Overcoming the challenges of mosquito (Diptera: Culicidae) sampling in remote localities: a comparison of CO2 attractants on mosquito communities in three tropical forest habitats

Comparison of the Trapping Efficacy of Locally Modified Gravid Aedes Trap and Autocidal Gravid Ovitrap for the Monitoring and Surveillance of Aedes aegypti Mosquitoes in Tanzania

The study assessed the trapping efficacy of locally modified (1) Gravid Aedes Trap (GAT) lined with insecticide-treated net (ITN) as a killing agent and (2) Autocidal Gravid Ovitrap (AGO) with sticky board in the semi-field system (SFS) and field setting. Fully balanced Latin square experiments were conducted to compare GAT lined with ITN vs. AGO, both with either yeast or grass infusion. Biogent-Sentinel (BGS) with BG-Lure and no CO2 was used as a standard trap for Aedes mosquitoes. In the SFS, GAT outperformed AGO in collecting both nulliparous (65% vs. 49%, OR = 2.22, [95% CI: 1.89-2.60], p < 0.001) and gravid mosquitoes (73% vs. 64%, OR = 1.67, [95% CI: 1.41-1.97], p < 0.001). Similar differences were observed in the field. Yeast and grass infusion did not significantly differ in trapping gravid mosquitoes (OR = 0.91, [95% CI: 0.77-1.07], p = 0.250). The use of ITN improved mosquito recapture from 11% to 70% in the SFS. The same trend was observed in the field. Yeast was chosen for further evaluation in the optimized GAT due to its convenience and bifenthrin net for its resistance management properties. Mosquito density was collected when using 4× GATs relative to BGS-captured gravid mosquitoes 64 vs. 58 (IRR = 0.82, [95% CI: 0.35-1.95], p = 0.658) and showed no density dependence. Deployment of multiple yeast-baited GAT lined with bifenthrin net is cost-effective (single GAT < $8) compared to other traps such as BGS ($160).

Do it yourself: 3D-printed miniature CDC trap for adult mosquito (Diptera: Culicidae) surveillance

The central component of mosquito and vector surveillance programs globally is the adult mosquito trap, which is intended to collect host-seeking mosquitoes. The miniature CDC trap is a widely distributed trap style in part due to its relative affordability and compact nature. Despite already being a simple trap, in-house production methods, such as 3D printing, could improve the accessibility of the CDC trap by eliminating some of the supply chain variables. We present here several trials with the Salt Lake City (SLC) trap, a three-dimensional (3D) printed trap design. Functional assessments were made on secondary components and found no statistically significant differences when comparing CO2 line height (above vs. below fan), battery types (sealed lead acid vs. USB battery pack), and trap body collection shape (funnel body vs. simple/straight body). The SLC trap was compared directly to a commercial equivalent, the ABC trap, with comparative assessment on species diversity and evenness in collections and found to be statistically equivalent on all metrics. Methods also detail an accompanying optional transport system for a pressurized CO2/regulator set-up, should a practitioner elect not to use dry ice. Our final design is presented here with the publicly published stereolithography (STL) files and a detailed outline of the transport container system. Alternative models are available for in-house manufacture of mosquito traps, and we contribute these designs in an effort to stimulate further growth in vector surveillance.

Evaluation of various substances and trap component configurations to increase mosquito collections in Biogents Gravid Aedes traps

Two independent studies were conducted in northeastern Florida to determine if Biogents Gravid Aedes Trap (GAT) mosquito collections could be enhanced with a variety of substances and structural configurations. The first study baited GATs with either: 1) an infusion of mixed Southern live oak leaf (Quercus virginiana) and slash pine needle (Pinus elliottii) litter, 2) Biogents Lure (BG Lure), 3) yeast-derived carbon dioxide), 4) yeast-derived carbon dioxide+ BG Lure, or 5) a combination of all three. Nine mosquito species were collected from traps in the first study with Psorophora ferox>Culex nigripalpus>Aedes aegypti>Cx. quinquefasciatus as the top four most abundantly collected species. No significant difference in mosquito abundance was observed among these species among treatments. However, when the overall number of mosquitoes for all nine species was pooled, GATs baited with the combination of yeast-derived carbon dioxide + BG Lure + leaf infusion numerically collected the greatest number of individuals compared with the other four treatments. The second study evaluated the separate and combined attractiveness of individual GAT structural components/configurations with and without Southern live oak leaf litter infusion and BG-Lure. Aedes albopictus, Ae. aegypti, Anopheles quadrimaculatus, and Cx. quinquefasciatus were collected from all these traps in the second study. Results generally revealed that the current commercially available GAT configuration consisting of a screened translucent top (with BG-Lure) fitted into the black reservoir baited with oak leaf infusion remained the most attractive combination for collecting northeastern Florida mosquitoes.

