The Pest in the River: Black Flies, Bti, and the Control That Happens Nowhere Near a Building

1. Introduction: a pest with no structural handle

This journal's article on repellents flagged biting flies as a gap and noted that they matter more in this province than the literature we were reading acknowledged. Ninety articles in, here they are.

1.1 Why the topic is unlike every other in this journal

Every other pest we write about has a structural dimension. This one breeds in rivers, flies in from a distance, and passes through the screens we would otherwise recommend. Sections 21 and 22 are about what that leaves a contractor to do.

2. The life cycle

The biology, which determines everything downstream.

Black flies undergo complete metamorphosis: egg, larva, pupa, and adult. Eggs are laid in running water habitats (e.g., streams and rivers) and are deposited mid-flight, on the water surface, or substrates near the surface. Larvae are filter feeders, catching organic matter in their specialized mouthparts, and attach the posterior end of their bodies to substrates (e.g., rocks, ropes, and trailing vegetation) in areas of flow, and filter particles from the current.²

2.1 The running water requirement

The larvae need fast running water to develop, and one route to control is removing vegetation and other material from rivers to minimise suitable sites.⁵

2.2 Only the females bite

Males and females feed on nectar. Male black flies do not bite, but females of most species must feed on blood to produce eggs. Some prefer to bite one type of host, and some species bite people in certain locales, but do not bite in other parts of the species' range.⁷

2.3 And the adults travel

Adults can travel considerable distances to find hosts or water suitable for egg laying.⁴

Which is the reason a property owner cannot solve this on their own land, and the reason §21 is as short as it is.

3. Under the ice

A detail that matters in this climate.

One account describes eggs laid in moving water where the larvae attach to rocks using tiny hooks and survive under ice, waiting for the spring thaw, pupating underwater feeding on passing organic debris and emerging in a bubble of air as flying adults, living about 4-6 weeks, depending on species, temperature, and food supply.¹⁰

3.1 Overwintering under river ice

Which means a Manitoba winter does not reset the population. The larvae are already in place when the ice goes, which is why control windows open early and close fast.

That inference is ours and it is the local version of what our degree-day article said about timing generally.

4. How the larvicide gets in

The mechanism, which is the most elegant thing in this article.

Control is mainly aimed at the larvae, through habitat modification and insecticide application, and larvicide application of BTi (Bacillus thuringiensis israelensis) has been used with success to minimise Black fly populations.⁵

An abatement district describes how the bacterial larvicide (i.e., Bti) is delivered and ingested by larvae, with a bacterium captured by the microtricha in the labral fan ray and the fans acting in flowing water.²

4.1 The feeding apparatus is the delivery system

A larva anchored in a current, straining particles out of the water, will strain a bacterial larvicide out of the water with equal efficiency. The behaviour that feeds it is the behaviour that poisons it.

4.2 Which is why it works in a river at all

A larvicide metered into flowing water is carried downstream and delivered to every filter feeder in the reach. An extension source describes the method as metering of Bacillus thuringiensis var. israelensis into the flowing water where larvae occur.⁹

5. Why that mechanism is worth admiring

Because this journal has spent a great deal of time on the opposite problem.

Our articles on bait aversion, on rodent neophobia, on glucose aversion and on repellency all describe the same difficulty: getting a target to accept a toxicant it can detect and avoid. Our boric acid article found an industry association arguing that lack of repellency is what makes a weak toxicant work.

5.1 A filter feeder cannot avoid anything

It is anchored in place and processing whatever the current brings. There is no acceptance decision to be made and no behavioural resistance available.

That is our observation, and it explains why a microbial larvicide with no mammalian toxicity is a genuinely good control for this pest and a mediocre one for most others.

5.2 And it explains why resistance is not the story here

Our resistance articles have found behavioural avoidance defeating toxicants in cockroaches, in rodents, in bed bugs and, at continental scale, in malaria mosquitoes shifting to outdoor feeding. A sessile filter feeder has no behavioural option available.

The historical record shows the chemistry changing for other reasons: programmes against river blindness used a persistent organochlorine, later replaced with pyrethroids, organophosphates and carbamates.⁵ We found no report of Bti resistance in black flies and note that as an absence in our search rather than a finding.

