Assessing AedesTech mosquito home system on yellow fever mosquito Aedes aegypti (Linnaeus) in Northern Malaysia

Abstract

This research evaluated the AedesTech Mosquito Home System (AMHS), an ovitrap employing autodissemination with pyriproxyfen, to monitor and manage mosquito populations. It involved 3 studies of the AMHS: a baseline study, an effectiveness study, and an autodissemination study on Aedes (Diptera: Culicidae) mosquitoes. Forty AHMS units filled with water were deployed for the baseline study. During the effectiveness study, 40 untreated AMHS units with water were placed alongside 40 AMHS units treated with Mosquito Home Aqua (MHAQ) solution, the retail solution used for AMHS. The autodissemination study featured 40 AMHS units treated with MHAQ alongside 40 control AMHS units without MHAQ, together with 25 Aedes aegypti (Linnaeus) larvae. Notably, treated traps in the effectiveness study exhibited a significant reduction in the Ovitrap Index (OI) compared to the baseline traps in the baseline study. The effectiveness study validated AMHS’s efficacy, with treated traps displaying a significantly lower OI than untreated counterparts (P < 0.05). The study also showed a decrease in the percentage of egg hatching and percentage of adult emergence in treated traps compared to untreated traps. Autodissemination was evident, marked by a significant percentage of adult emergence decrease of Ae. aegypti larvae, without affecting sex ratios. It strongly suggests that AMHS can effectively reduce Aedes populations through direct contact and autodissemination without affecting sex ratios.

Introduction

Every year, a staggering number of approximately 390 million people fall victim to dengue, and amidst this global health crisis, Malaysia finds itself confronting an alarming rise in cases (Packierisamy et al. 2015, Ebi and Nealon 2016, Liew et al. 2016, Chong et al. 2020). Nevertheless, in spite of this, a remarkable decline of 70.8% in dengue cases was witnessed between 2020 and 2021, potentially linked to the implementation of COVID-19 containment measures, which restrict access to blood meals and effectively the population density of disease-carrying vectors (Jindal and Rao 2021, Surendran et al. 2022, idengue 2023).

However, there has been a remarkable 158% rise in dengue occurrences and a substantial 183% escalation in the number of casualties for 2023, as of early June, in comparison to the equivalent timeframe preceding year (Asis 2023). In Penang, dengue has been a persistent issue since its inception in 1901, with a significant outbreak occurring in 1962 (Nazri et al. 2013, Packierisamy et al. 2015, Liew et al. 2016, Murphy et al. 2020). Specific regions of Penang, particularly the Southwest District of Penang Island, experience recurring outbreaks, and dengue transmission can occur through mosquito bites, transmission from mother to fetus, or via infected mosquito progenitors (Ferreira-De-Lima and Lima-Camara 2018, Hashim et al. 2019, Pitchaimuthu et al. 2020, Selvarajoo et al. 2020, Rahman and Rosidi 2022).

To combat the complex nature of dengue transmission, vector traps have been implemented as an effective approach, targeting various mosquito life stages and employing capture-kill or capture-release strategies (Buckner et al. 2017, WHO 2018, Faierstein et al. 2019). Among these, the Dengue Tech Challenge-winning AedesTech Mosquito Home System (AMHS) trap stands out, incorporating autodissemination and comprising a lidded bucket, an OviTo linen, and a Mosquito Home Aqua (MHAQ) (Ahmad et al. 2020, Mohd Ngesom et al. 2021). The OviTo linen, a specific type of fabric utilized in the trap, facilitates mosquito oviposition for data collection purposes (Yazan et al. 2020, Ngesom et al. 2021). Notably, the MHAQ contains pyriproxyfen (PPF) as an active component, which can be disseminated to other breeding sites by female mosquitoes visiting the AMHS trap for oviposition, resulting in a reduction of their population (Man et al. 2020, Ngesom et al. 2021).

The effectiveness of the AMHS in reducing mosquito populations has been demonstrated in several locations, including 17th College in Universiti Putra Malaysia and in undisclosed site in Kedah (Man et al. 2020, Yazan et al. 2020). Research has demonstrated that even in small amounts, PPF has a significant impact on killing mosquito eggs (Suman et al. 2013). In comparison to conventional ovitraps, the AMHS trap has exhibited 100% effectiveness in controlling Aedes mosquitoes, as measured by the OI (Yazan et al. 2020).

