Attractive toxic sugar baits mixed with pyriproxyfen sprayed on plants against adult and larval Aedes albopictus (Diptera: Culicidae)

Maximizing the Potential of Attractive Targeted Sugar Baits (ATSBs) for Integrated Vector Management

Due to the limitations of the human therapeutics and vaccines available to treat and prevent mosquito-borne diseases, the primary strategy for disease mitigation is through vector control. However, the current tools and approaches used for mosquito control have proven insufficient to prevent malaria and arboviral infections, such as dengue, Zika, and lymphatic filariasis, and hence, these diseases remain a global public health threat. The proven ability of mosquito vectors to adapt to various control strategies through insecticide resistance, invasive potential, and behavioral changes from indoor to outdoor biting, combined with human failures to comply with vector control requirements, challenge sustained malaria and arboviral disease control worldwide. To address these concerns, increased efforts to explore more varied and integrated control strategies have emerged. These include approaches that involve the behavioral management of vectors. Attractive targeted sugar baits (ATSBs) are a vector control approach that manipulates and exploits mosquito sugar-feeding behavior to deploy insecticides. Although traditional approaches have been effective in controlling malaria vectors indoors, preventing mosquito bites outdoors and around human dwellings is challenging. ATSBs, which can be used to curb outdoor biting mosquitoes, have the potential to reduce mosquito densities and clinical malaria incidence when used in conjunction with existing vector control strategies. This review examines the available literature regarding the utility of ATSBs for mosquito control, providing an overview of ATSB active ingredients (toxicants), attractants, modes of deployment, target organisms, and the potential for integrating ATSBs with existing vector control interventions.

Optimizing the Application Timing and Dosage of Metarhizium brunneum (Hypocreales: Clavicipitaceae) as a Biological Control Agent of Aedes aegypti (Diptera: Culicidae) Larvae

Aedes aegypti (Diptera: Culicidae) is the principal vector of dengue and other viruses that cause disease among 100 to 400 million people each year. The recent development of widespread insecticidal resistance has led to the rapid development of biological control solutions aimed at larval control. While the efficacy of Metarhizium brunneum has been shown against Aedes larvae, the impact of larval population dynamics will need to be determined to formulate effective control strategies. In this study, larvae were subjected to four concentrations of M. brunneum (105, 106, 107, 108 conidia ml-1). Larvae were found to be susceptible to M. brunneum with dose-dependent efficacy. When constant larval immigration was added as a parameter, peak mortality was consistently found to occur on the fourth day, before a significant reduction in control efficacy linked to a decline in conidial availability within the water column. This suggests that M. brunneum treatments should be applied at a concentration 1 × 107 conidia ml-1 every four days to effectively control mosquito larvae in the field, regardless of the fungal formulation, water volume, or larval density. Understanding fungal-mosquito dynamics is critical in developing appropriate control programs as it helps optimize the fungal control agent's dose and frequency of application.

Sugar Bait Composition Containing Ivermectin Affect Engorgement and Mortality of the Mosquito Aedes aegypti (Diptera: Culicidae)

Toxins and attractants have been studied and used in sugar baits for mosquitoes. However, little importance has been given to the combination of sugar concentration, bait composition, and their relationship with mosquito engorgement and mortality. Therefore, the present study evaluated the effects of three concentrations of sucrose on baits with and without an attractant (concentrated guava juice), on engorgement and mortality rates of adult Aedes aegypti (Linnaeus, Diptera: Culicidae). Toxic sugar baits (TSB) and attractant toxic sugar baits (ATSB) containing 10, 50, and 70% sucrose and 100 ppm ivermectin (IVM) were prepared to assess engorgement and mortality rates. Subsequently, different concentrations of IVM (0.312-100 ppm) in TSB and ATSB were prepared with sucrose concentrations of 10 and 70% to determine the lethal concentrations (LC50 and LC90) values. Engorgement on the baits was observed under a stereomicroscope, and mortality was followed up to 48 h after feeding. In general, more mosquitoes engorged on TSB regardless of the sugar concentration, while higher concentrations of sugar in ATSBs resulted in higher numbers of mosquitoes engorging. A large increase in the LC90 of IVM was observed for females feeding on ATSBs and TSBs with 70% sucrose relative to those feeding on baits with lower sugar concentrations. No such effect was observed for males.

