Collection and Rearing of Container Mosquitoes and a 24-h Addition to the CDC Bottle Bioassay

Assessment of Mosquito Pollination

Adult mosquitoes, sometimes in vast numbers, visit flowers in their search for floral nectar. However, the ability of mosquitoes to pollinate the flowers they visit is often neglected and sometimes even presumptively dismissed. Despite this, mosquito pollination has been reported in many instances, although many questions linger about its extent, importance, and the breadth of floral species or mosquito species which may be involved. In this protocol, I describe methodology to assess whether mosquitoes pollinate a flowering plant they visit, which can create a foundation for future investigations into this topic.

Developmental performance of Eristalis tenax larvae (Diptera: Syrphidae): Influence of growth media and yeast addition during captive rearing

In holometabolous insects, life-history characteristics can vary in response to diet. The main aim of this contribution was to examine which diet best promotes larval development and survival of the aquatic saprophagous hoverfly Eristalis tenax L. (Diptera: Syrphidae). This study was motivated by a need to optimize techniques for rearing these insects in captivity. We studied how adding yeast to several rearing media based on animal droppings or decaying plant material affected development and survival in captive larvae, and whether these effects could be optimized depending on the amount of yeast and the rearing medium. In addition, premature exit of larvae was examined in two medium volumes to investigate differences in pupation. Larvae in yeast supplemented rabbit growth medium pupated and emerged faster than those in horse and antelope growth media. A high number of adult females emerged when compared to males, and both seemed to have a shorter developmental period in yeast supplemented growth media. Pupal survival was significantly greater in a mixture of droppings and plant organic matter, and a high medium volume of 140 ml (p < 0.05). Between 10% and 17% of larvae prematurely exited the aquatic medium in high (140) and low (70 ml) medium volumes, respectively. These results provide additional information that may be crucial for the successful mass rearing of E. tenax in captivity, and suggest that apart from the addition of yeast, growth medium quality and volume may be limiting factors for the production of large colonies of adults.

Insecticide resistance compromises the control of Aedes aegypti in Bangladesh

BACKGROUND

With no effective drugs or widely available vaccines, dengue control in Bangladesh is dependent on targeting the primary vector Aedes aegypti with insecticides and larval source management. Despite these interventions, the dengue burden is increasing in Bangladesh, and the country experienced its worst outbreak in 2019 with 101 354 hospitalized cases. This may be partially facilitated by the presence of intense insecticide resistance in vector populations. Here, we describe the intensity and mechanisms of resistance to insecticides commonly deployed against Ae. aegypti in Dhaka, Bangladesh.

RESULTS

Dhaka Ae. aegypti colonies exhibited high-intensity resistance to pyrethroids. Using CDC bottle assays, we recorded 2-24% mortality (recorded at 24 h) to permethrin and 48-94% mortality to deltamethrin, at 10× the diagnostic dose. Bioassays conducted using insecticide-synergist combinations suggested that metabolic mechanisms were contributing to pyrethroid resistance, specifically multi-function oxidases, esterases, and glutathione S-transferases. In addition, kdr alleles were detected, with a high frequency (78-98%) of homozygotes for the V1016G mutation. A large proportion (≤ 74%) of free-flying and resting mosquitoes from Dhaka colonies survived exposure to standard applications of pyrethroid aerosols in an experimental free-flight room. Although that exposure affected the immediate host-seeking behavior of Ae. aegypti, the effect was transient in surviving mosquitoes.

CONCLUSION

The intense resistance characterized in this study is likely compromising the operational effectiveness of pyrethroids against Ae. aegypti in Dhaka. Switching to alternative chemical classes may offer a medium-term solution, but ultimately a more sustainable and effective approach to controlling dengue vectors is required. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Impacts of differential mosquito control treatment regimens on insecticide susceptibility status of Aedes aegypti (Diptera: Culicidae)

Abstract

Aedes aegypti (Linnaeus) is an invasive mosquito species and notable vector of several pathogens in the USA. Their cryptic and anthropophilic nature puts this species in close association with humans, where they can also be a nuisance. Mosquito control programs are the front line of defense for protecting the community from nuisance-biting and disease. However, the occurrence and prevalence of insecticide resistance in mosquitoes is a well-documented phenomenon that directly impacts the efficacy of insecticide applications. In Florida specifically, widespread resistance in Ae. aegypti has created a need for operational strategies that combat and, ideally, reverse resistance. Laboratory studies and the association between fitness costs and insecticide resistance indicate that this reversion is possible under the right conditions. For a 2.5-year period, the impact of varying operational treatment regimens on insecticide resistance in Ae. aegypti is evaluated using kdr genotyping and the CDC bottle bioassay. In an organophosphate treatment area, a decrease in frequency of a double homozygous resistant genotype was observed. CDC bottle bioassays did not reveal any clear trends in the data to indicate a reversion to insecticide susceptibility. However, the changes in genotype could indicate the first step back to insecticide susceptibility. This study provides preliminary data that has implications for resistance management in mosquito control operations.

Article Highlights

Bio-fabricated silver nanoparticles for controlling dengue and filaria vectors and their characterization, as well as toxicological risk assessment in aquatic mesocosms

The present study is focused on synthesis of silver nanoparticles from weeds and an assessment of their mosquito larvicidal efficacy. This study also presented the toxicological effects as well as the stability of these nanoparticles in aquatic mesocosms. The weed Digiteria sanguinallis was first time used for the synthesis of silver nanoparticles. The synthesized nanoparticles were characterized by various analytical techniques, such as UV-VIS, TEM, FESEM, EDX, XRD, FTIR, and zeta potential study. The result revealed that the nanoparticles are crystalline, spherical shape with band gap 2.44 eV, and average size 18 nm. The LC₅₀ value of synthesized AgNPs were recorded as 7.47 and 6.31 mg/L at 24 h against Cx. quinquefasciatus and A. albopictus respectively. In contrast, larvicidal activity of weed extract was insignificant against two target species. In aquatic mesocosm study, AgNPs (LC₅₀ dose) does not alter the nature of water parameters within experimental period. However only EC % and ORP were changes because of silver ion oxidation. In biochemical parameters, only stress enzymes for animal and plant species were moderately altered under long term exposure. But glycogen, protein, and AchE of two mosquito species were significantly changed under same mesocosm setup within short exposure. Comparatively, in control mesocosm, synthesized AgNPs are naturally change their nano form within 20 days with the presence of all non-target species and pond sediment. Therefore, it can be concluded that biosynthesized AgNPs could be used as a larvicidal agent in near future with negligible effects on aquatic organisms.