Entomology: Michael Riehle

Assistant Professor

Department of Entomology,
College of Agriculture & Life Sciences, University of Arizona
410 Forbes, PO Box 210036
Tucson AZ 85721-0036
Office: (520) 626-8500; Marley 641G
Lab: (520) 626-1731; Marley 603
Fax: 520- 621-1150
Email: mriehle@ag.arizona.edu

B.S. University of Wisconsin (1993) in Entomology/Biology
M.S. University of Wisconsin (1996) in Entomology
Ph.D. University of Georgia (2003) in Entomology

Research Program

Mosquito borne diseases impact the lives of billions worldwide. Malaria alone infects at least 300 million people annually, resulting in 1 to 3 million deaths, mostly children. Other diseases spread by mosquitoes, such as dengue and West Nile encephalitis, continue to broaden their range. Unfortunately, traditional mosquito control methods such as insecticide treatment have become less effective as mosquitoes develop resistance to these compounds. Thus, it is critical that we develop novel means of controlling these pests. Towards this goal, my lab is attempting to better understand the mosquito’s physiology and use this knowledge to reduce the mosquito’s ability to transmit disease.

Insulin signaling regulates reproduction

I am interested in the balance that exists between reproductive success and lifespan in insects. Many organisms are capable of suppressing their reproductive capacity during stressful times, instead devoting their available nutrients towards maintaining themselves. For example the nematode C. elegans enters into a hardy dauer form when resources are scarce in order to survive until conditions are better. In contrast, when nutrients are abundant reproductive output is increased at the price of an extended lifespan. This balance appears to be conserved in both invertebrates and vertebrates and is regulated, at least in part, by a highly conserved insulin signaling cascade. Flies, worms, and mice with defects in insulin signaling have lifespans up to double that of their normal siblings, but tend to be sterile or have severely reduced fecundity.

The mosquito represents an ideal model organism for examining the role of insulin signaling on reproduction and lifespan because reproduction only occurs after the females have consumed a discrete bloodmeal. This gives us precise control over the timing and number of reproductive cycles an individual mosquito has during its life. Due to this we were able to determine that insulin signal directly regulates the production of steroids in the ovaries of female mosquitoes. Since these steroids are required for the production of yolk proteins, the insulin signaling cascade is one of the key regulators of egg production in mosquitoes and most likely other invertebrates. We are continuing to expand our knowledge of this cascade and the hormones that initiate it.

Manipulating insulin signaling and lifespan

Another primary focus of the lab is to determine the genetics of aging in mosquitoes. One of the greatest challenges mosquito borne parasites face within the vector is the mosquito's limited lifespan. For example, An. gambiae mosquitoes typically survive only two to three weeks in the wild. Since any parasites still within the mosquito when it perishes die as well, it is in the parasite's best interest to move on to the next vertebrate host as quickly as possible. Surprisingly, many mosquito borne diseases require extended developmental periods in the mosquito before they can be passed back to the vertebrate host. This is known as the intrinsic incubation period. Some examples include malaria (10-14 days), dengue (8-12 days), filariasis (10-14 days), and West Nile encephalitis (10-12 days). This obligate incubation period within the mosquito provides an ideal target for controlling a range of insect borne diseases. By reducing the mosquito's lifespan to less than 12-16 days it would be possible to completely prevent the transmission of several important diseases. Even a modest drop in lifespan can have a significant impact on disease transmission by reducing the number of vertebrate hosts that the mosquito can infect. In fact, the daily probability of survival is one of the most important considerations when determining vector competence according to the McDonald formula. One of the primary goals of the lab is to genetically engineer mosquitoes with a shortened lifespan, but without a large decrease in fitness.

To accomplish this we are inserting constitutively active activators and inhibitors of the insulin signaling cascade into mosquitoes. Expression of these signaling components will be regulated through a tetracycline inducible system, allowing us to increase or decrease insulin signaling as needed. Our hope is that by increasing insulin signaling in the mosquito we can reduce the mosquito’s lifespan while increasing its fecundity, resulting in a mosquito with a reduced vectorial capacity that can still compete effectively with wild mosquito populations.

Selected Publications:

Riehle MA, Jacobs-Lorena M. 2005. Using bacteria to express and display anti-parasite molecules in mosquitoes: current and future strategies. Insect Biochemistry and Molecular Biology 35 (7): 699-707.

Krieger MJB, Jahan N, Riehle MA, Cao C, and Brown MR. 2004. Molecular characterization of insulin-like peptide genes and their expression in the African malaria mosquito, Anopheles gambiae. Insect Molecular Biology. 13(3). 305-315.

Riehle M.A., Sriniva P., Moreira C.K., and Jacobs-Lorena M. 2003. Towards genetic manipulation of wild mosquito populations to combat malaria: advances and challenges. Journal of Experimental Biology. 206, 3809-3816.

Riehle M.A. and Brown M.R. 2003. cDNA cloning and molecular analysis of the serine/threonine kinase Akt in the female mosquito Aedes aegypti. Insect Molecular Biology. 12(3). 225-232.

Riehle M.A., Garczynski S.F., Crim J.W., Hill C.A., and Brown M.R. 2002. Neuropeptides and peptide hormones in Anopheles gambiae. Science. 298. 172-175.

Riehle, M.A. and Brown, M.R. 2002. Insulin receptor expression during development and a reproductive cycle in the ovary of the mosquito Aedes aegypti. Cell and Tissue Research. 308(3). 409-420.

Stracker T.H, Thompson, S. Grossman, G.L, Riehle M.A., and Brown M.A. 2002. Characterization of the AeaHP gene and its expression in the mosquito Aedes aegypti. Journal of Medical Entomology. 39(2). 331-342.

Riehle, M and Brown, M.R. 1999. Insulin stimulates ecdysteroid production through a conserved signaling cascade in the mosquito Aedes aegypti. Insect Biochemistry and Molecular Biology. 29. 855-860.