In order to determine the efficacy of the AMHS trap, small-scale open trials were conducted, assessing its impact during the baseline, effectiveness, and autodissemination studies.

Materials and Methods

This study aimed to replicate outdoor conditions with modifications in accordance with the WHO protocol (WHO 2018), in which the modification pertained to the effective trap duration of 4 weeks as advised by the manufacturer, One Team Network Sdn. Bhd., located at 23, Jalan Anggerik Mokara 31/51, Kota Kemuning, 40460 Shah Alam, Selangor, Malaysia. Additionally, due to certain residents placing their belongings along the corridors, some traps were positioned at distances between 0.8 and 1 m from the autodissemination device for the autodissemination study, deviating from the minimum 1 m recommendation.

Study Location

This study was done in Apartment Asoka (5.30230, 100.25720), which is situated in Bayan Lepas, Pulau Pinang, Malaysia (Fig. 1). The selection of this location was based on the fact that it is considered a hotspot for dengue, according to the idengue website (2023). The small-scale study involved 4 levels of the building in the Apartment Asoka. Additionally, the building is in close proximity to a lush tropical forest area, which is less than one kilometer away.

Rearing

Other than the wild strain of Aedes aegypti, susceptible Ae. aegypti strains were obtained from the Vector Control Research Unit (VCRU). The egg was submerged in aged tap water in a plastic container under laboratory conditions at 27 ± 2 °C of 12:12 (L: D) and relative humidity of 80%–90% to provide the high numbers of hatching required in this study (Hogg and Hurd 1997, Zuharah and Lester 2010, WHO 2018). Approximately 1 g of larval food was added to the container. Larval food is fine powder prepared from dog biscuits, beef liver, yeast, and milk powder at a ratio of 2:1:1:1 (Ahbirami et al. 2014). Newly hatched larvae were moved into an enamel tray holding aged tap water with 100–200 larvae in each tray. They were fed every 2 days. The water was changed before every feeding (Dieng et al. 2018, 2019).

For the autodissemination study, late third and early fourth instar larvae of the VCRU strain were used in the control traps without MHAQ (WHO, 2018). The instar stages were identified based on Bar and Andrew (2013).

The Traps

The AMHS traps, along with OviTo linen and MHAQ, were supplied by One Team Networks Sdn. Bhd. (available at http://m.onedream.com.my/index.php...). It consists of a 13.0 cm (height) × 11.0 cm (bottom width) × 14.8 cm (top width) black polyethene opaque bucket, which is the base with a plum-colored lid (Fig. 2). Furthermore, the trap was lined with the OviTo linen surrounding the bucket base, which allows mosquitoes to oviposit on it. The size of OviTo linen is 7.5 cm long × 17.5 cm width. MHAQ, which contained 0.004% pyriproxyfen in a 500-ml bottle, was screwed in the middle of the bucket base. The flow of the MHAQ solution uses gravity force and allows the solution to be filled at the bottom of the bucket base.

Study Design

The study conducted at Apartment Asoka in Penang consisted of 3 distinct sections. The first part, focusing on baseline measurements, was conducted over a pretreatment period of 6 weeks. The second part assessed the effectiveness of the interventions and was carried out over a treatment period of 12 weeks. The final part of the study, which examined autodissemination, lasted for 6 weeks. For the purposes of this study, 5 days were considered equivalent to 1 week.

1. Baseline Study: This study (Study 1) comprised 6 weeks of pretreatment study and involved the utilization of forty AMHS traps (baseline traps), each prepared with 500 ml bottles filled with water and OviTo linen. Ten traps were strategically deployed at each level of Apartment Asoka, with a total of 4 levels. Across all 4 levels, 10 traps were deployed following the same layout as level 1 (Fig. 3A). These traps remained in place for 5 days to capture any existing mosquitoes on-site. The OviTo linen was replaced every 5 days, and the linen containing oviposited eggs was transported to the laboratory for manual counting. To assess the impact of treatments, the Ovitrap Index (OI) was compared before and during treatment, with calculations carried out in accordance with the methodologies described by Ishak et al. (2022) and Yazan et al. (2020):

2. Effectiveness Study: This experiment (Study 2) involved a 12-week treatment period and was set up using both treated and untreated traps to evaluate the overall effectiveness of the AMHS traps in reducing mosquito populations. Forty AMHS traps act as treated traps, prepared with MHAQ containing attractant and OviTo linen. The retail MHAQ contains an attractant. This attractant is a confidential secret held by the company and is not disclosed. For the untreated traps, 40 AMHS traps (without MHAQ) were set up in the same setting in the baseline study (Study 1), with 500 ml bottles filled with water and OviTo linen. Each level of Apartment Asoka, as shown in Fig. 3B, witnessed the deployment of a total of 10 untreated and 10 treated traps.

