Variable gut pH as a potential mechanism of tolerance to Bacillus thuringiensis subsp. israelensis toxins in the biting midge Culicoides sonorensis.

BACKGROUND: Toxins of Bacillus thuringiensis subsp. israelensis (Bti) are safer alternatives for controlling dipteran pests such as black flies and mosquitoes. The biting midge Culicoides sonorensis (Diptera: Ceratopogonidae) is an important pest of livestock in much of the United States and larval midges utilize semi-aquatic habitats which are permissive for Bti product application. Reports suggest that Bti products are ineffective at killing biting midges despite their taxonomic relation to black flies and mosquitoes. Here, we investigate the toxicity of a Bti-based commercial insecticide and its active ingredient in larval Culicoides sonorensis. A suspected mechanism of Bti tolerance is an acidic larval gut, and we used a pH indicator dye to examine larval Culicoides sonorensis gut pH after exposure to Bti. RESULTS: The lethal concentration to kill 90% (LC90) of larvae of the commercial product (386 mg/L) was determined to be almost 10 000 times more than that of some mosquito species, and no concentration of active ingredient tested achieved 50% larval mortality. The larval gut was found to be more acidic after exposure to Bti which inhibits Bti toxin activity. By comparison, 100% mortality was achieved in larval Aedes aegypti at the product's label rate for this species and mosquito larvae had alkaline guts regardless of treatment. Altering the larval rearing water to alkaline conditions enhanced Bti efficacy when using the active ingredient. CONCLUSION: We conclude that Bti is not practical for larval Culicoides sonorensis control at the same rates as mosquitos but show that alterations or additives to the environment could make the products more effective. © 2024 Society of Chemical Industry.

Preparation of a long-lasting tablet of spinosad microspheres and its residual insecticidal efficacy against the yellow fever mosquito, Aedes aegypti (Diptera: Culicidae) larvae.

BACKGROUNDS: In order to provide a long-lasting formulation for spinosad (SP) targeting larval stages of Aedes aegypti (Linnaeus) and others alike, a SP tablet was developed based on microspheres, using polylactic acid as inside coating material. The microspheres were encapsulated using polyethylene glycol and 1-hexadecanol to form a sustained-release SP tablet. Micromorphology, active ingredient loading, structure identification, photolysis resistance and biological activity were evaluated in this report. RESULTS: (i) The SP microspheres had an average particle size of 6.16 ± 2.28 µm, low adhesion and good dispersion as evaluated by scanning electron microscopy and morphology. (ii) The average active ingredient loading and encapsulation of SP microspheres were 32.80 ± 0.74% and 78.41 ± 2.22%, respectively. (iii) The chemical structure of encapsulated SP was confirmed by Fourier transform infrared and 1H-nuclear magnetic resonance. (iv) The photostability of the microspheres and the tablets were evaluated. The results showed that DT50 (time required to dissipate 50% of the mass originally present) of SP was 0.95 days in microspheres and 6.94 days in tablets. (v) The long-term insecticidal activity of SP tablets was investigated, and the tablet had a long-lasting activity against the mosquito larvae, showing 100% larval mortality for 63 days. CONCLUSIONS: The study provided a new long-lasting formulation of SP, which displayed good efficacy in the control of Ae. aegypti larvae. © 2024 Society of Chemical Industry.

Laboratory and Semi-Field Evaluation on S-Methoprene Formulations Against Anopheles sinensis (Diptera: Culicidae) - Yuxi City, Yunnan Province, China.

What is already known about this topic?: Anopheles sinensis (An. sinensis) is the predominant malaria vector in China. The impact of S-methoprene on the emergence process of mosquito larvae suggests its potential as a control method for vector mosquitoes. However, the efficacy of S-methoprene in controlling An. sinensis has not yet been demonstrated. What is added by this report?: The effectiveness of S-methoprene against An. sinensis was assessed in laboratory and semi-field conditions in Yunnan Province. What are the implications for public health practice?: These results offer valuable options and guidance for utilizing S-methoprene products in malaria reimportation prevention areas within Yunnan Province.

