BackgroundThe trend in chemical insecticide development has focused on improving the efficacy against mosquitoes while reducing the environmental impact. Lethal lures apply an “attract-and-kill” strategy that draws the insect to the killing agent rather than bringing the killing agent to the insect.MethodsIn this study, the mosquito oviposition pheromone was extracted from the eggs of Aedes aegypti (L.) and further investigated with a combination of pheromone and granular temephos as a lethal lure.ResultsThe compound caproic acid attracted significantly more egg-laying mosquitos at 1 ppm (660.83 ± 91.61) than the control (343.83 ± 56.24), which consisted of solvent only (Oviposition Activity Index: 0.316). Further investigation of the combination of caproic acid with granular temephos as a lethal lure attracted significantly more gravid female Ae. aegypti to oviposit their eggs than the temephos treated water and control.ConclusionsThis indicated the ability of caproic acid in acting as an attractant and counters the repellency effect of temephos. Additionally, the presence of temephos in the lethal lure also restricted the hatching of the eggs and killed any larvae that hatched.

We aim to investigate the effect of large-scale human movement restrictions during the COVID-19 lockdown on both the dengue transmission and vector occurrences. This study compared the weekly dengue incidences during the period of lockdown to the previous years (2015 to 2019) and a Seasonal Autoregressive Integrated Moving Average (SARIMA) model that expected no movement restrictions. We found that the trend of dengue incidence during the first two weeks (stage 1) of lockdown decreased significantly with the incidences lower than the lower confidence level (LCL) of SARIMA. By comparing the magnitude of the gradient of decrease, the trend is 319% steeper than the trend observed in previous years and 650% steeper than the simulated model, indicating that the control of population movement did reduce dengue transmission. However, starting from stage 2 of lockdown, the dengue incidences demonstrated an elevation and earlier rebound by four weeks and grew with an exponential pattern. We revealed that Aedes albopictus is the predominant species and demonstrated a strong correlation with the locally reported dengue incidences, and therefore we proposed the possible diffusive effect of the vector that led to a higher acceleration of incidence rate.

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Classification of Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse) by humans remains challenging. We proposed a highly accessible method to develop a deep learning (DL) model and implement the model for mosquito image classification by using hardware that could regulate the development process. In particular, we constructed a dataset with 4120 images of Aedes mosquitoes that were older than 12 days old and had common morphological features that disappeared, and we illustrated how to set up supervised deep convolutional neural networks (DCNNs) with hyperparameter adjustment. The model application was first conducted by deploying the model externally in real time on three different generations of mosquitoes, and the accuracy was compared with human expert performance. Our results showed that both the learning rate and epochs significantly affected the accuracy, and the best-performing hyperparameters achieved an accuracy of more than 98% at classifying mosquitoes, which showed no significant difference from human-level performance. We demonstrated the feasibility of the method to construct a model with the DCNN when deployed externally on mosquitoes in real time.

The impact of movement restrictions (MRs) during the COVID-19 lockdown on the existing endemic infectious disease dengue fever has generated considerable research interest. We compared the curve of weekly epidemiological records of dengue incidences during the period of lockdown to the trend of previous years (2015 to 2019) and a simulation at the corresponding period that expected no MRs and found that the dengue incidence declined significantly with a greater magnitude at phase 1 of lockdown, with a negative gradient of 3.2-fold steeper than the trend observed in previous years, indicating that the control of population movement did reduce dengue transmission. However, starting from phase 2 of lockdown, the dengue incidences demonstrated an elevation and earlier rebound by 4 weeks and grew with an exponential pattern. Together with our data on Aedes mosquitoes, we proposed a stronger diffusive effect of vector dispersal that led to a higher rate of transmission. From the result of the Aedes survey using human landing caught (HLC), we revealed that Aedes albopictus is the predominant species for both indoor and outdoor environments, with the abundance increasing steadily during the period of lockdown. We only recovered Aedes aegypti from the indoor environment, which is relatively fewer than Ae. albopictus, by contrasting their population growth, which suggested that Ae. albopictus invaded and colonized the habitat of Ae. aegypti during the period of lockdown. These findings would help authorities review the direction and efforts of the vector control strategy.Author summaryCOVID-19 pandemic is taking hold globally and dengue fever transmission is not on the top of the list of concerns. With a partial lockdown implemented by Malaysia on 18 March, we postulate the movement restrictions (MRs) of people in large-scale would hamper the regular dengue transmission and aim to reveal the impact of MRs on both dengue incidences and Aedes mosquitoes. We showed a significant decline of dengue incidences at the beginning of lockdown but later rebounded at an earlier time and higher rate compared to the corresponding period of previous years. Our result also reviews how adaptive the Ae. albopictus with the movement of the host, as the human contained in the house, the abundance of the mosquitoes increased significantly during the period of lockdown. We also suggest that Ae. albopictus could be the key substitution vector that contributes significantly to dengue virus circulation, and therefore, the vector control direction and strategies should be redesigned.