Both traps were left in the site for 5 days to allow the wild Ae. aegypti mosquitoes to lay eggs inside them. The OI was recorded from the OviTo linen collected and replaced every 5 days. After the eggs were counted on the OviTo linen, the eggs found in both traps were hatched and reared until adulthood. The percentages of egg hatching and adult emergence were calculated.

To evaluate the effect of meteorological data on the OI during the baseline study (Study 1) and the effectiveness study (Study 2), a comprehensive set of meteorological data was acquired from (https://meteostat.net/en/). The baseline study data covered the period from December 6, 2021, to January 5, 2022. For the effectiveness study, the data spanned from January 14, 2022, to March 15, 2022. This dataset included temperature, relative humidity, wind speed, and precipitation, which were subsequently subjected to separate rigorous analyses to determine their associations with the OI data in both studies.

1. Autodissemination Study: Conducted from March 30, 2022, to April 29, 2022, this study aimed to evaluate the autodissemination process of the pyriproxyfen insecticide in MHAQ by the wild female mosquitoes by assessing the mortality of Ae. aegypti larvae placed in the control traps (without MHAQ). We also assessed the occurrence of mosquito larvae collected in the treated traps. The autodissemination study was encompassed by a month-long study. Forty AMHS traps, referred to as treated traps, were prepared with MHAQ solution containing pyriproxyfen and OviTo linen. A total of 10 traps were deployed in each level of the Apartment Asoka. The traps were strategically placed on all 4 levels of the building, following the setup in Fig. 3C.

The OviTo linen that was placed in the treated traps was collected and changed every 5 days. The OviTo linen with the oviposited eggs was brought to the laboratory, and the number of eggs was calculated manually (Gopalsamy et al. 2021). OI also counted. After the counting process, each OviTo linen was then immersed in seasoned water separately with 1 mg of larvae food in different trays. After the larvae hatch, the percentage of egg hatching was counted. The larvae were subsequently raised until reaching adulthood to easily determine the percentage of adult emergence and identify the species level using the key by Andrew and Bar (2013).

At the same time, 40 AMHS traps were prepared as control traps (without MHAQ), and only seasoned water served as the solution. A total of 25 late third and early fourth instar larvae with 1 g of food were placed in these control (without MHAQ) traps. Control traps (without MHAQ) were deployed intermittently with the treated traps at the same time, as featured in Fig. 3C. Meanwhile, 25 larvae that were placed in the control traps (without MHAQ) were collected after 24 h of exposure. The exposed larvae were then brought back to the laboratory and reared separately according to the traps until adulthood. The percentage of mortality, percentage of adult emergence, and sex ratio were documented.

Statistical Analysis

For the baseline and effectiveness study, a comprehensive analysis of the OI (%) was first compared between pretreatment (baseline trap) and treatments (treated trap). Whereas the OI of the effectiveness study was compared between untreated and treated traps and the week of deployments. Data normality was assessed using the Shapiro-Wilk test. Subsequent General Linear Mixed Model (GLMM) analysis using the linear model was performed with OI serving as the response variable, considering the type of traps (pretreatment and treatment) and week (duration of deployment) served as fixed factors for Study 1. Meanwhile, the meteorological parameters (temperature, humidity, wind speed, and precipitation) were included as random effects. GLMM was also employed to explore the influence of the type of traps (treated and untreated) and week (duration of deployment) as fixed factors against OI for Study 2 with the same setting of random effects.

The analysis of the percentage of egg hatching and percentage of adult emergence data for the effectiveness study (Study 2) was first tested for data normality and ascertained through the Shapiro-Wilk test. A transformation to ln(X + 1) was applied because the distribution did not fulfill the normality assumption. The independent t-tests were used to analyze the mean differences between untreated and treated traps. Then, the independent t-tests were also employed to discern temporal variations in the percentage of egg hatching and percentage of adult emergence between untreated and treated traps for each week.