5.3 The non-target record

One account notes that successful suppression programmes operate worldwide, many of which have involved extensive studies demonstrating the lack of effect that Bti-based larvicides have on nontarget species.⁶ A veterinary reference describes it as a product with no mammalian toxicity.³

6. The Manitoba survey

The local primary source, which is rare in this journal.

Ten species of black flies were collected from the Souris River, Manitoba between April 1977 and October 1978. Adults of five named species were collected feeding on livestock and humans, and are well known pest species, while two further species were the least abundant.¹

6.1 Who did it

Two entomologists at the University of Manitoba in Winnipeg, published in a Canadian entomological journal.¹

This journal has repeatedly reported that no local data exists for the subject at hand. For once there is some, and it is nearly fifty years old.

7. The abundance paradox

The finding that structures everything else.

Simulium vittatum was the most abundant species, but was not a pest on man or domestic animals.¹

7.1 What that does to a monitoring programme

A count of black fly larvae in a river is not a measure of the problem. A river can carry an enormous population of a species nobody minds.

Which means every stage of the programme requires species-level identification, and this journal's article on automated identification accuracy is about how hard that is to do at scale. That connection is ours.

7.2 The same point our journal keeps arriving at

Our article on small fly source identification found that the species determines the source and the source determines the treatment. Our automated identification article found accuracy falling sharply outside curated conditions.

Identification is the step that everything else depends on, and it is the step most often skipped.

7.3 And what it does to a complaint

A resident who sees clouds of black flies near a river has not established that those flies are the ones biting them. The two populations may be different species.¹

8. Voltinism and the timing problem

How many generations, which differs by species in the same river.

Six named species appeared to be univoltine, meaning one generation a year, while four were multivoltine in the Souris River, meaning more.¹

8.1 One river, two reproductive strategies

A single-brooded species has one vulnerable window a year. A multiple-brooded species has several, and the two do not coincide.

8.2 Which is the degree-day problem again

Our article on degree-day models and treatment timing argued that intervention windows are properties of temperature and development rather than of the calendar. Here the same river contains species whose windows differ from each other, so a single well-timed treatment is well timed for some of them.

9. The two-treatment conclusion

What the authors recommended.

In a black fly control program of the Souris River, Manitoba two separate larvicide treatments in spring may be necessary. In the case of two treatments, the first should be aimed at late instar larvae of three named species, since the majority of two others develop later.¹

9.1 Aimed at late instar larvae

Not at a date. At a developmental stage, which has to be determined by sampling.¹

9.2 Which is the definition of a monitored programme

Sample the river, identify the species, stage the larvae, then treat. Our article on economic injury levels argued that structural pest control has no such apparatus. River black fly control does, and it was worked out here in the late 1970s.

10. The sampling finding

A methodological result this journal should record.

An evaluation of cone, plate, rope, and wire cage sampling devices for black fly larvae and pupae indicated that cone samplers provided a more representative sample for population assessment.¹

10.1 Four devices, different answers

The instrument changes the estimate, which our article on detection probability and our trap catch article both argued is the central and most-ignored fact about any monitoring programme.

Here somebody tested four and reported which was better. That is what a serious monitoring programme looks like and it is not what most pest monitoring is.

11. What all that implies

Assembling the requirements.

A review of the method lists the factors weighed before a treatment: number of larvae present, stage of development, river flow rate, seston types and levels, waterway characteristics, and potential rainfall.⁶

11.1 Six variables, none of them optional

Particle load matters because a river already full of suspended material dilutes the larvicide among the particles the larvae are filtering. Rainfall matters because it changes flow and concentration.⁶

11.2 Seston is the word worth noticing

It means the suspended particles in the water, which is what the larvae are filtering. A river already carrying a heavy load of organic material presents the larva with a great deal to eat alongside the larvicide, which dilutes the dose in the most literal sense.⁶

Which is the same competition-for-uptake problem our biocide article described for organic load consuming a disinfectant, arriving here by a completely different route. That comparison is ours.

11.3 And the scale problem

A veterinary reference notes that black fly control is difficult because of the large number of flowing water breeding sites, and that large-scale control is possible if public funds and trained supervisory personnel are available.³

Public funds and trained supervisory personnel. That is the honest statement of who can do this, and it is not a pest control contractor.

