Researchers look for genes linked to when mosquitoes bite

Written by Andrew Porterfield

Mosquitoes and other blood-feeding insects can cause a range of serious human diseases, including malaria, dengue, Zika, West Nile, chikungunya, and yellow fever. Since these diseases have so far evaded effective vaccines, insecticides and insecticide-treated mosquito nets have been among the most effective ways to limit their spread.

However, scientists have observed that these insecticide strategies create strong mosquito selection pressures, leading to the development of insecticide resistance and behavioral changes among mosquitoes. Behavioral changes include changing blood feeding times, as mosquitoes change their bites after they leave the nets in the morning hours and before they enter the evening.

The circadian molecular clocks that control these behaviors are genetically controlled feedback loops that respond to cycles of light and dark and temperature changes. Also, flight and feeding behavior are closely related, with flight time being an indicator of increased feeding among mosquitoes. This behavior has been observed to change, apparently in response to pesticide use, but its genetic basis has not been closely studied.

A team of researchers from the University of Notre Dame and the US Department of Agriculture’s Agricultural Research Service looked for the genetic basis that could underlie the difference in the timing of mosquitoes feeding blood. By studying the behavior and inheritance of two strains of mosquitoes in Colex Babies Researchers have discovered a previously unknown set of genes that can detail the genetic basis behind mosquitoes calibrating day and night for blood feeding. they The results were published in August in Journal of Medical Entomology.

Previous studies have shown that C. pipiens They generally feed at twilight and at night, but female flight activity has been observed to vary greatly between strains of mosquitoes. Researchers compared the behavior and genes of two Colex Breeds: Shasta breed (from Shasta County, California), an ancient isolate that feeds at any time of the day or night, and Trinidad breed, a newer breed from the West Indies that feeds only at night.

For the genetic part of the study, the researchers first mated a male from Trinidad with a female Shasta to form a cross generation (F2). Crosses create individuals or lineages with different parts of the genome inherited from parental lineages. Both phenotypes (in this case, feeding times and flight activity) and genotypes (genes that may be associated with these behaviors) were examined. The researchers then performed quantitative trait locus (QTL) mapping, a statistical analysis that attempts to identify a region on the chromosome associated with a phenotype (feeding times and flight activity). QTL analysis does not necessarily identify specific genes – only the region of the chromosome that appears to influence the trait being observed. In this experiment, 95 F2 progeny mosquitoes were used for QTL analysis.

Genetic association maps have been used to determine the genetic location of clock genes and other genes shown in previous work to play some role in feeding or locomotion. Then, flight activity was observed for 32 females of the two strains over a seven-day period, recording the frequency and time the mosquito broke the infrared beam in flight.

The researchers found a single QTL on chromosome 2 that was behind the differences in blood feeding time between the two strains. The QTL region was 67.4 Mb (huge bases), and contained 2062 genes. Of these, 21 were involved in regulating behaviour, feeding behaviour, daily behaviour, locomotor behaviour, or sleep. Flying activity was also significantly different between the two breeds, with the Trinidad breed being active at night, dusk and dawn, and the Shasta being active during the day.

Surprisingly, well-known clock genes such as a periodAnd the KhalidaAnd the Wall ClockAnd the CourseAnd the PAR 1 . domain proteinAnd the vrilleAnd the enlarged discsAnd the Cryptochromis 1 And the 2, you are not in the QTL. says lead author Paul Heckner, PhD, a research entomologist at USDA-ARS Knipling-Bushland, US Livestock Insect Research Laboratory, Kerrville, Texas, and a postdoctoral researcher at the University of Notre Dame. “Identifying QTLs with small effect is challenging and often requires analysis of a very large number of F2 offspring.”

How — and how quickly — this difference evolved between the strains remains unknown, says Heckner, “because we don’t know exactly which genes are involved. Colex Babies They are generally twilight and/or night feeders, but there has been consistent genetic variation in essential genes within the Shasta group that, in the right combination, can produce blood feed at any time of the day. “

could Colex Develop these behavioral changes without genetic change? It’s unlikely, Heckner says. Blood nourishment requires many physiological processes such as flight, sensory perception, metabolism and detoxification. These are generally partly related to the circadian clock. Blood feeding at any time of the day can represent a “disengagement” between these processes and the clock. “

The conditioning of diurnal feeding in nocturnal mosquitoes is not limited to C. pipiensThe researchers write. ‘Pimperena strain of Anopheles The Gambia It is almost exclusively for nocturnal blood feeding, while others A Gambia Lab strains feed during the day.”

Heckner and colleagues add: “Further studies are needed to determine whether the genetic mechanisms of shift in blood feeding times in laboratory colonies are related to those that underlie the shifts observed in field populations. A better understanding of the genetic basis of these behaviors could help identify measures to counteract These challenges are in the prevention of vector-borne diseases.”

Andrew Porterfield Writer, editor, and communications consultant for academic institutions, corporations, and nonprofit organizations in the life sciences. He resides in Camarillo, California. Follow him on Twitter at Tweet embed Or visit his site Facebook page.

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