Control Of Larvae Research Articles

The evaluation on control potential using X-ray to irradiate adult Spodoptera frugiperda (Lepidoptera: Noctuidae).

The sterile insect technique (SIT), involving the rearing of larvae for pupation followed by irradiating pupae, is employed for environmentally friendly invasive pest management. Despite its effectiveness, the cost of pupae production poses challenges for small farmers in developing countries. Alternatively, utilizing insect trapping techniques can capture abundant adult insects in their natural habitats, but application potential of adult SIT approach remains unclear. We used the invasive pest Spodoptera frugiperda (Lepidoptera: Noctuidae) to assess the effectiveness of X-ray irradiated moths on their sterility rates, mating competitiveness, flight ability, and larval control efficiency in the field. Our findings revealed that optimal X-ray doses for 1-, 3-, and 5-day-old adult S. frugiperda were 154, 173, and 180 Gy, respectively. These doses rendered males more than 80.0% infertile and females nearly completely infertile. Significantly, the flight ability of sterilized males remained unaffected by sub-sterilizing doses of irradiation. Furthermore, in a release ratio of 16:1:1 (irradiated males-unirradiated males-unirradiated females), irradiated males exhibited the highest mating competitiveness (0.79). In the field-cage experiments, the corrected leaf protection rate and the corrected population decline rate in the 16:1:1 release plot were 60.50% and 74.21%, respectively. These findings suggest that radiation-induced sterility in adult S. frugiperda holds promise for practical applications, offering a conceptual framework and novel approaches for advancing radiation-based pest control technology. © 2024 Society of Chemical Industry.

Household expenditure on control of urban mosquitoes Aedes albopictus and Culex pipiens in Emilia-Romagna, Northern Italy.

In 2007, the first outbreak of Chikungunya in Italy generated great alarm, highlighting the health risks caused by exotic species recently introduced in Europe and the need to strengthen control actions against the vectors. Besides health risks, mosquitoes cause nuisance, and citizens are required to adopt control measures. While the economic aspects of mosquito control by public agencies have been investigated, the scientific literature on the costs of mosquito protection incurred by families is scarce. This study assessed the households' expenditure on protective measures against mosquitoes in Emilia-Romagna, a region in Northern Italy. A phone questionnaire survey was conducted to collect data on the annual expenditure incurred by households for self-protection against mosquitos in relation to the perceived level of nuisance and the household and dwelling characteristics. Univariate and multivariate analyses were conducted to identify the main determinants influencing such expenditure, which resulted affected by dwelling characteristics, presence of children under 6 years of age, and health concerns of family members. The average annual household expenditure was estimated at 84.63 euros, about 30 times higher than the expenditure per household supported by regional and local administrations for interventions against mosquitoes in public areas, as calculated in a previous study. Household expenditure is mainly aimed at providing a direct defense against mosquito bites (mosquito nets, adulticides, skin-on repellents, etc.) while spending for more effective measures addressed to reduce mosquito density results marginal: e.g., only 3.5% of the total expenditure was dedicated to larval control. Control activities that lower the mosquito density in both private and public areas could reduce the use of household insecticides in urban environments and the related costs, and the risk of spread of imported arboviruses as well.

Characterization of Anopheles mosquito breeding habitats for malaria vector control in Mazowe and Shamva districts, Zimbabwe.

Area-specific identification and studies of Anopheles breeding habitat diversity, distribution, and productivity in different seasons are important in designing and advancing effective malaria vector control according to the local context and needs. This study identified and characterized Anopheles breeding habitats for targeted control of malaria vectors in Mazowe and Shamva districts. Repeated cross-sectional surveys were conducted in Mazowe and Shamva districts between April and December 2023. Habitat productivity and physicochemical parameters were measured. Anopheles larvae were collected, reared to adults, and identified using morphological keys. SPSS software was used for data analysis. One-way ANOVA, Fisher's exact, Pearson's correlation, and simple linear regression tests were conducted. Seven different types of Anopheles breeding habitats were identified from 56 sites. The highest mean density of larvae was recorded in stream edge pools during the post-rainfall period. Anophelespretoriensis (67.4%), An. gambiae s.l. (23.1%), An. rufipes (9.2%) and An. coustani (0.38%) were breeding in the study area. Anopheles pretoriensis bred in all habitat types, An. coustani in swamps only while An. gambiae s.l. and An. rufipes preferred stream edge pools, roadside pools, and hoof prints. There was a significant positive correlation between larval density and dissolved oxygen (r = 0.535; p < 0.001) and conductivity (r = 0.288; p = 0.032). Size, origin, and type of breeding habitat were positive indicators for different Anopheles species in the study area. Potential malaria vector breeding habitats should be targeted for larval control under the current malaria control and elimination phases in the two districts.

