1. Delina Dority and Morgan Alexander Ford Advisor: Lusha Tronstad, WYNDD
Does Mosquito Control Reduce the Aquatic Invertebrates in Spring Creek, Laramie, Wyoming?
Delina Dority and Morgan Alexander Ford
Advisor: Lusha Tronstad, WYNDD

2. West Nile Virus (WNV) West Nile Virus effects many western towns
Laramie controls mosquitos to reduce the threat of WNV
Spraying for mosquitos may have unintended consequences
West Nile Virus effects many Western towns in the U.S.
To help reduce the risk of infection many towns have increased

3. The Mosquito Life Cycle
Discuss what life stages are targeted with mosquito control practices
Most lay eggs in water
Bti is the insecticide used to kill mosquitos in standing water where they live as larvae
Live in standing water

4. Permethrin Regulations and Effects on Aquatic Ecosystems
Many studies have shown that Permethrin is toxic to aquatic animals, mainly anything with gills
1970s the EPA required a 100 foot open-water buffer restriction for Permethrin application sites
In 2006, the EPA removed the buffer restriction in an effort to control the spread of West Nile Virus in the United States

5. Permethrin Application in Laramie
In Laramie, Wyoming mosquito abatement protocols are similar to those across the country. Bti is applied to still-water environments to control larval mosquitos, and Permethrin containing compounds are applied via ultra-low volume (ULV) foggers to residential areas throughout the summer. This includes areas adjacent to an important tributary of the Laramie River known as Spring Creek.”
April/ May – September/ October (depending on mosquito detection)
Ultra Low-Volume foggers
Residential areas are treated on a rotating schedule
Parks are treated Sunday- Thursday nights
“We collected drift samples before, immediately after (~3-6 hours), and one day after (~28 hours) insecticide application. We measured a significant increase in abundance, biomass, and richness of drifting insects immediately after pesticide application. The increase in drifting invertebrates may have cascading effects on the ecosystem by altering resources available to fish and riparian birds. Understanding the unintended ecological impacts of pest control practices can lead to more effective and less detrimental management strategies.”
Laramie Mosquito Control Program/West Nile Virus Plan:
First adopted in 2003
Runs congruently with nuisance mosquito plan
Bacillus thuringiensis israelensis (Bti)
Permethrin and other insecticides
Ultra-low volume fogger

6. Spring Creek
Originates from a spring north of Grand Ave. (near Murdoch’s)
City of Laramie protects spring
Spring Creek exists entirely within City of Laramie

7. Spring Creek What’s so important about such a small stream?
Supports year-round population of brown trout (~1000 fish per mile)
Spawning habitat for trout from the Laramie river
Provides habitat and food for riparian birds, mammals, and amphibians
Several organizations are involved in habitat restoration on the Laramie River

8. What do we know?
Morgan measured invertebrate drift immediate before spraying, immediate after spraying and 1 day after spraying.
Discuss why invertebrates drift
Measuring Invertebrate Drift Drift = downstream transport of invertebrates

9. Trends in Drift Samples
The density and biomass of all aquatic invertebrates increased immediately following treatment of Permethrin.
Spraying
Up to 11x more invertebrate drifting immediately after spraying Permethrin
25th and 75th percentiles
Box holds 50% of data

10. Hess Sampling
Does mosquitoes control reduce the density and biomass of invertebrates living in Spring Creek?

11. Methods Collected Hess samples: Before spraying began in June
After 2 months of spraying in August
Sorted invertebrates
Identified invertebrates under a dissecting microscope
Measured length to calculate biomass

12. Invertebrate Density
Density of all invertebrates was lower after permethrin spraying for 2 months
(ind/m2)
Before
After

13. Invertebrate Biomass
Biomass of all invertebrates was lower after permethrin spraying for 2 months
(mg/m2)
Before
After

14. Density of non-insect decreased after spraying
Before
After
(ind/m2)
Density of non-insect decreased after spraying
Density of insects increased after spraying

15. Biomass of non-insects was lower after spraying
Before
After
Non-Insects Most Abundant
Biomass of non-insects was lower after spraying
Non-insects more abundant in Spring Creek
Insect body size was smaller after spraying (early instars)

16. Annelids and crustaceans most abundant non-insects
Before
After
(ind/m2)
Annelids and crustaceans most abundant non-insects
Densities decreased after 2 months of spraying

17. Before
After
(mg/m2)
Biomass of non-insects decreased after 2 months of spraying, including Annelids

18. True flies tolerant of poor conditions Tolerant mayfly in the stream
Before
After
(ind/m2)
Densities of true flies and mayflies increased after 2 months of spraying
True flies tolerant of poor conditions
Tolerant mayfly in the stream

19. Fewer Invertebrates in Spring Creek
Less food for fish
Fewer adult insects emerging for birds to eat
Fewer insects eating algae = greener stream
Smaller insects after spraying may indicate that few insects are surviving to develop into adults
Non-insects most abundant = sign of an impaired stream

20. What Does This Mean for Spring Creek?
Permethrin applications near Spring Creek appear to be reducing non-target aquatic animals
Re-evaluation of treatment practices to minimize impacts on Spring Creek animals while still effectively controlling mosquito populations may be in order

21. Acknowledgements Lusha Tronstad, Wyoming Natural Diversity Database
Scott Seville, Wyoming INBRE
Kieth Wardlaw, City of Laramie Mosquito Control Supervisor
Tony Hoch, Laramie Rivers Conservation District
Steve Gale, Wyoming Game and Fish Department
Biodiversity Institute
Wyoming Natural Diversity Database staff
Mark Anderson, Wyoming Natural Diversity Database
Christy Bell, Cody Bish, Tyler Dooley, Isaac Dority, Kyle Hack, Hunter McFarland, Oliver Wilmot, Aimee Wood