Susceptible in the Laboratory, Resistant at the Bait: House Flies and the Test That Forces Them to Eat

1. Introduction: a bait that should have worked

Our resistance articles have measured resistance as a number: how many times more insecticide a population survives. This one concerns a population whose number says the product should work, and it does not.

1.0b And the finding comes from the researchers themselves

Stated in their own abstract rather than inferred by us from their data, which is the strongest footing an article in this journal can have.²

1.1 Not a change in what the fly can survive

A change in what it is willing to eat.²

1.1b Which inverts what a resistance number is usually taken to mean

A low ratio is read as good news for a product. Here it was accurate and irrelevant at the same time.

1.2 What this article argues

That the standard resistance test forces exposure and therefore cannot see this kind of resistance, that the avoidance targets the insecticide itself, and that a ratio can be accurate and still describe the wrong thing. Sections 8, 12 and 24 are the case.

2. Why house flies

A gap in this journal.

We have written about cluster flies, drain flies and black flies and never about the most familiar fly of all. The house fly is described as a cosmopolitan species known for its pestiferous nature and potential to mechanically vector numerous human and animal pathogens.¹

2.0a Mechanical carriage is the concern

Pathogens moved on the fly's body and mouthparts rather than transmitted through a bite, which makes the contact between flies and food the thing that matters.¹

2.0b And the omission was ours rather than the literature's

House fly resistance is among the most studied problems in medical and veterinary entomology, which makes its absence from a hundred and thirty-eight articles a gap in our coverage rather than in the evidence.

2.0c And its breeding is fast

A short generation time and high reproductive output give selection many rounds per season, which is the condition under which resistance appears quickly.

That is general background rather than a sourced figure.

2.1 And it matters most where food is made or animals are kept

Dairies, poultry houses, food premises and waste handling, which is where the studies in this article were done.⁷⁸

3. How they are controlled

Mostly by feeding.

Control of adult house flies often relies on insecticides formulated into food baits.¹

3.0b Rather than contact with a treated surface

Which is how our bed bug and cockroach residual articles mostly describe exposure, and which does not require the insect's cooperation.

3.0c And a bait concentrates selection on feeding

Every fly that dies at a bait is one that ate it, so the survivors are enriched for whatever made them eat less, which is the selection pressure the rest of this article describes.

3.1 Which puts the fly's appetite at the centre of the method

A bait works only if the insect chooses to eat it, and that choice is exactly what this article is about.

4. Every registered class

The scale of the problem.

Due to the overuse of these baits, insecticide resistance has developed to all insecticide classes currently registered for use in the United States.¹

4.0b And overuse is named as the cause

Not the chemistry of any particular compound, but the way baits have been used, which is a claim about practice rather than about products.¹

4.0c Registered for use is the scope

The claim concerns the classes available for fly control in one country, not every insecticide in existence, which is still every tool a practitioner there can legally reach for.¹

4.1 All of them

Which is a stronger statement than any we have quoted about bed bugs or cockroaches, and it comes from the abstract of a 2024 peer-reviewed paper.¹

5. The ratios, where they are measured

Six dairy populations showed resistance ratios of 38 to 94 fold for abamectin and 13 to 36 fold for emamectin benzoate, more than tenfold for imidacloprid in all six and for fipronil in three, with indoxacarb and spinosad lowest at up to about seven and nine fold.⁷

5.1 Newer chemistry included

The compounds tested were chosen as insecticides with novel modes of action, and resistance was significant against most of them.⁷

5.1b And spinosad was lowest

Up to about ninefold, which is still resistance but leaves the most room among the compounds tested.⁷

5.2 Every one of these figures comes from forced exposure

Which is the point §8 develops, and why these ratios describe only part of what a bait faces in a barn.

