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To increase the effectiveness of adult mosquito control, more frequent ultra-low volume (ULV) applications have been suggested. In the Chicago area, weather may be a limiting factor to more frequent applications. To investigate this, ULV adulticidal application dates from the Northwest Mosquito Abatement District during June 2011 to September 2020 were compared to historical weather data-wind and rain patterns to determine optimum conditions for conducting ULV treatments. During the 85 applications performed during 2011-20, there would have been an opportunity, based on weather conditions, for an additional consecutive night for about half (48.2%) of the time. These opportunities diminished with each additional application. The most intensive response possible would have been a spray of 5 consecutive nights, which occurred once in 3 of the 10 years investigated., (Copyright © 2022 by The American Mosquito Control Association, Inc.)

Over the course of 2019 and 2020, 7 larvicide formulations for use in catch basins were evaluated using a standardized pass/fail protocol. A comparison between 1- and 2-pouch doses of VectoLex® water-soluble pouches (WSP; 10 g per pouch) and 20 g of VectoLex FG (loose granules) suggests that the WSP formulation may have a shorter duration than the FG formulation. Results also suggest that 20 g doses of each of 2 larvicides, Duplex™-G and Sumilarv® 0.5G, may have a minimum effective duration in basins for approximately 40 days. A 20 g dose of Altosid® XR-G and a single briquet Altosid XR each had an observed minimum effective duration of 20 days. Sustain MBG had an observed duration of only 7 wk posttreatment. These observations provide evidence that, in some locations, 20 g granular applications may have a longer effective duration than a single briquet. This work highlights the utility of applying a standardized protocol for routine quality control assessments of the thousands of catch basin larvicide applications performed seasonally by mosquito abatement districts., (Copyright © 2021 by The American Mosquito Control Association, Inc.)

During June through September 2018, the North Shore Mosquito Abatement District evaluated a quality control protocol for larvicide-treated catch basins that allowed for comparisons of larvicides with different modes of action. Results suggest that when applied at a rate of 2 tablespoons (approximately 20 g of product) per basin, these larvicides (VectoLex ® FG Lysinibacillus sphaericus , Natular™ G30 Spinosad, and Altosid ® Pellets Methoprene) could reduce the need for retreatment for up to 4 wk or longer. Using this same protocol, Spheratax ® SPH (50G) L. sphaericus was applied to a subset of approximately 900 basins and met the threshold for retreatment 1.1 wk postapplication. Despite these larvicide applications, pupae continued to be observed in non-Altosid ® treated basins, suggesting 100% mortality may not be attainable.

During June to September 2017, 7 mosquito control programs in the midwestern United States evaluated a total of 9 catch basin larvicide formulations using similar protocols. Treated basins were monitored among study sites to observe when larvicides failed to control mosquitoes in 25% or more basins within a site. Overall, when monitoring occurred within the maximum label duration of the larvicides, sites treated with a single larvicide tablet or briquet surpassed the 25% fail threshold more often than pellet and granular larvicide formulations. In 438 of the study basins, the depth from sump bottom to catch basin lid was measured. In basins that were deeper than 5 ft (1.5 m), larvicides failed to control mosquitoes significantly more often than those 5 ft or shallower.

Effectiveness in controlling mosquito larvae in stormwater catch basins in the North Shore Mosquito Abatement District (northeastern Cook County, IL) was determined for 2 extended-duration larvicides indicating up to 180 days of control on their labels (Natular™ XRT, FourStar® Briquet) and 3 larvicides indicating up to 30 days of control (Natular™ T30, Natular™ G30, and VectoLex® FG). Over the course of the 26-wk study, catch basins receiving the extended-release products were treated twice (an initial treatment in early April followed by a re-treatment after 16 wk), and catch basins receiving the shorter-duration products were treated every 28 days, with the 1st treatment occurring during the 1st week in April. Control in an individual catch basin was considered to have failed if late-stage larvae or pupae were found in 2-dip samples taken from the catch basin. Control for a treatment was considered to have failed if >25% of catch basins treated with the product failed at a given time period posttreatment. All of the products evaluated in the study demonstrated some degree of control; however, the Natular XRT-, FourStar Briquet-, and Natular T30-treated basins rarely achieved the effectiveness threshold of ≤25% of catch basins failing. By comparison, basins treated with Natular G30 were below that threshold for 3 of 4 wk every treatment round and VectoLex® FG was consistently below that threshold for all 4 wk posttreatment for every treatment round. Compared with untreated catch basins, the total season pupal production was reduced by approximately 48% in the Natular XRT-, FourStar Briquet-, and Natular T30-treated basins, and by 87% and 99% in the Natular G30- and VectoLex FG-treated basins, respectively. Operational quality control observations indicated that effective control (i.e., ≤25% of catch basins failing) ranged from 3 to 12 wk posttreatment for catch basins treated with Natular XRT and from 5 to 9 wk with VectoLex FG, and that there was considerable geographic variation in the duration of effectiveness. The results indicate that 30-day re-treatments with granular formulations in difficult-to-control areas may provide a more cost-effective outcome than using 1 or 2 applications of extended-duration larvicides.

The North Shore Mosquito Abatement District applies extended release larvicides including methoprene-based Altosid® XR Extended Residual Briquets to approximately 40,000 catch basins in the southern half of the District's operational area at the beginning of each season. Treatments begin in May and typically again 9 to 10 wk later when larvicide efficacy appears to wane. In 2013 spinosad-based Natular™ XRT tablets were applied to basins, and a subset were monitored for larvae and pupae weekly with a standard dipper. When setting the threshold for retreatment as 12 juveniles per dip sample it was observed that basins required a second application 9 wk after the initial application, a time period similar to Altosid despite utilizing a different active ingredient. Average counts of weekly larval samples appeared to be positively associated with average numbers of Culex pipiens collected the following week in a gravid trap located among catch basins, highlighting the importance of basins as sources of these mosquitoes.

Stormwater catch basins are the primary source of mosquitoes targeted by the North Shore Mosquito Abatement District, in the northern suburbs of Chicago. Over a 17-wk period (June to September 2011), 3 clusters of catch basins located within a 0.7-km2 area were monitored weekly with dipper samples of immature mosquitoes. During the 2nd week of monitoring, Natular XRT tablets (6.25% spinosad) were applied to northernmost cluster and FourStar Briquets (6% Bacillus û, 1% Bacillus thuringiensis israelensis) were applied to the southernmost cluster; the remaining middle cluster was kept untreated. Following 15 wk of monitoring in 20 basins in each cluster, both Natular and FourStar reduced immature numbers in treated catch basins for 8 consecutive weeks. These results suggest, if effectively timed, a single application of either larvicide may last an entire season.

In the northern suburbs of Chicago, stormwater catch basins are the primary source of vector mosquitoes targeted by the local mosquito abatement district, and therefore effective catch basin larvicides are needed. From June to September 2011, Natular XRT was applied at label rate to a cluster of 20 catch basins and compared to a cluster of 20 untreated basins all within a small 0.21 km2 area of catch basins known historically to have high levels of mosquitoes. All monitored basins held immature stages of mosquitoes at least once; however, significantly fewer immatures overall were observed from Natular-treated basins than in untreated basins during 14 wk of monitoring. During the study a portion of Natular-treated catch basins was cleaned as part of scheduled maintenance, and this appeared to remove both the larvicide and any control effects. Better timing of catch basin maintenance events is suggested, particularly if, as the results of this study suggest, a single larvicide treatment may be effective for an entire season.