The Barrier That Had to Be Paid For: Screwworm, Sterile Flies, and the Cost of Success

1. Introduction: the programme everyone cites

When pest control writers want an example of an insect eradicated rather than merely suppressed, they reach for this one. It is the best case there is, and it is currently going wrong.

1.0b And the pest is not a nuisance species

Its larvae feed on living tissue, entering through wounds or orifices, and infestations left untreated cause severe injury and death in livestock, wildlife and pets, and rarely in people.⁷

1.1 Sixty years between those two dates

Which is long enough for a success to stop looking like an ongoing effort.

1.1b And the technique is not in question

Nobody in our sources doubts that sterile flies work. The question is what happens to a programme whose success leaves nothing to look at.¹⁰

1.2 What this article argues

That the eradication was always a maintained frontier rather than an end state, that its success dismantled the capacity it depended on, and that this is the general shape of every exclusion this journal has examined. Sections 12, 16 and 25 are the case.

2. The idea

Simple to state and very hard to do.

Rear the insect in enormous numbers, sterilise the males, release them to outnumber wild males, and let wild females mate with sterile partners and lay eggs that never hatch.

2.0b And the numbers involved are the whole difficulty

Sterile males must outnumber wild ones by a wide margin, every generation, across the whole release area, which is why the history that follows is mostly a history of factories.

2.1 Described at its origin as autocidal

One entomologist began research in 1937 on what the archive calls an autocidal theory of total insect population management.¹

2.1b And it depends on a quirk of this species

The technique works best where a female mates once, so a sterile mating ends her reproductive contribution rather than merely diluting it. We state that as general background rather than from our sources.

2.1c And no residue means nothing is left behind to work later

The effect lasts exactly as long as the releases continue, which is the property that makes §12 unavoidable.

2.2 Which is the insect used against itself

No residue, no non-target kill, and no selection for resistance to a chemical, which is why it is admired.

3. Where it came from

From fruit fly genetics.

In 1950 a colleague introduced the originator of the idea to research on radiation-induced genetic mutations in fruit flies, and that year two researchers began tests on sterilising screwworms using radiation.¹

3.0b Which makes it an idea that crossed species

A finding about radiation in a laboratory fly became a control method for a livestock parasite, and the fruit fly connection returns in §24.1 when a fruit fly facility is converted to rear screwworms.¹¹⁰

3.1 Following earlier work on chemical control

The same laboratory had been working on artificial diets for rearing and on chemical wound treatments, including an insecticidal wound smear developed in 1938.¹

3.2 And took thirteen years from idea to method

Research on the sterile male approach beginning in 1937, radiation sterilisation tested from 1950, which is the pace of a genuinely new idea.¹

4. The first field tests

On islands, for the obvious reason.

A researcher arrived in Kerrville, Texas in 1951 to work on the sterile male approach, and Sanibel Island in Florida was the first field test.¹

4.0b The archive records the test and not the result

It names Sanibel as the first field trial without saying whether it succeeded, and we do not claim either way.¹

4.0c And the scale of an island is manageable

A release area with a coastline for a boundary needs a finite number of flies, which a single laboratory could plausibly produce.

4.1 An island controls immigration

Which is the condition the technique needs, since sterile males only work if fertile ones are not constantly arriving from outside the release area.

That reasoning is ours and becomes central in §9.

5. Curacao

The proof.

In 1954 the researcher travelled to Curacao and began successful screwworm eradication campaign using sterile male technique.¹

5.1 An island again

Which satisfies the condition in §4.1 and explains why the decisive demonstration happened offshore rather than on the mainland.

5.2 And the mainland followed within a year

With the same researcher returning to Florida in 1955 to work on eradication from the southeastern states.¹

6. Scaling up

Mass rearing techniques were developed from 1955, a production facility was built in Florida in 1955 to 1957, and the pest was eradicated from a 2,000 square mile test area near Orlando.¹ A second plant followed in 1958, and screwworms were eradicated from the southeastern United States in 1959.³

6.1 A test area first, then a region

Two thousand square miles near Orlando before the whole southeast, which is the same staged expansion the island trials began.¹

6.2 And a second plant within a year of the first

Built in 1958 to supply the regional campaign that finished in 1959.³

7. The whole country by 1966

Via the southwest.