6. And how much they vary

Three poultry farm populations in one country showed cyromazine ratios of 3.9, 10.98 and 62.5, high resistance to an organophosphate, and permethrin resistance in every population, which the authors describe as the first evidence of multi-resistance there.⁸

6.0a And an older chemistry alongside the newer

An organophosphate and a pyrethroid in the same populations, which is what multi-resistance means.⁸

6.0b And a larvicide as well as adult products

Cyromazine targets developing larvae in manure rather than adults at a bait, so resistance reaches both ends of the life cycle.⁸

6.1 Three farms, sixteenfold apart

Which is our resistance ratio article's warning about comparability, appearing within a single study.⁸

7. How a ratio is measured

The dairy study describes its reference measurement as the dose needed to kill more than 95 per cent of flies in no-choice feeding assays.²

7.1 Which is the standard for a reason

A forced test is repeatable and comparable between laboratories, because it removes the variable that would make results depend on what else the insect had to eat.

8. What forced feeding removes

Our argument.

A fly given treated sugar and nothing else must eat it or starve. The test therefore measures what the poison does once swallowed, and holds constant the one thing a bait depends on in the field, which is whether the fly swallows it.

8.0b And the field adds the variable back

A dairy has spilled feed, manure and water everywhere, so a bait competes with abundant untreated food, and a fly that refuses it loses nothing.

8.1 So a no-choice test measures physiology by design

Which is exactly what it is meant to measure, and why it is blind to behaviour.

8.1b And the same design is used for every species

The bed bug and cockroach ratios this journal has quoted come from forced exposure too, on treated surfaces or in treated food, so the blind spot is not peculiar to flies.

8.2 This is not a flaw in the test

It is a limit on what the test can answer, and the error lies in reading it as an answer to a question it was never asked.

9. The dairy

From 2008 to 2015, wild house flies from a southern California dairy developed a modest 3-fold increase in physiological resistance to imidacloprid.²

9.1 Seven years of monitoring at one site

Which is the kind of longitudinal record resistance work rarely has, and which is what allowed the two measures to be compared.²

9.1b At a single commercial facility

A working dairy rather than an experimental site, which is what makes the result directly relevant to practice.²

9.2 Modest is the authors' word

Chosen deliberately, since the point of the finding is that the physiological change was small.²

10. Threefold is not enough to survive

As the authors state.

That level is described as insufficient for these flies to survive exposure to a commonly utilized commercial fly bait whose imidacloprid concentration is three times the dose needed to kill more than 95 per cent of these flies in no-choice assays.²

10.0b Three times the lethal dose, by the researchers' own measure

Which rules out the obvious explanation that the bait was simply too weak for this population.²

10.1 The margin was designed in

A bait at three times the dose killing nearly all flies is formulated with room for exactly the modest resistance this population had.²

10.2 So on the physiological evidence the bait was sound

Which is what makes the field failure informative rather than merely disappointing.

11. And yet the flies survived

Because the field offered a choice.

When given a choice of food bait with or without imidacloprid, the flies behaved differently from how the no-choice result predicted, and resistance to the formulated bait was found to be primarily behavioural.²

11.0b The choice was ordinary food

Bait with or without imidacloprid, so the flies were choosing between the product and the same product without its active ingredient, which isolates the insecticide as the thing refused.²

11.1 In the field they seldom fed

A review records that in the field flies seldom visited or fed on imidacloprid-containing baits, and that field flies spent significantly less time feeding on them than susceptible laboratory flies.⁵

11.2 Which is resistance by any practical definition

The population survived the control measure applied to it, and a buyer would call that resistance whatever a bioassay said.

12. Which is a failure of measurement

Our reading.

A resistance monitoring programme using the standard test would have reported this population as modestly resistant and well within the bait's margin. It would have been right about the physiology and wrong about the outcome.

12.0a And the gap would not have been visible from the data

A threefold increase over seven years looks like slow, manageable drift, which is a comfortable story to tell about a product that is failing.

12.0b The monitoring would also have been blameless

Run correctly by the standard method and reported accurately, which is what makes this a problem of design rather than of execution.

12.0c And a manufacturer would see the same thing

Any registrant testing its bait against field-collected flies by forced feeding would find it effective, which connects to our efficacy data articles' concern about what testing is read.