Development of an Attractive Toxic Sugar Bait for the Control of Aedes j. japonicus (Diptera: Culicidae)

Both female and male mosquitoes consume sugar meals to obtain carbohydrates used for energy. This behavior has recently been identified as a possible mosquito control target, as the World Health Organization has urged for the development of integrated vector management. This is critical as many medically important mosquito species are developing insecticide resistance, resulting in current control strategies becoming less effective. Additionally, the traditional use of insecticides is detrimental to many beneficial insects such as pollinators. The main goal of this study was to develop an attractive toxic sugar bait (ATSB) to limit the populations of a local invasive mosquito, Aedes j. japonicus (Theobald) (Diptera: Culicidae). An ATSB is a lure bait composed of an attractant odorant, a toxic component, and sugar that the mosquitoes can feed on. ATSBs are cost-effective, sustainable, environmentally friendly, and can be species-specific. Mosquitoes were isolated into cages or cups and each group had access to either a toxic sugar solution (containing boric acid), a control solution or a choice between the two. We tested multiple fruits, including mango, peach, blueberries, and blackberries, as well as a soda and grape juice and monitored their survival for 96 h. We found that this species fed on all tested fruit solutions and that the groups that imbibed toxic solutions died within 48 h, indicating that boric acid is an effective oral toxin against Ae. j. japonicus. Further experiments will be conducted in the field to determine the ATSBs efficacy and to monitor potential effects on off-target species.

A Yeast RNA-Interference Pesticide Targeting the Irx Gene Functions as a Broad-Based Mosquito Larvicide and Adulticide

Simple Summary

It is critical that we identify new methods of preventing mosquito-borne infectious diseases, which threaten millions of people worldwide. In this investigation, we describe characterization of a new insecticide that turns off the mosquito Iroquois (Irx) gene, which is required for mosquito survival. The pesticide is synthesized in yeast, which can be fed to adult mosquitoes in a sugar bait solution or to juvenile mosquitoes that eat the yeast when it is placed in water where mosquitoes breed. Although the yeast kills several different types of mosquitoes, it was not found to affect the survival of other types of arthropods that consumed the yeast. These results indicate that yeast insecticides could one day be used for environmentally friendly mosquito control and disease prevention.

Abstract

Concerns for widespread insecticide resistance and the unintended impacts of insecticides on nontarget organisms have generated a pressing need for mosquito control innovations. A yeast RNAi-based insecticide that targets a conserved site in mosquito Irx family genes, but which has not yet been identified in the genomes of nontarget organisms, was developed and characterized. Saccharomyces cerevisiae constructed to express short hairpin RNA (shRNA) matching the target site induced significant Aedes aegypti larval death in both lab trials and outdoor semi-field evaluations. The yeast also induced high levels of mortality in adult females, which readily consumed yeast incorporated into an attractive targeted sugar bait (ATSB) during simulated field trials. A conserved requirement for Irx function as a regulator of proneural gene expression was observed in the mosquito brain, suggesting a possible mode of action. The larvicidal and adulticidal properties of the yeast were also verified in Aedes albopictus, Anopheles gambiae, and Culexquinquefasciatus mosquitoes, but the yeast larvicide was not toxic to other nontarget arthropods. These results indicate that further development and evaluation of this technology as an ecofriendly control intervention is warranted, and that ATSBs, an emerging mosquito control paradigm, could potentially be enriched through the use of yeast-based RNAi technology.