12. The livestock dimension

The economic driver on the prairies, which is not the nuisance complaint.

A veterinary college teaching resource notes that among roughly 1700 species in the genus, S. arcticum and, more recently, S. luggeri are the most important livestock pests in the prairies.⁴

12.1 What the flies do to cattle

The major problem for domestic animals, particularly cattle, is blood feeding by the adult females, which often move around and attack in swarms, behaviour that can be very distressing for affected animals and can interfere with grazing and production, while the nasty bite wounds themselves are often troublesome, and frequently take some time to heal.⁴

12.2 Why the livestock case drives the programmes

A nuisance complaint from residents is a quality-of-life matter. Interference with grazing and production is a measurable economic loss, and it is the kind of loss that justifies a public larviciding budget.⁴

Which is our reading of why prairie black fly programmes exist where they do, and it is the economic injury level argument from our thresholds article applied to an agricultural pest where the injury level is genuinely calculable.

12.3 The measures used

Recommended tactics include smoldering fires with dense smoke, repellents with permethrin or ivermectin ear tags, pour-on and spray formulations, white petroleum jelly inside the ears of horses, and providing shelters.⁸ A veterinary reference adds moving animals away from breeding grounds and providing shelter to avoid morning and evening attacks.³

13. What happened on the Saskatchewan

A species replacement worth recording, because it shows the population is not static.

One account describes that coincidental with the decline of one species there were dramatic increases in the numbers of S. luggeri larvae in the two branches of the Saskatchewan River in Saskatchewan, that larvae of that species occur in three prairie provinces, and that in one summer livestock in neighboring pastures were severely harassed by swarms of it.¹²

13.1 One species replacing another

Which means a control programme calibrated to one pest species can find itself facing a different one in the same river. The Souris survey's species list is a snapshot from 1977 and 1978, and this is the reason that matters.¹¹²

14. The bite

What it does, which is different from a mosquito.

Like horse and deer flies, black flies bite using their mouthparts like scissors to cut into skin and lap up the blood, resulting in painful bites that can produce bleeding, itching, inflammation and swelling, as well as allergic reactions that can be life-threatening. The flies may enter noses, ears and mouths, causing further discomfort.⁷

A repellent testing description records that black fly landing rates ranged from 14 to 40 per minute during the test period.¹¹

14.1 Cutting rather than piercing

A mosquito inserts a stylet into a vessel. A black fly cuts the skin and feeds from the resulting pool, which is why the wound bleeds and why it takes longer to heal.⁷⁴

14.2 Fourteen to forty landings a minute

Which is the figure that conveys what a bad day near a river is like, and it comes from a controlled trial rather than from a complaint. At the upper end that is more than one landing every two seconds on one arm.¹¹

It also explains why the agencies emphasise physical measures over repellents. A product reducing landings by most of that rate still leaves a considerable number, which is the qualification the extension source makes when it notes that swarming flies may still be annoying even when repellent is used.⁹

14.3 And they work in daylight

One account notes that unlike mosquitoes they keep at it through full daylight.¹³

Which removes the avoidance strategy that works for mosquitoes, where restricting outdoor activity at dawn and dusk is meaningful. Our article on the Winnipeg mosquito programme discussed that timing at length.

15. They pass through window screens

The fact with the most direct structural relevance.

A state health department states that if netting is used to screen off an area, it must be of very fine mesh because black flies can penetrate most window screens.⁷

15.1 Which removes the standard recommendation

Exclusion is this journal's most consistently endorsed control method, and screening is the version of it that applies to flying insects. For this pest the screen does not work.⁷

A contractor recommending screen repair for a black fly complaint is recommending something that will not help, and that is worth knowing before the visit.

16. But they do not bite through clothing

The compensating fact.