The southwestern programme began in 1962 with flies from the Kerrville laboratory and a mass production facility at Mission, Texas.³ The pest was last eradicated from the United States in 1966.⁶

7.1 Twelve years from island to nation

From the Curacao campaign in 1954 to national eradication in 1966, which is an extraordinary pace for any biological programme.¹⁶

7.2 And it was achieved with factories

Two in Florida and one at Mission, each producing flies at a scale nothing else in pest control has matched.³

8. Which was not the end

And the people running it knew that.

The originator's own oral history discusses how the programme spread across the country and the problems they encountered with sustaining the eradication.²

8.1 Said by the person with most reason to call it finished

The originator of the technique, describing his own programme, chose to discuss the difficulty of keeping it rather than only the achievement of it.²

9. The problem of sustaining it

Our explanation.

The screwworm did not stop at the border. Flies from the south kept arriving, and a mainland has no shoreline to stop them. The island condition from §4.1 does not exist on a continent, so eradication inside a boundary holds only while something prevents re-entry across it.

9.0b So the technique had a geographical condition built in

It could clear an area but could only keep it clear by controlling what arrived from outside, and on a continent that means another release zone further out.

9.0c And it applies to every eradication on a connected landmass

Whatever the technique, a cleared area bordering an infested one stays cleared only while the border is defended.

9.1 Which is the same problem our rat frontier article described

A province that keeps itself rat-free by patrolling its eastern edge has not eliminated rats. It has decided where they stop, and pays every year to keep that decision.

10. A continuous sterile barrier

The phrase the programme used.

The oral history describes the outbreak in 1972 that prompted the expansion of the program to Mexico in order to enforce a continuous sterile barrier.² A binational commission was established that year to coordinate eradication and move the barrier progressively southward.⁴

10.0b Continuous is the operative word

Not a campaign or a sweep but an unbroken presence, which is a commitment to operate a line rather than to finish a job.²

10.1 Which named the problem six years after eradication

An outbreak in 1972 is six years after the 1966 milestone, so the need for a barrier was demonstrated almost immediately.²

10.2 And the barrier moved south for two decades

From the Mexican border through Mexico and Central America to Panama, each advance clearing ground behind it.⁴

11. The narrowest point of the continent

Where the barrier was finally parked.

Rather than attempting global eradication, the United States and partner countries established a permanent containment barrier in the Darien Gap of eastern Panama by continuously releasing sterile flies to prevent northward spread from South America.⁴

11.0b The geography did the work

A continent narrows to its thinnest point there, so the length of barrier needed is at its minimum.

11.1 With its own institution

A Panama and United States commission established in 1994 to maintain the barrier, with a sterile fly production and dispersal facility that began operations in 2006.⁴

12. Which is a choice about permanence

Our reading.

Parking the barrier at the isthmus minimises the length of line to defend. It also converts a finite eradication campaign into an indefinite operating cost with no completion date.

12.0b And it was the sensible choice

Global eradication across South America was never on offer, and a short line at an isthmus is the cheapest line available.⁴

12.1 And the word permanent is the source's own

Which means the design assumed the releases would never stop.⁴

12.1a And the barrier needs the whole chain to work

Rearing, sterilising, transporting and dispersing, every week, so a failure at any stage thins the line.

12.1b And indefinite commitments are the hardest kind to keep

A campaign with a finish line recruits support. An operating cost with no end recruits only the people who remember why it started.

12.2 That assumption is the whole of the risk

Because a permanent cost is exactly the kind a budget process trims when nothing appears to be happening.

13. The peak

As described by a wildlife society.

In the heyday of screwworm eradication, the U.S. maintained various facilities, each producing hundreds of millions of sterile flies every week, one in Texas, one in Florida, one in southern Mexico and one in Panama.⁵

13.1 Which is a characterisation rather than a figure

Hundreds of millions per plant per week is an expert's summary, and §29 notes we found no production records to check it against.⁵

13.2 But the order of magnitude matters

Several plants at that scale against one at a hundred million is the difference between pushing a front and holding one.