A Simple CO2 Generating System Incorporated with CDC Light Trap for Sampling Mosquito Vectors

Simple Summary

This study successfully developed a CO₂ generating system that can be incorporated with a CDC light trap for the overnight collection of mosquitoes. We produced CO₂ continuously by dripping an aqueous solution of 12% w/w hydrochloric acid (HCl) (30 drops or 1.6 mL/min) controlled by an intravenous drip infusion set onto limestone powder (800 g) that produced an average of 55 mL CO₂/min (equivalent to the CO₂ exhalation from two chickens). The efficiency of this trap set for capturing mosquitoes was evaluated in the field compared with the light trap alone and the light trap baited with 1 kg dry ice. The results revealed that the trap with the acid and limestone significantly increased the number and species composition of mosquitoes collected compared with the light trap alone. It could collect all important vector species of Aedes, Armigeres, Coquilletidia, Culex and Mansonia as collected by the trap with dry ice, although the numbers were fewer. Our CO₂ producing system is reliable, simple and inexpensive, and could be an alternative method when dry ice is unavailable.

Abstract

Traps for capturing mosquitoes and other blood-feeding arthropods are often baited with carbon dioxide (CO₂) as an attractant. Dry ice is popularly used as a CO₂ source due to its high efficiency and ease of use. However, dry ice can be difficult to obtain in many rural and remote areas. The objective of this study was to develop a simple and inexpensive method that could continuously generate CO₂ overnight (about 10 h) while being used with CDC light traps for sampling adult mosquitoes. In principle, CO₂ was produced from the reaction between hydrochloric acid (HCl) (12% w/w) and limestone powder (mainly composed of calcium carbonate, CaCO₃). In laboratory experiments, an average of 256 mL of CO₂ was produced from 1 g of limestone. For continuous production of CO₂, an intravenous drip infusion set, as commonly used in hospitals, was modified for dripping the acid solution (1 L in a normal saline bag) onto limestone powder (800 g in a 1.5 L bottle) at a flow rate of 30 drops/min (about 1.6 mL/min). With this procedure, an average of 55 mL of CO₂ per min was obtained (approximately equivalent to the CO₂ exhaled by two chickens). The performance of this CO₂ generating system incorporated with CDC light traps for sampling mosquitoes was evaluated in three rural villages of Sanpatong District, Chiang Mai Province, Thailand. Three trap sets were used, i.e., Set I, light trap alone; Set II, light trap with dry ice (1 kg); and Set III, light trap with limestone and acid. In each village, mosquitoes were collected at three fixed sites, each with one of the three trap sets. They were rotated daily for three rounds (9 nights per village and 27 nights in total). A total of 1620 mosquitoes (97.7% being females) consisting of Aedes, Anopheles, Armigeres, Coquilletidia, Culex and Mansonia were captured across three different sampling sets from all villages. The predominant species collected were Culex vishnui (n = 760, 46.91%), Cx. bitaeniorhynchus (n = 504, 31.11%) and Cx. tritaeniorhynchus (n = 157, 9.69%). Light traps alone (Set I) collected very low numbers of mosquitoes (n = 12) and species (6 spp.), whereas light traps with dry ice (Set II) collected the highest numbers of mosquitoes (n = 1341) and species (14 spp.). Although the light trap with limestone and acid (Set III) collected fewer mosquitoes (n = 267) and species (9 spp.) than the trap set with dry ice (Set II), it collected all common vector species in the study areas as collected by Set II. The presence of an acid solution had no bias in the collection of mosquitoes with different physiological ages as determined by the parous rate. The present study demonstrated that this CO₂ generating system is reliable, simple and inexpensive, and could be an alternative to dry ice. The system can be modified to increase the amount of CO₂ generated for higher efficacy of mosquito collection. This CO₂ production method can be applied to collect other blood-sucking arthropods as well.