A state environmental agency advises wearing hats, pants and long-sleeved shirts for maximum skin protection, because black flies don't bite through clothing, and to tuck in shirts and pants to prevent adults from crawling under clothing.⁸

16.1 Crawling under, not biting through

Which makes the closure the issue rather than the fabric. One account notes that on people they crawl into sleeves and around boot tops, especially favoring the head just beneath the rim of a hat, and recommends that zippered front shirts will keep flies out better than button shirts.¹⁰

16.2 Which inverts the usual advice

For most flying biting insects the recommendation is a barrier: screen, netting, fabric. Here the fabric works and the screen does not, so the effective measure is worn rather than installed.⁷⁸

That is the opposite of almost everything else this journal recommends, where exclusion at the building envelope is the durable answer.

16.3 And colour

The same source states that light colors such as orange, yellow and light blue are less attractive to black flies than dark ones.¹⁰

That source is a hiking publication and we flag it as such. The colour claim appears widely and we did not find a controlled study behind it.

17. The repellent contradiction

Four government and institutional sources, three positions.

A state extension service states that the repellent DEET (diethyl toluamide) is somewhat effective in preventing black fly bites, although swarming gnats may still be annoying even when using repellent.⁹

A state department of agriculture advises to use insect repellent products, such as DEET and citronella oil to deter black flies and to re-apply repellents every few hours.¹⁴

A university livestock entomology page states that the most effective repellents are those containing DEET.⁸

And a state department of public health states that black flies are difficult to repel, that DEET-containing repellents that deter mosquitoes are much less effective at repelling black flies and have even been reported to attract the flies, and that permethrin-containing repellents are the alternative.⁷

17.1 Reported to attract the flies

That is not a difference of degree from the other three sources.⁷

17.2 We cannot resolve it

Four institutional sources of comparable standing, giving advice that ranges from most effective to actively counterproductive, about the same compound and the same insect. We report all four and adjudicate none.

18. The vanillin puzzle

A second contradiction, between a health department and a patent.

The health department states that suggested home remedy repellents, such as vanilla extract, have not been scientifically proven effective.⁷

A patent specification states that its author has found that minor proportions of vanillin with DEET cause a reduction in black fly landings on the skin and substantially complete elimination of bites by the few black flies that do land, compared to DEET alone, while vanillin by itself was not significantly effective in reducing the incidence of biting by black flies since fewer flies landed but most of those that did land showed a biting response.¹¹

18.1 The two statements are compatible

Vanilla extract alone is unproven, which the patent agrees with. Vanillin combined with a registered repellent is a different claim, made by a document arguing for its own invention.⁷¹¹

18.2 The premise is the interesting part

The patent opens by stating that it would be very desirable to enhance the effect of DEET against black flies, and reports that in earlier work vanillin combined with the same compound raised mosquito protection time from about five hours to twelve or fourteen without enhancing the degree of protection.¹¹

A patent seeking to improve a compound's performance against black flies is evidence, from an interested party, that the performance needed improving.

19. What our repellent article predicted

Which is why none of §17 should be surprising.

That article found protection times against mosquitoes ranking one way and protection times against ticks ranking the opposite way, with one active leading for ticks and trailing for mosquitoes. It concluded that a repellent ranking is specific to the taxon it was measured against.

19.1 Black flies are a third taxon

Different sensory apparatus, different host-finding behaviour, different feeding mechanism, and a mouthpart arrangement more like a horse fly than a mosquito. There is no reason a mosquito ranking should transfer.⁷

19.2 And the permethrin recommendation recurs

The health department names permethrin-containing products as the alternative,⁷ which is what our repellent article found for ticks, where treated clothing outperformed skin repellent. Two taxa, same conclusion, and it is a clothing treatment rather than a skin product in both.

20. The measures everybody agrees on

Where the sources converge, which is worth isolating from where they do not.

Cover skin and close the gaps. Long sleeves, long trousers, hat, everything tucked.⁸

Fine mesh head netting. Ordinary screen is insufficient, per §15.⁷

Eye protection. Two agencies recommend glasses or goggles to keep flies out of the eyes.⁸¹⁴

Smoke. Recommended by agencies for people and by veterinary sources for livestock, consistently and without quantification.⁸¹⁴

Moving air. Large fans can be operated to help deter the flies in patio settings and open structures.⁷

And do not wear scent. One agency advises against perfumes, colognes, deodorants, hairsprays and other toiletries, which may attract black fly gnats.¹⁴

20.1 And one that is agreed on for livestock

Shelter. Both the veterinary reference and the livestock entomology source recommend providing it, and the veterinary source specifically ties it to avoiding morning and evening attacks.³⁸

A structure the animal can enter is an exclusion measure that works because the animal chooses to use it, which is a different mechanism from sealing a building.