14. What became of the plants

The Mission, Texas plant closed in 1980, with a researcher who had worked there helping set up a laboratory elsewhere.² The Florida and Texas facilities stopped producing, and the southern Mexico facility closed in 2012.⁵

14.1 Each closure made sense at the time

A plant in Texas is unnecessary once the barrier is in Mexico, and a plant in Mexico is unnecessary once it is in Panama, so every closure followed the frontier south correctly.

14.2 What nobody kept was reserve

Capacity to push the line back north if it ever moved, which is the capacity now being built from nothing.

Sections 14.1 and 14.2 are ours.

15. One plant in the world

Stated plainly.

Unfortunately, only the facility in Panama remains.⁵ The federal response page describes it as the only sterile fly production facility for this pest currently in operation in North America, producing about 100 million flies a week.¹⁰

15.0b And it was built to hold a line, not to take ground

A plant sized for a static barrier has no reserve for pushing a front back once it moves, which is what §16.2 means.

15.1 And the 2012 closure is described as a loss

One expert is quoted saying it was a big loss when the facility was given to the Mexican government in 2012, that it was then shut down, and that we lost all of our investment as a nation.⁵

15.2 Funded jointly with Panama

Managed and paid for by the federal agency and Panama's agriculture ministry together, which makes the last line of defence a binational arrangement.¹⁰

16. Why capacity erodes

Our argument.

A plant producing flies for a barrier that is holding produces nothing anybody can see. The cattle are healthy, the wounds are clean, and the justification for the plant is an event that is not occurring.

16.0a And the plants are far from the people who benefit

A production line in Panama protecting ranches in Texas is an expense in one budget for a benefit in another place, which makes its value harder still to see.

16.0b And the cattle industry stops seeing the pest

Two generations of ranchers in the north never encountered it, which removes the constituency that would argue for the plants.

That is our inference and no source states it.

16.1 So every budget review sees a cost without a problem

And the rational response to a cost without a problem is to reduce the cost.

16.1b And the reduction is invisible too

A smaller plant still holding the line looks exactly like a larger plant holding it, until the line comes under more pressure than the smaller plant can meet.

16.2 Until the capacity left is enough to hold and not enough to recover

Which is the position one plant at a hundred million a week represents.

17. How do you measure something that does not happen

Said by somebody quoted in national reporting this month.

We don't value the preparedness aspect of a disease. How do you measure something that doesn't happen? It becomes difficult to justify continuing to spend money on a situation that hasn't been a problem.¹²

17.0b And it is a strange thing to hear during the response

Said while the capacity is being rebuilt, by somebody describing why it had been allowed to shrink.¹²

17.1 Which is the preparedness paradox

Stated by a participant rather than an observer, and it describes §16 exactly.

17.2 And it describes our trade's own measurement problem

Our recurring contract and credence good articles both turned on the difficulty of valuing a pest that does not appear, which is this sentence at household scale.

18. The barrier fails

In 2023, detections in Panama went from an average of 25 cases per year to more than 6,500 cases in one year.⁹

18.0b Measured by the programme built to prevent it

The detection system at the barrier worked, which is why the collapse is visible in a single year's count rather than discovered later.⁹

18.1 A factor of more than two hundred

From about 25 to more than 6,500 in a single year, which is not a gradual erosion but a collapse.⁹

18.2 And it happened at the barrier itself

Panama is where the line was held, so the surge was measured at exactly the point designed to prevent it.

19. Through Central America

The pest was then detected in Costa Rica, Nicaragua, Honduras, Guatemala, Belize, El Salvador and Mexico, north of the barrier that had contained it to South America for decades.⁹ It reached southern Mexico in November 2024.⁴

19.0b Seven countries in roughly a year

Which is the ground two decades of southward pushing had cleared, lost in a fraction of the time.⁹⁴

19.1 Why it failed we do not know

None of our sources explains what broke the barrier in 2023, which §29 records.

20. To the border

And across the dispersal line.

In January 2026 the agency shifted its sterile fly dispersal to include operations about 50 miles into Texas along the border with Tamaulipas.¹¹

20.1 Which means releasing inside the country the barrier protected

Flies that for decades were dispersed in Panama were being dispersed in Texas, which is the barrier arriving home.¹¹

20.2 From the same hundred million a week

Reallocated rather than increased, since the Panama plant's output was the only production available.¹⁰

21. Zavala County

The detection.