Comparative Analysis of Mosquito Trap Counts In the Peruvian Amazon: Effect of Trap Type and Other Covariates On Counts and Diversity

Efficient detection of multiple species of adult mosquitoes in various habitats using effective traps is a crucial 1st step in any disease prevention program. Novel trap types that target tropical vectors of human diseases require field testing in the habitat of the vector-disease system in question. This paper analyzes a series of mosquito trapping studies conducted at Mapacocha, San Juan Bautista District, Loreto, Peru, during August-September 2013 and April-May 2014. Six trap configurations were evaluated in forest and rural locations. Adult mosquito counts were analyzed using full Bayesian inference of multilevel generalized linear models and posterior probability point estimates of the difference of means of the combined trap catch by trap type comparisons of all species. Light traps (Centers for Disease Control and Prevention [CDC] incandescent, white light-emitting diode [LED], and ultraviolet LED) caught greater numbers of mosquitoes compared with traps baited with yeast-generated CO₂ and Biogents Sentinel^™ traps (battery powered traps without light and passive box traps). However, diversity measures (species richness, evenness, and similarity) were consistently nearly equal among trap types. Arbovirus vectors were more common in forest locations, while malaria vectors were more common near human habitations. Location had a significant effect on trap effectiveness and mosquito diversity, with traps from forest locations having greater numbers and greater species richness, compared with traps set near human habitations. The results of this study will inform mosquito surveillance trap choices in remote regions of central South America, including regions with emerging tropical diseases, such and dengue and Zika virus.

Searching for the proverbial needle in a haystack: advances in mosquito-borne arbovirus surveillance

Surveillance is critical for the prevention and control of mosquito-borne arboviruses. Detection of elevated or emergent virus activity serves as a warning system to implement appropriate actions to reduce outbreaks. Traditionally, surveillance of arboviruses has relied on the detection of specific antibodies in sentinel animals and/or detection of viruses in pools of mosquitoes collected using a variety of sampling methods. These methods, although immensely useful, have limitations, including the need for a cold chain for sample transport, cross-reactivity between related viruses in serological assays, the requirement for specialized equipment or infrastructure, and overall expense. Advances have recently been made on developing new strategies for arbovirus surveillance. These strategies include sugar-based surveillance, whereby mosquitoes are collected in purpose-built traps and allowed to expectorate on nucleic acid preservation cards which are submitted for virus detection. New diagnostic approaches, such as next-generation sequencing, have the potential to expand the genetic information obtained from samples and aid in virus discovery. Here, we review the advancement of arbovirus surveillance systems over the past decade. Some of the novel approaches presented here have already been validated and are currently being integrated into surveillance programs. Other strategies are still at the experimental stage, and their feasibility in the field is yet to be evaluated.

Development, Optimization, and Field Evaluation of the Novel Collapsible Passive Trap for Collection of Mosquitoes

Disease surveillance for mosquito-borne pathogens in remote areas can be challenging. Most traps used to collect mosquitoes either need a source of electricity or are bulky and inflexible, making transportation awkward. To reduce these issues we developed three Collapsible Passive Traps (CPTs) and conducted trials in Cairns, Australia to evaluate the optimal design for a CPT and compared them to traditionally-used traps such as Centers for Disease Control and Prevention (CDC) and Encephalitis Vector Surveillance (EVS) light traps. We found that two of the CPTs collected comparable numbers of mosquitoes and that one of the CPTs outperformed the CDC light trap in collecting Aedes species. Mosquitoes did not have to pass through a fan while entering the CPT, and thus were not damaged and were often alive. Our results suggest that the CPT can be an effective trap for mosquito surveillance, especially in remote areas.

Land Use Influences Mosquito Communities and Disease Risk on Remote Tropical Islands: A Case Study Using a Novel Sampling Technique

Land use changes, such as deforestation and urbanization, can influence interactions between vectors, hosts, and pathogens. The consequences may result in the appearance and rise of mosquito-borne diseases, especially in remote tropical regions. Tropical regions can be the hotspots for the emergence of diseases due to high biological diversity and complex species interactions. Furthermore, frontier areas are often haphazardly surveyed as a result of inadequate or expensive sampling techniques, which limit early detection and medical intervention. We trialed a novel sampling technique of nonpowered traps and a carbon dioxide attractant derived from yeast and sugar to explore how land use influences mosquito communities on four remote, tropical islands in the Australian Torres Strait. Using this technique, we collected > 11,000 mosquitoes from urban and sylvan habitats. We found that human land use significantly affected mosquito communities. Mosquito abundances and diversity were higher in sylvan habitats compared with urban areas, resulting in significantly different community compositions between the two habitats. An important outcome of our study was determining that there were greater numbers of disease-vectoring species associated with human habitations. On the basis of these findings, we believe that our novel sampling technique is a realistic tool for assessing mosquito communities in remote regions.