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.

Comparative bioactivity of S-methoprene and novel S-methobutene against mosquitoes (Diptera: Culicidae).

Mosquitoes and mosquito-borne illnesses significantly impact public health and human well-being. To address this concern, environmentally compatible larvicides have become a critical component of integrated mosquito management. However, the number of available larvicides is at a historical low. Currently, larvicides that harness microbials and insect growth regulators account for most products. Screening of new active ingredients (AIs) or improvement of existing AIs is thus necessary to augment the capacity for mosquito control. S-methoprene possesses a similar molecular structure and identical function to mosquito juvenile hormone and has been one of the main targets for research and development. The efficacy and safety of S-methoprene have been well documented since the late 1960s, and numerous products have been commercialized to combat pests of economic importance. However, S-methoprene is vulnerable to environmental factors that lead to its degradation, which has created challenges in formulation development, particularly where extended efficacy is desired. A derivative of S-methoprene, namely S-methobutene, with molecular modification has become available. This derivative has demonstrated an enhanced activity of inhibition of emergence (IE) against species across the Aedes, Anopheles, and Culex genera at IE10, IE50, and IE90. Furthermore, S-methobutene consistently outperformed S-methoprene during a 120-day aging process against the southern house mosquito Cx. quinquefasciatus, where the IE% in S-methobutene was significantly higher than that in S-methoprene on most aging intervals. The former had significantly longer residual activity than the latter. The potential of S-methobutene for further development and application is discussed in consideration of its enhanced activity and stability.

Small RNA sequencing of field Culex mosquitoes identifies patterns of viral infection and the mosquito immune response.

Mosquito-borne disease remains a significant burden on global health. In the United States, the major threat posed by mosquitoes is transmission of arboviruses, including West Nile virus by mosquitoes of the Culex genus. Virus metagenomic analysis of mosquito small RNA using deep sequencing and advanced bioinformatic tools enables the rapid detection of viruses and other infecting organisms, both pathogenic and non-pathogenic to humans, without any precedent knowledge. In this study, we sequenced small RNA samples from over 60 pools of Culex mosquitoes from two major areas of Southern California from 2017 to 2019 to elucidate the virome and immune responses of Culex. Our results demonstrated that small RNAs not only allowed the detection of viruses but also revealed distinct patterns of viral infection based on location, Culex species, and time. We also identified miRNAs that are most likely involved in Culex immune responses to viruses and Wolbachia bacteria, and show the utility of using small RNA to detect antiviral immune pathways including piRNAs against some pathogens. Collectively, these findings show that deep sequencing of small RNA can be used for virus discovery and surveillance. One could also conceive that such work could be accomplished in various locations across the world and over time to better understand patterns of mosquito infection and immune response to many vector-borne diseases in field samples.

A validated triplex RT-qPCR protocol to simultaneously detect chikungunya, dengue and Zika viruses in mosquitoes.