On 3 June 2026 the federal animal health agency confirmed screwworm in a three-week-old calf in Zavala County, Texas, with larvae identified in its umbilical area.⁷ The calf recovered and the individual case is now considered inactive.⁶

21.1 With a statement about time

All models showed New World Screwworm entering the country in 2025; however, thanks to the hard work across the entire Trump administration and our industry, state, and local partners, we were able to buy time for this moment.⁷

21.1b Delivered on the day of the first detection

Which is when an agency most needs to describe the outcome as something other than a failure.⁷

21.2 Which frames delay as the achievable goal

Not prevention, but postponement, which is an honest description of where the programme then stood.

21.3 And the case itself resolved

Which matters less than it seems, since a single recovered calf says nothing about whether flies are now breeding in the area.⁶

22. And beyond it

Within a week.

Detections reached six domestic animal cases by 9 June, including four cattle, a goat and a pet dog in Lea County, New Mexico.⁸

22.0a Four species of host within a week

Cattle, a goat and a dog among the first six cases, which shows how little the pest selects once it arrives.⁸

22.0b A pet dog in another state

Which is the case the source singles out as highlighting potential routes for further spread, since a companion animal travels with its owner.⁸

22.1 This was not the first incursion

A localised outbreak affected Key deer in Florida in 2016 and 2017.⁸

23. The rebuilding

A renovated fruit fly facility in Mexico was completed in late June 2026 and is ramping to 100 million flies a week,¹⁰ and a new production facility in Texas is targeted at 300 million a week.¹¹

23.0b Three times the output of the plant that remained

The Texas target alone is three times Panama's weekly production, which gives some measure of how far below need the surviving capacity had fallen.¹⁰¹¹

23.1 And the Texas plant will not produce this year

Expected in 2027, so the pest's first season inside the country is fought with capacity built for the barrier it breached.¹¹

23.2 Alongside a dispersal facility completed earlier

Which can release flies but not make them, so it depends on production elsewhere.

24. What the rebuilding costs that maintenance did not

Our argument.

Building plants during an emergency buys them at the worst price, on the shortest timeline, while the pest advances. Keeping one open would have cost a steady amount during years when nothing seemed to be happening.

24.0b And the price includes the animals

Cases in livestock, a dog and wildlife, treatments granted emergency authorisation, movement restrictions and quarantine zones, none of which appear in the construction budget.⁸¹¹

24.1 And the Mexican plant is being rebuilt from a fruit fly facility

Which shows the infrastructure is transferable and suggests the 2012 closure discarded something that could have been kept at modest cost.¹⁰

24.1b And the conversion was projected at about eighteen months

Announced with that timeline and completed in late June 2026, which is the order of lead time for recovering capacity once it has been lost, even when the work goes quickly.⁹¹⁰

24.2 We do not have the figures to prove this

No source compares the cost of maintained capacity with the cost of the rebuild, which §29 records.

25. The lesson for any maintained exclusion

Which is why a pest control journal should care about a livestock fly.

A pest held out by continuous effort has not been eliminated. It has been displaced to the far side of a recurring expense, and it returns when the expense stops, whether the barrier is sterile flies at an isthmus, a rat patrol at a provincial boundary, or water in a drain trap.

25.0b And the arithmetic is the same at every scale

A recurring small cost against an intermittent large loss, where the recurring cost is visible every year and the loss is visible only when it arrives.

25.1 And the failure is always silent until it is not

A dry trap, an underfunded plant and a lapsed patrol all look identical to a working one right up to the first arrival.

Sections 24 and 25 are ours.

25.2 And the phrase eradicated conceals this

A pest described as eradicated from a country sounds finished, when what the word describes is a state held in place by spending.

26. What we take from it

Three things.

An eradication held by a barrier is a permanent operating cost. Section 11.⁴

Success removes the visible case for paying it. Section 17.¹²

And rebuilding in an emergency is the expensive way to discover that. Section 24, which is our inference.

26.1 And one thing we cannot take from it

Whether more plants would have prevented the 2023 surge, which depends on a cause none of our sources identifies.

27. Our own position

The disclosure, which cuts against us twice.