The influence of autodissemination across weeks was explored. Data normality was tested using the Shapiro-Wilk test, followed by the application of linear regression to examine the relationship between the OI (%) and time. The study further encompassed the analysis of the percentage of egg hatching and percentage of adult emergence data from treated traps, with a transformation utilizing ln (X + 1) to ensure data homogeneity. Subsequently, an independent t-test was conducted to compare the percentage of egg hatching and the percentage of adult emergence, aiming to identify any differences in the number of emerged adults compared to hatched larvae.

To meet the assumptions of one-way ANOVA, we applied a logarithmic transformation (ln(X + 1)) to the dataset on larval mortality rates and percentage of adult emergence from the control trap (without MHAQ), contained 25 larvae in the context of autodissemination impacts. This transformation preceded the analysis, where weeks served as a factor for one-way ANOVA, and larval mortality was considered the dependent variable. From this part, we observed whether the larval mortality decreased over time. Subsequently, we conducted a separate analysis wherein the percentage of adult emergence replaced larval mortality as the dependent variable, while weeks remained a factor. This allowed us to assess whether the pyriproxyfen carried through autodissemination from wild mosquitoes still had an effect within the autodissemination study.

To investigate the effects of autodissemination on the sex ratio, a chi-square test was conducted to detect any significant differences between females and males. All of the analyses were run using Statistical Package for Social Sciences (SPSS) version 25.

Result

Baseline Study and Effectiveness Study

Figure 4 shows the OI (%) of the pretreatment (baseline trap) and treatment (treated trap). During the pretreatment period, the OI peaked at 80% during the second week, while it consistently remained below 55% in subsequent weeks and showed no significant difference between weeks (post-hoc, P > 0.001). OI in treatment (treated traps) with 44.4 eggs was lower compared to the pretreatment (baseline traps) with 53.1 eggs and showed no significant differences between pre- and during-treatment (GLMM: types of traps, F = 1.89, df = 1, P = 0.17; weeks of observation, F = 0.46, df = 11, P = 0.92). All of the meteorological parameters tested as a random effect can be ignored due to no significant effects on the model (GLMM, P > 0.05).

After deploying AMHS, the OI during the treatment phase significantly declined to 25.00% (week 7) and significantly further dropped to 20.00% (week 8) (post-hoc, P = 0.01 and P < 0.001, respectively). It is worth mentioning that OI readings in weeks 9 and 14 were higher than in the preceding weeks due to the reduction in the effectiveness of the MHAQ solution. It was found that this solution lasted between 4 and 6 weeks. Thus, a new replacement was done on week 12, causing the OI values to decrease to 25.00% in week 13 from 42.50% in week 12. Conversely, OI readings decreased during weeks 10 and 16, marking the fourth week after opening the MHAQ bottle. Additionally, significant variations in OI were observed due to the interaction between trap types and deployment duration.

Throughout the 12-week study (Fig. 5), we also compared the treated and untreated traps to confirm the effectiveness of AMHS traps. Treated traps consistently exhibited lower OI values when compared to untreated traps. The OI values for treated traps ranged from 20.00% to 57.50%, while untreated traps showed a wider range, fluctuating between 52.50% and 87.50%. Notably, the lowest OI value for treated traps was recorded in week 2 at 20.00%, in contrast to untreated traps, which exhibited a higher OI of 57.50%. GLMM analysis confirmed this observation, revealing a significantly lower OI for the treated traps (44.4 eggs) in comparison to the untreated traps (66.7 eggs) (F = 44.62, df = 1, P < 0.001) and not impacted by the deployment durations (GLMM, F = 0.89, df = 11, P = 0.55). Same as in Study 1, random effects of meteorological parameters had no significant impact on the OI values during Study 2 (GLMM, P > 0.05). This might be due to a limited discrepancy in the meteorological parameters in tropical areas.

Percentage of Egg Hatching and Percentage of Adult Emergence of Untreated Traps and Treated Traps

The percentage of egg hatching (%) in treated traps exhibited a significantly lower reading compared to the untreated traps (F = 703.75, df = 958, P < 0.001), as shown in Table 1. Conversely, the percentage of egg hatching (%) of the treated traps displayed a notable rise from week 1 (2.1%) to week 3 (19.1%), but still significantly lower than the untreated traps (P < 0.05). It can be seen that the percentage of egg hatching increased to 22.5% (week 6), which requires the replacement of MHAQ. After the installation of a new MHAQ, week 7 showed a reduction in the percentage of egg hatching to 3.2%.

