Understanding Resistance

Resistance is defined as a change in the sensitivity of a pest population to a pesticide. This means even the correct application of the pesticide fails to control the pest. Resistance can develop when the same pesticide or a pesticide with a similar mode of action are used over and over again.

It was presumed the pests changed or mutated to become resistant. However, it is not the individual pest (insect, weed, or microorganism) that changes, but the population.

When a pesticide is applied to a crop or treatment site, a tiny proportion of the pest population (for example, one insect or weed in 10 million) may survive exposure to the pesticide due to its genetic makeup. When the surviving pests breed, some of their young will inherit the genetic trait that confers resistance to the pesticide. Through subsequent generations, the less-susceptible individuals in the population increase.

A case in point: DDT

We saw this with the use of DDT on bed bugs during the second world war. DDT was used extensively to control pests within troop quarters from 1939. By 1940, bed bugs were already proving resistant to the potent chemical. After DDT was banned in 1972, people started using pyrethroid pesticides, like deltamethrin and lambda-cyhalothrin. Pyrethroids kill insects in a similar way as DDT. Both pyrethroids and DDT target the same part of an insect’s nervous system. Because of this, some bed bugs that were resistant to DDT were also resistant to pyrethroids, even if they had never been around pyrethroids before. This is called cross-resistance and is a contributing factor in our current resurgence of bed bug issues.

How a Professional Pest Controller Deals with Pesticide Resistance.

When the efficacy of a treatment drops, the pest controller will generally use higher rates and more frequent applications until the pesticide provides little or no control. This is NOT the way a professional pest controller will do things.

Identify your pest correctly

Older broad-spectrum pesticides may have worked on any living thing and didn’t require exact identification, but new chemistries are designed to kill
only the target pest and have less effect on beneficial insects.

Get the Timing Right

Timing is critical. Correct timing of a pesticide application can be the
difference between success and failure. New pesticide chemistries may
target only a certain life stage of the pest, like eggs or larvae, so timing the
application to the correct life stage is more critical than ever. Even with older
chemistries, contact insecticides may only be effective on a certain life stage,
like scale crawlers. It takes time to scout and determine exactly when the
crawlers are exposed but applying too early or too late will be a waste of time,
money and pesticide. Some pesticides should only be applied a certain number of times or amount per year, so you must time the application to maximize its effectiveness.

Sulfuryl Fluoride (ProFume) has proven efficacy on ALL life stages of pest but Research by the Queensland Department of Agriculture and Fisheries, with GRDC investment, has shown that effective control of all insect life stages with sulfuryl fluoride requires seven-day exposure for grain above 25°C, and 10-day exposure for grain between 20°C and 25°C. When grain is below 20°C, fumigation with sulfuryl fluoride is unlikely to be 100% successful as the insect life cycle is too slow, meaning the gas is not absorbed by the adolescents.

Coverage is Paramount

Coverage is another critical aspect of treatments.  If the pesticide does not reach the target pest, it will be ineffective. This may not be critical with systemic pesticides, but it is important when using a contact pesticide.

Factors to consider when applying a contact pesticide:

• Are you applying too quickly?
• Are the droplet sizes/nozzles right for the application?
• If using an airblast sprayer, are the nozzles correctly selected and adjusted for the various levels of height?
• Is the wind blowing too much at the time of application?
• Do you need to add an adjuvant to alter the droplet size or spread?

We can all be lazy, but don’t let the importance of coverage escape your attention.

Factors to consider when applying fumigant treatments

All fumigants, including sulfuryl fluoride, require gas-tight sealable storage to effectively control insects at all life stages. Unsealed storages will not hold a high-enough gas concentration for a long-enough period of time to kill the eggs, larvae and pupae.

Unlike methyl bromide which can be sealed using regular duck tape, sulfuryl fluoride requires a specialised tape such as Fumico’s specifically engineered PINK TAPE. 

Environmental Conditions

Wind and rain can wreak havoc on any pest treatment.  Temperature extremes can inactivate chemicals or, as in the case of oil based chemicals, make it phytotoxic to the crop. Temperatures also effect the development of pests: cooler conditions slow the life cycle while warmer conditions offer a robust breeding, developing phenomenon. Cooler environments will need longer exposure times to irradicate pests through the entire life cycle.

Sulfuryl fluoride is a heavy gas at 3.7 times the density of the atmosphere. Most applicators will introduce the gas into the top of a storage, anticipating it will settle to the bottom. Best practice is to have some form of sealed recirculation system to gently transfer gas through the storage to ensure an even concentration throughout the grain bulk for the duration of the fumigation.

Without recirculation, it will take longer for the gas to reach all parts of the storage and, as it sinks, it will likely leave the top of the storage with a sub-lethal gas concentration.