Prevention of resistance to spinosad by a combination of spinosad and Bacillus thuringiensis subsp. israelensis in Culex quinquefasciatus (Diptera: Culicidae).

Spinosad consists of spinosyn A and spinosyn D that are produced by the soil-dwelling actinomycete Saccharopolyspora spinosa. It has been used to control a wide variety of arthropod pests of economic importance. Formulations of spinosad have been used to control larval mosquitoes since approximately 2010. However, the target site- and metabolism-based resistance to this neurotoxin has been reported since 2000 in agricultural pests The current studies aim to further evaluate resistance risk and develop resistance prevention tactics in the southern house mosquito Culex quinquefasciatus. The first comparison group involved selection at lethal concentration, 75% (LC75) of technical spinosad for 30 generations, resulting in baseline resistance ratios (RRs) of 51.1-fold at LC50 and 45.4-fold at LC90 in Cx. quinquefasciatus. However, under the same conditions, selection by a combination of spinosad and Bacillus thuringiensis subsp. israelensis (B.t.i.), negated resistance development to spinosad, RRs ranging 1.00-1.75-fold at LC50 and 0.83-1.76-fold at LC90. At the same time, the selected population remained susceptible to the combination throughout the selection process, RRs fluctuating 0.74-1.38-fold at LC50 and 0.63-1.23-fold at LC90. Combination of spinosad and B.t.i. negates resistance development to spinosad, as opposed to spinosad alone in Cx. quinquefasciatus. Moreover, the species tested does not develop resistance to this combination upon repeated exposures, implying the potential for further developing this combination as a viable product for larval mosquito control. © 2024 Society of Chemical Industry.

COMPARATIVE LABORATORY ACTIVITY AND SEMI-FIELD EFFICACY OF OMNIPRENE® G AND ALTOSID® PELLETS AGAINST AEDES AEGYPTI.

Mosquito larval control by biorational larvicides plays a crucial role in mosquito and mosquito-borne disease management. However, the availability of larvicides that meet the criteria of efficacy, safety, and quality is limited and conventional pesticides are no longer preferred for larval control. Although efforts are made to research new active ingredients (AIs), it is equally important to innovate new formulations based on currently available AIs such as microbial agents and insect growth regulators. Studies were therefore conducted to compare the laboratory activity and semi-field efficacy of OmniPrene® G and Altosid® Pellets with DR-tech, both containing 4.25% S-methoprene, at 2.8 kg/ha and 11.2 kg/ha against the yellow fever mosquito Aedes aegypti (L.) in outdoor microcosms. Both products performed equally in bioassays against the test species with comparable inhibition of emergence activities. In the semi-field study, the lower dose of Altosid Pellets at 2.8 kg/ha, showed lower efficacy than OmniPrene G during the initial 6 weeks; this difference became negligible on week 7, followed by higher efficacy in Altosid Pellets on weeks 8 and 9. More uniform efficacy was observed at the higher dose of 11.2 kg/ha. Equal performance was revealed during weeks 2 to 6, with the OmniPrene G outperforming the Altosid Pellets in week 1, but the opposite during weeks 7 to 9. Mortality patterns were similar in both products, i.e., majority of mortality occurred before emergence, although more incomplete emergence was noted in lower doses, particularly in Altosid Pellets. Overall, newly available OmniPrene G provided comparable activity and efficacy with Altosid Pellets against the test species, with the advantages of fast initial AI release and even coverage, particularly when applied at low doses.

