PLoS One: Mosquitoes Less Deterred By DEET After Previous Exposure

 

# 6954

 

 

In May of 2010 in  From the `Nature Bats Last’ Dept, we looked at a PNAS study by James Logan et al. that looked at the reasons behind the small but growing number of mosquitoes that are not repelled by DEET - or N,N-Diethyl-m-toluamide.

Among some specially bred female Aedes aegypti mosquitoes, researchers found resistance to DEET to be caused by a single dominant gene, one that could be passed down to subsequent generations even if inherited from one parent.

 

Today, these same researchers are back with a new study that finds it doesn’t require a genetic change to reduce a mosquito’s susceptibility to DEET, all it really takes is time.

 

Roughly three hours.

 

 

Aedes aegypti Mosquitoes Exhibit Decreased Repellency by DEET following Previous Exposure

Nina M. Stanczyk, John F. Y. Brookfield, Linda M. Field, James G. Logan

Abstract

DEET (N,N-Diethyl-m-toluamide) is one of the most widely used mosquito repellents. Although DEET has been shown to be extremely effective, recent studies have revealed that certain individual insects are unaffected by its presence.

 

A genetic basis for this has been shown in Aedes aegypti mosquitoes and the fruit fly Drosophila melanogaster, but, for the triatomine bug, Rhodnius prolixus, a decrease in response to DEET occurred shortly after previous exposure, indicating that non-genetic factors may also be involved in DEET “insensitivity”.

 

In this study, we examined host-seeking behaviour and electrophysiological responses of A. aegypti after pre-exposure to DEET. We found that three hours after pre-exposure the mosquitoes showed behavioural insensitivity, and electroantennography revealed this correlated with the olfactory receptor neurons responding less to DEET.

 

The change in behaviour as a result of pre-exposure to DEET has implications for the use of repellents and the ability of mosquitoes to overcome them.

 

 

Follow the link to read the entire open-access study.  How long this acquired `resistance’ lasts in an exposed mosquito has not been determined.

 

Coming off a near-record setting year for West Nile Virus infections in the United States (see DVBID: Final West Nile Report For 2012), and with the continued  global spread of Dengue, Chikungunya, Malaria, Yellow Fever and other mosquito-borne pathogens, mosquito repellants are an important disease preventative.

 

In a press release from the Public Library of Science,  lead author James Logan explains further:

 

Mosquitoes exposed to DEET once are less repelled by it a few hours later

(EXCERPT)5

"Our study shows that the effects of this exposure last up to three hours. We will be doing further research to determine how long the effect lasts", says Logan.

<SNIP>

He adds, "This doesn't mean that we should stop using repellents - on the contrary, DEET is a very good repellent, and is still recommended for use in high risk areas. However, we are keeping a close eye on how mosquitoes can overcome the repellent and ways in which we can combat this."

From the `Nature Bats Last’ Dept

 

 

# 4548

 

 

There is an old joke that goes; as a soon as somebody invents a better mousetrap, nature will begin to work on making a better mouse.

 

And so it seems that whenever we create technological solutions to the challenges nature throws at us, its incredible laboratory begins working to come up with a workaround.

 

Bacteria learn to resist antibiotics, viruses learn to ignore antivirals and drift antigenically to evade vaccines, and eventually your neighbor’s dog learns how to burrow under your fence to get at your prized petunias.

 

Hence the old saying that Nature always bats last.

 

DEET, or N,N-Diethyl-m-toluamide  (a name that, for some reason, never really caught on with the public) is one of our most effective mosquito repellants, and has been for decades. 

 

 

Hands treated with DEET (Left) and untreated (Right).

Credit PNAS  Searching for a better mosquito repellent

 

In recent years, some Aedes aegypti mosquitoes have been observed to lose their sensitivity to DEET.  This is concerning since Aedes aegypti are very efficient vectors of diseases like Malaria, Dengue, and Yellow Fever.

 

While there are a great many unanswered questions here, this fascinating report shows that DEET resistance is apparently an inherited genetic trait, and that it can be passed down to subsequent generations of mosquitoes.

 

First this summary from Nature News, followed by the PNAS study abstract.

 

Mosquitoes inherit DEET resistance

Genetic trait explains how some insects are unaffected by powerful repellent.

Janelle Weaver

The indifference of some mosquitoes to a common insect repellent is due to an easily inherited genetic trait that can be rapidly evolved by later generations, a new study suggests.

 

By selective breeding, James Logan and colleagues at Rothamsted Research in Harpenden, UK, created strains of Aedes aegypti mosquitoes in which half of the females do not respond to DEET (N,N-diethyl-meta-toluamide) — a powerful insect repellent. They suggest that this rapidly evolved insensitivity is due to a single dominant gene — one that confers resistance even if the trait is inherited from only one parent.

(Continue  . . . )

 

 

Behavioral insensitivity to DEET in Aedes aegypti is a genetically determined trait residing in changes in sensillum function

Nina M. Stanczyka,b, John F. Y. Brookfieldb, Rickard Ignellc, James G. Logana,1, and Linda M. Fielda

Abstract

N,N-Diethyl-m-toluamide (DEET) is one of the most effective and commonly used mosquito repellents. However, during laboratory trials a small proportion of mosquitoes are still attracted by human odors despite the presence of DEET. In this study behavioral assays identified Aedes aegypti females that were insensitive to DEET, and the selection of either sensitive or insensitive groups of females with males of unknown sensitivity over several generations resulted in two populations with different proportions of insensitive females. Crossing experiments showed the “insensitivity” trait to be dominant. Electroantennography showed a reduced response to DEET in the selected insensitive line compared with the selected sensitive line, and single sensillum recordings identified DEET-sensitive sensilla that were nonresponders in the insensitive line. This study suggests that behavioral insensitivity to DEET in A. aegypti is a genetically determined dominant trait and resides in changes in sensillum function.