A 70% Reduction in Mosquito Populations Does Not Require Removal of 70% of Mosquitoes

New tools for Aedes control: mass trapping

Aedes aegypti, the main vector of dengue, chikungunya, and Zika viruses uses artificial containers around homes to undergo immature development, making household-level detection and control extremely difficult in large urban areas. Mass trapping is an emerging methodology to control container-Aedes species such as Aedes aegypti and Aedes albopictus because effective traps for adult stages of these mosquitoes were developed recently. There are three main approaches to mass-trapping these mosquitoes: 1) Pull (attract/kill), 2) push (repel)-pull (attract/kill), and 3) pull (attract/contaminate/infect)-push (fly away). Effective mass-trapping depends on trap quality (capture efficiency, sturdiness, frequency of servicing), trap density and areal coverage, community involvement, and safety. Recent studies showed that Ae. aegypti populations can be sustainably controlled by mass trapping, although more area-wide studies showing effectiveness at preventing disease are needed for all trapping systems. Cost-effectiveness studies are needed for all emerging Aedes control approaches.

Surveillance and Control of Culex quinquefasciatus Using Autocidal Gravid Ovitraps

We monitored trap captures of Culex quinquefasciatus using an interrupted time-series study to determine if autocidal gravid ovitraps (AGO traps) were useful to control the population of this mosquito species in a community in southern Puerto Rico. Data for this report came from a previous study in which we used mass trapping to control Aedes aegypti, resulting in a significant 79% reduction in numbers of this species. The AGO traps used to monitor and control Ae. aegypti also captured numerous Cx. quinquefasciatus. Culex quinquefasciatus was monitored in surveillance AGO traps from October 2011 to February 2013, followed by a mosquito control intervention from February 2013 to June 2014. Optimal captures of this mosquito occurred on the 2nd wk after the traps were set or serviced, which happened every 8 wk. Changes in collection numbers of Cx. quinquefasciatus were positively correlated with rainfall and showed oscillations every 8 wk, as revealed by sample autocorrelation analyses. Culex quinquefasciatus was attracted to and captured by AGO traps, so mass trapping caused a significant but moderate reduction of the local population (31.2%) in comparison with previous results for Ae. aegypti, possibly resulting from female mosquitoes flying in from outside of the study area and decreased attraction to the traps past the 2nd wk of trap servicing. Because Ae. aegypti and Cx. quinquefasciatus are frequently established in urban areas, mass trapping to control the former has some impact on Cx. quinquefasciatus. Control of the latter could be improved by locating and treating its aquatic habitats within and around the community.

Multi-Year Mass-Trapping With Autocidal Gravid Ovitraps has Limited Influence on Insecticide Susceptibility in Aedes aegypti (Diptera: Culicidae) From Puerto Rico

Mass-trapping has been used to control outbreaks of Aedes aegypti (Linnaeus) (Diptera: Culicidae) in Puerto Rico since 2011. We investigated the effect of multi-year, insecticide-free mass trapping had on the insecticide susceptibility profile of Ae. aegypti. Eggs collected in southern Puerto Rico were used to generate F1 populations that were tested for susceptibility to permethrin, sumethrin, bifenthrin, deltamethrin, and malathion according to CDC bottle bioassays protocols. All populations of Ae. aegypti were resistant to the synthetic pyrethroids and mosquitoes from two locations were partially resistant to malathion. Population genetic analysis, using a double digest restriction sites associated DNA sequencing (ddRADseq) approach, indicated a large amount of migration between study sites effectively homogenizing the mosquito populations. Mass-trapping using noninsecticidal autocidal gravid ovitraps did not restore susceptibility to five active ingredients that are found in commercial insecticides. Migration between communities was high and would have brought outside alleles, including resistant alleles to the treatment communities. Further investigation suggests that household use of commercially available insecticide products may continue to select for resistance in absence of public health space spraying of insecticides.

Mosquito Attractants

Vector control and personal protection against anthropophilic mosquitoes mainly rely on the use of insecticides and repellents. The search for mosquito-attractive semiochemicals has been the subject of intense studies for decades, and new compounds or odor blends are regularly proposed as lures for odor-baited traps. We present a comprehensive and up-to-date review of all the studies that have evaluated the attractiveness of volatiles to mosquitoes, including individual chemical compounds, synthetic blends of compounds, or natural host or plant odors. A total of 388 studies were analysed, and our survey highlights the existence of 105 attractants (77 volatile compounds, 17 organism odors, and 11 synthetic blends) that have been proved effective in attracting one or several mosquito species. The exhaustive list of these attractants is presented in various tables, while the most common mosquito attractants - for which effective attractiveness has been demonstrated in numerous studies - are discussed throughout the text. The increasing knowledge on compounds attractive to mosquitoes may now serve as the basis for complementary vector control strategies, such as those involving lure-and-kill traps, or the development of mass trapping. This review also points out the necessity of further improving the search for new volatile attractants, such as new compound blends in specific ratios, considering that mosquito attraction to odors may vary over the life of the mosquito or among species. Finally, the use of mosquito attractants will undoubtedly have an increasingly important role to play in future integrated vector management programs.