Posted: April 12th, 2022

Horse Fly as a Disease Vector

Horse Fly as a Disease Vector

Introduction
A horse fly belongs to the Tabanidae family of insects, group order Diptera, and genus Tabanus (Cilek, 2008). These insects are found in almost every continent apart from the Antarctica. Horse fly tends to thrive under tropical climates because as studies show, most diverse species of these insects are found around the tropics (Cilek, 2008). The external morphology of an adult horsefly is characterized by stout-bodies with prominent antennae that extend anteriorly (Mehlhorn, 2016). They have eyes that are patterned brilliantly with different colors ranging from yellow, orange, green or violet. In addition, adult flies tend to be very strong and fast. Horse flies are normally found around wooded areas, marshes and streams (Mehlhorn, 2016). Horse flies pose a huge risk to both humans and animals through sucking of blood where studies show that they can suck close to three ounces of blood daily from a host. Moreover, they are carries of different animal diseases like anthrax and trypanosomiasis in humans (Cilek, 2008). This research paper aims to understand various aspects of a horse fly as a disease vector to understand its impact on the host population, its role in ecosystems, control measures and the possibility and relevance of its eradication.
The Lifecycle of Horse fly
The development life cycle of a horse fly begins with the first stage where eggs which are 1-3 mm long are deposited in large masses of approximatey25 to 1,000 eggs which are deposited on vegetation near wetlands or muddy places (Mehlhorn, 2016). This is followed by a larvae stage which takes about 6-13 larval molts (Mehlhorn, 2016). This larvae stage develops in muddy conditions, stream banks or wetlands. The third stage is the purple stage which precedes the adult stage. A horse fly can go through these stages of development from an egg to the adult stage within a span of 6 weeks (Mehlhorn, 2016).
A Horse Fly’s Impact on Its Host Population
Adult Horse flies have a striking appearance due to their large features and biting habits that can be aggressive. These flies are common with most people living around the tropics as they can ruin your day with persistence annoyance of numerous bites in search for a blood meal. Their strong mouth parts are designed to capture before subduing their prey. The large mouth arts are made up of bladelike mandibles with maxillary laciniae whose main role is to lacerating the host’s skin (Cilek, 2008). These insects are classified as pool feeders where they cut their hole within the host’s skin to suck their blood. Studies show that male horse flies do not take a host blood but only the females so that they can lay eggs (Cilek, 2008). Their preferred areas to bite their host are around the head or shoulders in humans while the legs are the ideal spots in livestock.
Horst Preference
The host preference of horse flies does vary where studies have shown that some horse fly species prefer small mammalian hosts with man being their most favorite prey (USDA.gov, 2019). Other species of horse flies prefer preying on the legs of livestock (Cilek, 2008). In most cases, horse fly is active during the day which is when they are likely to attack their host with very little activity at night. The common animal attacked by horse flies includes cattle’s such as horses, cows and other mammals as well as humans. Studies suggest that the reason why horse flies prefer mammals as their prey is because of their warm blood and also blood has important elements that help the female horse fly to lay eggs (Cilek, 2008).
Disease Transmission
Horse flies are associated with different types of diseases in different parts of the world for both humans and animals. A common disease cause by horse flies is the Equine Infectious Anemia or the swamp fever commonly prevalent in the south eastern part of the United States (Cilek, 2008). Research suggests that the pathogens causing this disease are found on the horse flies body before it is transmitted to livestock when the fly preys on the hosts during bites, or when the host’s skin is ruptured (Poinar, 2010). This disease is viral and their effect on the host includes weight loss, casing lethargy while in severe cases it can cause death. Poinar (2010) further argues that the virus of this disease has two strains where there is a minor and severe strain with this severe strain casing death within a very short span after the host contracts it. These shows that horse flies are very dangerous disease vectors in livestock, a matter that is of great concern.
In humans, horse fly bites tend to be very itchy and painful. This is because these bites usually develop into red, large and swollen bumps within a matter of minutes. In most cases, these horse fly bites tend to be harmless in humans but they create an extremely uncomfortable feeling. In some cases, people have reported feeling weak, hot and dizziness as a result of these horse fly bites. Such cases develop when a horse fly bite is infected leading to the redness of the skin, oozing and feeling of extreme pains from the resulting wounds from the bite (Poinar, 2010). In some extreme cases, some people experience allergic reactions from these bites with the common systems being dizziness, breathing difficulties, skin rash, as well as severe swelling that can be visible on the victims tongue or lips (Poinar, 2010). Horse fly bites that are left untreated act as inlets to various disease causing pathogens which is why it is important to treat the wounds from these bites.
Veterinary Impact
Heavy horse flies attacks can lead to huge weight loss among livestock due to the loss of a lot of blood and the vector diseases that comes from these horse fly bites. The adult horse fly acts as a disease vector for numerous disease agents such as viruses, protozoans, nematodes, bacteria, among others. Moreover, the overall milk yield of livestock is also likely to go down significantly due to the poor health and anemic conditions caused by persistent horse fly bites (Cilek, 2008).
Other impacts on livestock result from horse fly bites in reduced efficiencies in feed utilization while the hide of these animals becomes damages as a result of punctured wounds. Moreover, horses under constant horse fly bites tend to be very irritable due to the distractions caused by these bites as they try to avoid them. In some situations, animals have even injured themselves as they tried to escape these horses fly bites. As studies would suggests, animals under stress or disturbed tend to lower their productivity in milk yield while they also fail to grow appropriately (Cilek, 2008). As such, horse flies have a very negative on the overall well being and productivity of livestock and other animals.
Horse Fly Role in Ecosystems
Horse flies serve many different roles in the ecosystem, key among them being pollination, predator and prey, decomposers and diseases vectors. Horse flies play the role of pollination to different variety of plants. Horse flies travel from one flower to another and though they may not be as effective in the carrying of pollen grain like bees, house files act as pollinators to different plants which in some cases bees may not visit (Kondratieff, 2009). For instance, most flowers pollinated by bees have flowers which bees go to extract nectar but plans without such flowers may not be attractive to insects like bees, which mean hat house flies take up the role of pollination in them. Among the common plant species pollinated by these horse flies includes red trillium, paw-paw, and certain orchids, among others (Kondratieff, 2009). By serving the role of a pollinating agent, horse flies ensure that the plant ecosystem continues.