This journal has criticised recurring service contracts as seller-side cash flow smoothing. The screwworm story is the strongest case we have found for the opposite view: continuous preventive spending that genuinely was the thing preventing the problem, and that let it back in when it stopped.

27.0b And the correction belongs in the record

Our seasonality article described recurring contracts as smoothing seller cash flow. That remains true of their pricing, but the underlying claim that continuous effort can prevent recurrence is better supported than we allowed.

27.1 It does not follow that any given contract is doing that

A barrier at an isthmus against a documented migrating population is not the same thing as a quarterly visit to a house with no evidence of pressure.

27.1a And the screwworm had a measured front

A population whose position was known, which is exactly what our residential work almost never has.

27.1b The distinguishing question is evidence of pressure

A barrier justified by a documented population pushing against it is different from one justified by a population that might arrive, and our contracts are usually the second kind.

27.2 But the argument against maintenance is weaker than we have written it

And we should say so rather than leave the earlier articles standing uncorrected.

28. The Manitoba position

28.1 This is a southern pest

Nothing in our sources places it anywhere in Canada, and we make no claim about its northern range.

28.1b And the technique has no local application we know of

We found no sterile insect release programme against any pest in this province, which §28.3 records alongside the other gaps.

28.2 The relevance here is institutional

Our rat frontier and sewer articles describe barriers maintained in this province, and this is the fullest documented account we have found of what happens when one is allowed to lapse.

28.2b And both local barriers depend on somebody remembering

A provincial patrol funded year after year against an animal most residents have never seen, and a drain trap nobody thinks about until it dries.

28.3 What we could not find

Any Canadian role in the programme, any Canadian surveillance for the pest, or any assessment of exposure through livestock movement.

29. Limitations and open questions

We do not know why the barrier failed. Sections 18 and 19 report that it did in 2023, and none of our sources explains the cause, whether reduced release density, animal movement, climatic change or something else.⁹

That is the most important limitation because §16 argues the failure followed from eroded capacity, and without knowing the cause that argument is an interpretation the evidence permits rather than one it establishes.

Two sources were read only as search extracts. The congressional research report and the national news article refused automated access, so the containment barrier description, the 1972 commission, the 2006 start date and the preparedness quotation come from search result extracts.⁴¹²

The preparedness speaker is unidentified. The extract carries the quotation without the name or role of the person speaking.¹²

The peak capacity is characterised rather than measured. Hundreds of millions a week per plant comes from a wildlife society article quoting an expert, and we found no production figures for the individual historical plants.⁵

We have no cost comparison. Section 24 argues rebuilding costs more than maintenance would have, without figures for either.

Sections 4.1, 9, 12, 16, 21.2, 24, 25 and 27 are our reasoning. The account of the island condition, the reading of the barrier as a permanent cost, the argument that success eroded capacity and the generalisation to other maintained exclusions are ours rather than sourced positions.

30. Conclusion

The sterile insect technique grew out of research begun in 1937 on what its archive calls an autocidal theory of total population management, took its method from radiation genetics in 1950, was tested on Sanibel Island and proved on Curacao in 1954.¹ Mass-reared flies from Florida plants cleared the southeastern states by 1959, the southwestern programme began at Mission, Texas in 1962, and the pest was last eradicated from the United States in 1966.³⁶ It is the best example in pest control of an insect removed rather than suppressed, and the people running it knew from the start that removal on a continent was not an end state: the originator's oral history speaks of the problems of sustaining the eradication, and of a 1972 outbreak that forced expansion into Mexico to enforce a continuous sterile barrier.² The barrier was pushed south and finally parked at the Darien Gap, as a permanent containment line held by continuous release, with its own commission from 1994 and a production plant from 2006.⁴

A permanent cost with nothing visible to show for it is exactly what a budget process trims. At its peak the programme ran several plants each producing hundreds of millions of flies a week; the Texas plant closed in 1980, the Mexican one in 2012, and by the time it mattered a single plant in Panama was producing about a hundred million a week.²⁵¹⁰ A person quoted in national reporting this month put the mechanism plainly: how do you measure something that does not happen?¹² In 2023 detections in Panama rose from about 25 a year to more than 6,500, the pest moved through Central America and into southern Mexico by November 2024, sterile fly dispersal was pushed fifty miles into Texas in January 2026, and on 3 June a three-week-old calf in Zavala County became the first American case since 1966.⁹⁴¹¹⁷ The agency said the models had predicted entry a year earlier, and that the effort had bought time. New plants in Mexico and Texas are now being built at emergency pace.¹⁰¹¹

