They Must Feed; Give Them Flesh! Feeding Screwworms on a Budget

Featured Image Caption: Screwworm flies lay eggs on unsuspecting hosts so larvae (maggots) can develop underneath the skin.  “Screwworm-Cochliomyia hominivorax” by Judy Gallagher is licensed under CC by-SA 4.0 Deed via inaturalist

Source article: Hickner, P. V., Sagel, A., Quintero, G., Vasquez, M., Tietjen, M., Lohmeyer, K. H., & Arp, A. P. (2024). An alternative chicken-based diet for mass-rearing screwworm flies. Journal of economic entomology117(1), 348–357.

Screwworm fly larvae use breathing tubes to avoid detection in the skin. “New World Screw-worm Fly (Cochliomyia hominivorax)” by carogame is licensed under CC-BY-NC 4.0 Deed via inaturalist

A fly is generally harmless when it lands on your arm, until the sci-fi nightmare becomes a reality. After a female lays her eggs, the larvae emerge. With fanglike mandibles, larvae tear at the skin of unsuspecting prey and grow under the skin until they are ready to leave at maturity. Dinner of choice? Livestock, animals, and humans. As if the scenario wasn’t scary enough, under extreme circumstances, they can migrate to other areas of the body and cause serious health complications.
So, if these flies are so horrible, why are screwworm flies’ mass-reared and released along the Panama-Colombia border?

The answer is simple: population control.

Commission for the Eradication and Prevention of Screwworm (COPEG)

Map showing distribution of Screwworm fly. “Distribution of the New World screw-worm fly (Cochliomyia hominovorax) by Carport. Licensed under CC BY-SA 3.0 Deed via Wikimedia commons

On February 11th, 1994, Panama and the US entered a cooperative agreement to eradicate and prevent infestations of screwworms.
The Panama-United States Commission for the Eradication and Prevention of Screwworm (COPEG) is a collaboration between the Panama Ministry of Agricultural Development and the United States Department of Agriculture to improve the health and food security of Panama and North America.

Through joint investment by the two countries, a sterile fly production plant was built. Overall, more than 20 million sterile flies are produced every week. The purpose of releasing male sterile flies is to outcompete wild flies so that the remaining flies in the area fail to reproduce. This approach is called the sterile insect technique (SIT).
Thanks to the efforts of implementing the sterile insect technique (SIT), screwworms have been virtually eradicated from the U.S, apart from the Florida Keys outbreak incident in 2016.

Economic Problems

Although the efforts for addressing outbreaks and eradiation are largely successful, maintaining production is not without its complications. Addressing parasitic insects is not only a scientific effort, but an economic undertaking as well. Production costs impact a facilities’ ability to feed and maintain an insect colony. Seemingly trifling details such as shipping, food ingredients, and reliable food suppliers can impact a facility’s capacity to supply insects.

In the screwworm fly case, the price for ingredients used to feed maggots ingredients such as eggs and milk have risen, in part due to depopulation of chicken to control the avian flu.

To address increasing costs of production ingredients, Dr. Hickner and colleagues from USDA-ARS have tested an alternative diet containing chicken by-products and soy on screwworm colonies. The goal was to assess whether colonies fed on the alternative diet were just as viable as colonies fed their regular diet.

In Panama, chicken by-products such as chicken viscera and feathers, are in abundance and be used as a cheaper method to feed these insects. According to the researchers, the chicken diet formulation would save hundreds of thousands of dollars annually. Furthermore, they assert that these efforts combined with shipping savings from obtaining the ingredients locally could translate to more savings down the production cost line.

How to Feed Hundreds of Thousands of Worms on a Budget

At the facility in Pacora, Panama, the standard food formulation is bovine red blood cells and plasma, dried egg, milk replacement powder, formaldehyde, and cellulose fiber as a thickening agent. In this experiment, scientists used chicken by product alternatives for egg and milk powders. The chicken by-products and milk substitute ingredients were locally sourced. To test the new diet, several generations of flies were allowed to develop from eggs to adulthood. As they grew, they measured egg hatch rate, weight of pupae, sex ratio, life span, and mating success.

In addition, they tested the nutritional content of their new formula using three techniques: gas chromatography, high performance liquid chromatography (HPLC), and mass spectroscopy. Collectively, these tests help determine important nutrition information such as protein and vitamin content in comparison to the traditional diet.

Worms, How Did Your New Diet Go?

Overall, diet did not significantly alter lifespan or mating success of screwworm flies. In comparison to the traditional diet, Hickner and colleagues are able to demonstrate that nutritional quality is comparable. However, Hickner and colleagues disclose that they did not test how consistent the nutritional content was between feeding batches of the new diet. Nutritional analysis such as the ones carried out in this study are important to make sure that the nutritional content is the same in each feeding with the substitutions used. The methodology in this study is simple, but necessary when determining how to standardize cheaper diets.

This study is a sobering example of how production cost management can affect how well COPEG can respond to zoonotic diseases in the future. In 2016, the Florida Keys outbreak was swiftly addressed because of COPEG’s ability to release 188 million flies over a 6-month period. Human-insect interactions are part of everyday life and tied to our well-being. It remains to be seen whether these measures will be able to cut costs without compromising the environmental impact of disease prevention. However, such measures are necessary when keeping up with the intersection of economics and science.

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Christina Andrea Alvear

Christina Andrea Alvear

I am a coordinator for a nonprofit organization in San Antonio, Texas. I earned a MS in Biology at the University of Texas at San Antonio. My goal is to make primary research fun and accessible to everyone while connecting with other science writing enthusiasts. I've explored a variety of careers from research, education, and nonprofit mental health, substance abuse, and healthcare programs. When I am not writing or working, I like to lounge around at a coffee shop on a weekend or enjoy a board game with friends.

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