A Broad-Based Mosquito Yeast Interfering RNA Pesticide Targeting Rbfox1 Represses Notch Signaling and Kills Both Larvae and Adult Mosquitoes

Prevention of mosquito-borne infectious diseases will require new classes of environmentally safe insecticides and novel mosquito control technologies. Saccharomyces cerevisiae was engineered to express short hairpin RNA (shRNA) corresponding to mosquito Rbfox1 genes. The yeast induced target gene silencing, resulting in larval death that was observed in both laboratory and outdoor semi-field trials conducted on Aedes aegypti. High levels of mortality were also observed during simulated field trials in which adult females consumed yeast delivered through a sugar bait. Mortality correlated with defects in the mosquito brain, in which a role for Rbfox1 as a positive regulator of Notch signaling was identified. The larvicidal and adulticidal activities of the yeast were subsequently confirmed in trials conducted on Aedes albopictus, Anopheles gambiae, and Culex quinquefasciatus, yet the yeast had no impact on survival of select non-target arthropods. These studies indicate that yeast RNAi pesticides targeting Rbfox1 could be further developed as broad-based mosquito larvicides and adulticides for deployment in integrated biorational mosquito control programs. These findings also suggest that the species-specificity of attractive targeted sugar baits, a new paradigm for vector control, could potentially be enhanced through RNAi technology, and specifically through the use of yeast-based interfering RNA pesticides.

Applicability of attractive toxic sugar baits as a mosquito vector control tool in the context of India: a review

Vector-borne diseases (VBD) constitute 17% of all infectious diseases that pose a major public health concern around the world. In India, VBD like malaria and dengue continue to account for a significant disease burden. Management of these diseases is dependent in part upon effective vector control and hence several vector control strategies are in use for controlling mosquito populations. However, vectors evolve over time and become capable of averting many of the used control measures, leading to a constant need to find for novel and improved interventions. Attractive toxic sugar bait (ATSB) is a novel vector control strategy that is highly effective at regulating vector density in a particular area. ATSBs exploit the sugar feeding behaviour of mosquitoes. They are developed by combining small amounts of toxins with sugar. A chemical attractant is also included to lure the mosquito into the toxic sugary trap. Although effective, ATSB testing has been limited in scope around the world and ATSBs are completely unexplored in India. In this review, we provide an in-depth account of the development of ATSBs. We highlight the potential of ATSBs in controlling major Indian vectors of malaria and dengue, and we discuss possible challenges that could affect the efficacy of ATSBs in India. © 2020 Society of Chemical Industry.

Pyriproxyfen Ingested With Attractive Toxic Sugar Baits Is Carried by the Feces and Reduces the Reproductive Potential of Adult Female Aedes aegypti (Diptera: Culicidae)

In the search for new strategies to control Aedes aegypti Linnaeus (Diptera: Culicidae), several studies have successfully related pyriproxyfen (PPF) tarsal transference to breeding sites (autodissemination), as well as the sterilization potential of females exposed to PPF. Potential PPF autodissemination by mosquito feces after the ingestion of sugar baits has also been proposed. Therefore, the present work evaluated several parameters, e.g., fecal production, residuality under dry and aqueous conditions, PPF excretion affecting emergence inhibition (EI) by fecal deposits of Ae. aegypti fed with attractive toxic sugar baits (ATSBs) containing PPF as well as their reproductive potential. Females were fed with ATSBs offered as droplets and the feces were collected using filter paper and transferred to plastic cups with L3 larvae to evaluate EI. The residual effect of feces in aqueous and dry conditions and PPF excretion on EI was obtained by keeping the feces in water or dried for different time intervals and using feces collected at 24-h intervals, respectively. Females received a bloodmeal after feeding on ATSBs, eggs and larval counting expressed the reproductive potential. The fecal mass was not affected by PPF concentration, but EI increased from 33 to 54% as the PPF concentration increased. The PPF excretion in the feces exceeded 96 h. The residual effect in the EI for feces kept in water was reduced by more than 60% after 30 d but was not affected under dry conditions. The fecundity and fertility of the females were reduced up to 51% and 97%, respectively.