BACKGROUND & OBJECTIVES: Recently, the incidences of chikungunya, dengue and Zika infections have increased due to globalization and urbanization. It is vital that reliable detection tools become available to assess the viral prevalence within mosquito populations. METHODS: Based on the previous publications on clinical diagnosis in human infections, for the first time, we described a customized triplex RT-qPCR protocol for simultaneous detection of chikungunya virus (CHIKV), dengue virus serotypes 1-4 (DENV1-4) and Zika virus (ZIKV) in mosquitoes. RESULTS: In preliminary assessment to determine the specificity and sensitivity of primers and probes, all six targets were detected individually with the following thresholds as indicated by calculated pfu equivalents: 3.96x100 for CHIKV, 3.80x101 for DENV1, 3.20x101 for DENV2, 8.00x104 for DENV3, 1.58x100 for DENV4, and 6.20x100 for ZIKV When tested in a full combination of six targets (CDZ mix), CHIKV, DENV1-4 mix or ZIKV were all detected with the thresholds of 1.32x100 for CHIKV, 3.79x100 for DENV1-4 and 2.06x100 for ZIKV All targets, individually or in full combination were detected in the mixtures of Aedes aegypti (L.) homogenate and viral lysates. A robust evaluation with three replicates in each of three plates for CHIKV, DENV1-4 and ZIKV individually or in full combination was conducted. In individual assays, CHIKV was detected to 3.96x10-1, DENV1-4 to 1.14x100 and ZIKV to 3.20x100. In full combination assays, CHIKV was detected to 1.32x104, DENV1-4 to 3.79x101 and ZIKV to 1.07x100. INTERPRETATION & CONCLUSION: This triplex RT-qPCR assay appears to consistently detect all six targets and does not cross react with Ae. aegypti homogenate, making it a feasible, practical, and immediately adoptable protocol for use among vector control and other entities, particularly in the endemic areas of CHIKV, DENVs and ZIKV.

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.

Pyrethroid insecticides in urban catch basins: A potential secondary contamination source for urban aquatic systems.

Pesticide contamination is a threat to many aquatic habitats, and runoff from residential homes is a major contributor of these chemicals in urban surface streams and estuaries. Improved understanding of their fate and transport can help identify areas of concern for monitoring and management. In many urban areas, runoff water congregates in numerous underground catch basins before draining into the open environment; however, at present essentially no information is available on pesticide presence in these systems. In this study, we collected water samples from a large number of underground urban catch basins in different regions of California during the active pest management season to determine the occurrence and profile of the widely used pyrethroid insecticides. Detectable levels of pyrethroids were found in 98% of the samples, and the detection frequency of individual pyrethroids ranged from no detection for fenpropathrin to 97% for bifenthrin. In the aqueous phase, total pyrethroid concentrations ranged from 3 to 726 ng/L, with a median value of 32 ng/L. Pyrethroids were found to be enriched on suspended solids, with total concentrations ranging from 42 to 93,600 ng/g and a median value of 2,350 ng/g. In approximately 89% of the samples, whole water concentrations of bifenthrin were predicted to have toxic units >1 for sensitive aquatic invertebrates. The high detection frequency of bifenthrin and overall pyrethroid concentrations, especially for particle-bound residues, suggest that underground urban catch basins constitute an important secondary source for extended and widespread contamination of downstream surface waters by pesticides such as pyrethroids in urban regions.

Characterization of the Blood-Feeding Patterns of Culex quinquefasciatus (Diptera: Culicidae) in San Bernardino County, California.

West Nile virus (WNV) is a zoonotic disease that is endemic in North America and is known to cause a range of symptoms from mild to life threatening in humans. Culex quinquefasciatus is one of the most prominent vectors of WNV in Southern California. The goal of this study was to identify which animal species are most fed upon by these mosquitoes in various habitats in the West Valley area of San Bernardino County, California, and determine the relationship between blood-feeding patterns and WNV activity in the region. Culex quinquefasciatus specimens were collected by West Valley Mosquito and Vector Control District during 2011 from 32 different sites. The bloodmeals of 683 individuals (92.4% of those tested) were identified using the mitochondrial gene cytochrome c oxidase 1 (COI). These bloodmeals comprised 29 vertebrate species across four different habitats. Species richness (ranging from 10 to 17) was not significantly different between habitats when rarified to account for sample size. Across habitats, the highest percentage of avian bloodmeals were taken from house sparrows (18.8-39.1%) and house finches (2.6-31.5%). Bloodmeals were identified from five mammalian species, accounting for 5.1-59.2% of bloodmeals by habitat, including humans (0-4.1%). A seasonal shift towards increased mammalian bloodmeal prevalence, specifically for domestic dog and human bloodmeals, was observed in urban habitats. The WNV activity during 2011 in San Bernardino County occurred mostly in urban and suburban areas as indicated by minimum infection rate (MIR) in Culex quinquefasciatus, notable as all human bloodmeals were identified from these two habitats.

