The effectiveness of heat treatment for eliminating bed bugs

Bed bugs are notoriously difficult to eradicate. They have continued to be a major pest in the human environment over the last few decades, despite the use of modern pesticides and treatments. The overuse and misuse of organic pesticides has resulted in widespread resistance, making them a continued threat to hotels, care homes, hospitals, residential buildings and even aircrafts.

Heat treatment is well known as an effective method for killing bed bugs without leaving environmentally harmful residues. So far, no super bed bug has emerged that is resistant to the high temperatures of heat treatment. However, it still needs to be applied correctly to ensure that it reaches all the bed bugs and their eggs in a room for a sufficient length of time to eliminate them.

This article explores the multifaceted ways in which heat affects bed bug physiology, reproduction and offspring development.

Behavioural responses to heat

Bed bugs respond to the temperatures found on a human body by moving towards the source, but they only respond to this heat at distances of about 3cm. The primary means for locating a food source over distances greater than this is human body odour.

As the temperature increases, more bed bugs become active and the speed at which they move towards a heat source increases. Bed bug feeding response increases with temperature up to about 38–43°C above which it decreases.

Production of alarm pheromones

Bed bugs emit chemical signals, called alarm pheromones, to communicate danger and induce behavioural responses in other bed bugs. These pheromones are released when they are under threat or stress, prompting nearby bed bugs to move away from the source of the alarm. Situations that cause alarm pheromone release include being uncovered, crushed, or exposed to high temperatures or sublethal heat. 

We know the major chemical components of the alarm pheromone, which are (E)-2-hexenal and (E)-2-octenal in a 70:30 blend. A synthetic mixture of these two chemicals alone has been tested and found to produce the same response as the natural pheromone. Nymphs emit a slightly different blend of chemicals and females emit more than males. These induce a strong response over a 50mm radius and less so up to 100mm, so bed bugs can only warn others close by. 

The bed bug response to alarm pheromone is:

• Repulsion: bed bugs quickly move away from the source of the pheromone.
• Frantic movement: bed bugs change direction frequently in trying to escape and have even been recorded as wedging themselves under objects in “desperation”.

There are several implications for pest control of bed bug alarm pheromones when considering heat treatment.

• Exposure to heat can cause bed bugs to disperse to find cooler areas, and their frantic movement may mean at least some could find an escape route from a heated room.
• Understanding bed bug response to alarm pheromones may help to develop better control methods.
• Synthetic alarm pheromones could be used in bed bug control, such as to cause bed bugs to disperse from their hiding places for monitoring purposes.

The effect of heat on bed bug metabolism and development

Heat stress causes a range of physiological changes that harm bed bugs and affect their behaviour. The optimal temperatures for bed bug development are 25–30°C (77–86°F). As the temperature rises, their metabolic rate increases and the time required to progress through their life stages reduces. Eggs hatch faster and the nymphs develop into adults more quickly. 

As temperatures rise above the optimal range, bed bug development slows and survival declines, particularly above 37°C (98.6°F) when prolonged exposure can cause harm. Different temperatures are lethal to bed bugs depending on the time of exposure.

• The immediately lethal temperature for adult bed bugs is 48.3°C, while for eggs it is 54.8°C. 
• A temperature of 40°C can kill bed bugs in 2 days, and 38.5°C can kill them in 9 days.
• A temperature of 45°C gives a 99% mortality rate in 95 minutes.
• At 45°C bed bug eggs survive 7 hours, and at 48°C they survive about 70 minutes. 

It should also be noted that different studies can show different times because of variations in the survivability of different bed bug populations.

The physiological mechanisms by which heat affects bed bugs are complex and not fully understood. Heat stress triggers a cascade of physiological changes, including protein denaturation, accumulation of toxic byproducts, DNA damage, pH change, nutrient deprivation, desiccation and disruption of essential cellular processes. 

While bed bugs possess some defence mechanisms against heat stress, such as the production of heat shock proteins that give some protection, prolonged exposure can overwhelm these defences, leading to lasting negative consequences. So far, laboratory studies have not found long-lasting heat resistance over multiple generations

The effect of sublethal heat on bed bugs

Sublethal heat can impact the survival of bedbugs in several ways. Studies have shown that there is a critical temperature range from 37.0–40.0°C in which long exposure has detrimental effects and even small increases have a big impact. 

• Adult survival is strongly reduced when bed bugs are exposed close to 40.0°C for an extended time. 
• Fecundity is temporarily reduced and the effect is greater as time and temperature increase. 
• Nymphs are more vulnerable to heat stress. Sublethal heat impacts feeding and moulting, reducing the chance of maturing into adults. Exposure of adults to heat also affects bed bug offspring. Nymphs hatched from parents exposed to sublethal heat have difficulties in feeding and moulting, ultimately causing death. This shows sublethal heat can restrict population growth.
• Eggs have relatively low heat tolerance after undergoing development and being laid while the parent is under heat stress. This results in reductions in hatching success, which even occurs after exposure to long periods as low as 34°C.

Interestingly, the impact of heat stress appears to extend beyond direct physiological damage, potentially affecting the delicate symbiotic relationship between bed bugs and Wolbachia bacteria. These bacteria, which are present in many insect species, reside in specialized organs called mycetomes. They provide bed bugs with essential B vitamins, playing a crucial role in their growth and reproduction. 

Sublethal heat stress may disrupt this symbiotic relationship, either by directly harming the Wolbachia bacteria or by hindering their transmission from mother to offspring. This disruption can have far-reaching consequences for bed bug populations, contributing to reduced fecundity, poor egg-hatching success, and hindering nymph development.