12.1 And the error runs in the reassuring direction

Which is the dangerous direction, since a clean laboratory result is what persuades a customer to keep buying a product that has stopped working.

Sections 8 and 12 are ours.

13. What the avoidance is

Behavioural resistance to imidacloprid in this species is described as inherited as a polygenic trait, expressed as a contact and concentration-dependent phenotype.⁴

13.1 Polygenic rather than a single switch

Several genes contributing, which fits a behaviour that varies by degree rather than appearing all at once.⁴

13.2 And reducing contact reduces mortality

The mechanism is simply less poison taken in, which is why the definition centres on avoiding the lethal effect rather than on surviving it.⁴

14. Contact rather than smell

Which matters for how the bait works.

The behaviour is expressed as a contact-dependent avoidance that reduces the length of time a fly is in contact with, and feeds on, imidacloprid-treated sucrose.⁶

14.0b And the duration is what shortens

Time on the bait and time feeding, rather than the decision to approach, which is the measurement a field technician never takes.⁶

14.1 So the attractant still attracts

A fly that detects the insecticide only on contact has already been drawn to the bait and landed on it, which means the lure is doing its job and the kill is not.

14.1b And the fly still takes a little

Shortened feeding rather than none, so some insecticide is ingested at doses the population can evidently survive, which is a sublethal exposure repeated across every visit.⁶

14.2 Which is why a station can look busy and achieve nothing

Flies visiting a bait are not flies dying at it, and our monitoring articles have warned before about counting the wrong event.

14.3 And contact is how the research could see it

Video observation of individual flies at treated food, which records the duration of feeding rather than only whether the fly died.⁵

15. The insecticide rather than the bait

The distinction the research drew.

Resistance was determined to be both contact-dependent and specific to the insecticide (imidacloprid) rather than to a non-insecticidal component of a bait matrix as previously documented.³

15.1 As previously documented is the telling phrase

Earlier avoidance had been attributed to bait components, and this work established that the insecticide itself was being detected.³

15.1b And the test isolated it cleanly

Offering the same food with and without the active ingredient leaves the insecticide as the only difference the fly could be responding to.²³

15.2 Which is the harder problem

An insect that avoids a sugar can be offered another sugar. An insect that avoids the poison has to be offered a different poison.

16. Which distinguishes it from our cockroach finding

Directly.

Our glucose aversion article described cockroaches evolving to reject a sugar used in baits, which is avoidance of a bait ingredient that can be fixed by reformulating the bait around a different sugar. This fly avoids the active ingredient itself.

16.0b Both are behavioural and both defeat baits

Which is what the two findings share, and why a journal that covered one should have been looking for the other.

16.1 So reformulation cannot fix it

Changing the sugar, the colour or the attractant leaves the thing the fly is detecting in place.

16.1b Unless the replacement uses a different active ingredient

Which is a rotation question rather than a formulation one, and our rotation articles found the evidence for rotation weaker than its reputation.

16.2 And the source makes the same comparison

Noting that aversion to complex sugars in glucose-averse cockroaches can be seen as a form of cross-resistance to sugars formulated into baits.⁴

17. Concentration dependence

A property named without, in our extracts, a direction.

The review characterises the behavioural resistance as contact-dependent, specific to imidacloprid, and concentration-dependent.⁵

17.1 Alongside contact dependence

Two properties together describing a fly that responds to how much insecticide it touches, which is the kind of graded sensory response a taste-based rejection would produce.⁴

17.2 That interpretation is ours

A separate 2024 study used a proboscis extension assay to examine the mechanism, and we did not read its findings.

18. And what that implies for stronger baits

Our inference, stated cautiously.

If avoidance rises with concentration, as the phrase suggests, then the ordinary response to a failing bait, which is a stronger bait, could make the insecticide easier to detect and the bait easier to refuse.

18.0b It would also run against intuition

Our pyrethroid knockdown article found that more insecticide does not always mean more kill for other reasons, and this would be a behavioural reason to add to them.

18.1 We could not confirm the direction

None of our extracts states whether the effect rises or falls with dose, and §29 records it.

