Influence of seasonal activities and traffic conditions on the accumulation and particle size distribution of gully pot sediments.

Gully pots (GPs) are ubiquitously used in urban catchments, to direct surface runoff into piped sewer systems, reduce the risk of sediment-induced pipe blockages and the loading of solids and associated contaminants on the receiving waters. Over time, the build-up of sediments in GPs will lead to impaired hydraulic performance, putting the urban catchment at risk of flooding. However, GP maintenance strategies lack both a robust evidence base and clear aims against which their effectiveness can be benchmarked. An improved understanding of the factors influencing long-term in-situ solids accumulation in GPs is required for further assessment and optimisation of the GP maintenance scheme. As a contribution to addressing these knowledge gaps, sediments from 27 GPs located in urban catchments associated with three street feature types (roundabout; crossing; straight road) and varied traffic intensities were collected on two occasions, representing two distinct seasonal accumulation periods. Parameters including GP fullness levels, particle size distribution (PSD), and solids mass accumulation rates were evaluated with regards to the impacts of seasonal activities, traffic conditions as well as configuration and dimension of GPs. The results indicate impacts of seasonal activities on solids accumulation rates were not consistent across all GPs, with the magnitude of the difference larger following winter-spring catchment practices. Additionally, synergistic impacts of seasonal activities and traffic conditions on PSD and solids accumulation rates were observed. For example, the winter road safety measures may enhance the impacts of the characteristic vehicle turning motions at roundabouts, contributing to the negative correlation identified between traffic intensities and solids accumulation rates. The overall exhibited large variations in sump fullness levels (4 %-73 %) and solids dry mass (0.5-51 kg) directly challenged the commonly adopted generalised GP maintenance frequency without taking the catchment-specific activities into consideration.

Improving stormwater quality at source using catch basin inserts.

Stormwater runoff transports contaminants, including gross pollutants (GPs) accumulated on surfaces to nearby receiving water bodies. These may clog storm drainage systems, seal side entry pits and increase dissolved pollutants in receiving water bodies. Best management practices (BMPs) such as oil and grit separators, grassed swales, vegetated filter strips, retention ponds, and catch basin inserts (CBIs) are implemented to reduce stormwater pollutants in urban runoff. However, the information on physicochemical characteristics of the pollutants are still few in literature but important to improve the design of BMPs, considering qualitative aspects, and their operation. CBIs are devices used to remove GPs at source without requiring any extra land use because they are typically mounted within a catch basin (e.g. side entry pit) or existing drain. In this study, improvement of stormwater quality was investigated at two different sites (Subiaco, a residential area and Hillarys Boat Harbour, a commercial-marine-recreational area; Western Australia) where a new CBI made of non-woven polypropylene geotextile was installed in side entry pits to capture GPs at source. Influent and effluent water from the CBIs was collected and analyzed for BOD, COD, TSS and PO4-P with maximum improvements in water quality of 90%, 88%, 88% and 26% respectively. The heavy metals in influent and effluent water were found very low and below the guideline values. Analysis of particle size distribution, specific surface area of solids, SEM images and heavy metal content (Cu, Fe, Ni, Pb, Zn, Cd) in solids showed that the residential area contained more finer particles than the commercial area but that solids in the commercial area contained greater concentrations of heavy metals than those from the residential area. The specific surface area was found to be higher in the residential area and particles were thought to be largely sourced from traffic. However, these characteristics may be monitored for longer term for more CBIs installed in different locations.

Hazardous and odorous pollutants released from sewer manholes and stormwater catch basins in urban areas.

To learn more about the emission characteristics of odorants released from sewer manholes and stormwater catch basins (SCBs) in an urban environment, we measured the emission concentrations of major odorants including 22 target compounds designated as offensive odorants by the Korean Ministry of Environment (KMOE). All of our measurements were made from urban sewer manholes and SCBs in a highly commercialized location in Seoul, Korea. The results of our study were analyzed to identify the major odorants from such sources and to assess their contribution to odor intensity. The malodor strengths at both types of underground sources were considerably higher in the afternoon than in the morning. The assessment of odor intensity (OI) and odor activity value (OAV) confirmed the dominance of key odorants like H2S, CH3SH, and ammonia along with various volatile fatty acids (VFAs) and phenol. The concentration of these major odorants (H2S, CH3SH, and NH3) exceeded the maximum permissible limit given as the odor prevention law in Korea. As such, significantly high levels of odorants released from these underground sources were greatly distinguished from those seen at above ground locations.

Assessment of Reactive Catch Basin Larvicide Treatments Toward Improved Water Quality Using FourStar(®) Briquets and CocoBear™ Larvicide Oil.

