Mosquitoes (Diptera: Culicidae) are a key threat for millions of people worldwide, since they act as vectors for devastating pathogens and parasites. In this scenario, vector control is crucial. Mosquito larvae are usually targeted using organophosphates, insect growth regulators, and microbial agents. Indoor residual spraying and insecticide-treated bed nets are also employed. However, these chemicals have negative effects on human health and the environment and induce resistance in a number of vectors. Newer and safer tools have been recently implemented to enhance control of mosquitoes. Here, I focus on some crucial challenges about eco-friendly control of mosquito vectors, mainly the improvement of behavior-based control strategies (sterile insect technique (“SIT”) and “boosted SIT”) and plant-borne mosquitocidals, including green-synthesized nanoparticles. A number of hot areas that need further research and cooperation among parasitologists, entomologists, and behavioral ecologists are highlighted.

Research in mosquito control: current challenges for a brighter future.

Genetics can potentially provide new, species-specific, environmentally friendly methods for mosquito control. Genetic control strategies aim either to suppress target populations or to introduce a harm-reducing novel trait. Different approaches differ considerably in their properties, especially between self-limiting strategies, where the modification has limited persistence, and self-sustaining strategies, which are intended to persist indefinitely in the target population and may invade other populations. Several methods with different molecular biology are under development and the first field trials have been completed successfully.

/pdf/genetic-control-of-mosquitoes-323levzu0k.pdf

Genetic Control of Mosquitoes

Vector-borne disease is one of the greatest contributors to human mortality and morbidity throughout the tropics. Mosquito-transmitted diseases such as malaria, dengue, yellow fever and filariasis are the main contributors to this burden. Although insecticides have historically been used to try to control vector populations, over the past 15 years, substantial progress has been made in developing alternative vector control strategies ranging from biocontrol methods through to genetic modification of wild insect populations. Here, we review recent advances concerning these strategies and consider the potential impediments to their deployment, including the challenges of obtaining regulatory approval and community acceptance.

/pdf/beyond-insecticides-new-thinking-on-an-ancient-problem-1zzawitxhz.pdf

Beyond insecticides: new thinking on an ancient problem

The genus Wolbachia is an archetype of maternally inherited intracellular bacteria that infect the germline of numerous invertebrate species worldwide. They can selfishly alter arthropod sex ratios and reproductive strategies to increase the proportion of the infected matriline in the population. The most common reproductive manipulation is cytoplasmic incompatibility, which results in embryonic lethality in crosses between infected males and uninfected females. Females infected with the same Wolbachia strain rescue this lethality. Despite more than 40 years of research and relevance to symbiont-induced speciation, as well as control of arbovirus vectors and agricultural pests, the bacterial genes underlying cytoplasmic incompatibility remain unknown. Here we use comparative and transgenic approaches to demonstrate that two differentially transcribed, co-diverging genes in the eukaryotic association module of prophage WO from Wolbachia strain wMel recapitulate and enhance cytoplasmic incompatibility. Dual expression in transgenic, uninfected males of Drosophila melanogaster crossed to uninfected females causes embryonic lethality. Each gene additively augments embryonic lethality in crosses between infected males and uninfected females. Lethality associates with embryonic defects that parallel those of wild-type cytoplasmic incompatibility and is notably rescued by wMel-infected embryos in all cases. The discovery of cytoplasmic incompatibility factor genes cifA and cifB pioneers genetic studies of prophage WO-induced reproductive manipulations and informs the continuing use of Wolbachia to control dengue and Zika virus transmission to humans.

/pdf/prophage-wo-genes-recapitulate-and-enhance-wolbachia-induced-qp03s9i0az.pdf

Prophage WO genes recapitulate and enhance Wolbachia -induced cytoplasmic incompatibility

Harnessing mosquito-Wolbachia symbiosis for vector and disease control.

Background: Lymphatic filariasis (LF) is a globally significant disease, with 1.3 billion persons in 83 countries at risk. A coordinated effort of administering annual macrofilaricidal prophylactics to the entire at-risk population has succeeded in impacting and eliminating LF transmission in multiple regions. However, some areas in the South Pacific are predicted to persist as transmission sites, due in part to the biology of the mosquito vector, which has led to a call for additional tools to augment drug treatments. Autocidal strategies against mosquitoes are resurging in the effort against invasive mosquitoes and vector borne disease, with examples that include field trials of genetically modified mosquitoes and Wolbachia population replacement. However, critical questions must be addressed in anticipation of full field trials, including assessments of field competitiveness of transfected males and the risk of unintended population replacement. Methodology/Principal Findings: We report the outcome of field experiments testing a strategy that employs Wolbachia as a biopesticide. The strategy is based upon Wolbachia-induced conditional sterility, known as cytoplasmic incompatibility, and the repeated release of incompatible males to suppress a population. A criticism of the Wolbachia biopesticide approach is that unintended female release or horizontal Wolbachia transmission can result in population replacement instead of suppression. We present the outcome of laboratory and field experiments assessing the competitiveness of transfected males and their ability to transmit Wolbachia via horizontal transmission. Conclusions/Significance: The results demonstrate that Wolbachia-transfected Aedes polynesiensis males are competitive under field conditions during a thirty-week open release period, as indicated by mark, release, recapture and brood-hatch failure among females at the release site. Experiments demonstrate the males to be ‘dead end hosts’ for Wolbachia and that methods were adequate to prevent population replacement at the field site. The findings encourage the continued development and extension of a Wolbachia autocidal approach to additional medically important mosquito species.

/pdf/open-release-of-male-mosquitoes-infected-with-a-wolbachia-3d933rujqk.pdf

Open release of male mosquitoes infected with a wolbachia biopesticide: field performance and infection containment.