In this study, the toxicology of two commercial larvicides--cyromazine (Neporex 50SP) and ChCy (combination of chlorpyrifos and cypermethrin, Naga 505)--and five commercial adulticides--thiamethoxam (Agita 10WG), cyfluthrin (Responsar WP), lambda-cyhalothrin (Icon 2.8EC), fipronil (Regent 50SC), and imidacloprid (Toxilat 10WP)--was examined against the WHO/VCRU (World Health Organization/ Vector Control Research Unit) susceptible strain and the AYTW (Ayer Tawar) field strain of house fly, Musca domestica L. These pesticides were administered topically, in the diet, or as a dry residue treatment on plywood. Probit analysis using at least five concentrations and the concentration that was lethal to 50% (LC(50)) of the organisms was applied to compare the toxicology and resistance levels of the AYTW population to different insecticides. In the larvicide laboratory study, ChCy was more effective than cyromazine, with a significantly lower LC(50) value when administered topically or in the diet, although the AYTW population was susceptible to both larvicides with a resistance ratio (RR) <10. For the adulticide laboratory study, cyfluthrin and fipronil exhibited the lowest LC50 values of the adulticides, indicating that they are both effective at controlling adult flies, although lambda-cyhalothrin showed moderate resistance (RR = 11.60 by topical application; 12.41 by plywood treatment). Further investigation of ChCy, cyromazine, cyfluthrin, and fipronil under field conditions confirmed that ChCy and cyromazine strikingly reduced larval density, and surprisingly, ChCy also exhibited adulticidal activity, which significantly reduced adult fly numbers compared with the control group. Cyfluthrin and fipronil were also confirmed to be effective, with a significant reduction in adult fly numbers compared with the control group.

Larval age and nutrition significantly affected the insect’s physiology. These influences are important when rearing a population of vectors that is used to monitor the resistance level, in which standardized conditions are crucial for a more harmonized result. Little information has been reported on the effects of larval age and nutrition on the susceptibility of insects to insecticides, and therefore, we studied the effects on the susceptibility of Culex quinquefasciatus Say’s (Diptera: Culicidae) larvae to temephos by comparing the median lethal concentration (LC50) after 24 hr between the second and fourth instar larvae and between the larvae that fed on protein-based and carbohydrate-based larval diets. The susceptibility of the larvae was significantly affected by the larval diets, as the larvae that fed on protein-based beef food and milk food demonstrated significantly higher LC50 value compared with the larvae that fed on carbohydrate-based food: lab food and yeast food. The larval diet interacted significantly with the larval age: while the second instar larvae were susceptible to temephos when supplied with carbohydrate-based food, the second and fourth instar larvae had no significant effect when supplied with protein-based diets, implying that a protein-rich environment may cause the mosquito to be less susceptible to temephos. This study suggested the importance of standardizing nutrition when rearing a vector population in order to obtain more harmonized dosage–response results in an insecticide resistance monitoring program. Future research could focus on the biochemical mechanism between the nutrition and the enzymatic activities of the vector.

Megaselia scalaris (Loew) is one of the best-known diets for the swiftlet. Previous studies have addressed the problem of some mass rearing conditions for this insect; unfortunately, the details of the nutritional composition of the life stages and cost of the breeding materials were insufficiently reported, even though this information is crucial for farming the edible-nest swiftlet. We aimed to investigate the nutritional composition of the life stages of M scalaris on a cost basis using 3 common commercial breeding materials: chicken pellets (CPs), fish pellets (FPs), and mouse pellets (MPs). Modified Association of Official Analytical Chemists (AOAC) proximate and mineral analyses were carried out on the insect’s third instar larvae, pupal, and adult stages to determine the nutritional composition. Regardless of the breeding materials, the adult stage of M scalaris had significantly higher crude protein than the other stages; the pupae were rich in calcium, which is required for egg production; and the third instar larvae had the highest amount of crude fat compared with the other stages. Regarding the energy content, there were no significant differences among the stages according to the breeding materials. In terms of nutritional cost, CP was the most economic breeding material and generated the highest amount of nutrients per US dollar (US $). Different life stages of M scalaris were used by the swiftlets by supplying the required nutrients, and future studies should focus on effective diet feeding methods.