Because it is often logistically impossible to monitor all catch basins within an operational area, local mosquito control programs will preemptively treat catch basins with larvicides each season. However, these larvicides can, ostensibly, be considered water quality pollutants. To experimentally reduce the use of larvicides toward improving water quality, 30 basins within a small 0.7-km(2) residential area were monitored weekly for the presence of larvae and pupae for 14 wk in the summer of 2013. Once a basin was found to reach a threshold of 12 mosquitoes per dip sample, it received a FourStar® Briquet (a 180-day briquet formulation of 6% Bacillus sphaericus and 1% B. thuringiensis israelensis). Each week a FourStar-treated basin surpassed this threshold, it was treated with an application of CocoBear™ oil (10% mineral oil). By the end of trials, all but one basin received a briquet and 13 required at least 4 treatments of CocoBear, suggesting that preemptive treatment is appropriate for the study area.

Use of Centers for Disease Control and Prevention Gravid Trap in Catch Basins: Proof-Of-Concept Trials.

Gravid traps are commonly used by mosquito control agencies to collect local populations of Culex pipiens, which are then tested for the presence of West Nile virus. Culex pipiens adults disperse a relatively short distance (~2.5 km) from their breeding site, so it can be challenging to position a sufficient number of gravid traps to accurately monitor these mosquitoes in large urban areas. As placement of these traps is often limited to locations out of public?view, the potential for placing these traps belowground in commonly found storm-water catch basins was investigated. We compared the numbers of mosquitoes isolated in the Centers for Disease Control and Prevention (CDC) gravid traps placed aboveground with various types of CDC gravid traps placed in nearby catch basins. We found that the gravid traps placed in catch basins collected significantly fewer Culex pipiens females as compared to the aboveground traps. However, the 2 types of catch basin traps continued to function and collect mosquitoes despite heavy rainfall and runoff, demonstrating their utility for sample collection in an urban setting. The potential advantages and disadvantages of using catch basins for the placement of CDC gravid traps are discussed.

Evaluation of Culex pipiens Populations in a Residential Area with a High Density of Catch Basins in a Suburb of Chicago, Illinois.

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.

Microplastics in gully pot sediment in urban areas: Presence, quantities and characteristics.

Stormwater is widely recognized as a pathway for transporting pollutants, including microplastics, from sources in urban environments to receiving waters. Gully pots are often where urban runoff drains into the piped network; they typically include a trap where sediments accumulate. The aim of this work was to contribute to a better understanding of the fate of microplastics as they enter into the urban drainage system, and the role of gully pots in trapping microplastics. Sediment samples collected from 29 gully pots were analysed for non-carbon-black and carbon-black (e.g. tire wear particles) microplastics larger than 40 µm using µ-FTIR and ATR-FTIR, respectively. Commonly found polymers in descending order were PP > EPDM > EVA > PS > SBR, PP was most common both by mass and by number of microplastics. The total concentration of carbon black and non-carbon black microplastics ranged from 709 to 10 600 items/100 g dry matter (DM), (median: 2960 items/100 g). Estimated mass of non-carbon black microplastics ranged from 0.19 to 490 mg/100 g, (median: 3.66 mg/100 g). In total 21 different types of microplastics were detected, the majority of these (13) were carbon black and eight non-carbon black polymer types. By number and the carbon black particles accounted for up to 68% of the microplastics (average 30%), this stress the importance of using analytical methods enabling the detection of both carbon-black and non-carbon black microplastics. Furthermore, the results indicate that gully pots can act as temporary sinks for microplastics, mainly for microplastics larger than 125 µm. The amount of microplastics found in gully pots, together with the very large number of gully pots sited in urban areas, indicates that gully pots can potentially trap large amounts of microplastics, and thus if gully pots are fitted and maintained properly they could significantly contribute to reducing the amount of microplastics reaching receiving waters.

A Case Report on Product Rotation to Manage Severe Lysinibacillus sphaericus Resistance in Culex pipiens from Salt Lake City, Utah.