Extreme resistance to S-methoprene in field-collected Culex pipiens (Diptera: Culicidae) across the Chicago, IL region

Insect growth regulators, like S-methoprene, are heavily relied upon worldwide for larval mosquito chemical control due to their target specificity and long-lasting effects. In this study, susceptibility to S-methoprene was evaluated in Culex pipiens, a globally important vector species. Populations from 14 sites throughout the Chicago area with a long history of S-methoprene use and two sites with minimal use in Wisconsin were examined. Using a bioassay methodology and probit analyses, LC50 and LC90 values were calculated and compared to a susceptible laboratory strain to develop resistance ratios, then categorized for resistance intensity. The resistance ratios observed required the addition of another category, termed ‘extreme’ resistance, indicating resistance ratios greater than 100. ‘Low’ to ‘extreme’ levels of resistance to S-methoprene were detected throughout Illinois populations, with resistance ratios ranging from 2.33 to 1010.52. Resistance was not detected in populations where S-methoprene pressure has been very limited. These 'extreme’ resistance ratios observed have never been documented in a wild vector species mosquito population. The relationships between historical S-methoprene use, resistance detected with laboratory bioassays, and the potential for field product failure remain unclear. However, the profound resistance detected here demonstrates a potential critical threat to protecting public health from mosquito-borne diseases.

Human-Environment Interactions Shape Mosquito Seasonal Population Dynamics.

Mosquito species, including the Asian tiger mosquito, can transmit disease-causing pathogens such as dengue, Zika, and chikungunya, with their population dynamics influenced by a variety of factors including climate shifts, human activity, and local environmental conditions. Understanding these dynamics is vital for effective control measures. Our study, conducted in Jardí Botanic Marimurtra from May to November 2021, monitored Ae. albopictus activity using BG-Traps and investigated larval control effects. We employed Generalized Linear Mixed Models to analyze variables like weather, human presence, and larvicidal control on adult mosquito abundance. Adults of Ae. albopictus exhibited a seasonal pattern influenced by temperature but with bimodal peaks linked to cumulative rainfall. Proximity to stagnant water and visitor influx directly affected mosquito captures. Additionally, the effectiveness of larvicide treatments depended on interactions between preceding rainfall levels and treatment timing. Our research emphasizes the significance of studying vector ecology at local scales to enhance the efficacy of control programs and address the escalating burden of vector-borne diseases. Considering the impacts of extreme weather events and climate shifts is essential for the development of robust vector control strategies. Furthermore, our distinct findings serve as a prime illustration of utilizing statistical modeling to gain mechanistic insights into ecological patterns and processes.

Deployment of attractive targeted sugar baits in western Zambia: installation, monitoring, removal, and disposal procedures during a Phase III cluster randomized controlled trial

BackgroundAttractive Targeted Sugar Baits (ATSBs) offer a complementary vector control strategy to interventions targeting blood feeding or larval control by attacking the sugar feeding behaviour of adult mosquitoes using an attract-and-kill approach. Western Zambia was the first location to receive and deploy ATSB Sarabi version 1.2 stations in a Phase III cluster randomized controlled trial. This paper describes ATSB station installation, monitoring, removal, and disposal, quantifies ATSB station coverage, and reports major reasons for ATSB station replacement.MethodsATSB stations were deployed during two annual transmission seasons, through scheduled installation and removal campaigns. During deployment, monitoring was conducted per protocol to maintain high coverage of the ATSB stations in good condition. Routine monitoring visits during the trial captured details on ATSB station damage necessitating replacement following pre-defined replacement criteria. Annual cross-sectional household surveys measured ATSB station coverage during peak malaria transmission.ResultsA total of 67,945 ATSB stations were installed in Year 1 (41,695 initially installed+ 26,250 installed during monitoring) and 69,494 ATSB stations were installed in Year 2 (41,982 initially installed+ 27,512 installed during monitoring) across 35 intervention clusters to maintain high coverage of two ATSB stations in good condition per eligible household structure. The primary reasons for ATSB station replacement due to damage were holes/tears and presence of mold. Cross-sectional household surveys documented high coverage of ATSB stations across Year 1 and Year 2 with 93.1% of eligible structures having ≥ 2 ATSB stations in any condition.DiscussionATSB station deployment and monitoring efforts were conducted in the context of a controlled cRCT to assess potential product efficacy. Damage to ATSB stations during deployment required replacement of a subset of stations. High coverage of eligible structures was maintained over the two-year study despite replacement requirements. Additional research is needed to better understand the impact of damage on ATSB station effectiveness under programmatic conditions, including thresholds of threats to physical integrity and biological deterioration on product efficacy.ConclusionsOptimizing ATSB stations to address causes of damage and conducting implementation research to inform optimal delivery and cost-effective deployment will be important to facilitate scale-up of ATSB interventions.