Pesticide Storage

Unsuitable storage conditions can impact the quality of the pesticide and harm application effectiveness. Some pesticides, especially biologicals or biorationals, have stringent storage requirements and can be inactivated
above or below certain temperatures. Some pesticides were just not created
to maintain effectiveness if stored for too long or under conditions above
40° C – which many areas of South Africa can experience regularly.

Some pesticides have a use-by date. Pesticides should be stored on a “first-in, first-out” basis.

Sulfiryl Fluoride (ProFume Fumigant Gas) is classed as a hazardous chemical and therefore transportation and storage of cylinders are strictly controlled.

Rotate Chemical Treatments

Never rely on a single pesticide class. Rotate modes of action, especially
when there is more than one generation of the pest in a year. For example, rotating phosphine fumigation with sulfuryl fluoride will protect against the development of phosphine resistance.  Read More about Sulfuryl Fluoride can break phosphine resistance…

Best Pest Control Practice

Your goal should always be to apply pesticides at the recommended rate with thorough coverage. Using a higher rate is illegal and may not be more effective. Using a lower rate can also be ineffective. Applying pesticides
without calibrating your equipment or checking the deposition uniformity can
be dangerous and wasteful.

“If at first you don’t succeed, try again” does not apply to pesticide applications of the same chemical. If control with a pesticide fails, do not retreat with the same chemical or another with the same mode of action.

Re-examine your checklist:

• Did you properly identify the pest?
• Did you use the correct dosage and timing?
• Is yourequipment properly calibrated and
  do you have good deposition?
• Were environmental conditions correct for
  the application?
• Was your pesticidequality still good and not out of date?

If you answer yes to all these, then try another pesticide with a different mode of action or a tank mix with two different modes of action. Pest resistance is something we all need to work together to avoid

A history of bed bug problems

Bed bugs and humans are as common to each other as dogs and fleas. Cave drawings depict bed bugs. Photographs of them were captured on the first cameras in the 1800’s. Bed bugs have found a sleeping human to be a delicious companion.

Culturally, bed bugs have also shaped human history. Some historians suggest the annual practice of spring cleaning may have begun as an attempt to flush out bed bugs. They are less active during the colder winter months, but become reinvigorated in the spring and summer.

Chemical warfare on bed bugs

Insecticide has been used to quell bed bugs for over a century. DDT was used before the 1950’s but by 1956 pest controllers reported deminishing effectiveness of this potent chemical.  The repetitive exposure of bed bugs to DDT led to the survival of bed bugs with genetic mutations that allowed them to survive DDT exposure. this gave rise to newer generations with the same mutations. A new chemical was introduced; pyrethroids–synthetic insecticides widely used for residential pests. However, there was an unforeseen consequence of DDT resistance: bed bugs with DDT resistance demonstrated resistance to other pesticides, including pyrethroids, even if they had never encountered pyrethroids. This phenomenon is known as cross-resistance.

DDT was banned in 1972 which compelled the United States to turn to organophosphates.  These chemicals largely eliminated bed bugs from the developed world. However, toxic effects on human health were discovered and they were banned too. This gave the bugs a break. Broader international trade rules also opened the exchange of goods across the world. “Bed bugs became a problem after we went through the ban on organophosphates indoors,” says Jody Gangloff-Kaufmann, an entomologist at the New York State Integrated Pest Management program at Cornell University. The bugs came back in the early 2000s, spread primarily along trade routes from developing nations to industrialized countries, and flourished in a new world with less aggressive chemical attacks.

In 2010, cities like New York experienced massive bed bug infestations. Alarming sightings closed retail stores in Soho and South Street Seaport. Even workplaces weren’t immune, as the insects infiltrated Time Warner’s headquarters near Central Park as well.

Knockdown Resistance a root cause for bed bug resurgence

The current surge in bed bug infestations is not merely a revival of a longstanding problem; it is a complex issue intertwined with the development of resistance to insecticides. This mechanism is known as knockdown resistance. This mechanism, along with three other main resistance mechanisms, has enabled these insects to defy chemical-intensive control methods 

Knockdown resistance is a significant factor contributing to the resistance exhibited by bed bugs to insecticides, especially pyrethroids. The mechanism plays a central role in countering the action of these insecticides, which target the nervous system of bed bugs, causing paralysis and eventual death. Knockdown resistance provides the genetic adaptation that provides bed bug populations with resistance to insecticides. It inhibits the effectiveness of certain insecticides. Bed bugs with the mutation have a genetic advantage that allows them to survive exposure to these chemicals. 

Pest Management Protocols.

