6 minute read
natural defenses: monitoring mosquito populations with biocontrol
allison gentry
is a second year at the University of Chicago, currently on the pre-med track and majoring in English. On campus, alongside writing for SISR, Allison sings with the University Women's Chorus, is involved with Southside Scribblers, and is an editor for PULSE, the on-campus pre-med publication. In her free time, she enjoys exploring the city, visiting as many museums as she can, and finding the best spots to eat around Chicago.
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You can’t avoid swatting away pesky mosquitoes during the hot and muggy days of August in Houston: in the rainy season, stagnant water provides a perfect breeding ground for these blood-sucking pests. Without access to proper medication or city-wide protection programs like pesticide spraying, the health of the population of a mosquito-infested city may be at risk. However, in cities like Houston, researchers are working to find a more sustainable solution to control these deadly insects. In particular, researchers are using biocontrol, a century-old practice, to control pests by the introduction of a natural enemy or predator.
No animal on earth is nearly as deadly as the mosquito. Mosquitoes act as vectors for many deadly tropical viral diseases. 4 Female Asian Tiger, Southern House, and Yellow Fever mosquitoes are often carriers of Zika virus, West Nile virus, Chikungunya, and dengue fever, since females that need protein-rich
blood transfer these diseases to human hosts (Packard, 2019). The presence of these diseases varies from region to region, and the mortality rates in each region are significantly affected by access to proper preventative measures and medicine. In 2017, malaria alone was the cause of nearly 435,000 deaths worldwide. 3 These health concerns will only increase over time, since the effects of climate change are leading to significant changes in the population distribution of these disease-carrying pests in various parts of the globe. 2
Biocontrol groups around the world are researching methods to diminish mosquito populations, especially in more humid or marshy areas. Anita Schiller, Director of the Biocontrol Mosquito Initiative in Harris County in Houston, Texas, is developing an innovative and eco-friendly way to control the population of mosquitoes in Harris County using a natural predator of mosquitoes: Toxorhynchites rutilus, commonly known as the mosquito assassin. 4 Schiller plans to release a batch of mosquito assassins each month at the Cockrell Butterfly Center at the Houston Museum of Natural Science and monitor the numbers of both mosquitoes and mosquito assassins in the closed environment.
Mosquito assassins look physically similar to their deadlier counterparts; however, the distinct differences make them a species of interest to biocontrol researchers. One such difference is that adult mosquito assassins have a proboscis, which is incapable of biting. Instead of feeding on blood, they drink plant nectar and serve as pollinators. They lay their eggs in stagnant water, and once they hatch, the larvae feed on other eggs or larvae—especially those of regular mosquitoes. It is this protein-rich diet early on in life that allows these insects to subsist on nectar rather than on blood when they develop into adults. 3
When introducing mosquito assassins into an environment, the researchers have noted that the mosquito population decreases significantly. Additionally, since the mosquito assassins are native to Texas, the introduction of higher numbers of these assassins will not harm other populations present in the study or, eventually, in external environments. 3 The possibility for a natural defense against rising mosquito populations would also ease many public concerns over the dangers of mosquitoes and help address problems with current global preventative measures.
A reduction in the mosquito population would help tackle many global health concerns, such as the ability to lower the amount of pesticides being pumped into the atmosphere, especially during the summer months. Previous attempts in other locations to introduce mosquito assassins resulted in lowering mosquito populations by 98%, whereas pesticides only reduced the mosquito population by 29%. 1 As a city with a high risk of flooding, Houston has extremely high numbers of mosquitoes due to the presence of stagnant water, which serves as a breeding ground in which mosquito eggs are laid. Therefore, the possibility of biocontrol methods would be extremely beneficial for the city.
Maintaining the natural balance is one of the major challenges of biocontrol research, as an introduced species can interfere with the established ecosystem. There are many infamous examples of failed biocontrol, and many times non-native species have later been proven to be invasive. For example, in 1935, non-native cane toads were introduced to Australia in order to control cane beetle populations. Since there were no natural predators for the toads themselves, the toad population soon spiraled out of control, and they are still a common pest in Australia. 5 However, in the case of the Harris County research group, it is important to remember that the Asian Tiger mosquito is the “cane toad” of the situation, since they are the invasive species, whereas the
mosquito assassin is a native species found in various parts of Texas.
While this infamous example may seem discouraging, with proper preparation and study, biocontrol
methods have also proved beneficial. For example, in the 1940’s, researchers in California searched for a solution to the growing presence of the invasive Klamath weed, which proved toxic when ingested by livestock. Scientists sourced two types of beetles from Australia which were natural predators of the weed, and, after extensive testing to ensure they did not have any adverse effects on the growth of other plants in the area, were released and successfully lowered the presence of the weed in areas around the United States. In the following years, California reportedly saved around $3,500,000 per year due The biocontrol studies at the Houston Museum of Natural Science demonstrate the possibility of using nature’s designs to our advantage, and may provide the opportunity to address major health concerns worldwide. With the proper research and consideration, biocontrol methods can continue to develop and evolve into systems which are in place globally, and in the case of mosquito assassins, may lead to a reduction in viral diseases like malaria, helping solve one of the major health crises of the modern century.
References
1 Wells, C. (2019). Fighting Nature with Nature: Using Mosquito Assassins to Make Summer Safer. Houston Museum of Natural Science: Beyond Bones. https://blog.hmns.org/2019/05/ fighting-nature-with-nature-using-mosquito-assassins-to-make-summer-safer/
2 Elflein, J. (2019). Mosquito-borne diseases in the U.S. - Statistics & Facts. Statista. https:// www.statista.com/topics/4264/mosquito-borne-diseases-in-the-us/#targetText=Mosquito%2Dborne%20diseases%20include%20the,%2C%20yellow%20fever%2C%20and%20more.
3 Green, J. (2019). The Nature of An Assassin: Harnessing Deadly Killers to Fight Pests. Houston
Museum of Natural Science: Beyond Bones. https://blog.hmns.org/2019/08/the-nature-ofan-assassin-harnessing-deadly-killers-to-fight-pests/
4 Schiller, A.; Allen, M.; Coffey, J.; Fike, A.; Carballo, F. (2019). Updated Methods for the Production of Toxorhynchites rutilus septentrionalis (Diptera, Culicidae) for Use as Biocontrol Agent Against Container Breeding Pest Mosquitoes in Harris County, Texas. Journal of Insect Science. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6407668/
5 Shelton, A.; Eccelston, J. (1996). Successes in Biological Control. Cornell University College of Agriculture and Life Sciences. https://biocontrol.entomology.cornell.edu/success.php