Efficacy of entomopathogenic nematodes in laboratory and field conditions of Cicer arietinum against cotton bollworm, Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

BackgroundThe chickpea Cicer arietinum (Fabaceae) field has suffered significant economic losses due to the presence of cotton bollworm, Helicoverpa armigera Hübner (Lepidoptera: Noctuidae). Attempts to control the larval population through chemical pesticides led to some reduction but also resulted in the development of resistance among the larvae. Consequently, the H. armigera population experienced a rapid resurgence in the field. Given the substantial losses caused by Helicoverpa larvae, there is now a growing interest in adopting eco-friendly methods for management. The application of biocontrol agents has emerged as a promising solution for effectively managing the infestation.ResultsIn the laboratory experiment, the entomopathogenic nematodes (EPNs) Steinernema pakistanense NNRC-NB.14, S. balochiense NNRC-NB.23, and S. abbasi NNRC-NB.33 were evaluated for their infectivity and mortality effects on mature cotton bollworm at various concentrations. The study demonstrated that the highest mortality rates were achieved at a concentration of 250 infective juveniles (IJs) per larva after 72 h. Steinernema pakistanense and S. balochiense exhibited higher mortality rates (95–98%) compared to S. abbasi (77%) at higher application concentrations. The field trial results reinforced the laboratory findings, demonstrating a significant decrease in H. armigera larval populations when employing EPN strains, particularly NNRC-NB.14 and NNRC-NB.33, compared to NNRC-NB.23. Despite the initial applications showing relatively low mortality percentages, the most effective larval control occurred after the third application of EPNs. The field trials revealed that, following the third spray, mortality percentages significantly increased from the initial range of 20–32% to a more substantial 70–90%. This cumulative impact highlights the importance of multiple applications in achieving optimal pest control.ConclusionThe findings of these studies highlight the promising potential of EPN as an eco-friendly and sustainable method for controlling the cotton bollworm. However, the successful implementation of EPN-based control strategies in agricultural systems requires careful consideration of factors such as nematode species selection, application methods, environmental conditions, and integration with other pest management practices. Further research is needed to optimize the efficacy and practicality of using EPN on a larger scale, addressing issues such as nematode production, formulation, and compatibility with existing farming practice.

Larvicidal Activity of Red Betel Leaves (Piper ornatum) Ethanolic Extract&amp;nbsp;Against Mosquito Larvae

Larvae are the initial carriers of dengue hemorrhagic fever (DHF) and culex, making them significant in disease transmission. Excessive chemical larvicides pose serious risks to human health, thus driving the development of biological alternatives like red betel leaf extract. This study aimed to assess the efficacy of red betel leaf extract in larval control. Using 300 larvae, concentrations of 5%, 6%, and 7% were tested with three replicates over 24 h. The bioassay involved placing the larvae into a plastic container filled with the extract. It was found that ethanol extract from Piper ornatum leaves contained alkaloids, tannins, saponins, flavonoids, and terpenoids. After 24 h, results revealed 83% mortality at 5%, 98% at 6%, and 100% at 7% of extract concentration. Consequently, the 7% concentration showed the fastest efficacy in killing mosquito larvae (100% in 50 min). The LC50 value, representing the concentration at which 50% of larvae are killed, was determined to be 0.04%. Additionally, the LT50 value, indicating the time required to kill 50% of larvae (based on the LC50 value), was found to be 3.34 hours. In conclusion, red betel leaf extract demonstrated promising larvicidal activity against mosquito larvae. Future research is anticipated to prove its safety via in vitro and in vivo test.

Mitigating dengue incidence through advanced Aedes larval surveillance and control: A successful experience from Pakistan.