This section underscores a significant disparity in the percentage of adult emergence (%) between the untreated and treated traps, with higher values observed in untreated traps when compared to the treated ones (F = 1543.35, df = 953, P < 0.001) except in week 7. The emergence of 0.2% of adult Ae. aegypti in week 4 within the treated traps suggests the necessity of changing the MHAQ solution in line with the company’s recommended guidelines. It is important to highlight that the percentage of adult emergence of the treated traps during week 7 (0.0%) was lower than that observed in week 6 (0.3%), following the introduction of the new MHAQ solution at week 6.

Effects of Autodissemination Over Periods

It is noteworthy that the highest OI reading, at 47.50%, was recorded during the initial week (week 1) (see Fig. 6). Subsequently, the OI readings experienced a consistent decline until week 3. While there was a slight increase in OI values observed in weeks 4 and 6, they remained comparatively lower when compared to the initial reading in week 1.

The percentage of adult emergence significantly displayed consistently minimal values in comparison to the percentage of egg hatching (F = 173.56, df = 478, P < 0.001; Fig. 7A). With virtually no adult emergence was recorded in the majority of weeks, except for a slight increase observed during week 2 through week 4, with rates of only 1.11%, 0.22%, and 0.22%, respectively. This observation underscores the efficacy of the AMHS in effectively suppressing mosquito emergence.

Proving the Autodissemination Occurrence

As illustrated in Fig. 7B, the mortality rate of the larvae exhibited a consistent decrease over the course of the 6-week autodissemination period (F = 3.90, df = 5, P = 0.002). This outcome suggests that a substantial portion of these larvae were effectively prevented from maturing into adult mosquitoes. It is notable that the early stages of the autodissemination period demonstrated the highest mortality rate within the initial 24 h after being collected from the field, which gradually declined over time. Week 1 marked the highest mortality rate, at 35.20%, after 24 h, and this was significantly higher than the lowest rate observed in week 6, which stood at 19.50% (P = 0.002).

The autodissemination study lacked data from control traps designed the same as the control trap without MHAQ (containing 25 larvae and no treatment) but without exposure to wild mosquitoes or any treatment, to serve as a comparison. This limitation should be kept in mind when interpreting the findings, as the observations were made without the inclusion of a proper control group.

Based on Table 2, the sex ratio was found not to be significantly different between females and males for all tested weeks (chi-square, P > 0.05), with the overall sex ratio of 1:0.94 between females and males. These results strongly suggest that the implementation of the AMHS had no discernible impact on modifying the natural allocation of male and female mosquitoes in the field.

Discussion

The effectiveness of the AMHS in controlling Aedes populations through autodissemination and direct contact was evaluated over a 24-week period. This study utilized MHAQ in treated traps during the effectiveness and autodissemination studies to assess its impact on eggs, mosquito larvae, and the emergence of adults. Notably, the AMHS demonstrated a significant reduction in the percentage of adult emergence in our study, which indicates its potential as an effective tool for mosquito control (Suttana et al. 2019, Iyaloo et al. 2021).

During the pretreatment, which served as the baseline study, the maximum OI of the baseline trap reached a peak value of 80.00% before the deployment of AMHS. The rise in the OI is speculated to be a consequence of heightened humidity and precipitation levels, both of which are acknowledged to exert influence on Aedes oviposition behaviors, as substantiated by prior investigations (Sang et al. 2014, Lamy et al. 2023). It is worth noting that gravid mosquitoes skillfully detect humidity gradients using ionotropic receptor Ir93a-dependent sensors, allowing them to precisely navigate to suitable locations for oviposition (Laursen et al. 2023).

In our study, AMHS traps treated with MHAQ solution had a lower OI compared to both the baseline traps and the untreated traps. This is possibly due to repellent elements and mosquito avoidance of harmful substances (Hwang et al. 1984, Afify and Galizia 2015, Day 2016, Hamid et al. 2019, Mohd Ngesom et al. 2021). Though the study by Lwetoijera et al. (2014), Harburguer et al. (2016), and Iyaloo et al. (2021) stated repellent effects are not linked to pyriproxyfen (PPF), however, emphasizing the need for ongoing research to enhance trap effectiveness.