20.2 The fan recommendation is the one we would emphasise

Because it is a small-bodied weak-flying insect, and because a fan is a physical measure with no resistance risk and no repellent controversy attached. That reasoning is ours.

21. What a contractor can offer

Honestly, and it is a short list.

Correct identification. Distinguishing a black fly complaint from a mosquito, midge, stable fly or drain fly problem determines whether anything we do is relevant, and our small fly article is about how often that goes wrong.

Telling the client what will not work. Screening, perimeter spraying of a yard, and treatment of the structure. None of these addresses a population breeding in a river kilometres away.

Fan and shelter advice for outdoor areas. Per §20.

And referral. A municipal or provincial programme is the only body positioned to larvicide a watercourse, and it requires public funds and trained supervisory personnel.³

22. And what we cannot

Stated plainly because the commercial temptation runs the other way.

A client with a black fly problem has a problem a pest control contractor cannot solve, and a contractor who sells a yard treatment for it is selling something the biology does not support.

22.1 The specific risk

Adults arriving from a river are replaced continuously, so a residual application to vegetation kills whatever is present and is refilled from upstream. Our articles on treatment failure and on rebound describe the same pattern in other settings.

The client will see an effect, because a barrier spray kills flies, and will see the problem return. That sequence is indistinguishable from a treatment that did not work, which is our credence good article's subject.

22.2 And the honest commercial note

Declining work is not something a small contractor does lightly. But a job that cannot succeed produces a dissatisfied client, a callback, and a reputation cost that outlasts the invoice.

22.3 What we would say instead

That this is a landscape-scale problem with a seasonal peak, that personal protection is the available remedy, and that the larval control decision belongs to whoever manages the watercourse.

23. The Manitoba position

Unusually, there is something to report.

A University of Manitoba study established the species composition, voltinism, pest status and recommended treatment strategy for a Manitoba river, with a sampler comparison attached.¹

23.1 And it is from 1977 and 1978

The fieldwork spans April 1977 to October 1978.¹ Section 13 records a documented species replacement in an adjacent province's river system, which is exactly the kind of change that would make a fifty-year-old species list obsolete.¹²

23.2 Why a current species list would matter

Because §7 establishes that abundance does not indicate pest status, §8 that the treatment window depends on which species are present, and §13 that species composition in prairie rivers has demonstrably changed.¹¹²

A programme operating on a fifty-year-old list is treating for the species that used to be there.

23.3 What we could not find

Any current Manitoba black fly surveillance, any published species list for the Red or Assiniboine systems, and any indication of whether larviciding is conducted in this province today. We do not conclude that none exists; we did not find it.

Which is the same finding this journal reaches in most articles, except that here the earlier work was done and appears not to have been continued in any form we could locate.

24. Limitations and open questions

The local study was read as an abstract. Species names, voltinism assignments, the sampler comparison and the treatment recommendation all come from the published abstract rather than the paper.¹

And it is nearly fifty years old. Everything in §§6 to 10 describes a river as it was in 1977 and 1978.¹

The repellent evidence is contradictory and we did not resolve it. Section 17 is four institutional sources disagreeing, and we found no controlled comparison to settle it.⁷⁹

Several sources are non-specialist. A hiking publication, an almanac and two patents, each flagged in the reference list.¹⁰¹³¹¹

We found no Bti efficacy figures. No percentage reduction, no dose, no duration of suppression. The method is described as successful without being quantified anywhere we read.⁵⁶

Horse flies, deer flies and stable flies are not covered. They were part of the gap our repellent article identified and they remain uncovered; this article is about one family only.

And we have no Manitoba incidence data. How much of a problem this is here, in which weeks, and where, is not something we could establish.

