Bed Bugs Display Aversion to Fruity Aromas

Researchers have tested two naturally-derived substances as potential bed bug insecticides, with encouraging initial results.

It is well documented that bed bugs (Cimex spp.) pose a serious threat to human physical and mental health, especially in areas of high housing density. Using an effective repellent can prevent or reduce the number of bed bug bites suffered.

Long considered the gold standard of insect repellents, DEET (N,N-diethyl-3-methyl benzoyl amide) has high repellency and long-term effectiveness, and is the most commonly used repellent for preventing bites. However, increasing evidence suggests DEET causes a number of side effects in the human body, including allergic reaction, blood pressure reduction and heart rate deceleration. DEET also poses a threat to aquatic life when it enters waterways, making it an environmental hazard too. The search for alternative insect repellents is a current research focus for researchers across the globe.

In a study published in Pest Management Science in October 2023, an international team of researchers investigated the repellent effect of two safe food additives: ethyl anthranilate (EA), a scent found in grapes that is added to foods to give a fruity aroma; and butyl anthranilate (BA), a sweet, fruity flavour often used in perfumes and medicines. EA and BA are not new to this field of research; EA and/or BA have already been shown to display excellent repellent activity against many different species of insects, such as fruit flies, mosquitoes and ants. Consequently, these two anthranilates are thought to have the potential to be used as environmentally friendly and safe insect repellents for a wider range of pests than has been studied to date.

In this study, researchers from China and the US tested these two food additives against the tropical bed bug, Cimex hemipterus. This is different from most repellent screening studies, which have typically focused on the common bed bug, Cimex lectularius. The aim was to test the comparative repellency of EA and BA against C. hemipterus and to determine how long the repellent effect lasted. The team also wanted to identify which body parts of C. hemipterus were used to detect the two additives.

The results showed that when offered a choice between treated and untreated surfaces, both EA and BA had a strong repellent effect against tropical bed bugs and their repellency was similar to that of DEET, with the repellent effect lasting at least seven days. However, when a source of carbon dioxide was present (to replicate the breathing of a human, or other potential host) EA and BA were less effective than DEET, although EA continued to repel bed bugs at around 80-90%.

Not only did the researchers test if the repellents acted as a barrier to prevent bed bugs from reaching a host or a location, they also tested whether bed bugs would bite a host treated with repellent. Bed bugs are wingless and can only search for hosts by crawling; therefore, applying repellent to the host’s skin can be a highly effective way to reduce the number of bites inflicted.

The researchers found that applying a treatment of 20% EA or BA to the skin significantly reduced feeding by C. hemipterus for two hours. The effect disappeared after eight hours, suggesting that both EA and BA have short-term effectiveness as skin-based repellents. This level of performance was similar to DEET.

Knowing that DEET affects mosquitoes not only via smell and ingestion, but also via contact, the researchers wanted to determine how the bed bugs were picking up on the repellents. To do this, they ablated (removed) some parts of the bed bugs’ anatomy – the antennae, mouthparts, or both.

Interestingly, even after these parts were removed, the bed bugs could still accurately perceive EA and BA. In the choice bioassays, both the normal and ablated bed bugs preferred to spend significantly more time on the untreated surfaces. The researchers speculated that C. hemipterus likely perceives the presence of repellents in multiple ways. Additional research is needed to gain more a clearer understanding of the various mechanisms at play.

In conclusion, both ethyl anthranilate and butyl anthranilate showed strong repellency against the tropical bed bug C. hemipterus, with EA being more repellent. However, this study only evaluated two-hour and eight-hour periods after treatment, so it is important for additional research to use a greater number of evaluation points. In addition, the study used the amount of blood taken by bed bugs as the variable for measuring the repellent effect. Yet, the act of biting the host’s skin should also be one of the criteria for evaluating the effectiveness of repellents, as even a single bite may trigger allergic reactions for certain individuals. Whilst there is certainly room for further research, these preliminary findings suggest that these two food additives are worth exploring further.

 

Further reading: Zhang, Jingsheng & Xia, Yanwei & Liang, Jiayong & Wang, Changlu & Qiu, Hua-Long & He, Yurong & Ma, Tao & Wang, Lei & Wang, Desen. (2023). Repellency of two anthranilates against the tropical bed bugs, Cimex hemipterus (Hemiptera: Cimicidae) demonstrated in laboratory assays. Pest Management Science. DOI:10.1002/ps.7829

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