The Salt Lake City Mosquito Abatement District (SLCMAD) detected a 20,000-fold resistance to Lysinibacillus sphaericus (Lsph) in Culex pipiens occurring in catch basins of Salt Lake City during 2016. In response, SLCMAD suspended use of Lsph and rotated use of spinosyn and s-methoprene products for the next three years. At the end of the third year, Lsph was evaluated again and efficacy similar to susceptible colony strains. During the second year of Lsph use, technicians observed lack of control of larvae at some urban sites. Bioassays performed during 2021 showed recurrence of some resistance to Lsph to varying degrees across SLCMAD urban areas. The rapidity with which resistant phenotypes reemerged clarifies that SLCMAD cannot in the near future rely on repeated use of Lsph, even after suspending use for three years and using within-season product rotations. Prior reports in other research groups have found long-term selection to Lsph, as is the case at SLCMAD, to not regress in spite of halting use of the products. However, our findings offer some optimism that regression may be relatively quick. More operational review is needed, and future work should characterize resistance alleles in field populations. Collectively, there is a lack of concrete data supporting the prevailing assumptions from adjacent industries that were adopted into mosquito abatement. We provide this short note as additional guidance for mosquito and vector control districts weighing options to remediate Lsph resistance.

SEASONAL MOSQUITO PRODUCTION IN STORM SEWER CATCH BASINS OF THE NORTH SHORE SUBURBS OF CHICAGO, 2021 TO 2024.

From 2021 to 2024, the number of pupae found in storm sewer catch basins in the North Shore suburbs of Chicago were assessed as part of routine quality control and improvement efforts. Over the course of these 4 yr, pupae were collected at least once during all calendar months, allowing for some insight into monthly mosquito production in catch basins. Thus, the intent of this study was to use those data to describe the number of pupae found in these structures across calendar months. In total, 1,993 unique catch basins were sampled. Pupae were found during the months of April through December, with the highest levels seen during June through November. Results suggest that basins may remain productive a month or more after local abatement districts end their routine Culex adult surveillance with gravid traps in late September and early October each year. These observations can help with the timing and intensity of larvicide treatments in Chicago area catch basins and may serve as a baseline for comparison to future seasonal changes.

Impacts of seasonal activities and traffic conditions on the contamination and accumulation of gully pot sediments: Metal(loid)s and organic substances.

Gully pots (GPs) are an integral urban drainage component, transferring surface runoff into piped systems and reducing sediment and contaminant load on downstream sewers and receiving waters. Sediment build-up in GPs impairs their hydraulic performance, necessitating maintenance for hydraulic function recovery. The variations in sediment accumulation rates between GPs suggested by earlier studies challenge the effectiveness of adopting a generalised maintenance frequency. This study addresses the knowledge gap regarding how various factors influence sediment contamination in GPs. The impacts of seasonal activities and traffic conditions on the contamination of sediments in 27 GPs in areas with varying traffic intensities and street features (roundabouts, intersections, and straight roads) were examined. Over one year, GPs were emptied twice, with sediments collected for winter-spring and summer-autumn accumulation periods. These sediments were analysed for 84 substances, including metal(loid)s, hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), alkylphenols, phthalates, per- and polyfluoroalkyl substances and organotins. Significant temporal changes were identified in key parameters such as electrical conductivity, total organic carbons, tungsten (W), heavy-molecular-weight PAHs (PAH-H) and diisodecyl phthalate (DIDP) in GP sediments, influenced by winter road safety measures and autumn leaf abscissions. Significantly higher concentrations of 4-tert-octylphenol, DIDP, diisononyl phthalate, antimony and W were identified in GP sediments from roundabouts compared to those at the other two street features, exclusively during the winter-spring period. This is attributed to the synergistic effect of winter road safety measures and stop-and-go traffic patterns at roundabouts. No consistent spatial and temporal patterns were identified for substance concentration and mass accumulation rates. Results underscore the potential to develop a prioritisation-based maintenance strategy as an opportunity to enhance the efficiency of GP maintenance operations, ensuring better resource allocation and reduced environmental impact.

Comparative Activity And Efficacy of Sumilarv 0.5G and Altosid Xr Briquet Against Culex Quinquefasciatus and Aedes Aegypti in Simulated Catch Basins.

Mosquito control plays a crucial role in the mitigation of mosquito-borne diseases. Larviciding that targets one of the aquatic stages is among the routine practices in mosquito control operations. One of the most extensive and challenging mosquito production sources in urban environments is underground storm drain systems. Along with the research and development of biorational larvicides in recent decades, numerous products based on microbial and insect growth regulators have become available. However, the performance of these products often varies because of product design and challenges associated with urban storm drain systems. This paper validates the comparative bioactivity and semifield efficacy of 2 control release products based on pyriproxyfen and S-methoprene. In laboratory bioassays, pyriproxyfen was significantly more active than S-methoprene against the test species, Culex quinquefasciatus Say and Aedes aegypti (L.). Culex quinquefasciatus was less susceptible than Ae. aegypti to both test materials. During a 26-wk-long semifield evaluation using the cast concrete simulated catch basins, the inhibition of emergence pretreatment and posttreatment in untreated control was negligible. The Sumilarv 0.5G applied at 75 g per catch basin provided 100% IE, whereas the Altosid XR briquet applied at 1 per catch basin yielded only partial control fluctuating from 12.7% to 82.7% (average 40.7%) of Cx. quinquefasciatus and 8.0% to 78.8% (average 37.4%) of Ae. aegypti. The Altosid XR briquet had an average residual weight of 59.9% at the end of semifield evaluation. Results are discussed in relation to field mosquito control operations in urban storm drain systems.

