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Effects of Resmethrin Spray on Monarch ( Danaus Plexippus ) Butterflies and Larvae

Effects of Resmethrin Spray on Monarch ( Danaus Plexippus ) Butterflies and Larvae. By Rosemary Lelich 2004-05. www.mlmp.org. Background: resmethrin. Type 1 pyrethoid Synthetic version of natural insecticide produced by chrysanthemum flowers

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Effects of Resmethrin Spray on Monarch ( Danaus Plexippus ) Butterflies and Larvae

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  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 Cage containing milkweed leaves and monarch larvae • 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

  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 larvaeSignificant 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 3rd instars only, p = 0.3008.

  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 • 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

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