Does Homeostatic Sleep Pressure Buildup Explain Objective Excessive Daytime Sleepiness in Adults With ADHD? An Exploratory Study

Background: Excessive daytime sleepiness (EDS) is central in Attention deficit hyperactivity disorder (ADHD) but its causes remain unclear. The aim of this study was to explore objective EDS and homeostatic sleep pressure buildup, evaluated by power theta-alpha frequency (PTAF), in drug-free sleepy adults with ADHD and controls. Methods: Participants were placed during a 36-h period of extended wakefulness under constant routine protocol to strictly control sleep time, sleep duration, and circadian zeitgebers. Results: Eight drug-free sleepy patients with ADHD and 7 matched controls were included. The ADHD group had significantly shorter sleep latency on the Maintenance of Wakefulness Test (MWT) throughout extended wakefulness than the control group. There was no significant difference between the groups in PTAF evolution during extended wakefulness and in kinetic sleep pressure buildup, evaluated by the time constant of saturating exponential function. Limitations: The sample was small, so the findings cannot be generalized. Moreover, psychiatric comorbidities and circadian regulation should be taken into account in future studies. Conclusion: In very controlled conditions, mean sleep latency on the MWT during the whole extended wakefulness was significantly shorter in sleepy patients with ADHD than in control subjects. However, the difficulty to remain awake during soporific circumstances observed in these patients with ADHD cannot be explained by changes in the kinetic of sleep pressure buildup. Clinical Trials Registration: www.clinicaltrials.gov/, Identifier: NCT02217371.

Environmental safety and mode of action of a novel curcumin-based photolarvicide

Aedes aegypti is the vector of important diseases like dengue, zika, chikungunya, and yellow fever. Vector control is pivotal in combating the spread of these mosquito-borne illnesses. Photoactivable larvicide curcumin obtained from Curcuma longa Linnaeus has shown high potential for Ae. aegypti larvae control. However, the toxicity of this photosensitizer (PS) might jeopardize non-target aquatic organisms. The aim of this study was to evaluate the toxicity of this PS to Daphnia magna and Danio rerio, besides assessing its mode of action through larvae biochemical and histological studies. Three PS formulations were tested: PS in ethanol+DMSO, PS in sucrose, and PS in D-mannitol. The LC₅₀ of PS in ethanol+DMSO to D. rerio was 5.9 mg L^-1, while in D. magna the solvents were extremely toxic, and LC₅₀ was not estimated. The PS formulations in sugars were not toxic to neither of the organisms. Reactive oxygen species (ROS) were generated in D. magna exposed to 50 mg L^-1 of PS in D-mannitol, and D. rerio did not elicit this kind of response. D. magna feeding rates were not affected by the PS in D-mannitol. Concerning Ae. aegypti larvae, there were changes in reduced glutathione and protein levels, while catalase activity remained stable after exposure to PS in D-mannitol and sunlight. Histological changes were observed in larvae exposed to PS in sucrose and D-mannitol, most of them irreversible and deleterious. Our results show the feasibility of this photolarvicide use in Ae. aegypti larvae control and its safety to non-target organisms. These data are crucial to this original vector control approach implementation in public health policies.

Locomotion Inhibition of Cimex lectularius L. Following Topical, Sublethal Dose Application of the Chitin Synthesis Inhibitor Lufenuron

To date, few studies have evaluated chitin synthesis inhibitors against bed bugs, although they would provide an alternative mode of action to circumvent insecticide resistance. Acute and sublethal effects of lufenuron were evaluated against two strains of the common bed bug. Combined acute and sublethal effects were used to calculate effective doses. The dose that was effective against 50% of Harlan strain bed bugs was 0.0081% (w/v), and was much higher against Bradenton strain bed bugs (1.11% w/v). Sublethal doses were chosen to determine the effect that leg abnormalities had on pulling force. Both Harlan and Bradenton strain bed bugs had significantly lower locomotion ability (p < 0.0001) following topical application of lufenuron. The observed sublethal effects that limit locomotion could prevent bed bugs from moving within a domicile and taking a blood meal, subsequently reducing a bed bug population over time.