Accumulation and contamination of gully pot sediments from varied land-use types: metal loads, concentrations and speciation.

Urban stormwater typically enters sewer networks through gully pots, which allow a primary sedimentation of solids upstream of the piped network. The regular removal and disposal of retained sediment are necessary, costly and can involve environmental risks due to the contamination of sediments with substances from the urban environment such as metals. The concentrations and speciation of Cd, Cr, Cu, Ni, Pb and Zn were analysed in sediments from 26 gully pots located in different land use areas in Stockholm, Sweden. In addition, accumulation rates of both sediment and metal masses were evaluated, providing a basis for optimising maintenance practices and better understanding of impacts of characteristic urban land use types. Metal concentrations varied by at most a factor of eight between samples and were always below Swedish polluted site guidelines for less sensitive land use, with only eight samples exceeding the guideline values for Cu and Zn for sensitive land use. Sequential extraction showed Pb and Zn to be the most mobile metals. Sediment accumulation rates varied from 0.003 to 0.197 kg/m2 impermeable surface/year. Metal accumulation rates were much more variable than metal concentrations, with a factor of up to 172 between the highest and lowest rates and the highest metal accumulation rates corresponding to the lower range of mass loads in road runoff. Differences in metal concentrations, sediment or metal mass accumulations could not be solely attributed to either traffic or catchment land use. In contrast, traction grit used for winter road maintenance, which has low (but detectable) metal concentrations, is identified as a major component of gully pot sediments, with a combined effect of both moderating metal concentrations and contributing to total mass.

Evaluation on the Activity and Efficacy of Omniprene™ WSP and XWSP Against the Southern House Mosquito Culex quinquefasciatus in Simulated Catch Basins.

Mosquitoes and mosquito-borne diseases remain one of the major public health burdens. In most cases, vector control is the main or the only intervention to mitigate these problems. We are facing the challenges of traditional, emerging, or resurging vectors and diseases, yet the availability and affordability of safe and effective mosquito control products are at a historical low. Development of new active ingredients (AI) and novel formulations based on currently available AI are demanded by mosquito control operations. This paper validated the bioactivity in the laboratory and evaluated the semi-field efficacy for 2 newly registered controlled-release products based on juvenile hormone analog S-methoprene: OmniPrene™ water-soluble pouch (WSP) and extended water-soluble pouch (XWSP). Along with technical S-methoprene, these 2 formulations showed high inhibition of adult emergence in laboratory bioassays against Aedes aegypti, Ae. albopictus, and Culex quinquefasciatus that are commonly found in catch basins. High initial and long-term residual efficacy were demonstrated in simulated catch basins against Cx. quinquefasciatus, where the OmniPrene WSP consistently provided over 90% control for 15 wk (105 days) and OmniPrene XWSP did the same for 38 wk (266 days). Considering the need for reliable mosquito control products, combined with commonly encountered product performance issues in catch basins, OmniPrene WSP and XWSP can be viable tools to combat mosquito species of public health concern that are associated with urban drainage systems.

Operational Basin Larvicide Evaluations in Northern Cook County, Illinois During 2019 and 2020.

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.

The community-wide effectiveness of municipal larval control programs for West Nile virus risk reduction in Connecticut, USA.

BACKGROUND: Mosquito larval control through the use of insecticides is the most common strategy for suppressing West Nile virus (WNV) vector populations in Connecticut (CT), USA. To evaluate the ability of larval control to reduce entomological risk metrics associated with WNV, we performed WNV surveillance and assessments of municipal larvicide application programs in Milford and Stratford, CT in 2019 and 2020. Each town treated catch basins and nonbasin habitats (Milford only) with biopesticide products during both WNV transmission seasons. Adult mosquitoes were collected weekly with gravid and CO2 -baited light traps and tested for WNV; larvae and pupae were sampled weekly from basins within 500 m of trapping sites, and Culex pipiens larval mortality was determined with laboratory bioassays of catch basin water samples. RESULTS: Declines in 4th instar larvae and pupae were observed in catch basins up to 2-week post-treatment, and we detected a positive relationship between adult female C. pipiens collections in gravid traps and pupal abundance in basins. We also detected a significant difference in total light trap collections between the two towns. Despite these findings, C. pipiens adult collections and WNV mosquito infection prevalence in gravid traps were similar between towns. CONCLUSION: Larvicide applications reduced pupal abundance and the prevalence of host-seeking adults with no detectable impact on entomological risk metrics for WNV. Further research is needed to better determine the level of mosquito larval control required to reduce WNV transmission risk.