Dengue fever is a viral disease caused by one of four dengue stereotypes (Flavivirus: Flaviviridae) that are primarily transmitted by Aedes albopictus (Skuse) and Aedes aegypti (L.). To safeguard public health, it is crucial to conduct surveys that examine the factors favouring the presence of these species. Our study surveyed 42 councils across four towns within the Bhakkar district of Punjab Province, by inspecting man-made or natural habitats containing standing water. First, door-to-door surveillance teams from the district health department were assigned to each council to surveillance Aedes species and dengue cases. Second, data collection through surveillance efforts, and validation procedures were implemented, and the verified data was uploaded onto the Dengue Tracking System by Third Party Validation teams. Third, data were analysed to identify factors influencing dengue fever cases. The findings demonstrated the following: (1) Predominantly, instances were discerned among individuals who had a documented history of having travelled beyond the confines of the province. (2) Containers associated with evaporative air coolers and tyre shops were responsible for approximately 30% of the Aedes developmental sites. (4) Variability in temperature was responsible for approximately 45% of the observed differences in the quantity of recorded Aedes mosquito developmental sites. (5) Implementation of dengue prevention initiatives precipitated a 50% reduction in Aedes-positive containers, alongside a notable 70% decline in reported cases of dengue fever during the period spanning 2019 to 2020, while the majority of reported cases were of external origin. Aedes control measures substantially curtailed mosquito populations and lowered vector-virus interactions. Notably, local dengue transmission was eliminated through advanced and effective Aedes control efforts, emphasising the need for persistent surveillance and eradication of larval habitats in affected regions.

Factors associated with mosquito control among construction workers: A systematic review.

Workers in the construction industry frequently work in construction sites with numerous areas that can potentially accumulate water, such as tanks, wet cement surfaces, or water puddles. These water collection sites become ideal breeding grounds for mosquito infestation, which leads to a higher prevalence of mosquito-borne diseases, especially malaria and dengue among construction workers. Despite that numerous factors have been identified in controlling vector-borne diseases, the specific factors that influence mosquito control at construction sites have yet to be explored. This systematic review aims to determine the factors associated with mosquito control among construction workers. Primarily, articles related to factors associated with mosquito control among construction workers were collected from two different online databases (ScienceDirect and EBSCOhost). Two independent reviewers were assigned to screen the titles and abstracts of the collected data, stored in Microsoft Excel, against the inclusion and exclusion criteria. Afterwards, the quality of the included articles was critically assessed using the Mixed Method Appraisal Tool (MMAT). Of the 171 articles identified, 4 were included in the final review. Based on the thorough evaluation, mosquito-related knowledge, practical mosquito prevention measures, and Larval Source Management (LSM) were identified as vital factors associated with mosquito control among construction workers. The significant association between mosquito-related knowledge and control practices indicates higher knowledge linked to effective practices, particularly among female workers and those who were recently infected with malaria. Concurrently, there were notable challenges regarding sustainable preventive measures and larval control methods in construction settings. Implementing effective mosquito control, including knowledge and practice on mosquito control together with vector control, is highly required to suppress the expanding mosquito population. It is recommended that employers provide continuous mosquito control education and training to their employees and reward them with incentives, while employees should comply with the guidelines set by their employers to ensure successful mosquito control and reduce the spread of mosquito-borne diseases in the construction industry.

Can we manage alien invasive insects without altering native soil faunal communities? A field trial on Popillia japonica

Biological and integrated pest control are key assets to environmentally friendly management of cropland. Use of entomopathogens against target pests is common, yet the effects of such released organisms on native, non-target invertebrates are currently poorly known. This is particularly true for relatively inconspicuous components of agroecosystems such as soil biological biota. Popillia japonica, a polyphagous alien invasive scarab beetle native to Japan, is now present in Europe where huge efforts are being conducted to control the pest and slow its spread. In particular, entomopathogenic nematodes and fungi have been used for larval control. Here we test the effects of those agents on both P. japonica larvae and non-target soil biota by comparing soil arthropod assemblages before and after treatment of field plots in an irrigated perennial meadow.Application of an indigenous strain of the nematode Heterorhabditis bacteriophora resulted in significant reduction in numbers of P. japonica larvae. In contrast, an indigenous strain of the entomopathogenic fungus Metarhizium robertsii failed to provide significant control. We found no evident effect on non-target edaphic arthropods under either treatment in comparison to untreated control plots. Some taxa, namely Collembola and Acarina, showed a disproportionate increase in treated plots, suggesting that some changes may occur in the long term, at least in particular arthropod groups. Our results suggest the selected strain of H. bacteriophora is an excellent candidate for managing P. japonica larvae with minimal adverse impact on non-target species and ecosystem functioning.