Attractive Toxic Sugar Bait (ATSB) For Control of Mosquitoes and Its Impact on Non-Target Organisms: A Review

Mosquito abatement programs contend with mosquito-borne diseases, insecticidal resistance, and environmental impacts to non-target organisms. However, chemical resources are limited to a few chemical classes with similar modes of action, which has led to insecticide resistance in mosquito populations. To develop a new tool for mosquito abatement programs that control mosquitoes while combating the issues of insecticidal resistance, and has low impacts of non-target organisms, novel methods of mosquito control, such as attractive toxic sugar baits (ATSBs), are being developed. Whereas insect baiting to dissuade a behavior, or induce mortality, is not a novel concept, as it was first introduced in writings from 77 AD, mosquito baiting through toxic sugar baits (TSBs) had been quickly developing over the last 60 years. This review addresses the current body of research of ATSB by providing an overview of active ingredients (toxins) include in TSBs, attractants combined in ATSB, lethal effects on mosquito adults and larvae, impact on non-target insects, and prospects for the use of ATSB.

Attractive Toxic Sugar Bait (ATSB) Mixed With Pyriproxyfen for Control of Larval Aedes albopictus (Diptera: Culicidae) Through Fecal Deposits of Adult Mosquitoes

Studies were conducted to determine if pyriproxyfen, an insect growth regulator (IGR) added to attractive toxic sugar baits (ATSBs) and ingested by adult Aedes albopictus (Skuse), could be fecally disseminated into water to inhibit emergence of mosquitoes (EI). Experimental treatments consisted of four dilutions of pyriproxyfen (0.5, 1, 5, and 10 ppb) in ATSB, with attractive sugar bait (ASB) serving as the negative control. To ensure no tarsal transfer of the IGR, the experimental treatments were dispensed in collagen sausages. Mosquito excrement was collected on card stock at the bottom of the mosquito cages at 1, 4, 6, and 8 h during the study. There were no differences between the EI times at which the fecal cards were collected (F_19,88=1.8, P = 0.1592). The highest dilution of pyriproxyfen in ATSB (10 ppb) inhibited mosquito emergence in the most amounts (57%), as compared with the EI of other pyriproxyfen dilutions: 0.5 ppb = 42%, 1 ppb = 34%, and 5 ppb = 46% (F_19,88=1.8, P = 0.1592). This study demonstrates that pyriproxyfen can be fecally disseminated into water and control larvae through adult mosquito ingestion and excretion of pyriproxyfen in ASB.

The Eye of the Tiger, the Thrill of the Fight: Effective Larval and Adult Control Measures Against the Asian Tiger Mosquito, Aedes albopictus (Diptera: Culicidae), in North America

The Asian tiger mosquito, Aedes albopictus (Skuse), is a highly invasive container-inhabiting species with a global distribution. This mosquito, similar to other Stegomyia species such as Aedes aegypti (L.), is highly adapted to urban and suburban areas, and commonly oviposits in artificial containers, which are ubiquitous in these peridomestic environments. The increase in speed and amount of international travel and commerce, coupled with global climate change, have aided in the resurgence and expansion of Stegomyia species into new areas of North America. In many parts of their range, both species are implicated as significant vectors of emerging and re-emerging arboviruses such as dengue, chikungunya, and now Zika. Although rapid and major advances have been made in the field of biology, ecology, genetics, taxonomy, and virology, relatively little has changed in the field of mosquito control in recent decades. This is particularly discouraging in regards to container-inhabiting mosquitoes, because traditional integrated mosquito management (IMM) approaches have not been effective against these species. Many mosquito control programs simply do not possess the man-power or necessary financial resources needed to suppress Ae. albopictus effectively. Therefore, control of mosquito larvae, which is the foundation of IMM approaches, is exceptionally difficult over large areas. This review paper addresses larval habitats, use of geographic information systems for habitat preference detection, door-to-door control efforts, source reduction, direct application of larvicides, biological control agents, area-wide low-volume application of larvicides, hot spot treatments, autodissemination stations, public education, adult traps, attractive-toxic sugar bait methods, lethal ovitraps, barrier-residual adulticides, hand-held ultra-low-volume adulticides, area-wide adulticides applied by ground or air, and genetic control methods. The review concludes with future recommendations for practitioners, researchers, private industry, and policy makers.

