, J., Pham-Delegue, M., Deneubourg, J. L., & Camazine, S. (1999). Self-organized defensive behavior in honeybees. Ecology, 96(22), doi: /pnas

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