Sections 1.1, 3.1, 4.1, 5.1, 7.1, 8.2, 9.2, 10.1, 11.1, 14.1, 15.1, 19, 20.1, 21, 22 and 23 are our reasoning. The overwintering inference, the reading of the Bti delivery mechanism, the filter feeder argument, the consequences of the abundance paradox, the timing comparison, the sampling observation, the repellent taxon argument and the practical advice are ours rather than sourced positions.

25. Conclusion

Black flies lay eggs in flowing water, the larvae hold to rocks through a Manitoba winter under ice, and in spring they filter the current for particles until they pupate and emerge in a bubble of air.²¹⁰ That filter-feeding apparatus is how the bacterial larvicide reaches them: an anchored animal straining whatever the river brings cannot decline the dose.² After ninety articles largely about targets that detect and avoid what we offer them, this is the one case where the pest's own feeding strategy does the work.

The Manitoba study found ten species in one river, five of them biting livestock and people, and the most abundant biting neither; six single-brooded and four not, requiring two spring treatments timed to larval instar rather than to a date, with cone samplers giving the most representative count.¹ That is a properly specified monitoring programme, worked out here, and published in 1978.

Everything available to a contractor sits outside it. The adults arrive from kilometres away, they pass through most window screens, and they bite in full daylight.⁴⁷¹³ They do not bite through clothing, which makes closure rather than fabric the issue, and four institutional sources disagree about whether the standard repellent is the most effective option available or actively attracts them.⁸⁷ The honest position for this trade is that a black fly complaint is not a structural problem, that a yard treatment will produce a visible effect and no durable one, and that the decision that matters is made by whoever manages the river.

