THE WATERMILFOIL WEEVIL (EUHRYCHIOPSIS LECONTEI): DEVELOPING A SAMPLING PROGRAM AND INVESTIGATING THE INFLUENCE OF BIOTIC AND ABIOTIC FACTORS ON ITS DISTRIBUTIONByThomas G. AlwinEuhrychiopsis lecontei is used in North America as a biocontrol agent for the invasive aquatic plant Myriophyllum spicatum. E. lecontei can suppress M. spicatum and lake-wide M. spicatum declines have been attributed to E. lecontei. However, investigations at the whole lake scale are lacking. The aim of my field research was to quantify minimum sample size for lake-wide E. lecontei estimation and investigate the influence of M. spicatum metrics and abiotic factors on E. lecontei presence and density. Four Michigan lakes were sampled. Power analysis revealed precise lake-wide E. lecontei abundance estimation (μ ± 20%) required a large sample size (>300 quadrats) and sizeable effort (261 hrs) and lower precision (μ ± 50%) required 49 samples and 41.8 hrs. Zero-inflated binomial regression found abiotic factors positively influenced and M. spicatum metrics negatively influenced E. lecontei presence (p<0.014), and density was positively influenced by M. spicatum metrics and negatively influenced by abiotic factors (p<0.001). My research illustrates the importance of sample size when estimating E. lecontei populations and suggests that both M. spicatum metrics and abiotic factors influence E. lecontei presence and abundance.
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