We performed longitudinal surveys of mosquito larval abundance (mean mosquito larvae per dip) in 87 stormwater ponds and constructed wetlands in Delaware from June to September 2004. We analyzed selected water quality factors, water depth, types of vegetation, degree of shade, and level of insect predation in relation to mosquito abundance. The 2004 season was atypical, with most ponds remaining wet for the entire summer. In terms of West Nile virus (WNV) vectors, wetlands predominantly produced Aedes vexans, Culex pipiens pipiens, and Culex restuans. Retention ponds generally produced the same species as wetlands, except that Cx. p. pipiens was more abundant than Cx. restuans in retention ponds. Aedes vexans and Culex salinarius were the most abundant species in Conservation Restoration Enhancement Program ponds. Sand filters uniquely produced high numbers of Cx. restuans, Cx. p. pipiens, and Aedes japonicus japonicus, a newly invasive vector species. Sites that alternately dried and flooded, mostly detention ponds, forebays of retention ponds, and some wetlands often produced Ae. vexans, an occasional WNV bridge vector species. Overall, seasonal distribution of vectors was bimodal, with peaks occurring during early and late summer. Ponds with shallow sides and heavy shade generally produced an abundance of mosquitoes, unless insect predators were abundant. Bright, sunny ponds with steep sides and little vegetation generally produced the fewest mosquitoes. The associations among mosquito species and selected vegetation types are discussed.

https://bioone.org/journals/journal-of-the-american-mosquito-control-association/volume-22/issue-2/8756-971X(2006)22[282:SPCWAO]2.0.CO;2/STORMWATER-PONDS-CONSTRUCTED-WETLANDS-AND-OTHER-BEST-MANAGEMENT-PRACTICES-AS/10.2987/8756-971X(2006)22[282:SPCWAO]2.0.CO;2.pdf

Stormwater ponds, constructed wetlands, and other best management practices as potential breeding sites for West Nile virus vectors in Delaware during 2004.

Lycoriella mali Fitch (Diptera: Sciaridae) infests mushroom crops early in the crop cycle. Recent observations in mushroom houses indicated a difference in emergence time and size of adult L. mali developing on various strains of commercial mushrooms. Samples of adult flies from isolated mushroom houses growing Portabella mushrooms were significantly heavier then those from oyster mushroom houses, whereas flies from shiitake mushroom houses were lightest in weight. Flies collected from isolated Portabella mushroom houses were reared on four strains and species of Agaricus and Pleurotus mushrooms. After the adults emerged, females were weighed, mated, and allowed to oviposit. The number of eggs laid increased as the weight of the female increased. Flies collected from isolated Portabella mushroom houses were reared on eight strains and species of mushrooms. Flies were reared for four generations on each host mushroom mycelium then switched to different host mushrooms. Overall, the hybrid strain of Agaricus bisporus (Lange) Imbach (Agaricales: Agaricomycetideae) was the most favorable host for L. mali, whereas the wild strain of A. bisporus was the least favorable host. Mushroom hosts influence developmental time, survivorship, weight, and reproduction of L. mali.

https://bioone.org/journals/journal-of-economic-entomology/volume-98/issue-2/0022-0493-98.2.342/Mushroom-Host-Influence-on-Lycoriella-mali-Diptera--Sciaridae-Life/10.1603/0022-0493-98.2.342.pdf

Mushroom Host Influence on Lycoriella mali (Diptera: Sciaridae) Life Cycle

Adult numbers and sizes of mosquitoes were monitored for 2 yr in neighboring habitats on the western coast of Raiatea (Society Archipelago) in anticipation of testing new vector control technologies Aedes polynesiensis Marks females comprised the overwhelming majority (≈99%) of the three species of mosquitoes captured in Biogent Sentinel traps placed at fixed sites on three small satellite islands (motus) of the western lagoon and on the shoreline of Raiatea Aedes polynesiensis males, Aedes aegypti (L), and Culex quinquefasciatus Say rarely were collected Numbers of Ae polynesiensis females per collection differed among trapping dates and locations, with the majority of females captured on two motus, Horea and Toamaro Shoreline and Horea females had significantly longer mean wing lengths than females from Tiano and Toamaro Thus, wing lengths were influenced more by local developmental conditions than overall numbers of adults Significantly more females were captured during the wet season than the dry season Nonetheless, at least on the two highly productive motus, dry-season females had larger wing lengths than their wet season counterparts Local weather patterns predicted about half the variation in mosquito numbers Differences in vector abundance observed when comparing neighboring motus are likely because of differences in human activity and mosquito suppression

https://bioone.org/journals/journal-of-medical-entomology/volume-49/issue-1/ME11087/Monitoring-Temporal-Abundance-and-Spatial-Distribution-of-Aedes-polynesiensis-using/10.1603/ME11087.pdf

Monitoring Temporal Abundance and Spatial Distribution of Aedes polynesiensis using BG-Sentinel Traps in Neighboring Habitats on Raiatea, Society Archipelago, French Polynesia

Linda O'Connor

Papers

Open release of male mosquitoes infected with a wolbachia biopesticide: field performance and infection containment.

Stormwater ponds, constructed wetlands, and other best management practices as potential breeding sites for West Nile virus vectors in Delaware during 2004.

Mushroom Host Influence on Lycoriella mali (Diptera: Sciaridae) Life Cycle

Monitoring Temporal Abundance and Spatial Distribution of Aedes polynesiensis using BG-Sentinel Traps in Neighboring Habitats on Raiatea, Society Archipelago, French Polynesia