Control methods against invasive Aedes mosquitoes in Europe: a review

Five species of invasive Aedes mosquitoes have recently become established in Europe: Ae. albopictus, Ae. aegypti, Ae. japonicus japonicus, Ae. koreicus and Ae. atropalpus. These mosquitoes are a serious nuisance for people and are also competent vectors for several exotic pathogens such as dengue and chikungunya viruses. As they are a growing public health concern, methods to control these mosquitoes need to be implemented to reduce their biting and their potential for disease transmission. There is a crucial need to evaluate methods as part of an integrated invasive mosquito species control strategy in different European countries, taking into account local Aedes infestations and European regulations. This review presents the control methods available or in development against invasive Aedes mosquitoes, with a particular focus on those that can be implemented in Europe. These control methods are divided into five categories: environmental (source reduction), mechanical (trapping), biological (e.g. copepods, Bacillus thuringiensis var. israelensis, Wolbachia), chemical (insect growth regulators, pyrethroids) and genetic (sterile insect technique and genetically modified mosquitoes). We discuss the effectiveness, ecological impact, sustainability and stage of development of each control method.

Indoor use of attractive toxic sugar bait (ATSB) to effectively control malaria vectors in Mali, West Africa

BACKGROUND

Attractive toxic sugar bait (ATSB) solutions containing any gut toxins can be either sprayed on plants or used in simple bait stations to attract and kill sugar-feeding female and male mosquitoes. This field study in Mali demonstrates the effect of ATSB bait stations inside houses as a vector control method that targets and kills endophilic African malaria vectors.

METHODS

The studies were conducted in five villages located near the River Niger, Mali. Baseline village-wide assessments of densities for female and male Anopheles gambiae sensu lato were performed by pyrethrum spray collections (PSC) in ten houses in each of five villages. To determine the rate of mosquito feeding on bait stations, one bait station per house containing attractive sugar bait (ASB) (without toxin) plus a food dye marker, was set up in ten houses in each of the five villages. PSC collections were conducted on the following day and the percentage of female and male mosquitoes that had fed was determined by visual inspection for the dye marker. Then, a 50-day field trial was done. In an experimental village, one bait station containing ATSB (1% boric acid active ingredient) was placed per bedroom (58 bedrooms), and indoor densities of female and male An. gambiae s.l. were subsequently determined by PSC, and female mosquitoes were age graded.

RESULTS

In the five villages, the percentages of An. gambiae s.l. feeding inside houses on the non-toxic bait stations ranged from 28.3 to 53.1% for females and 36.9 to 78.3% for males. Following ATSB indoor bait station presentation, there was a significant reduction, 90% in female and 93% in male populations, of An. gambiae s.l. at the experimental village. A 3.8-fold decrease in the proportion of females that had undergone four or more gonotrophic cycles was recorded at the experimental village, compared to a 1.2-fold increase at the control village.

CONCLUSION

The field trial demonstrates that An. gambiae s.l. feed readily from ATSB bait stations situated indoors, leading to a substantial reduction in the proportion of older female mosquitoes. This study demonstrates that ATSB inside houses can achieve impressive malaria vector control in Africa.