Establishment of the Invasive Aedes aegypti (Diptera: Culicidae) in the West Valley Area of San Bernardino County, CA.

The yellow fever mosquito, Aedes aegypti (Linnaeus, 1762), is the most aggressive invasive mosquito species with worldwide distribution. In addition to being a notorious nuisance species, it can pose significant public health concern because of its ability to transmit various viral pathogens. The first adult capture in the West Valley area of San Bernardino County, CA, occurred in September 2015 in Montclair. A strategic surveillance plan was implemented accordingly by the West Valley Mosquito and Vector Control District to document the infestation. The Biogent Sentinel (BG-2) trap augmented with BG-Lure and carbon dioxide (CO2) was deployed as a routine surveillance tool during 2017-2019. Extensive trapping revealed an expanding infestation, when positive trap nights (TN) increased from 14.2% in 2017 to 23.9% in 2018 and 55.6% in 2019. The average counts/TN increased from 0.65 in 2017 and 0.90 in 2018 to 3.83 in 2019. The cities of Montclair, Chino, and Ontario had much higher infestation than other cities in the district with the highest positive TN of 46.0% in Montclair, and highest average trap count of 3.23/TN in Chino. It was interesting to note that males coincided with females with more profound trend during warmer months of July to October when ratios of males ranged 28.4-35.0%. The BG-2 trap significantly outperformed the CO2 trap and gravid trap. The establishment of this invasive species in semiarid inland Southern California was further confirmed by concurrent larval collections.

Cross Resistance in S-Methoprene-Resistant Culex quinquefasciatus (Diptera: Culicidae).

The juvenile hormone analog S-methoprene is the only synthetic biopesticide that is registered with the United States Environmental Protection Agency to control arthropods of economic importance in public health, livestock, pets, urban, and stored products. The high activity, relative target specificity, and benign environmental profile of S-methoprene have been well documented. While the risk of resistance in mosquitoes to S-methoprene is generally low, there is a lack of information regarding cross resistance in S-methoprene-resistant mosquitoes to other pesticides. In this paper, a population of the southern house mosquito Culex quinquefasciatus Say from southern California acquired low levels of resistance to S-methoprene in the field, where the resistance ratios ranged 7.0- to 8.8-fold as compared with a laboratory reference colony. After 30 generations of laboratory selections by S-methoprene when resistance was elevated to 57.4- to 168.3-fold relative to an unselected population, various levels of cross resistance to other commonly used pesticides were revealed in the selected population. Cross resistance to the microbial mosquito larvicide Lysinibacillus sphaericus (Meyer & Neide) (Bacillales: Bacillaceae) was the most profound, amounting to 77.50- to 220.50-fold. The mechanism and potential management tactics toward cross resistance are discussed to preserve the unique value of this synthetic biopesticide.

Deployment and Fact Analysis of the In2Care® Mosquito Trap, A Novel Tool for Controlling Invasive Aedes Species.

During April-October 2019, the West Valley Mosquito and Vector Control District (Ontario, CA) deployed large numbers of In2Care® mosquito traps in a preliminary study to evaluate the trap's potential effectiveness at controlling invasive Aedes aegypti (L.) and Ae. albopictus (Skuse) in 6 cities of San Bernardino County, CA. The trap was used to attract ovipositing females, expose them to the juvenile hormone mimic pyriproxyfen and the entomopathogenic fungus Beauveria bassiana, and autodisseminate pyriproxyfen to other water sources prior to their death from fungal infection. The trap attracted Ae. aegypti and Culex quinquefasciatus, with the latter species predominating at much higher larval densities in the trap reservoirs. Field-collected larvae and pupae from the trap reservoirs showed complete adult emergence inhibition. Furthermore, the trap reservoirs retained high levels of residual larvicidal, pupicidal, and emergence inhibition activity after they were retrieved from the field, as indicated by laboratory bioassays against laboratory colony of Cx. quinquefasciatus. Results of this study support more detailed quantitative local evaluations on trap efficacy to measure the impact of the In2Care mosquito trap on wild invasive Aedes and Culex populations in future mosquito control efforts.