We do not know why the barrier failed in 2023, and the argument that eroded capacity caused it is an interpretation rather than a finding. What the history does establish is the shape of the thing. A pest held out by continuous effort has not been eliminated; it has been displaced to the far side of a recurring expense. That is true of sterile flies at an isthmus, of a rat patrol at a provincial boundary, and of water standing in a drain trap, and in each case the failure is silent until the first arrival. It is also, we should admit, the strongest argument we have found for continuous preventive spending, which this journal has been sceptical of in its own trade. The screwworm does not show that any particular maintenance contract is doing useful work. It does show that when maintenance genuinely is the barrier, stopping it because nothing is happening is how the thing starts happening again.

References

1. Finding aid for artifacts in the screwworm eradication programme records, held by the national agricultural library of the United States. Official archival material. Source for the timeline entries recording that in 1937 one researcher began work on controlling screwworms by chemical means while another began research on the sterile male technique, described as an autocidal theory of total insect population management; that an insecticidal wound treatment was developed in 1938; that in 1950 a colleague introduced the originator to research on radiation-induced genetic mutations in fruit flies and two researchers began tests on sterilising screwworms using radiation; that in 1951 a researcher arrived in Kerrville, Texas to work on the sterile male technique and Sanibel Island, Florida was the first field test; that in 1954 he travelled to Curacao and began a successful eradication campaign; that mass rearing techniques were developed from 1955; and that a mass production facility was built in Florida in 1955 to 1957 with eradication achieved in a 2,000 square mile test area near Orlando. https://www.nal.usda.gov/finding_aids/artifacts-screwworm-eradication-program-records
2. Oral history collection within the screwworm eradication programme records, held by the same national agricultural library. Official archival material summarising recorded interviews. Source for the summary of the originator's interview, in which he discusses the research behind the technique, the island experiments and mainland eradication, how the programme spread across the United States and the problems encountered with sustaining the eradication, and the 1972 outbreak that prompted expansion of the programme to Mexico in order to enforce a continuous sterile barrier; and for the summary of another interview recording that the Mission, Texas plant closed in 1980 and that the interviewee, who had previous experience with organophosphate resistance and worked on strain development and genetic sexing, then helped establish a research laboratory elsewhere. https://www.nal.usda.gov/collections/special-collections/oral-histories-screwworm-eradication-program-records
3. Finding aid for audiovisual materials in the screwworm eradication programme records, held by the same national agricultural library. Official archival material. Source for the timeline entries recording that a second mass fly production facility was built in Florida in 1958, that screwworms were eradicated from the southeastern United States in 1959, and that the southwestern eradication programme began in 1962 with flies produced at the Kerrville laboratory and a mass production facility built at Mission, Texas; and for the description of the collection as relating largely to the southern Mexico plant. https://www.nal.usda.gov/finding_aids/audiovisual-materials-screwworm-eradication-program-materials
4. Report on New World screwworm background and issues for the national legislature, published by the congressional research service in 2026 and read only as a search result extract because the site refused automated access. Official research material. Source for the statement that following a decades-long campaign beginning in the 1950s the pest was eliminated from the United States, Mexico and most of Central America using the sterile insect technique; for the statement that rather than attempting global eradication the United States and partner countries established a permanent containment barrier in the Darien Gap of eastern Panama by continuously releasing sterile flies; for the establishment in 1972 of a binational commission with Mexico to coordinate eradication and move the barrier progressively southward; for the establishment in 1994 of a Panama and United States commission to maintain the barrier, with a production and dispersal facility beginning operations in 2006; and for the statement that from 2023 the pest spread beyond the barrier and reached southern Mexico in November 2024. https://www.congress.gov/crs-product/R49124
