Balancing Act: Examining Mosquito Control’s Hidden Ecological Costs on Macroinvertebrate Populations

Balancing Act: Examining Mosquito Control’s Hidden Ecological Costs on Macroinvertebrate Populations 
 
 Holly Stanley^1*, Samantha Hamilton^2*, Melanie Hoffmann-Cannizzo^3*

¹Colorado Mesa University, Grand Junction, CO
²Colorado Mesa University, Grand Junction, CO
³Colorado Mesa University, Grand Junction, CO

The goal of this project was to provide RiversEdge West baseline aquatic macroinvertebrate data, a methods comparison study, and recommendations for a future monitoring plan to assess the non-target impacts of the mosquito control operations on macroinvertebrate communities. This project was focused in Horsethief Canyon State Wildlife Area (HCSWA) in Fruita, Colorado, where the Grand River Mosquito Control District (GRMCD) treats active mosquito populations. GRMCD applies the bacterial larvicide, VectoBac G, to control the mosquito population where activity is detected. 

Three replicates were collected from three different sites, utilizing two different methods, for a total of 18 samples collected. Macroinvertebrate identification was performed for six samples which included one for each method at each site. Baseline water quality parameters were recorded at each site including temperature, pH, and dissolved oxygen. The collection methods examined were the Petersen Grab device and a dip net sampler; both were assessed for sampling efficacy. Samples were processed and identified in the laboratory at Colorado Mesa University (CMU). Species richness, abundance, evenness, and BBI were calculated following macroinvertebrate identification.

The results showed that the macroinvertebrate community in the area varies by the water body sampled. Site A, which had been established the longest, had the highest diversity and most individual macroinvertebrates, all of which were collected with the dipnet. Site B was the only site that yielded macroinvertebrate samples for both methods. There were no macroinvertebrates obtained from Site C, which had been inundated most recently. The dip net was determined to be the more effective method as it collected more individuals from Sites A and B than the Peterson Grab device. The most Class I and II (i.e. most sensitive) organisms were found at Site A. Future recommendations are to sample earlier, separate macroinvertebrates from sediment in the field, and implement methods that are proven more effective than the Petersen Grab.