EVALUATION OF THERMAL FOGGER FOR EFFECTIVENESS OF LARVICIDE-ADULTICIDE MIXTURE AGAINST AEDES AEGYPTI

A hand-held thermal fogger was evaluated to spray a mixture of adulticide (Aqualuer 20-20® containing permethrin and piperonyl butoxide) and a biological larvicide (VectoBac®12AS, containing Bacillus thuringiensis subspecies israelensis). Adulticide was applied at maximum label rate of 37 mL/ha while larvicide rates were 0.58, 1.76, 2.64, and 3.50 L/ha (Maximum label rate 2.34 L/ha). Two rows, 7.6 m apart, of bioassay cages containing susceptible 25, 5-7 days old female Aedes aegypti were used to assess effectiveness of the adulticide. Along with each cage were two 473 mL empty plastic cups at 0 and 1.3 m above ground to collect the larvicide. Two control cages and two empty cups were placed upwind in the field for five minutes and removed before the spray. The study was conducted in the evening with five separated replications of a rate. The exposed cages and cups were retrieved from the field and brought back to the laboratory for further observations and tests to determine mortality at 24 and 48 h, respectively. All the adults in all treatment cages and all tests died within 24 h of the spray application. In the lab, larval mortality was assessed by introducing Ae. aegypti larvae, where mortality decreased with increasing distance from the spray line and increased with increasing application rate. The larval mortality at all distances was strongly correlated with application rate (R2 = 0.98). The highest rate used produced 64 -95% larval mortality at all distances. The results indicate that Aqualuer 20-20 and VectoBac 12AS can be applied simultaneously as a mixture achieving complete adult control and considerable larval control.

An analytically tractable, age-structured model of the impact of vector control on mosquito-transmitted infections.

Vector control is a vital tool utilised by malaria control and elimination programmes worldwide, and as such it is important that we can accurately quantify the expected public health impact of these methods. There are very few previous models that consider vector-control-induced changes in the age-structure of the vector population and the resulting impact on transmission. We analytically derive the steady-state solution of a novel age-structured deterministic compartmental model describing the mosquito feeding cycle, with mosquito age represented discretely by parity-the number of cycles (or successful bloodmeals) completed. Our key model output comprises an explicit, analytically tractable solution that can be used to directly quantify key transmission statistics, such as the effective reproductive ratio under control, Rc, and investigate the age-structured impact of vector control. Application of this model reinforces current knowledge that adult-acting interventions, such as indoor residual spraying of insecticides (IRS) or long-lasting insecticidal nets (LLINs), can be highly effective at reducing transmission, due to the dual effects of repelling and killing mosquitoes. We also demonstrate how larval measures can be implemented in addition to adult-acting measures to reduce Rc and mitigate the impact of waning insecticidal efficacy, as well as how mid-ranges of LLIN coverage are likely to experience the largest effect of reduced net integrity on transmission. We conclude that whilst well-maintained adult-acting vector control measures are substantially more effective than larval-based interventions, incorporating larval control in existing LLIN or IRS programmes could substantially reduce transmission and help mitigate any waning effects of adult-acting measures.

Identifying the Key Role of Plutella xylostella General Odorant Binding Protein 2 in Perceiving a Larval Attractant, (E,E)-2,6-Farnesol.

There is currently a lack of effective olfaction-based techniques to control diamondback moth (DBM) larvae. Identifying behaviorally active odorants for DBM larvae and exploring their recognition mechanisms can provide insights into olfaction-based larval control strategies. Through the two-choice assay, (E,E)-2,6-farnesol (farnesol) was identified as a compound exhibiting significant attractant activity toward DBM larvae, achieving an attraction index of 0.48 ± 0.13. PxylGOBP1 and PxylGOBP2, highly expressed in the antennae of DBM larvae, both showed high affinity toward farnesol. RNAi technology was used to knock down PxylGOBP1 and PxylGOBP2, revealing that the attraction of DBM larvae to farnesol nearly vanished following the knockdown of PxylGOBP2, indicating its critical role in recognizing farnesol. Further investigation into the PxylGOBP2-farnesol interaction revealed the importance of residues like Thr9, Trp37, and Phe118 in PxylGOBP2's binding to farnesol. This research is significant for unveiling the olfactory mechanisms of DBM larvae and developing larval behavior regulation techniques.