5. Article on warnings of another screwworm incursion, published by a professional society for wildlife scientists in February 2026. Professional society news material quoting a named expert. Source for the description that in the heyday of screwworm eradication the United States maintained various facilities, each producing hundreds of millions of sterile flies every week, in Texas, Florida, southern Mexico and Panama, and that only the facility in Panama remains; for the statement that the Florida and Texas facilities stopped producing and the southern Mexico facility closed in 2012; and for the quoted expert's statement that it was a big loss when the facility in Chiapas was given to the Mexican government in 2012, that it was then shut down, and that the nation lost all of its investment. https://wildlife.org/another-screwworm-incursion-inevitable-experts-warn/
6. Emergency information page on New World screwworm published by a state animal health commission. Official state government material. Source for the statement that on 3 June 2026 the pest was confirmed in a calf in Zavala County, Texas, that the calf has since recovered and the individual case is considered inactive, that federal and state partners work jointly in the infested zone on surveillance and epidemiological investigation, and that the pest was last eradicated from the United States in 1966 using the sterile insect technique, with sterile fly dispersal now under way in affected areas. https://www.tahc.texas.gov/emergency/nws.html
7. Press release from the federal animal and plant health agency confirming the presence of New World screwworm in the United States, dated 3 June 2026. Official government material. Source for the confirmation of the pest in a three-week-old calf in Zavala County, Texas, with larvae identified in its umbilical area and no further detections at the time; and for the statement by a named under secretary that all models showed the pest entering the country in 2025 but that the work of the administration and its partners had bought time for this moment. https://www.aphis.usda.gov/news/agency-announcements/usda-confirms-presence-new-world-screwworm-united-states
8. Update from a swine health information centre on screwworm detections in Texas and New Mexico, published in June 2026. Industry association material summarising official announcements. Source for the statement that the June 2026 detection was the first confirmation since the pest was eradicated from the United States in the 1960s, aside from a localised outbreak in Key deer in Florida in 2016 and 2017; and for the statement that detections had increased to six domestic animal cases by 9 June 2026, including four cattle, one goat and one pet dog in Lea County, New Mexico. https://www.swinehealth.org/usda-confirms-new-world-screwworm-detections-in-texas-and-new-mexico-in-june-2026/
9. Article on the federal agency's Texas screwworm facility and eradication strategy, published by a national veterinary association. Professional association news material reporting federal figures. Source for the figure that detections in Panama went from an average of 25 cases per year to more than 6,500 cases in one year in 2023, as reported by the federal agriculture department; for the list of countries where the pest was subsequently detected north of the barrier, comprising Costa Rica, Nicaragua, Honduras, Guatemala, Belize, El Salvador and Mexico; and for the projection that renovation of the Metapa facility would yield 60 to 100 million sterile flies a week once completed in about eighteen months. https://www.avma.org/news/usda-unveils-texas-screwworm-facility-eradication-strategy
10. Page on sterile fly production and dispersal facilities on the federal screwworm response site. Official government material. Source for the statement that the federal agency and Panama's agriculture ministry jointly manage and fund the only sterile fly production facility for this pest currently in operation in North America, producing and dispersing approximately 100 million flies a week; and for the statement that a renovated fruit fly facility in Metapa, Mexico was completed in late June 2026 and is ramping up to full production of 100 million flies a week. https://www.aphis.usda.gov/animals/animal-health/livestock-and-poultry-disease/sterile-fly-production-dispersal-facilities
11. Article on the federal response as screwworm neared the Texas border, published by the same national veterinary association in February 2026. Professional association news material. Source for the statement that the agency was shifting its sterile fly barrier zone 50 miles into southern Texas, for the grant of emergency use status to an injectable ivermectin solution for preventing infestations in cattle, and for the statement that a sterile fly production facility at Moore Air Base in Texas has a targeted maximum capacity of 300 million flies a week, with construction expected to begin that spring. https://www.avma.org/news/us-response-ramps-new-world-screwworm-nears-texas-border
12. National news article on sterile fly production and the screwworm response, published in September 2026 and read only as a search result extract because the site refused automated access. News material, flagged because the quotation it supplies is unattributed in the extract we saw. Source for the quotation that the preparedness aspect of a disease is not valued, asking how one measures something that does not happen, and stating that it becomes difficult to justify continued spending on a situation that has not been a problem; and for the statement that capacity is being rebuilt but will take time to reach its former level. https://www.cnn.com/2026/09/07/health/screwworm-billion-flies