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Title: Effects of Reserpine on Reproduction and Serotonin Immunoreactivity in the Stable Fly Stomoxys Calcitrans (L.)

Author
item Liu, Samuel
item Li, Andrew
item WITT, COLLEEN - University Of Texas At San Antonio
item Perez De Leon, Adalberto - Beto

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/28/2012
Publication Date: 9/3/2013
Citation: Liu, S.S., Li, A.Y., Witt, C.M., Perez De Leon, A.A. 2013. Effects of reserpine on reproduction and serotonin immunoreactivity in the stable fly Stomoxys calcitrans (L.). Journal of Insect Physiology. 59:974-982.

Interpretive Summary: The stable fly, Stomoxys calcitrans, is one of the most economically important pests of livestock, particularly cattle in North America. Economic damages of the stable fly to cattle production in the United States are estimated at over two billion U.S. dollars annually. The stable fly is difficult to control due to its feeding and reproductive behaviors. In addition, stable fly populations developed resistance to insecticides. It is necessary to understand the molecular and physiological mechanisms of key behaviors including feeding and reproduction in order to develop novel insecticides or behavioral disruptors for effective control of the stable fly. Here, reserpine was used as a biogenic amine-depleting chemical agent to study the roles of a neurotransmitter, serotonin, in stable fly reproduction, specifically sperm transfer and female oviposition. Sperm viability dyes were used to visualize sperm in males and female reproductive tracts. Feeding five-day old males with reserpine-treated cattle blood resulted in a significant reduction of mating success, while younger males were less sensitive to reserpine treatment. Reserpine treatment of five-day old females caused a significant reduction in the number of eggs laid, but did not have effect on egg hatch rate. A tissue staining technique involving the use of antibodies was applied to detect serotonin in the male reproductive system after reserpine treatment. Experimental results showed that reserpine depleted the neurotransmitter from nerves innervating male testis, which resulted in failure of mating behavior. The findings obtained in this study indicate that biogenic amines play an important role in stable fly reproduction. The disruption of this process provides an avenue to develop new insecticides for effective stable fly control.

Technical Abstract: Biogenic amines are known to play critical roles in key insect behaviors such as feeding and reproduction. This study documents the effects of reserpine on mating and egg-laying behaviors of the stable fly, Stomoxys calcitrans (L.) (Diptera: Muscidae), which is one of the most economically significant biting fly pests affecting cattle. Two sperm-staining techniques were adapted successfully to reveal the morphology of stable fly sperm and to determine mating success in females through the assessment of sperm transfer for the first time. This approach was also applied to assess sperm transfer by males treated with different doses of reserpine. Mating did not occur in flies during the first 3 days (d) after emergence. Thereafter, the percentage of females that mated increased with age. Reserpine treatment of males reduced sperm transfer in a dose dependent manner. Older males were more sensitive to reserpine treatment than younger flies. Reserpine treatment of 5 d old females reduced the number of eggs laid, but had no effect on egg hatching rates. Results of immunoreactivity (IR) experiments indicated that serotonin in the neuronal processes innervating male testes was completely depleted by reserpine within five hours after treatment. This effect was transient as the serotonin IR signal was recovered in 33.3% of the males at 1 d post treatment and in 94.4% of the flies at 3 d post treatment. The results of this study concur with previous findings in other insect species and extend our knowledge of the critical roles biogenic amines play in mating and oviposition behaviors of the stable fly. The knowledge provides the foundation to further characterize the specific roles of individual biogenic amines and their receptors in stable fly reproduction.