New World Screwworm, Call to Action

See below letter from LE Feeds and a link to abundant proven research involving various treatment options against screwworm, including the incredible Florida Key deer success story from 2016-17. Please take the time to read all of the material. For those claiming, “There is nothing we can do for wildlife.”, think again. There is abundant proof for those willing and able to use it that it works. If feed treatment options are approved for wildlife use, that doesn’t mean you HAVE to use it, but it does mean you now have an option to do so. Sitting back and acknowledging, “there is nothing we can do for wildlife,” is unacceptable. I am sure glad Florida Fish and Game didn’t take that approach and sit back and watch the endangered Key deer disappear. Instead, they asked for voluntary public assistance, they treated bread and doughnuts and built homemade feeders and they worked their tails off to save the little deer from massive losses. They bought time with the medicated feed/doughnuts, and they asked for help until the sterile flies arrived to once and for all end the threat.

Texas--and Texans—should continue to seek solutions, meet the challenge head on and do the same. Texas needs an emergency approval treatment for feed simply to buy the time required for the sterile fly to reach full production and delivery capacity to finally end the threat. The research is there, the clear and proven roadmap from Florida is there, the facts are in place. Texas should be approved for emergency feed support use, along with soliciting the public’s assistance to get prepared and organized in order to buy the needed time to combat this pest until the sterile fly can finally be delivered to the front lines to protect all livestock, wildlife and domestic pets. Texas should not have to be the follower here, but we are. We can learn from Florida’s success story, and we can use the exact same protocols to protect our hunting and outdoor industry immediately. We have a lot riding on our immediate actions now, so if we intend to save our wildlife and abundant outdoor industries, time is not on our side. The ball is clearly in our court now and actions speak louder than words.

I will stand for Texas wildlife today, always and forever.

Macy Ledbetter

Below is the letter Macy referenced on the New World screwworm threat from Lyssy & Eckel Feeds dated June 16, 2025:

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In the past four weeks we have searched through many science-based documents to come to a practical understanding of how to prepare for and manage a New World screwworm (NWS) threat. All of our findings have been freely shared with the Texas Grain & Feed Association and thousands of ranchers.

Collectively, these studies provide strong and consistent evidence that macrocyclic lactones, particularly ivermectin and doramectin (Dectomax), are effective agents in the treatment and control of NWS.

Where we are today is based on the following reports: 

1. “The efficacy of ivermectin against larvae of the screw-worm fly (Chrysomya bezziana)” Spradbery et al. 1985 

2. “Disease strategy screwworm fly” Australian Primary Industries Ministerial Council, 2007 

3. “Evaluation of ivermectin against the screwworm (Cochliomyia hominivorax) in vitro”, Ring D.R., 1982 

4. “Prevention of cutaneous myiasis caused by screw worm larvae (cochliomyia hominivorax)” Anziani O.S., et al 1992 

5. “Final Report for APHIS Veterinary Services (VS) Response to the 2016-2017 Outbreak of New World Screwworm (NWS) in Florida”, USDA, 2017 

6. “Use of multiagency approach to eradicate New World screwworm flies from Big Pine Key, Florida following an outbreak of screwworm infestation (September 2016-March 2017)”, JAVMA, 2019 

7. “Florida Key Deer Screwworm. Final Report. (Phase I)”, Texas A&M Natural Resource Institute and U.S. Fish & Wildlife Service, 2016 

The most current success story of the use of macrocyclic lactones is the use of Dectomax in the eradication of NWS in the endangered Key deer in 2016-2017. At the beginning of the infestation, the Key deer herd had an estimated total of 1000 head. The agencies leading this rapid eradication were USDA-Aphis, Florida Department of Agriculture, U.S. Fish & Wildlife, Texas A&M Natural Resources Institute and Florida Fish & Wildlife.

• July 1, 2016. First presumptive case in Key deer.

• September 30, 2016. First confirmed case in Florida Keys.

• October 17, 2016. First release of sterile flies.

• October 21, 2016. Dectomax was made available to Key deer.

• October 2016. 100 Key deer die.

• January 10, 2017. The last confirmed case of NWS in the Florida Keys.

• July 1, 2016-January 10, 2017. 135 Key Deer were confirmed to have died from NWS.

• March 23, 2017. U.S.D.A. declares eradication of NWS.

The Dectomax protocol used in the Florida Keys was:

• Dectomax-dosed bread and doughnuts were fed as treats to Key Deer by residents and tourists.

• Dectomax-dosed textured feed was made available free-choice to deer who would not approach humans.

• Dectomax- dosed paint rollers were used to topically medicate Key deer at feeding stations.

“The decline in screwworm infestations in the last 2 weeks of October and first 2 weeks of November suggests the impact of doramectin(Dectomax) treatments, application of sterile flies, and decline in rutting behavior is likely resulting in a decline in the screwworm infestation for the Key deer population” (Texas A&M Natural Resources Institute, 2016). It is evident the introduction of Dectomax into the management protocol effectively killed the larvae and stopped the life cycle of NWS. Furthermore, by stopping the life cycle of NWS larvae, the treatment significantly reduced the number of viable flies emerging from wounds. This reduction in native fly populations allowed the sterile fly release program to gain greater traction, improving its ability to suppress reproduction in the remaining wild population. In effect, Dectomax helped tip the balance in favor of the sterile fly technique, accelerating the path toward eradication.

All agencies agreed that the sterile fly was the ultimate tool in eradicating NWS. The Florida Department of Agriculture suggested the idea of using Dectomax as a means of slowing the spread of NWS. Florida Fish & Wildlife officials stated they were initially skeptical of the Dectomax idea, but skepticism soon changed to optimism as they treated open wounds on Dectomax-dosed deer and found zero larvae in the wounds. These wounded deer inhabited one of the Keys that was still infested with NWS.

This scientific and proven approach bolsters the utilization of macrocyclic lactones (Dectomax and ivermectin) as a verified preventative measure to protect our livestock and wildlife. The protocol we have suggested follows the same success story used in the Florida Keys and allows for a large-scale voluntary mobilization of ivermectin as an oral feed-through option for livestock and wildlife producers. While Dectomax, as an injectable or pour-on provides a 21-day level of protection, there is currently no dry Dectomax powder available on the market. We have located a dry oral feed-through ivermectin powder that has the stability to make it through the pelleting process.

All our efforts are being guided by parasitologist Donald H. Bliss, PhD. He has confirmed that if Dectomax worked to protect the Key deer from NWS, ivermectin would have the same impact.

The Center for Veterinary Medicine (CVM) and the Food and Drug Administration (FDA) are currently working through an application for the approved utilization of ivermectin as an oral feed-through. This will give all ranchers the opportunity to protect their livestock and wildlife. We must continue to stress the need for approval from the CVM and FDA.

Historical FDA Approval of Macrocyclic Lactones 

• Fever Ticks on the Texas/ Mexico Border - √

• New World Screwworms in the Florida Key - √

• Potential New World Screwworms 2025 - ?

Please use this link to access all accompanying research and data: https://drive.google.com/file/d/1d2ycC3X9gFOo1LcIDyd2bhpFVhzqApwc/view?usp=sharing