Production of Culex pipiens in Stormwater and Combined Sewer Catch Basins.

Man-made stormwater and sewage infrastructure, particularly roadside catch basins, provides widespread habitats for immature mosquitoes in urban and suburban environments. Historically, throughout much of the USA, stormwater, sewage, and industrial wastewater were conducted together through "combined" sewer systems, discharging a combination of stormwater and wastewater into streams. Within recent decades, many cities have replaced these combined sewers with "stormwater only" systems that separate stormwater from wastewater. The objective of this research was to evaluate the implications of this infrastructure conversion for production of Culex pipiens, a primary vector for West Nile virus. On a weekly basis over 14 wk, 20 catch basins (10 combined sewer and 10 stormwater only) were sampled for mosquito larvae and emerging adults using the dipping collection method and floating emergence traps. Abundance of larval Cx. pipiens was higher in combined sewer compared with stormwater-only catch basins, while to the contrary, abundance of adult Cx. pipiens was lower in combined sewer compared with stormwater-only catch basins. This study is the first to reveal that habitat attractiveness and quality for Cx. pipiens may vary between combined sewer and stormwater-only catch basins, and our results contribute to a growing body of research to inform vector management and urban planning efforts as municipalities consider the environmental and public health implications of conversion from combined sewage management to separation of stormwater and wastewater.

Standardized Back Checks of Catch Basin Larvicides Across Three Modes of Action in the North Shore Suburbs of Chicago, USA.

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.

Extremely High Biting Densities of Aedes albopictus (Skuse) (Diptera: Culicidae) at a University Campus in Nagasaki, Japan.

Aedes albopictus (Skuse) transmits several arboviral diseases. This mosquito was the vector responsible for both the past and recent dengue outbreaks in Japan. Sites with a high density of A. albopictus are at risk of outbreaks of arboviral diseases. This study describes extremely high biting densities of A. albopictus at a campus of Nagasaki University, southwestern Japan. In August of 2015 and 2016, an 8 min human-bait-sweep collection obtained on average 33.4 and 38.9 females, respectively. In both 2015 and 2016, the highest and the second highest biting densities were observed at sites densely shaded by trees and covered with a large number of understory plants. In addition, major A. albopictus breeding sites were identified near these locations in 2016. A predaceous larval mosquito, Lutzia vorax Edwards, appeared to strongly suppress the breeding of A. albopictus in catch basins near the site with the highest adult density, although its effect was insufficient to maintain A. albopictus density at a low level. After the catch basins had been cleaned, A. albopictus immatures became more abundant, especially in shallow catch basins in shaded sites.

An Operational Evaluation of 3 Methoprene Larvicide Formulations for Use Against Mosquitoes in Catch Basins.

Effectiveness in controlling mosquitoes in storm water catch basins in the North Shore Mosquito Abatement District (northeastern Cook County, Illinois) was determined for 3 formulations of methoprene-based larvicides (Altosid XR 150-day Briquets, Altosid 30-day Pellets, Altosid 30-day Granules) in 2017 using a pass/fail evaluation criterion, in which emergence of a single adult from pupae collected from the basin constituted a control failure. Over the course of the 16-week study, basins receiving the 150-day briquets were treated once and basins receiving the pellet and granular formulations were treated every 4 weeks, with the first treatment occurring during the last week of May. Untreated basins were also observed for comparison with the treated basins. Over the course of the study, adult mosquitoes emerged from pupae collected in 94.2% of the untreated basins that contained pupae. All of the formulations evaluated in the study demonstrated some degree of control compared with the untreated basins, with pupae successfully emerging as adults in 64.6%, 55.5%, and 21.8% of samples from 150-day briquet, 30-day tablet, and 30-day pellet-treated basins that contained pupae, respectively. Pellets reapplied every 28 days provided significantly more effective control than the other formulations. The simple pass/fail criterion for evaluating control effectiveness proved to be a useful procedure for comparing effectiveness to untreated basins and among treatments.

Standardized Operational Evaluations of Catch Basin Larvicides from Seven Mosquito Control Programs in the Midwestern United States During 2017.

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.