Heat-based bed bug control methods

Heat is a highly effective, non-toxic method for controlling bed bugs. It can kill them at all life stages. However, it is most effective when used as part of a comprehensive pest management strategy. There are several methods for applying heat that are lethal for bed bugs.

1. Whole-room heat treatment

Industrial heaters are used to raise the temperature of a room or apartment to 50-60°C (122-140°F) and maintain it for several hours. Large fans circulate hot air into all areas of the room to ensure they reach a lethal temperature. This method ensures that heat penetrates furniture, walls, and other hiding places, killing bed bugs at all life stages.

This method requires professional equipment to heat the space safely and monitoring to ensure no cold spots remain where bed bugs could survive. Additionally, some items may need to be removed to prevent heat damage.

2. Steam treatment

This method uses a steam cleaner with a nozzle temperature of at least 93°C (200°F) to treat surfaces like bed frames, mattresses, sofas and carpets. The steam penetrates cracks and crevices where bed bugs hide and kills bed bugs on contact. 

Steam is particularly useful for localized infestations and can be applied by non-professionals, such as hotel staff with some training. It must be applied slowly to ensure that enough heat reaches the bed bugs and their eggs. However, this means it is time-consuming to do effectively. Also, steaming does not offer long-term residual protection and very thick surfaces may not be fully penetrated by steam.

3. Portable heat chamber

A specialised heat chamber, large enough to take small items of furniture, luggage, bedding and clothing, can be assembled onsite. Hot air is blown into the chamber, or heating elements can be embedded in the walls, to generate a lethal temperature (above 50°C / 122°F) and maintain it for a sufficient time. To be most effective, several temperature sensors should be placed in the chamber and the temperature monitored.

A heating chamber is ideal for treating items that cannot be easily washed or treated with insecticides. It is easy to use and prevents re-infestation from movable items and travellers’ luggage. However, it is limited to smaller items and does not deal with wider infestations in a building.

4. Clothes/ tumble dryer

An electric clothes dryer can be used to treat infested clothing and fabrics by subjecting them to high heat for at least 30 minutes. This will kill bed bugs and their eggs, but can only be used for heat-tolerant fabrics and products. A drying rack can be used for items that cannot be tumbled. 

This method should be used in conjunction with other treatment methods to eliminate the whole infestation in the building.

How to use sublethal heat to weaken bed bugs

Sublethal heat can be used in certain situations as part of an IPM strategy to weaken bed bug populations before a full heat treatment can be applied. 

• Ensure consistent exposure: Studies show that disrupted heat stress is less effective than constant exposure, as bed bugs can partially recover during periods of relief. Maintaining a consistent temperature within the sublethal range is crucial for maximising the detrimental effects.
• Consider duration and intensity: The impact of sublethal heat is dependent on both temperature and exposure time. Lower temperatures, such as 34-36°C, require longer durations (weeks) to achieve significant effects. Higher temperatures, closer to 38°C, can induce more rapid mortality and reproductive impairment but may not be suitable for all environments or belongings.
• Manage energy consumption: Sustained heat treatments can be energy-intensive. Carefully selecting the target temperature and considering the insulation of the treatment area can help manage energy costs.
• Address potential dispersal of bed bugs: Heat stress may induce bed bugs to seek cooler areas, potentially leading to dispersal to other rooms. Implementing preventive measures, such as sealing cracks and crevices and applying barrier treatments with desiccant dust, can help contain the infestation.

Tailor the approach to the specific situation: The most effective way to incorporate sublethal heat will depend on the specific circumstances of the infestation, such as the size and location, the availability of time before professional treatment, and the sensitivity of belongings to higher temperatures.

Advantages of heat treatment

Heat treatment is an effective and efficient method of controlling bed bugs that has numerous advantages.

• Non-toxic: The application of heat treatments uses no pesticides to eliminate bed bugs.
• Reduced use of insecticides: Using heat treatments as part of an integrated pest management plan can reduce the amount of insecticide needed to control bed bug infestations in a building.
• Kills all life stages: Heat treatments can immediately kill all bed bug life stages, including eggs, which can be difficult to eliminate with chemical methods. Bed bugs have not developed resistance to the lethal temperatures of 48.3°C for adults and nymphs, and 54.8°C for eggs.
• Effective on resistant populations: Bed bugs have developed resistance to many insecticides, making traditional chemical control less effective. Heat treatment is an effective option against these insecticide-resistant populations.
• Treats a diversity of articles: Heat can be used to treat a wide range of items that may be infested. This includes items that cannot be treated with insecticides for safety reasons, such as mattresses, electronics, clothing, luggage and various other household goods.
• Treats hard-to-reach areas: Heat can penetrate the inner parts of items and other hard-to-reach areas where bed bugs can hide, and especially in the form of steam, can penetrate cracks, crevices and seams.

Whole-room treatment: Whole-room heating systems allow for the treatment of the entire space, eliminating the need to remove or bag belongings. This can save time and effort for both the resident or business and the pest control professional.

Conclusion

Heat treatment is a highly effective solution for eradicating bed bug infestations. Its ability to eliminate all life stages of bed bugs, including eggs, through lethal temperatures, makes it a reliable and efficient approach. While preparation and specialized equipment managed by professionals may be necessary when applied at a larger scale, the benefits of heat treatment, including its non-chemical nature and ability to penetrate hiding spots, outweigh the drawbacks.

As a versatile solution applicable to various settings, heat treatment is an essential tool that can be used in certain situations by the non-professional, and for the professional as part of an integrated pest management programme for customers.