Another role played by horse flies in the ecosystem system is acting as predators and preys to certain animals and insects within the food chain. For instance, horse flies are important food sources to many different species of birds, mammals, fish and other insects. Given the fact that horse flies lay and hatch their eggs near swampy and muddy places, certain fish species and insects take advantage to feed on their larvae (Gerry, Peterson & Mullens, 2007). As such, horse flies in this case serve the role of a prey within the ecosystem. On the other hand, horse fly larvae play the role of a predator to livestock and humans. Horse flies are always looking to suck blood from the legs of livestock and neck region in humans as part of their feeding (Gerry, Peterson & Mullens, 2007). Based on this understanding, we can conclude that horse flies play the role of both a predator and prey within the ecosystem.
Horse flies are also dedicated decomposers within the ecosystem. For instance, the larva of these flies develops in swampy and dumpy paces where it feeds on decomposing materials thus enhancing the decomposition process (Gerry, Peterson & Mullens, 2007). By feeing on decomposing flesh, the larvae of horse flies aid n the overall decomposition process. As dedicated decomposers, horse flies play their role in completing the food chain as the process results in the release of nutrients that are later used up by plants, fungi and other bacteria.
Finally, horse flies play the role of being a disease vector within the ecosystem. Horse flies are able to travel for many miles with very little effort being involved. As such, these flies are bound to carry with them disease causing pathogens and bacteria as they move from one place to another. For instance, a horse fly may walk through a heap of manure or dirty at one moment and in another on, it could be walking through a plate of food (Gerry, Peterson & Mullens, 2007). As such, hose flies are common with spreading diseases like typhoid, dysentery to humans and anthrax in livestock. The act of spreading these diseases is a representation of the true nature and role of these horse flies within the ecosystem.
Horse Flies Control Measures
Horse fly control can be quite challenging to achieve especially in an area with very many of its species. This is because horse flies do not stay in contact with their host for a long time where they only spend a few minutes to suck blood and go away for a period of 3 to 4 days after which they come back when hungry (Cilek, 2008). Moreover, the fact that a horse fly can go through its different stages of development from an egg to the adult stage within a span of 6 weeks means that their population grows very quickly if they are in an area with the right conditions to support their growth. This behavior makes it very difficult to use pesticide as a control measure while aerial treatment and larvae applications are ineffective (Krčmar & Gvozdić, 2016). Several control methods against horse flies have been tested with varying degrees of success with the common ones being dialing or oiling their feeding places. Others have tried covering heir livestock with blankets to prevent horse fly attacks or pasturing them from the areas heavily infested with these horse flies (Krčmar & Gvozdić, 2016). However, in recent history, some of the methods that have proved to be the most effective have included using biological control agents or using traps.
One of the most effective control measures against horse flies has involved the use of biological agents to cannibalize or parasite against the larvae of these flies using other less harmful insects like wasps. Research studies show that wasps prey on eggs and larvae of horse flies, a factor that makes them very good biological agents of control (Nazir, Khan, & Qiu, 2019). As such, as a control measures against horse files, wasps should be released or bread in an environment heavily infested with hose flies because they will feed on their eggs and larvae thus reducing on the number of horse flies that mature into adults. Given the fact that this is a method that has been proven to work well through different scientific research studies, it means that it should be tried as a technique of controlling or eliminating the population f horse flies within a given area.
Other control measures that have been tried include trapping these insects. According to research, female horse flies tend to attracted t bright moving objects with many of them appearing to prefer objects with spherical in shape (Gerry, 2015). They also tend to have a high attraction to carbon dioxide and an octenol which is a synthetic compound which resembles cattle emissions. There are still other types of traps developed to attract these insects and if well utilized they can lead to very effective results. Having these traps in place can attract a large pool of horse flies after which effective measures can be applied to eliminate them. However, though these traps have been used as a good tool to control horse fly population, they have not been effective enough to eliminate or eradicate the insects from a given area mainly because they do away with their bleeding habitats. As such, it would only be advisable that traps are used with other control mechanisms such as draining or oiling common breeding grounds for these insects. Having a collaborative effort that involves the use of different control techniques may work well to eliminate horse flies from a geographical location.
Final Thoughts/ Discussion
One thing that stands out while undertaking this research s that there is inadequate research about horse flies as diseases vectors and the significant role they play in an ecosystem. In most cases, insect studies focus mainly on species that tend to be very irritant to human beings or likely to cause serious illness to animals and humans. In my opinion, more research is needed to understand the different horse fly species in different geographical regions so to come up with effective control mechanisms. Moreover, having a better understanding of these different species will aid in understanding the various disease vectors that are transmitted by these flies and how they can be overcome without causing significant damage on an animal or humans. Enhancing the overall research about the different horse fly species will go a long way in promoting the right practices that will lead to effective control measures.
As seen in this research paper, horse flies play a significant role as diseases vectors particularly in livestock. For instance, adult horse flies act as a disease vector for numerous disease agents such as viruses, protozoans, nematodes, bacteria, among others. Moreover, the overall milk yield of livestock is also likely to go down significantly due to the poor health and anemic conditions caused by persistent horse fly bites. Such effects means that the overall productivity of a given herd of livestock is likely to go down as they try to cope with the huge loss of blood and illness that results from the disease agents caused by horse flies. The fact that livestock experience reduced efficiencies in feed utilization while the hide of these animals becomes damages as a result of punctured wounds shows that horse flies impact on the overall livestock economy and well being. These challenges are enough prove on the need to establish effective measures that will promote more research in horse fly control mechanisms.
Finally, despite horse flies proving to be a nuisance to both humans and animals, they do have a significant role to play in the ecosystem. For instance, they act as pollination agents to different plants species. The fact that they can travel from one flower to another like bees means that they are good pollinators especially given the fact that they can visit different plants which in some cases bees may not visit. Moreover, horse flies play the role of dedicated decomposers; where they are decomposing agents to different organisms. As such they have an important role to play in completing the food chain as the process results in the release of nutrients that are later used up by plants, fungi and other bacteria. However, despite having these numerous benefits in completing the ecosystem, there are a nuisance to humans and pose a great threat to other animals like livestock, which means that their shortcomings outweigh the benefits. A such, it is justified to come up with appropriate methods or techniques of controlling horse fly population particularly in areas inhabited by humans and livestock.