Susceptibility Profile of Aedes aegypti L. (Diptera: Culicidae) from Montclair, California, to Commonly Used Pesticides, With Note on Resistance to Pyriproxyfen.

The peridomestic anthropophilic Aedes aegypti L. (Diptera: Culicidae) is originated from the wild zoophilic subspecies Aedes aegypti formosus in sub-Saharan Africa, and currently has a broad distribution in human-modified environments of the tropics and subtropics worldwide. In California, breeding populations were initially detected in 2013 in the cities of Fresno, Madera, and San Mateo, and now can be found in 188 cities of 12 counties in the state. Recent genetic studies suggest that this species invaded California on multiple occasions from several regions of the United States and northern Mexico prior to initial detection. As an invasive species and vector for numerous arboviruses, Ae. aegypti is a primary target of surveillance and control in California. In southern California city of Montclair, a population was identified in September 2015, from which a short-term colony was established in an insectary. The susceptibility of this field population to commonly used pesticides with various modes of action, including 15 formulations against larvae and four against adults, was determined, in reference to a susceptible laboratory colony of the same species. No resistance was shown to most pesticides tested. However, tolerance or reduced susceptibility to spinosad, spinetoram, diflubezuron, and fipronil was detected, and modest levels of resistance to pyriproxyfen (resistance ratio = 38.7-fold at IE50 and 81.5-fold at IE90) was observed. Results are discussed based on the field usage and modes of action of the pesticides tested. Strategic selection and application of pesticides against this population of Ae. aegypti in the urban environments should be taken into consideration.

High Resistance to Bacillus sphaericus and Susceptibility to Other Common Pesticides in Culex pipiens (Diptera: Culicidae) from Salt Lake City, UT.

Biorational mosquito larvicides based on microbial organisms and insect growth regulators (IGRs) have played a vital role in integrated mosquito control, particularly since the invasion of West Nile virus to the United States in 1999. Products that are formulated with technical powder of the bacterium, Bacillus sphaericus Neide (recently Lysinibacillus sphaericus Meyer and Neide), are among the ones that have been extensively applied to combat Culex and other mosquito species. Due to the simplicity of the binary toxins, resistance to this pesticide in laboratory and field populations of Culex pipiens L. complex has occurred globally since 1994. A Cx. pipiens population with a high level of resistance to B. sphaericus (VectoLex WDG) was identified in Salt Lake City, UT, in September 2016. The resistance ratios in this population were 20,780.0- and 23,926.9-fold at LC50 and LC90, respectively, when compared with a susceptible population of a laboratory reference colony of the same species. This B. sphaericus-resistant population remained mostly susceptible to other commonly used pesticides to control arthropods of public health and urban significance, including ones based on microbial organisms (Bacillus thuringiensis subsp. israelensis, spinosad, spinetoram, abamectin), IGRs (pyriproxyfen, methoprene, diflubenzuron, novaluron), organophosphate (temephos), neonicotinoid (imidacloprid), phenylpyrazole (fipronil), oxadiazine (indoxacarb), and pyrethroid (permethrin). Results are discussed according to the modes of action of the pesticides tested, and suggestions are made to manage B. sphaericus-resistant mosquito populations.

Validation of an Improved Statistical Theory for Sea Surface Whitecap Coverage Using Satellite Remote Sensing Data.