Our investigation employed AMHS traps with a 0.004% PPF concentration, mirroring the concentration used in the study by Mohd Ngesom et al. (2021). Their research yielded intriguing results whereby the laboratory test demonstrated a negligible deterrent effect of MHAQ by Aedes mosquitoes. Meanwhile, the small-scale field trials revealed an unexpected outcome, with MHAQ-treated traps outperforming hay infusion traps, serving as a mosquito attraction. These findings emphasize the importance of field trials in evaluating the true efficacy of mosquito control methods.

The literature presents varied in outcomes with different PPF concentrations. Sihuincha et al. (2005) reported no discernible oviposition preference at 0.003% PPF concentration, marginally lower than our MHAQ solution. This subtle difference might account for preference variations. Corroborating these findings, Tsunoda et al. (2021) observed no significant disparity in oviposition preference between PPF-treated water and untreated water for Ae. aegypti and Aedes albopictus, even at a substantially higher 2% PPF concentration. These diverse results highlight the complex relationship between PPF concentration and mosquito oviposition preference, suggesting that other factors beyond concentration alone may influence responses.

OI fluctuations in relation to MHAQ degradation highlight the importance of maintenance (Lim Chee Hwa, personal communications 2021; Okal et al. 2015, Valbon et al. 2021). In our study, the OI index increased after 4–5 weeks of AHMS deployment, suggesting the degradation of MHAQ, which contains pyriproxyfen.

As the study progressed, it became evident that the effectiveness of MHAQ containing pyriproxyfen (PPF) diminished over time as the PPF was used in a water medium (Valbon et al. 2021). In the initial weeks of the effectiveness study, the suppressive effect on adult mosquito emergence in treated traps was robust, highlighting the efficacy of PPF as an insect growth regulator (Rhyne and Richards 2020). However, starting from week 4, there was a gradual decline in effectiveness, leading to an emergence of 0.2% of adult mosquitoes from treated traps. This aligns with research suggesting that certain compounds may become less effective over time (Okal et al. 2015). This implies that PPF in MHAQ may weaken as time passes.

Despite this gradual decline, the treated traps also consistently exhibited a lower percentage of adult emergence compared to the untreated traps, indicating the successful suppression of approximately 99.95% of hatched larvae. This significant difference validates the efficacy of PPF as an intervention method. Nevertheless, achieving complete suppression of mosquito populations may depend on factors such as application coverage, emphasizing the need for continued research in this area (Seixas et al. 2019).

The study also explored the phenomenon of autodissemination, wherein mature mosquitoes transfer chemical substances to other breeding sites (WHO 2018). The data revealed a high OI reading during the initial week of the autodissemination study, indicating the attraction of wild mosquitoes to the treated sites (Lim Chee Hwa, personal communications 2021). However, there was a subsequent decline in OI readings from weeks 1 to 3. The decrease in OI shows that the mosquito population decreased, indicating that the implemented treatment was effective in eliminating the mosquitoes (Hamid et al. 2019).

Despite the fluctuations in OI readings during the autodissemination study, the study consistently demonstrated that the AMHS effectively inhibited mosquito emergence. Pyriproxyfen (PPF) in the MHAQ acted as an insect growth regulator, contributing to the decline in mosquito emergence rates (Yazan et al. 2020, Aldridge et al. 2022). Although the percentage of egg hatching showed an increase after week 1, the AMHS remained effective in preventing adult mosquito emergence. According to Alomar and Alto (2022), Ae. aegypti larvae in contact with PPF can greatly impede their transition into adult mosquitoes. However, attaining a complete 100% inhibition rate was not accomplished due to the variability in mosquito reproduction and the percentage of adult emergence observed with the introduction of pyriproxyfen (Rhyne and Richards 2020). However, our study effectively retarded the adult emergence up to 99.74% from wild eggs attached to OviTo linen.

Over time, the PPF effectiveness decreases, making it difficult to eliminate Aedes populations completely (Hustedt et al. 2020). To retain its efficacy in autodissemination, it is recommended that MHAQ bottles be replaced every 4–6 weeks. The study supported successful PPF autodissemination by wild mosquitoes and found no significant sex ratio distortion in Aedes mosquitoes. In contrast, other insecticides like Nyguard altered sex ratios, which could affect disease transmission (Aldridge et al. 2022). However, the exposure to PPF in Daphnia magna led to a significant skew towards male offspring (Salesa et al. 2023). Notably, the Nix gene plays a key role in masculinization in Ae. aegypti (Zhao et al. 2022).

