Wednesday, May 05, 2010

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


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.

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