References

1. Ecology of black flies of the Souris River, Manitoba as a basis for control strategy. Journal article in a Canadian entomological title by two authors at a Manitoba university entomology department, read as published abstract. Used for the finding that ten species were collected from the river between April 1977 and October 1978; that adults of five named species were collected feeding on livestock and humans and are well known pest species; that one named species was the most abundant but was not a pest on man or domestic animals; that two further named species were the least abundant; that six named species appeared to be univoltine while four were multivoltine in that river; that an evaluation of cone, plate, rope and wire cage sampling devices for larvae and pupae indicated cone samplers provided a more representative sample for population assessment; and for the authors' conclusion that in a control programme for that river two separate larvicide treatments in spring may be necessary, with the first aimed at late instar larvae of three named species since the majority of two others develop later. https://www.cambridge.org/core/journals/canadian-entomologist/article/abs/ecology-of-black-flies-diptera-simuliidae-of-the-souris-river-manitoba-as-a-basis-for-control-strategy/300254533C13CA001D53A42679DC498D
2. Black fly life cycle and biology, pest abatement district information page. Public abatement agency source. Used for the description of the family as a semi-aquatic nuisance fly group with significant public health implications undergoing complete metamorphosis through egg, larva, pupa and adult; for the account that eggs are laid in running water habitats and deposited mid-flight, on the water surface, or on substrates near the surface including aquatic vegetation; for the description of larvae as filter feeders catching organic matter in specialised mouthparts, attaching the posterior end of their bodies to substrates such as rocks, ropes and trailing vegetation in areas of flow and filtering particles from the current; and for the description of how the bacterial larvicide is delivered and ingested by larvae, with a bacterium captured by fine structures in the labral fan ray and the fans acting in flowing water. https://www.bhcbugs.org/insect-programs/black-fly-control/pages/black-fly-life-cycle-biology
3. Black flies of animals, veterinary reference manual entry. Used for the statement that large-scale control requires systematic destruction of larvae in breeding sites, early seasonal intervention to prevent bites including moving animals away from breeding grounds and providing shelter to avoid morning and evening attacks, and treatment of animals with insecticides or repellents; for the statement that if public funds and trained supervisory personnel are available, large-scale control is possible by treating breeding streams with an approved larvicide; for the observation that control is difficult because of the large number of flowing water breeding sites; and for the description of the microbial larvicide as a product with no mammalian toxicity. https://www.merckvetmanual.com/integumentary-system/flies/black-flies-of-animals
4. Simulium species, black flies or buffalo gnats. Veterinary college parasitology teaching resource at a prairie university. Used for the statement that the genus contains approximately 1700 species, among which two named species are the most important livestock pests in the prairies, one of them more recently; for the description of the life cycle involving egg laying in fast-flowing water and development of hatched larvae through several stages before pupation, still in the water, and emergence of adults; for the statement that the major problem for domestic animals, particularly cattle, is blood feeding by adult females which often move around and attack in swarms, behaviour that can be very distressing and can interfere with grazing and production, with bite wounds often troublesome and slow to heal; and for the note that adults can travel considerable distances to find hosts or water suitable for egg laying, and will also attack people, causing considerable irritation. https://wcvm.usask.ca/learnaboutparasites/parasites/simulium-species-black-flies-or-buffalo-gnats.php
5. Blackfly entry, insecticide resistance industry working group pest information page. Industry committee source, cited as attributed material. Used for the statement that control is mainly aimed at the larvae through habitat modification and insecticide application, that larvae need fast running water to develop, and that removing vegetation and other material from rivers minimises suitable sites for larval development; for the statement that larvicide application of the named bacterial agent has been used with success to minimise populations; and for the historical note that programmes aimed at controlling river blindness used a persistent organochlorine applied to rivers to control larvae, later replaced with pyrethroids, organophosphates and carbamates. https://irac-online.org/pests/simulium-spp/
6. Microbial control of black flies with a named bacterial subspecies. Chapter in an edited scientific volume, read as an extract. Used for the list of factors considered before initiating an effective larvicide application, namely number of larvae present, stage of development, river flow rate, seston types and levels, waterway characteristics and potential rainfall; for the statement that successful suppression programmes are operated around the world, many of which have involved extensive studies demonstrating the lack of effect that such larvicides have on nontarget species; and for the note that two named larvicides have been successfully applied to rivers of greatly varying sizes to suppress both nuisance and vector biting in settings ranging from forested areas to peri-urban areas. https://www.sciencedirect.com/science/chapter/edited-volume/abs/pii/B9780128035276000251
7. Black flies, state department of public health information page. Government public health source. Used for the description of the insects as small dark flies appearing in late spring and early summer when they swarm and bite birds and mammals including domestic animals and people; for the statement that males and females feed on nectar, that males do not bite, and that females of most species must feed on blood to produce eggs, with some preferring one type of host and some species biting people in certain locales but not in other parts of their range; for the description that like horse and deer flies they bite using their mouthparts like scissors to cut into skin and lap up the blood, resulting in painful bites that can produce bleeding, itching, inflammation and swelling as well as allergic reactions that can be life-threatening, and that the flies may enter noses, ears and mouths; for the prevention advice to wear long-sleeved shirts, long trousers and a hat with netting, and the suggestion of hard hats smeared with oil or petroleum jelly; for the statement that large fans can be operated in patio settings and open structures to help deter the flies; for the statement that if netting is used to screen off an area it must be of very fine mesh because black flies can penetrate most window screens; and for the statements that black flies are difficult to repel, that suggested home remedy repellents such as vanilla extract have not been scientifically proven effective, and that repellents containing the standard mosquito active are much less effective against black flies and have even been reported to attract them, with permethrin-containing repellents named as the alternative. https://dph.illinois.gov/topics-services/environmental-health-protection/structural-pest-control/black-flies.html