The whitecap coverage at the sea surface is affected by the ratio of kinetic energy to potential energy, θ, the wave spectrum width parameter, ρ, and other factors. This paper validates an improved statistical theory for surface whitecap coverage. Based on the theoretical analysis, we find that the whitecap coverage is more sensitive to ρ than to θ, and the improved statistical theory for surface whitecap coverage is suitable in regions of rough winds and waves. The satellite-derived whitecap coverage data in the westerly wind zone is used to validate the improved theory. The comparison between the results from theory and observations displays a better performance from the improved theory relative to the other methods tested.

Resistance to Lysinibacillus sphaericus and Other Commonly Used Pesticides in Culex pipiens (Diptera: Culicidae) from Chico, California.

Bacillus sphaericus Neide, recently renamed as Lysinibacillus sphaericus Meyer and Neide, is a spore-forming bacterium that possesses various levels of larvicidal activity, depending on the strains, against some mosquito species. Products based on most active strains such as 2362, 2297, 1593, C3-41 that bear binary toxins, as well as mosquitocidal toxins at various levels, have been developed to combat mosquito larvae worldwide. Resistance in wild Culex mosquito populations has been reported since 1994 from France, Brazil, India, China, Thailand, and Tunisia. Laboratory studies to evaluate resistance development risk have been conducted by many groups of scientists worldwide. Products based on L. sphaericus strain 2362 were registered in the United States in 1990s, and their use for mosquito control has been increased considerably since invasion of West Nile virus. This report documents the first occurrence of high-level resistance to L. sphaericus in a natural population of Culex pipiens L. in Chico, CA, where resistance ratio was 537.0 at LC50 and 9,048.5 at LC90 when compared with susceptible laboratory colony of the same species. Susceptibility profile to other groups of pesticides with different modes of action was also determined. Various levels of resistance or tolerance were noticed to abamectin, pyriproxyfen, permethrin, and indoxacarb. Resistance management and susceptibility monitoring strategies are discussed and recommended.

Lack of Resistance in Aedes vexans Field Populations After 36 Years of Bacillus thuringiensis subsp. Israelensis Applications in the Upper Rhine Valley, Germany.

Bacillus thuringiensis subsp. israelensis (Bti) has been widely and solely used against floodwater mosquitoes, mostly Aedes vexans, for 36 years in the Upper Rhine Valley by the German Mosquito Control Association. During this period, almost 5,000 tons of Bti formulations were applied to an area of approximately 400,000 ha. To investigate a possible resistance development after such a long-term and widespread application of Bti, the susceptibility of Ae. vexans larvae to Bti in 3 untreated (Lake Constance) and 6 treated areas on both sides of the Rhine within the Upper Rhine Valley was assessed by bioassays following World Health Organization guidelines. Comparing log-probit analyses, it was shown that neither the median lethal concentration (LC50 values) nor slopes of the probit lines of bioassays of the larvae deriving from treated and untreated areas showed significant differences. These results have been confirmed by resistance ratios, which varied from 0.80 to 1.12 in all tests. The results provided the evidence that no restistance in the target species Ae. vexans has developed in the areas of the Upper Rhine Valley, despite the large-scale use of Bti for 36 years.

Impact of Storage and Handling Temperatures On the Activities of Mosquito Larvicides.

Larvicides based on Bacillus thuringiensis israelensis, Lysinibacilus sphaericus (formerly Bacillus sphaericus), Saccharopolyspora spinosa and insect growth regulators such as methoprene, and a few others are the most commonly used mosquito control products in the United States and elsewhere because of their relative specificity and high effectiveness against target organisms, safety to nontarget species, and compatibility with the environment. Using standard laboratory bioassay, we have evaluated the loss of larvicidal activities of various formulations after being exposed to different storage and handling temperatures. Transportation of products under outdoor conditions for an extended period of time caused more activity loss compared with other conditions. Results are discussed based on their active ingredients as well as physico-chemical properties of the formulations reported. Recommendations are made for proper inventory control, storage, and handling of larvicides to minimize loss of larvicidal activity.