18.1b And stronger baits exist on the market

Products differ in concentration, and a practitioner facing failure can reach for a stronger one without any evidence about which way the behaviour responds.

18.2 But the possibility alone argues against escalation

A remedy that might strengthen the resistance it is meant to overcome should not be the default response.

19. It is inherited

Which is what makes it resistance.

The successful selection of fly strains for increasing behavioural resistance indicated that behavioral resistance to imidacloprid is a heritable trait.⁵

19.0b Which rules out learning as the explanation

A behaviour that increases across generations under selection and maps to specific chromosomes is carried in genes rather than acquired by experience.⁵²

19.1 By selection in the laboratory

Strains selected over generations for increasing avoidance, which is the experimental design that distinguishes an evolved trait from a learned one.⁵

19.2 And its stability has been tested

One strain was re-examined after 23 and 30 generations with no further imidacloprid, which bears on our reversion article's question of whether resistance fades when selection stops. Our extract does not give the result, and §29 records that.⁶

20. On two chromosomes

Mapped precisely.

Behavioral resistance was mapped to autosomes 1 and 4. Inheritance of resistance was shown to be neither fully dominant nor recessive.² Factors on the two autosomes independently conferred contact-dependent avoidance and a feeding preference for sugar alone, or for sugar with a different neonicotinoid, over imidacloprid.²

20.0a And the two factors do different things

One governing avoidance on contact and the other a preference between foods, which suggests the behaviour is assembled from more than one component.²

20.0b Intermediate dominance has a practical meaning

Offspring of a resistant and a susceptible parent show part of the behaviour, so the trait is not masked in mixed populations and can be selected steadily rather than only once it becomes common.

That reading is ours.

20.1 Described as a first

The study calls itself the first linkage analysis of a behavioural trait in the house fly.²

21. A definition worth having

Because the term gets used loosely.

Behavioural resistance is defined as an evolved response to the selective pressures exerted by a toxicant or formulation that enhances the ability of a population to avoid the lethal effects of that toxicant or formulation.⁴

21.0b And it includes the formulation

The definition covers avoidance of a toxicant or of its formulation, which is broad enough to include both the fly case and the cockroach case.⁴

21.1 Evolved is the operative word

It excludes an individual insect learning to avoid something, which is behaviour but not resistance.

21.2 And typical for that insect taxon is a useful clause

It anchors the definition to a change from how the species ordinarily behaves, which is what a selection experiment measures.⁴

22. How quickly it appeared

Very.

Within a few years of the commercial release of imidacloprid fly bait, both physiological and behavioural resistance were documented in house flies.⁶

22.0b Both kinds together

Physiological and behavioural resistance appearing in the same window, which means the population was being selected on two routes at once.⁶

22.1 Which is what a short generation and heavy use produce

A fly that breeds in days, exposed continuously to one product in a confined facility, is the textbook setting for rapid selection.

22.1b A few years is shorter than a product's commercial life

Which means a bait can lose its field value well before it leaves the market.⁶

22.2 Before anybody was looking for it

Which is the usual pattern: a mechanism nobody is measuring is established by the time anybody thinks to.

23. Whether it spreads to related compounds

An open question the programme addressed.

A 2024 study examined whether behaviourally resistant flies avoided other neonicotinoids as well, noting it had been unclear whether the behaviour was specific to imidacloprid or extended across the class.⁴

23.0a And the answer bears on a whole product category

Several fly baits on the market use neonicotinoids, so class-wide avoidance would remove more than one option at once.

23.0b Which matters for what to switch to

If the avoidance is specific to one compound, another neonicotinoid bait might still be eaten. If it extends across the class, the switch has to be further.

23.1 The earlier genetic work points to specificity

Since resistant flies preferred sugar treated with a different neonicotinoid over imidacloprid, which would not happen if they avoided the class generally.²

24. What this does to our resistance ratio article

It adds a second problem.

That article argued a ratio is only as good as its reference strain. This one shows that even a ratio with a perfect reference measures only the physiological half of resistance, because it comes from a test that forces exposure.

