Improvement and Quantification of Extraction Methods for Annual Bluegrass Weevil Larval Populations

The annual bluegrass weevil (ABW), <i>Listronotus maculicollis</i> (Kirby), is a significant pest of short-mown turfgrass in eastern North America. Proper monitoring of this pest may reduce insecticide applications. We investigated the extraction rate and labor involved in modifications of the two currently available methods for sampling ABW larvae: submersion of turf cores in saturated saline solution and heat extraction of cores on modified Berlese funnels. Using 5.7 cm diameter cores, submersion extracted 1.8× more larvae in saline solution than in water. Among the salt extraction variants, splitting the cores into four pieces before submersion was the best compromise between extraction rate and time requirement. Using intact cores extracted 40% fewer larvae while taking 18% less time, whereas destructive searching cores before submersion extracted 24% more larvae but required 64% more time. Using smaller cores (3.5 cm diam) took 18% less time and extracted 23% more larvae, but required more time sampling in the field. Larval stage averages did not differ significantly between salt extraction variants. Heat extraction, including destructively searching the desiccated core, extracted 60% more larvae but required 87% more time than four-piece salt extraction. Excluding the desiccated core, heat extracted as many larvae as four-piece salt extraction and required 16% less time. However, heat extraction requires three to four days and space that can be kept at around 32 °C. The method of choice for ABW larval extractions depends on whether the sampler prefers a high extraction rate, less labor, or quicker results, and whether space for heat extractions is available.