References
Cilek, J. E. (2008). Horse Flies and Deer Flies (Diptera: Tabanidae). Encyclopedia of Entomology, 1116–1117. doi: 10.1007/0-306-48380-7_2076
Gerry, A. C. (2015). How to Manage Pests. Dept. of Entomology, University of California, Riverside. Retrieved from http://ipm.ucanr.edu/PMG/PESTNOTES/pn7457.html.
Gerry, A. C., Peterson, N. G., & Mullens, B. A. (2007). Predicting and Controlling Stable Flies on California Dairies. doi: 10.3733/ucanr.8258
Kondratieff, B. (2009). An introduction to the aquatic insects of North America. 4th edition. Journal of the North American Benthological Society, 28(1), 266–267. doi: 10.1899/28.1br.266.1
Krčmar, S., & Gvozdić, V. (2016). Field studies of the efficacy of some commercially available essential oils against horse flies (Diptera: Tabanidae). Entomologia Generalis, 36(2), 97–105. doi: 10.1127/entomologia/2016/0121
Mehlhorn, H. (2016). Horse Flies. Encyclopedia of Parasitology, 1286–1286. doi: 10.1007/978-3-662-43978-4_1498
Nalen, C. M. Z., Kline, D. L., Sutton, B. D., Müller, G., & Cilek, J. E. (2015). An Annotated Checklist of the Horse Flies, Deer Flies, and Yellow Flies (Diptera: Tabanidae) of Florida. Florida Entomologist, 98(2), 479–488. doi: 10.1653/024.098.0214
Nazir, T., Khan, S., & Qiu, D. (2019). Biological Control of Insect Pest. Pests – Insects, Management, Control [Working Title]. doi: 10.5772/intechopen.81431
POINAR, G. (2010). 16. Horseflies and Deerflies. What Bugged the Dinosaurs?, 131–134. doi: 10.1515/9781400835690.131
USDA.gov . (2019). U.S. Forest Service. Retrieved from https://www.fs.fed.us/wildflowers/pollinators/animals/flies.shtml.

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