24.0b And they do not push the same way

An old reference strain can inflate a ratio, and a forced test can miss avoidance entirely, so the number can be too large for one reason and too small for another.

24.1 So the two problems compound

An uncertain denominator, and a numerator that leaves out the behaviour that decides the field result.

24.2 And our other resistance articles inherit the problem

Every ratio we have quoted for a bait product came from a design that could not have seen avoidance, so each describes physiology only.

25. Why the field result is the one that matters

For anybody paying for control.

A buyer does not care whether the fly could survive the poison. They care whether the flies go away, and only a choice test or a field observation measures that.⁵

25.0a And a buyer can observe it roughly

Flies still present despite a bait nobody has changed, which is the one outcome in pest control a customer can see for themselves.

25.0b And the field is where resistance does its damage

A laboratory survival figure matters only as a predictor of what happens in a barn, and here the predictor failed.

25.1 And choice tests exist

The research programme used feeding preference assays and video observation precisely because the standard test could not see what it was looking for.⁵

26. What we take from it

Three things.

A no-choice test measures physiology and cannot see avoidance. Section 8.²

A fly can be susceptible in the laboratory and resistant at the bait. Section 11.²

And avoidance of the active ingredient cannot be fixed by reformulating around it. Section 16.³

26.1 And one thing we cannot take from it

How common this is beyond the one population where it was shown to dominate, which no source in our set measures.

27. Our own position

The disclosure.

We use fly baits in commercial accounts and judge them by whether flies are seen feeding and whether dead flies appear. This article says feeding visits can be brief and non-lethal, and we have no way of telling a bait that is being refused from one that is simply not being found.

27.0a And a fly bait is a small part of our work

Which is why we had not thought about it carefully until writing this, and why the house fly was missing from this journal for so long.

27.0b And our monitoring cannot tell the cases apart

A station with few dead flies may be poorly placed, facing low pressure, or being visited and refused, and nothing we record separates the three.

27.1 And our response to failure has been to change products

Which is the right instinct if the new product has a different active ingredient and the wrong one if it merely has a different bait base.

28. The Manitoba position

28.1 The studies are from warm dairies

California, Pakistan and Argentina, with no northern or Canadian population in any of our sources.⁷⁸

28.1c And indoor facilities remove the seasonal break

A heated barn or food premises breeds flies year-round, which gives selection the same continuous run a warm climate would.

28.1b But the mechanism is not climate-specific

Selection by heavy bait use in a confined facility can happen in any barn, and nothing about behavioural resistance depends on a warm winter.

28.2 What we could not find

Any resistance testing of house flies in this province, any choice-test data anywhere in Canada, and any record of which fly bait actives are used most heavily here.

28.2b And food premises are where we would meet it

Restaurant and processing accounts with bait stations near waste, which is our own commercial exposure to everything in this article.

28.3 And the season is short

Which means fewer generations per year of selection outdoors, though livestock barns and food premises provide heated breeding sites through the winter.

29. Limitations and open questions

The central finding rests on one population. The dairy result in §§9 to 11 concerns a single southern California site, and the authors themselves qualify it as holding for at least that population.²

That is the most important limitation because the article generalises from that case to a claim about how resistance is measured, and one population demonstrates the possibility rather than its frequency.

We read abstracts and extracts. The genetic, behavioural and field findings reach us through abstracts, a review and a research-sharing listing rather than full papers.¹⁵⁶

One source's attribution is uncertain. The research-sharing listing for the genetic study carries passages that appear to come from a related later study, so the statements we cite from it about timing and contact-dependence may belong to a different paper in the same programme.⁶

The direction of concentration dependence is unknown to us. Section 18 reasons from a phrase whose direction our extracts do not state.⁵

The stability result is not reported here either. Section 19.2 describes a re-examination after 23 and 30 generations without exposure and not its outcome, which a separate 2024 paper on stability would contain.⁶

The cross-resistance result is not reported here. Section 23 describes the question the 2024 study asked and not its answer, which our extract did not include.⁴

Sections 3.1, 8, 12, 14.1, 16, 18, 22.1, 24 and 27 are our reasoning. The argument that forced exposure removes the operative trait, the comparison with our cockroach finding, the inference about stronger baits and the consequences for our resistance ratio article are ours rather than sourced positions.