Nevertheless, it is important to acknowledge the limitations of our observations regarding the percentage of egg hatching and percentage of adult emergence mortality rate of the 25 larvae in control trap (without MHAQ) traps during the autodissemination study, primarily due to the absence of a control group. Control groups are fundamental in experimental studies for evaluating treatment effects and accounting for variables that cannot be eliminated (Moser 2019). Without data from control traps designed similarly to the control trap (without MHAQ) and not exposed to wild mosquitoes or any treatment, we cannot conclusively attribute these mortality rates to the autodissemination effect.

This limitation is particularly significant because natural mortality or failure in emergence in certain field populations is common. A study conducted in Guangzhou, China, demonstrated this variability, where the mortality rate of Ae. albopictus was calculated to be 17.5%, with rates fluctuating from July to November as temperatures changed. Average temperatures ranged from 29.6 ± 1.3 °C in July to 21.7 ± 3.5 °C in November, illustrating the seasonal impact on mosquito survival (Yang et al. 2020). Similarly, a study on Ae. albopictus derived from wild populations in Penang reported a higher 28% generational mortality rate, further emphasizing the variability in natural mortality rates across different environments (Aida et al. 2011).

To distinguish between natural mortality and treatment effects, careful experimental design is crucial. Caputo et al. (2012) demonstrated this in a comparative study using control trap (without MHAQ) sites, each containing 25 larvae. Control sites were enclosed in white nets to prevent mosquito entry and potential treatment contamination. In their study of a mosquito control agent (pyriproxyfen), they observed a maximum mortality rate of 2.4% in control sites compared to 71.2% in treated control trap (without MHAQ) sites, with environmental factors like temperature (lowest mean daily temperature at 23.8 °C) also recorded.

For future studies, it is suggested to incorporate control traps designed identically to the control trap (without MHAQ) traps but without any probability of exposure to the treatment. These control traps should be placed during the pretreatment study or lined with nets, as in Caputo et al. (2012), to accurately assess the impact of any interventions against the backdrop of natural mortality rates. This approach, similar to that used in an autodissemination study in New Jersey, where researchers incorporated control sites alongside treatment sites, allows for a more robust assessment of the intervention’s effectiveness by controlling for environmental and other confounding factors (Unlu et al. 2017).

Overall, this study highlights the potential of the AMHS in reducing mosquito populations through the autodissemination of pyriproxyfen (PPF). However, it also underscores the gradual decline in effectiveness over time, underscoring the necessity for ongoing research to optimize mosquito control strategies.

Its user-friendly nature makes trap installation accessible even to inexperienced individuals, in contrast to the more complex fogging methods (Abeyasuriya et al. 2017). However, the potential challenges of large-scale deployment and maintenance, as well as cost considerations, should not be overlooked. Furthermore, community engagement campaigns are vital for raising awareness and promoting the widespread adoption of autodissemination traps. By integrating the deployment of these traps with community involvement, significant strides can be taken to reduce the mosquito population and control dengue transmission.

Disclosure

All authors have thoroughly reviewed and unanimously concurred with the content presented in this manuscript. There are no conflicts of interest, encompassing financial interests, relationships, or affiliations pertinent to the subject matter discussed in this paper.

Acknowledgments

We would like to acknowledge One Team Networks Sdn. Bhd. for sponsoring the research project. This project was funded by the Fundamental Research Grant Scheme, Ministry of Higher Education Malaysia (FRGS/1/2023/STG03/USM/02/4).

Author contributions

Fatin Nabila (Conceptualization [equal], Data curation [lead], Formal analysis [equal], Investigation [lead], Methodology [equal], Project administration [lead], Writing—original draft [lead]), Lim Hwa (Funding acquisition [lead], Resources [lead], Supervision [supporting]), and Wan Fatma Zuharah (Conceptualization [lead], Data curation [equal], Formal analysis [equal], Funding acquisition [lead], Investigation [equal], Methodology [lead], Project administration [lead], Supervision [lead], Validation [lead], Writing—review & editing [lead])

References