Research 

The Effects of Two Commonly Applied Pesticides, Resmethrin and Methoprene on a Key Salt Marsh Predator

Vashtidevi B. Mahadeo

Advisor: Dr. Matthias Foellmer

​

The pesticide Scourge and the larvicide Altosid are used on Long Island salt marshes to control mosquito populations. Pesticides often affect non-target species by increasing mortality or by altering behavior or physiology with further sub-lethal or fitness-decreasing effects. Since the wolf spider Pardosa littoralis is a key predator in this ecosystem, changes in their behavior have the potential to affect ecosystem function. This study investigates the behavioral effects of Scourge’s active ingredient resmethrin along with synergist piperonyl butoxide on adults, and the active ingredient of Altosid, methoprene, on juvenile individuals. Locomotion abilities were tested for both pesticides. Scourge was tested at 1µg /L and 5µg /L with combinations of salinity (0.01 % and 0.05% NaCl) since pyrethroids have been shown to effect voltage regulated sodium channels. Juvenile spiders were tested at 10 mg/L of methoprene, which has been shown to affect mosquito development as a juvenile growth hormone mimic. We found that at high salinity, exposure to resmethrin resulted in increased average burst distances when compared to the control. Low salinity was associated with decreased burst speed. Therefore, lower salt concentrations may be stressful, leading P. littoralis to be more susceptible to the effects of resmethrin. Body size and condition was consistently positively related to performance measures. However, exposure to methoprene did not cause any significant differences in speed, endurance, or development. Neither pesticide had an effect on P. littoralis’ lifespan. Methoprene and resmethrin may not directly negatively affect P. littoralis’ speed and endurance; however, presence of stressors in the environment can alter these outcomes and lead to other immediate fitness consequences.