30. Conclusion

House fly control leans on insecticides formulated into food baits, and resistance is now reported to every insecticide class registered for fly control in the United States.¹ Where it is measured, the numbers are what this journal is used to: ratios up to 94 fold for one compound in six dairy populations, and a sixteenfold spread for one larvicide across three farms in a single country.⁷⁸ Those numbers come from tests that force exposure. A fly offered treated sugar and nothing else eats or starves, so the test measures what the poison does once swallowed and holds constant whether it is swallowed at all.

At one southern California dairy that turned out to be the whole story. Between 2008 and 2015 the flies gained a threefold increase in physiological resistance to imidacloprid, which the researchers state was insufficient to survive a commercial bait carrying three times the dose that kills more than 95 per cent of them under forced feeding.² The bait failed anyway, because given a choice the flies did not eat enough of it. Resistance to the formulated bait was primarily behavioural: contact-dependent, so the attractant still draws the fly in; specific to imidacloprid rather than to another bait ingredient, which distinguishes it from the glucose aversion our cockroach article described and means no reformulation of the bait base will help; concentration-dependent; heritable under selection; and mapped to autosomes 1 and 4 with intermediate dominance.³⁵² It was documented within a few years of the bait's commercial release.⁶

That is a single population, and it establishes a possibility rather than a frequency. But the possibility is enough to change how a resistance number should be read. Our reference strain article argued that a ratio depends on its denominator. This one adds that even a perfect ratio measures only the physiological half of resistance, because the test that produces it removes the behaviour that decides the field outcome, and the error runs in the reassuring direction. A population can test susceptible and still defeat the bait. What a buyer is paying for is the flies going away, and only a choice test or a field observation measures that.