8. Black fly entry, university livestock veterinary entomology information page, together with a state environmental protection department protection page. Used for the statement that to get the best control it is best to aim for the larval stage since larvae are easier to target due to their specific habitats and concentrated developing habits, while treating adults with repellents and pour-on products gives small results at high cost; for the statement that the named bacterial larvicide is typically used to treat waterways worldwide for larvae and that the most effective repellents are those containing the standard mosquito active; for the livestock tactics of smouldering fires with dense smoke, repellents containing permethrin or ivermectin ear tags, pour-on and spray formulations, white petroleum jelly inside the ears of horses, and provision of shelters; and, from the environmental department page, for the advice to wear hats, trousers and long-sleeved shirts because black flies do not bite through clothing, to tuck in shirts and trousers to prevent adults crawling under clothing, to wear glasses or goggles, to use an insect head net in areas of high populations, that smoke from campfires and similar sources repels them, and to avoid perfumes, colognes, deodorants, hairsprays and other toiletries which may attract them. https://livestockvetento.tamu.edu/insectspests/black-fly-simuliidae/
9. Biting flies, state university extension service fact sheet. Used for the statement that problems can sometimes be avoided by personal protection measures such as appropriately coloured clothing, insect repellents and avoiding times of day when biting is most intense; for the observation that while all biting flies are blood feeders, none aside from mosquitoes are known to transmit human diseases in that state, though some flies transmit animal diseases, and that bites can be painful or produce swelling and intense itching as the result of injected saliva; for the statement that the standard mosquito repellent active is somewhat effective in preventing black fly bites although swarming flies may still be annoying even when using repellent; and for the description of larval control as metering of the named bacterial larvicide into the flowing water where larvae occur, using the same products used for mosquito larval control. https://extension.colostate.edu/resource/biting-flies/
10. Black fly season, outdoor recreation publication article. Non-specialist source, cited as attributed material. Used for the account that eggs are laid in moving water where larvae attach to rocks using tiny hooks and survive under ice awaiting the spring thaw, pupating underwater while feeding on passing organic debris and emerging in a bubble of air as flying adults, living about four to six weeks depending on species, temperature and food supply; for the note that when they hatch they are often preyed upon by fish; for the description that on people they crawl into sleeves and around boot tops, especially favouring the head just beneath the rim of a hat; and for the clothing advice that closely fastened sleeves and fronts with trousers tucked into socks or high boots offer good protection, that zippered front shirts keep flies out better than button shirts, that light colours such as orange, yellow and light blue are less attractive than dark ones, and that shoulder-length head nets are sometimes useful and can be impregnated with repellents. https://sectionhiker.com/black-fly-season/
11. United States patent specifications concerning repellent compositions and repellent testing methods. Patent documents arguing for their own claimed inventions, flagged as commercial advocacy. Used for the statement that it would be very desirable to enhance the effect of the standard repellent active against black flies without decreasing its effect against mosquitoes; for the cited earlier work in which vanillin combined with that active at higher weight ratios raised mosquito protection time from about five hours to about twelve to fourteen without enhancing the degree of protection; for the claimed finding that minor proportions of vanillin with that active cause a reduction in black fly landings on the skin and substantially complete elimination of bites by the few black flies that do land, compared to the active alone; for the statement that vanillin by itself was not significantly effective in reducing the incidence of biting, since fewer flies landed but most of those that did showed a biting response; and, from the testing method specification, for the description of protection time as the interval between treatment and the first confirmed bite, for the use of a ratio of protection times against a standard repellent as the best measure of effectiveness, and for the report that black fly landing rates ranged from 14 to 40 per minute during the test period. https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/4427700
12. Some recent changes in black fly populations of prairie river systems. Journal article in a Canadian water resources title, read as a document extract. Used for the account that one named species continued to threaten livestock in adjacent areas while, coincidental with its decline, there were dramatic increases in the numbers of a second named species in the two branches of a named river system; for the statement that larvae of the second species occur in three prairie provinces; and for the report that in one summer livestock in neighbouring pastures were severely harassed by swarms of that species. https://www.tandfonline.com/doi/pdf/10.4296/cwrj0203090
13. Black fly season guidance, general interest almanac publication. Non-specialist consumer source, cited as attributed material. Used for the statements that the season opens in late May across the northern United States and southern Canada, that the bites itch for days and the swarms cloud around the face, and that unlike mosquitoes they keep at it through full daylight; and for the report of an extension service recommendation that permethrin be applied only to clothing and never to skin, and be allowed to dry fully before wear, together with the note that it is toxic to fish, cats and honey bees. https://www.farmersalmanac.com/black-flies
14. Black fly personal protection, state department of agriculture guidance sheet. Government agricultural agency source. Used for the advice to tuck in shirts and trousers to prevent adults crawling under clothing, to wear glasses or goggles to help prevent adults entering the eyes, to use insect repellent products such as the standard mosquito active and citronella oil, to re-apply repellents every few hours to maintain maximum effectiveness, and for the note that smoke from various sources repels black flies; together with the advice that if bitten one should avoid scratching, which can worsen allergic reactions. https://mda.maryland.gov/plants-pests/documents/blackfly.protection.pdf