Effects of Pesticide Application on Cyprinidon variegatus in a Salt Marsh Ecosystem Long Island has extensive salt marsh ecosystems that are frequently sprayed with pesticides to control mosquito populations. Resmethrin and Methoprene are the two pesticides used. Resmethrin is an adulticide that kills adult forms of mosquitoes and is used when there is a public health threat, such as presence of West Nile Virus. Methoprene is a larvicide that prevents the juveniles to morph into adults by blocking biochemical pathways. These pesticides are directly sprayed onto the marshes and can accumulate into the ditch systems present in the majority of Long Island ditches. This accumulation of toxins may have an acute negative effect on the naturally occurring biota found in the ditches. To test the effects of these pesticides cages of young Cyprinidon variegatus (Sheepshead minnow) were placed in these ditches during spray events to monitor acute mortality. In situ gauges monitored the physical parameters of the ditches during the course of a six day experiment. Control Sites that were not sprayed were used as controls to test the effects the pesticides. INTRODUCTION Adulticide Results The adulticide experiments were conducted late in the summer of The spray site where the adulticide was applied was Johns Neck in Mastic/Shirley surrounded by residential housing. The control site was Havens Point in East Moriches which is also surrounded by housing and a boatyard with a park. The first experiment showed little effect with more mortality at the control site and little mortality at the spray site. The second experiment showed drastically different results with a sharp decrease in the survival in the cages directly after the spraying event. Overall, there is no clear evidence that suggests a definite acute effect from adulticide application, but there is also no evidence that shows that the fish are not harmed by the adulticide. Larvicide Results The first two larvicide experiments show a decrease in survival after application that shows a strong relationship between elevated mortality and larvicide application The second half of the larvicide applications displays stark differences than that of the first half. The second half do not show a pattern of increased mortality with pesticide application. Just as in the adulticide experiments half of the experiments support acute effects and half do not. The above graphs of the gauges in the ditches may show the most important story of the whole experiment. As the summer progressed, the dissolved oxygen percent decreased, most likely due to increased heat and light intensity. This would create periods of extremely stressful conditions that cold be enough to kill small, juvenile fish without the aid of toxic pesticides. This may also explain why the earlier experiments show a negative effect while later experiments in the more stressful conditions cannot show distinct results. The take home message from this work shows that these environments are extremely stressful and hostile that can create a serious challenge for survival. Adding pesticides to such a stressed area cannot improve the conditions and an alternative method for vector control should be explored to ease the anthropogenic stresses introduced to such important and delicate environments. Conclusion Brian Gibbins. Southampton College - SCERP research project