Unlike mosquitos and ticks, which government groups address with wide-scale, community-wide spraying and eradication efforts, bed bugs are seen more as an individual, rather than a societal, problem.

Bed bugs don’t transmit diseases like mosquitos and ticks do. While they feed on human blood, they don’t pass on whatever they pick up, since they have a unique ability to fracture the DNA of pathogens they ingest so they are no longer capable of causing disease. “If you imagine the DNA of a virus like polio or HIV or influenza as a glass vase, once it is ingested by a bed bug, it shatters,” says Gail Ridge, an associate scientist at The Connecticut Agricultural Experiment Station, a state and federally funded research facility. “That makes controlling bed bugs a hard sell for government intervention, since they don’t technically cause public harm other than a general sense of anxiety and discomfort.

Combined Arms Management: Physical and Chemical treatments for bed bugs

The best way to irradicate bed bugs is a combination of physical and chemical treatments. Bed bugs do not stray far from their food source. A professional pest company will examine the area within close proximity of the infected bed; under the box frame, head board, cracks in the floorboards, drapes, curtains and wall paper as well as the linens, pillows and mattress. Any form of ‘clutter’ can be a hiding area for bed bugs.

In multi-home establishments (apartments) it is important to seal any access routes from neighbouring homes too.

Vacuuming and high temperature treatments (steam clean, hot wash and tumble drying) are effective on clothing and linens. The most effective bed bug pesticides are available to commercial pesticide applicators only.

Insecticides may be applied as liquids directly to cracks, crevices, bed frames, baseboards, and other similar sites, or they may be applied as dusts in cracks and crevices. Pesticides aren’t generally applied to mattresses or bedding because of potential risk to people. Over-the-counter total-release aerosol foggers has been shown to be ineffective for bed bug control and potentially harmful to residents; they are not recommended.

Liquid insecticide formulations used by professional pest controllers include:

• Products containing the botanical insecticide pyrethrin, which gives quick knockdown but little long-term control
• Various synthetic pyrethroid products (e.g., cyhalothrin, bifenthrin, deltamethrin, and permethrin)
• Mixtures of pyrethroids and neonicotinoids (e.g., Temprid and Transport)
• Various botanical oils
• Newer types of products including the pyrrole insecticide chlorfenapyr (Phantom) and the insect growth regulator (IGR) hydroprene (Gentrol)

Aprehend is a fungus-based treatment used by licensed pest control specialists. The treatment is a spore in a liquid form that is sprayed on affected areas; the contact with the fungus gives the bugs a dermal infection that kills them.

Sulfuryl Fluoride used for bed bugs

Fumigation using the active ingredient sulfuryl fluoride is commercially available for bed bug control and can be highly effective in appropriate situations.

Field Evaluations of Sulfuryl Fluoride Fumigation for Control of the Common Bed Bug (Hemiptera: Cimicidae), Using a 1.9× Dosage Factor in Motor Vehicles and Filled Cargo Trailers  In this study, a mini van and a tightly packed trailer (85% capacity) were infected with bed bugs and fumigated with sulfuryl fluoride using 1,9x dosage factor. Upon aeration the sentinel bugs, nymph and eggs were removed and monitored for 23 days post fumigation. It was concluded sulfury fluoride was 100% effective against bed bugs through all life stages.

Future controls for bed bugs

Cockroaches are the natural predator of bed bugs (they consume the eggs) but cockroach control is fundamental to hygiene and pest management… bed bugs may be a challenge far into the future.

Inbreeding is suicide for most species since mating with genetically related members can introduce dangerous, and potentially lethal, mutations. Bed bugs don’t have such limitations; a single female carrying eggs can seed a new colony of bugs in a location as the future generations breed among themselves. “We have seen brother-sister matings for 20 to 30 generations and nothing happens,” says DeVries. “The later generations are just as happy and healthy as the first.”

Resistant bugs are getting hardier and hardier. Cross breeding with different populations makes them even more fertile, says Ridge. She has crossed two different lab populations of bed bugs and found that the fecundity of the females doubled. “I can only assume that’s happening in the wild as well,” she says, especially since bugs from different parts of the world are likely mixing and matching thanks to widespread human travel.”

Integrated pest management remains the only successful means to control bed bugs. While bed bugs can certainly find their way to luxury hotels and hitch a ride home on the Louis Vuitton luggage; the wealthy can afford to treat the problem as it occurs.

For those in tightly packed disadvantaged communities such as nursing homes and hostels, bed bugs become just another burden limited funds cannot control.

As the globe continues its fast paced integration with humans travelling en masse via public transport, goods are shipped worldwide and the common bed bug codes future bugs with DNA  to resist chemicals used… Paris is just a foretaste for future cities which will no doubt face bed bugs for centuries yet.