Sibling species of the major malaria vector Anopheles gambiae display divergent preferences for aquatic breeding sites in southern Nigeria

Background When integrated with insecticide-treated bed nets, larval control of Anopheles mosquitoes could fast-track reductions in the incidence of human malaria. However, larval control interventions may deliver suboptimal outcomes where the preferred breeding places of mosquito vectors are not well known. This study investigated the breeding habitat choices of Anopheles mosquitoes in southern Nigeria. The objective was to identify priority sites for mosquito larval management in selected urban and periurban locations where malaria remains a public health burden. MethodsMosquito larvae were collected in urban and periurban water bodies during the wet-dry season interface in Edo, Delta, and Anambra States. Field-collected larvae were identified based on PCR gel-electrophoresis and amplicon sequencing, while the associations between Anopheles larvae and the properties and locations of water bodies were assessed using a range of statistical methods.ResultsMosquito breeding sites were either man-made (72.09%) or natural (27.91%) and mostly drainages (48.84%) and puddles (25.58%). Anopheles larvae occurred in drainages, puddles, stream margins, and a concrete well, and were absent in drums, buckets, car tires, and a water-holding iron pan, all of which contained culicine larvae. Wild-caught Anopheles larvae comprised Anopheles coluzzii (80.51%), Anopheles gambiae sensu stricto (s.s.) (11.54%), and Anopheles arabiensis (7.95%); a species-specific PCR confirmed the absence of the invasive urban malaria vector Anopheles stephensi among field-collected larvae. Anopheles arabiensis, An. coluzzii, and An. gambiae s.s. displayed preferences for turbid, lowland, and partially sunlit water bodies, respectively. Furthermore, An. arabiensis preferred breeding sites located outside 500 m of households, whereas An. gambiae s.s. and An. coluzzii had increased detection odds in sites within 500 m of households. Anopheles gambiae s.s. and An. coluzzii were also more likely to be present in natural water bodies; meanwhile, 96.77% of An. arabiensis were in man-made water bodies. Intraspecific genetic variations were little in the dominant vector An. coluzzii, while breeding habitat choices of populations made no statistically significant contributions to these variations.ConclusionSibling malaria vectors in the An. gambiae complex display divergent preferences for aquatic breeding habitats in southern Nigeria. The findings are relevant for planning targeted larval control of An. coluzzii whose increasing evolutionary adaptations to urban ecologies are driving the proliferation of the mosquito, and An. arabiensis whose adults typically evade the effects of treated bed nets due to exophilic tendencies.

MOSQUITO CONTROL AND SCRAP TIRES: SAME OLD PROBLEM, NO RELIABLE STRATEGIES

Artificial breeding sites in urban areas have favored the domestication of mosquito vectors. Scrap tires are an important breeding source for mosquito larvae. Few efforts have been made to establish appropriate management measures for used tires, which poses a challenge for larval control activities. Here we mention the inconveniences of tire disposal and the physical and chemical control alternatives. We also note the available methods of larvicide application against larvae in tires and the advantages and disadvantages of each method. The possible effect of overdose/underdose on the development of resistance is considered. Finally, we mention that the actions of vector control programs, the local or state government policies, and active community participation must be interconnected to develop effective tire management.

Comparison of yeast microencapsulated fluralaner to commercially available mosquito larval control products, 2023

Comparison of yeast microencapsulated fluralaner to commercially available mosquito larval control products, 2023

Larvicidal effect of Spinosad and Bacillus thuringiensis var. israelensis on Aedes aegypti (Linnaeus, 1762) (Diptera: Culicidae)

The use of biological larvicide based on Bacillus thuringiensis var. israelensis (Bti) has stood out for its effectiveness in controlling mosquito Aedes aegypti. The larvicide Spinosad is used in the National Dengue Control Program. This study evaluated the effect of Spinosad and Bti larvicide at various temperatures in a laboratory environment. The assays were performed with 10 larvae in quintuplicate, at temperatures of 18° C, 25° C and 32° C, with 24-hour monitoring. The larvae exposed to Bti were eliminated within 0.5 hours at ambient and hot temperatures (32° C), while at colder conditions (18° C) it took 1.5 hours for complete elimination. Regarding Spinosad, 50% survived for 11 hours, but all larvae were killed after 24 hours. The results reinforce the indication of these products for larval control of the species under the conditions of temperature fluctuation.