Assessing Carbon Dioxide and Synthetic Lure-Baited Traps for Dengue and Chikungunya Vector Surveillance (3)

The Aedes mosquito vectors of dengue virus (DENV) and chikungunya virus (CHIKV) are attracted to specific host cues that are not generated by traditional light traps. For this reason multiple companies have designed traps to specifically target those species. Recently the standard trap for DENV and CHIKV vectors, the BG-Sentinel (BGS) trap, has been remodeled to be more durable and better suited for use in harsh field conditions, common during military operations, and relabeled the BG-Sentinel 2 (BGS2). This new trap was evaluated against the standard Centers for Disease Control and Prevention (CDC) light trap, Zumba Trap, and BG-Mosquitito Trap to determine relative effectiveness in collecting adult Aedes aegypti and Ae. albopictus. Evaluations were conducted under semifield and field conditions in suburban areas in northeastern Florida from May to August 2014. The BGS2 trap collected more DENV and CHIKV vectors than the standard CDC light trap, Zumba Trap, and BG-Mosquitito Trap, but attracted fewer species, while the BG-Mosquitito Trap attracted the greatest number of mosquito species.

Field Comparison of Cyclopentanone Versus Carbon Dioxide as an Attractant for Adult Mosquitoes in Southeast Queensland, Australia

Cyclopentanone is a saturated monoketone typically used as an intermediate in the manufacture of pharmaceuticals, biologicals, insecticides, and rubber chemicals. Recently, it has been demonstrated that cyclopentanone activates the cpA CO2 receptor neuron on the maxillary palp of mosquitoes, suggesting that it may be a viable alternative to CO2 as an attractant for mosquitoes. Furthermore, semifield experiments showed that traps baited with cyclopentanone attract Culex quinquefasciatus Say at a similar rate to those baited with CO2. We evaluated the field efficacy of cyclopentanone as an alternative to CO2 in Centers for Disease Control (CDC) light traps and counterflow geometry (CFG) traps commonly used to collect mosquitoes in surveillance programs. Three pairwise trials and four Latin square trials were conducted across three peri-urban sites, comprising two saltwater sites and one freshwater site, in southeast Queensland, Australia. In all trials, CO2-baited traps outperformed traps baited with cyclopentanone. Carbon dioxide-baited CDC traps collected significantly more total mosquitoes, Aedes vigilax (Skuse), Culex sitiens Weidemann, and Culex annulirostris Skuse, than those baited with ≥99% cyclopentanone in pairwise trials. Similarly, in almost all Latin square trials, CO2-baited CDC and CFG traps collected significantly greater numbers of total mosquitoes, Ae. vigilax, Cx. annulirostris, Culex orbostiensis Dobrotworsky, and Cx. sitiens when compared with CFG traps baited with 20% cyclopentanone. Our trials indicate that cyclopentanone is not effective as a mosquito attractant in the field and cannot be used as a simple substitute for CO2 in commonly used mosquito surveillance traps.

Field assessment of yeast- and oxalic Acid-generated carbon dioxide for mosquito surveillance

Carbon dioxide (CO2) sources improve the efficacy of mosquito traps. However, traditional CO2 sources (dry ice or compressed gas) may be difficult to acquire for vector surveillance during military contingency operations. For this reason, a new and convenient source of CO2 is required. Two novel CO2 generators were evaluated in order to address this capability gap: 1) an electrolyzer that converts solid oxalic acid into CO2 gas, and 2) CO2 produced by yeast as it metabolizes sugar. The flow rate and CO2 concentration produced by each generator were measured, and each generator's ability to attract mosquitoes to BG-Sentinel™ traps during day surveillance and to Centers for Disease Control and Prevention light traps with incandescent bulbs during night surveillance was compared to dry ice and compressed gas in Jacksonville, FL. The electrolyzed oxalic acid only slightly increased the number of mosquitoes captured compared to unbaited traps. Based on the modest increase in mosquito collection for traps paired with the oxalic acid, it is not a suitable stand-in for either of the 2 traditional CO2 sources. Conversely, the yeast-generated CO2 resulted in collections with mosquito abundance and species richness more closely resembling those of the traditional CO2 sources, despite achieving a lower CO2 flow rate. Therefore, if dry ice or compressed gas cannot be acquired for vector surveillance, yeast-generated CO2 can significantly improve trap capability.