Catnip Cultivation May Offer Natural Mosquito Repellent Alternative

High-Speed Thermal Imaging Helps Researchers Quantify Catnip’s Effect

Setup of FLIR A8303sc InSb with a 50mm lens, 3.0-5.0 um, f/4.0
Figure 1

Online — Mosquitoes are a pervasive problem in tropical regions because they vector deadly diseases such as Malaria and Dengue Fever, as well as the Zika virus, which causes birth defects.
By the end of August 2016, the World Health Organization reported evidence of Zika transmission in 72 countries – 15 of which saw high numbers of babies born with microcephaly and other central nervous system malformations.
Amid the global efforts to control outbreaks of Zika and other mosquito-borne diseases, new efforts are underway to develop natural mosquito repellents that can grow easily in affected regions.
The ancient tradition of using plants to deter insects is prevalent throughout rural tropical communities; they’re inexpensive, easy to obtain, and perceived as safer than chemicals1.
Some plant-based repellents, such as citronella (derived from lemongrass oil), have gained popularity in developed countries as well. But while these natural solutions can be as effective as DEET initially, most evaporate too quickly – leaving the user unprotected2.
One plant showing promise is catnip (Nepeta cataria). Catnip produces essential oils containing nepetalactone, an organic compound that attracts cats and repels biting insects such as mosquitoes and ticks.
While nepetalactone is as effective as DEET, non-domesticated catnip produces only small amounts
of essential oil and nepetalactone concentration. The plant is too expensive to grow commercially as a repellent, and like other natural options, the oils volatilize quickly.
Dr. James Simon with New Use Agriculture and Natural Plant Products Program at Rutgers University, hopes to resolve these issues with a robust line of catnip called CR9.
He and graduate Ph.D. student, William Reichert, developed this “super-catnip” specifically to enhance the bio-active compounds while making it easier to grow commercially.

Why Not Just Use DEET?

DEET, or N,N-diethyl-meta-toluamide, deters biting insects by jamming their odor receptors: they don’t bite because they can’t smell a human nearby.
While the CDC and the EPA consider DEET safe for use on anyone over the age of two months, this harsh chemical can be harmful if swallowed.
Additionally, both agencies recommend against spraying DEET directly onto the face or skin. Spraying the chemical onto clothing is preferred, although it can damage synthetic fabrics such as those used in breathable hiking clothes.
While DEET is widely available in the US and developed countries, it can be more difficult to obtain in regions where mosquito-borne illnesses are a most prevalent. For these areas, growing their own natural mosquito repellent may make more sense.
But traditional catnip would be an inefficient crop: the perennial herb tends to grow along the soil floor and has small leaves that produce low amounts of the necessary biomass.
In contrast, the CR9 catnip has larger leaves, an upright growth habit, more essential oil production
and higher Z,E-nepetalactone yields. The researchers also designed it to survive northern winters, making commercial growth easier in temperate regions.

Testing the Efficacy of Catnip

FLIR A8300sc MWIR Camera
FLIR A8300sc MWIR Camera

To verify whether CR9 essential oils repel mosquitoes effectively, Dr. Simon used a FLIR A8303sc camera outfitted with a 50 mm lens and extender rings to observe night feeding mosquitoes (Figure 1).
The A8303sc is a 3.0-5.0 ?m MWIR, 1280 x 720 HD camera with a cooled indium antimonide detector.
It offers fast integration times of less than 500 ns and a full window frame rate of 60 Hz, allowing the user to stop motion on fast moving subjects, such as the mosquito.
Dr. Simon’s experiment involved attracting Aedes aegypti and Anopheles gambiae mosquitoes to a heat source and counting them.
Initially, the researchers used a high definition visual camera in night vision mode, but it didn’t provide the accuracy they needed.

“We needed a camera that could see in the dark – so we went with infrared. We needed to be able to count mosquitos landing on a hot pack, because they’re attracted to the heat,” explains Reichert.

The FLIR A8303sc camera allowed the researchers to visualize mosquito behavior with a high level of accuracy. This was important because the insects often crowd each other, making them difficult to count.
With the camera set for ¼ windowing, the researchers were able to record 388 frames per second as time-lapse photography – a fast enough frame rate to stop motion on the mosquitoes for more accurate data collection.

“In the low light or no light testing environment, the FLIR camera was instrumental in counting mosquitos on the control pad versus the active agent pad,” explains Reichert.
He adds, “while specifics will be released in a peer reviewed journal publication later, I can say the results were very promising.”

From Cultivation to Commercialization

So far, Dr. Simon and Reichert’s research has focused on the A. aegypti and A. gambiae mosquitoes, but they plan to test the repellent against other species as well. Then, the next step would be to find a way to make it last longer.

“Right now there is a problem with nepetalactone in that it volatizes too quickly, so people have to keep spraying it on.” Reichert explains. “We’re going to try to extend its efficacy.”

In the meantime, Ball Horticulture in Illinois has licensed CR9 for seed production. They could be available to commercial farmers as soon as 2017.

1. Maia, M.F. & Moore, S.J. “Plant-based insect repellents: a review of their efficacy,
development and testing.” Malaria Journal, vol 10 (Suppl. 1) S11, 2011.
2. Ibid.

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