1. Effects of Resmethrin Spray on Monarch (Danaus Plexippus) Butterflies and Larvae By Rosemary Lelich 2004-05 www.mlmp.org

2. Background: resmethrin Type 1 pyrethoid Synthetic version of natural insecticide produced by chrysanthemum flowers Nerve poison - acts on sodium ion channels in nerve cell membranes www.free.de/WiLa/derik/Resmethrin.gif

3. Background: resmethrin, cont. Used to control mosquito populations Sprayed in wooded areas and fields where milkweed can grow Recent use has increased in Minnesota due to spread of West Nile Virus No previous studies on effects of resmethrin on monarchs exist

4. Background: Larvae Monarch larvae (caterpillars) non-target insect for insecticide sprayings Terrestrial Only eat milkweed (Asclepias) http://www.mbsf.org/news.html

5. Previous study: permethrin Similar pyrethoid Study done by Sara Brinda (2003) Estimated % mortality for 1st, 2nd, and 3rd instars, respectively, to be 92%, 89%, 71% Photo used with permission of Sara Brinda

6. Goals and Hypotheses 1. Estimate the percent mortality of monarch larvae and adult monarchs due to resmethrin exposure Hypothesis: Resmethrin is lethal to monarchs 2. Determine if there are sub-lethal effects of resmethrin exposure on monarch larval development time and adult size Hypothesis: Sprayed larvae will develop more slowly and will be smaller adults

7. Procedure: Round 1 Kept 8 cages of larvae, used as controls Set out cages of larvae and cages of mosquitoes Resmethrin only reached stations downwind side of spray path Photo by Bruce Leventhal Cage containing milkweed leaves and monarch larvae

8. Resmethrin Sprayer Photo by Bruce Leventhal

9. Procedure Recorded each time a larva molted to the next instar (growth stage) Recorded all mortality Continued until all monarchs emerged as adults http://asclepias.homestead.com/files/ xmonlarvae.JPG

10. Results: Round 1 larvae Significant effect of treatment. More dead larvae in downwind treatment than the control or upwind treatments. Comparing downwind larvae to control, p = 0.0000.

11. Mortality rates for 1st and 3rd Beginning Instars (Downwind only) p = 0.0273. Assuming missing larvae died, p = 0.4568.

12. Mass of emerged adult butterflies that were sprayed as larvae (with s.d.), p = 0.2862. Control upwind downwind

13. AOV for total development time for beginning 3 rd instars only, p = 0.3008. Positionn ( Sample Size) Mean (days) S.E. Upwind1522.4 d0.3344 Downwind623.330.5287 Control1722.880.3141

14. Downwind larval mortality rates with respect to distance, p = 0.7541.

15. Procedure: Round 2 Redesigned field set up before spraying Added to each station –Horizontal cages of larvae –Milkweed plant with larvae on leaves (on ground) –Milkweed plant with no larvae (on ground) –Cage of adult butterflies (on ground) Wind variable; reached both up and down wind stations

16. Dead Larvae: downwind during round 2 spraying Photos by Brij Basin and Rosemary Lelich

17. Results: Round 2 Larvae  2 comparing larval mortality rates Testp-value Control vs. Sprayed0.0151 Upwind vs. Downwind0.1655 No downwind/upwind effect -- wind too variable Significant mortality rates of sprayed larvae

18. Larval, adult monarch, and mosquito mortality rates by station, p = 0.0001.

19. Larvae placed directly on milkweed plants and unsprayed larvae fed sprayed leaves produced significantly high mortality These exposures most closely mimic larvae’s natural positioning This suggests that round 1 underestimates larval mortality

20. Percent mortality of sprayed larvae compared to sprayed mosquitoes

21. Discussion Accept hypothesis 1: Resmethrin is lethal to monarch species Reject hypothesis 2: Sprayed larvae did not emerge as significantly smaller adults Resmethrin is likely a factor responsible for decrease in monarch populations –Very important to understand consequences of using resmethrin in order to preserve monarch species

22. Future Study Conduct another round of resmethrin spraying, again including larvae and adults. Position more larvae downwind, attempt to retain large sample sizes for more significant results

23. Acknowledgements Dr. Karen Oberhauser Everyone in the lab (especially Ben, Alma, Reba, Erin, and Jolene) Metropolitan Mosquito Control District, especially Dr. Stephen Manwieler Sara Brinda Ms. Lois Fruen Team Research Photo courtesy of Lois Fruen

24. Effects of Resmethrin Spray on Monarch (Danaus Plexippus) Butterflies and Larvae By Rosemary Lelich, 2004-05 www.mlmp.org