References

1. Evaluation of the inheritance and dominance of behavioural resistance to imidacloprid in the house fly, published in an insect science journal in 2024 and read as its indexed abstract. Peer-reviewed material. Source for the description of the house fly as a cosmopolitan species known for its pestiferous nature and potential to mechanically vector numerous human and animal pathogens; for the statement that control of adult house flies often relies on insecticides formulated into food baits and that, due to the overuse of these baits, insecticide resistance has developed to all insecticide classes currently registered for use in the United States; for the statement that field populations have developed resistance to imidacloprid, the most widely used neonicotinoid insecticide for fly control, through both physiological and behavioural resistance mechanisms; and for the description of the study as a comprehensive analysis of inheritance and dominance in a laboratory selected behaviourally resistant strain. https://pubmed.ncbi.nlm.nih.gov/38227570/
2. Genetic evaluation and characterisation of behavioural resistance to imidacloprid in the house fly, published in a pesticide biochemistry and physiology journal and read as an extract of its abstract and introduction. Peer-reviewed material and the source of this article's central finding. Source for the mapping of behavioural resistance to autosomes 1 and 4 with inheritance neither fully dominant nor recessive; for the finding that factors on the two autosomes independently conferred contact-dependent avoidance of imidacloprid and a feeding preference for sugar alone or for sugar with dinotefuran over imidacloprid; for the description of the work as the first linkage analysis of a behavioural trait in the house fly; for the statement that resistance to imidacloprid formulated into food bait was shown to be primarily due to a change in fly behaviour, at least for one wild population in southern California; and for the finding that from 2008 to 2015 wild flies from a southern California dairy developed a modest threefold increase in physiological resistance, insufficient to survive a commonly used commercial bait whose imidacloprid concentration is three times the dose needed to kill more than 95 per cent of these flies in no-choice feeding assays, with different behaviour when given a choice of bait with or without imidacloprid. https://www.sciencedirect.com/science/article/abs/pii/S0048357520302364
3. Selection, reversion and characterisation of house fly behavioural resistance to imidacloprid, published in a medical entomology journal in 2020 and read as its indexed abstract. Peer-reviewed material. Source for the statement that house fly resistance to imidacloprid has been selected for in field populations through both physiological and behavioural resistance; and for the determination, through behavioural observation and feeding preference assays, that the resistance is both contact-dependent and specific to the insecticide imidacloprid rather than to a non-insecticidal component of a bait matrix as previously documented. https://pubmed.ncbi.nlm.nih.gov/32516402/
4. Study examining imidacloprid behaviourally resistant house flies for neonicotinoid cross-resistance, published in a medical entomology journal in 2024 and read as an extract of its introduction. Peer-reviewed material. Source for the definition of behavioural resistance as an evolved response to the selective pressures exerted by a toxicant or formulation that enhances the ability of a population to avoid its lethal effects and exhibit behaviour different from that typical of the taxon; for the statement that behaviourally resistant insects often reduce contact with or consumption of insecticides, decreasing their mortality; for the statement that behavioural resistance to imidacloprid in the house fly is inherited as a polygenic trait expressed as a contact and concentration-dependent phenotype; for the statement that it had been unclear whether the behaviour was specific to imidacloprid or extended to other neonicotinoids; and for the comparison noting that aversion to complex sugars in glucose-averse cockroaches can be seen as a form of cross-resistance to sugars formulated into baits. https://academic.oup.com/jme/article/61/6/1443/7740907
5. Review of behavioural resistance to insecticides, its current understanding, challenges and future directions, published in an insect science review journal in 2024 and read as an extract. Peer-reviewed review material. Source for the account of earlier work documenting that in the field flies seldom visited or fed on imidacloprid-containing baits and that field flies spent significantly less time feeding on imidacloprid baits than susceptible laboratory flies; for the statement that the successful selection of fly strains for increasing behavioural resistance indicated that it is a heritable trait; and for the characterisation of the phenotype through video observation and feeding preference assays as contact-dependent, specific to imidacloprid, and concentration-dependent. https://www.sciencedirect.com/science/article/pii/S2214574524000191
6. Research-sharing listing for the genetic evaluation study in reference 2, read as a search extract. Secondary listing material, flagged because its extract appears to include passages from a related later study in the same research programme, so the statements cited from it may belong to a different paper. Source for the statement that within a few years of the commercial release of imidacloprid fly bait both physiological and behavioural resistance were documented in house flies; for the description of the behaviour as a contact-dependent avoidance that reduces the length of time a fly is in contact with, and feeds on, imidacloprid-treated sucrose; and for the note that one behaviourally resistant strain was further examined after 23 and 30 generations without additional exposure. https://www.researchgate.net/publication/345772726_Genetic_evaluation_and_characterization_of_behavioral_resistance_to_imidacloprid_in_the_house_fly
7. Study of resistance to newer chemical insecticides in house flies from dairies in Punjab, Pakistan, published in a parasitology journal in 2013 and read as an extract of its abstract. Peer-reviewed material. Source for the description of the house fly as a major pest in dairy operations that has developed resistance to insecticides with different modes of action; and for the findings across six dairy populations of resistance ratios at the median lethal level of 38.40 to 94.44 fold for abamectin and 13.16 to 36.30 fold for emamectin benzoate, above tenfold for fipronil in three populations and for imidacloprid in all populations, and lowest for indoxacarb at 3.02 to 7.12 fold and spinosad at 2.91 to 9.0 fold. https://link.springer.com/article/10.1007/s00436-013-3365-8
8. Study of insecticide resistance in house flies from poultry farms in Argentina, published in a parasitology journal in 2009 and read as its abstract. Peer-reviewed material. Source for the resistance ratios to cyromazine of 3.9, 10.98 and 62.5 in three populations; for the finding of high resistance to the organophosphate dichlorvos with ratios of 45.4 to 62.5 and of permethrin resistance in every population relative to the susceptible strain; for the description of this as the first evidence of a multi-resistance pattern in that country's house flies; and for the authors' call for an insecticide monitoring programme on poultry farms to prevent field control failures. https://link.springer.com/article/10.1007/s00436-009-1425-x