The human landing catch (HLC) method is the internationally recognized gold-standard technique for directly measuring human–mosquito contact in vector surveillance and control research. This article provides a comprehensive, step-by-step guide to the experimental procedures of the human landing catch method, covering pre-experiment preparation, field collection protocols, specimen processing, safety measures, and data analysis. It serves as a practical technical reference for vector surveillance programs, repellent efficacy trials, and entomological research laboratories worldwide.
Technical Overview
The human landing catch (HLC) method is a WHO-endorsed entomological surveillance technique in which a human volunteer serves as live bait and a trained collector captures female mosquitoes at the moment they land on exposed skin, ideally before the mosquito takes a blood meal. First standardized in the mid-20th century, the method directly measures the human landing rate—the number of mosquitoes landing on one person per hour or per night—which is the most direct available estimate of human–vector contact. Because the HLC captures mosquitoes actively seeking a human host, it is routinely used as the reference standard against which CDC light traps, BG-Sentinel traps, and other sampling devices are validated. The method supports malaria and arbovirus vector monitoring, evaluation of insecticide-treated nets and indoor residual spraying, and efficacy testing of topical repellents. Because collectors are intentionally exposed to biting mosquitoes, the method must be conducted under strict ethical review, informed consent, chemoprophylaxis, and continuous medical supervision.
Testing Samples
Host-Seeking Adult Female Mosquitoes
The primary biological sample obtained through HLC is live, host-seeking adult female mosquitoes. Depending on the region and season, target taxa include Anopheles species (malaria vectors, largely nocturnal), Aedes aegypti and Aedes albopictus (dengue, Zika, and yellow fever vectors, diurnal), Culex species (filariasis and arbovirus vectors), and Mansonia species. Male mosquitoes are occasionally captured and must be recorded separately.
Specimens by Physiological Status
Collected females are graded by abdominal appearance as unfed, freshly blood-fed, half-gravid, or gravid. This physiological grading is essential for interpreting biting behavior, distinguishing host-seeking from resting populations, and supporting parity determination in age-structure studies.
Associated Environmental Data
Each sampling session generates paired environmental records—temperature, relative humidity, wind, rainfall, and moon phase—which are treated as an integral part of the sample dataset when interpreting fluctuations in landing density.
Testing Items
The human landing catch workflow supports the following quantitative testing items:
- Human landing rate, expressed as mosquitoes per person per hour or per person per night
- Man-biting rate and seasonal abundance indices by species
- Species composition and relative density
- Biting rhythm profiles, including hourly, nocturnal, and diurnal activity patterns
- Indoor versus outdoor biting proportions
- Parity rate and population age structure through ovarian dissection
- Sporozoite infection rate by ELISA or PCR for malaria parasites, and virus detection by PCR or isolation for arboviruses
- Blood meal source identification (human, cattle, or other hosts) by ELISA or PCR
- Entomological inoculation rate (EIR), calculated as human landing rate multiplied by sporozoite rate
Testing Methods
Pre-Experiment Preparation
Rigorous preparation determines both data quality and collector safety. The preparatory steps are as follows:
- Obtain approval from an institutional ethics committee and written informed consent from all volunteer collectors after explaining infection risks and protective measures.
- Provide malaria chemoprophylaxis, relevant vaccinations where available, and medical screening; establish a documented emergency medical response plan.
- Select representative sampling stations, typically paired indoor and outdoor positions at three to five fixed sentinel houses per study site, located away from livestock, smoke, and competing light sources.
- Prepare and calibrate equipment, including mouth aspirators fitted with HEPA filters or battery-powered aspirators, labeled paper cups with nylon mesh covers, torches with red filters, timers, printed data sheets, transport boxes, and cold-chain materials such as ice packs or dry ice.
- Train all collectors in standardized capture technique, hourly labeling, safety rules, and the correct use of protective clothing on non-exposed body parts.
Field Collection Procedure
The standard all-night protocol for nocturnal vectors proceeds through the following steps:
- Commence collection in the first hour after sunset, typically at 18:00, and continue until dawn at 06:00; for diurnal Aedes vectors, sample during the morning and late-afternoon activity peaks instead.
- Seat the human volunteer with the lower legs exposed from the knee downward, or with forearms exposed according to protocol, while the remainder of the body remains fully clothed and protected. Collectors must not use repellents, perfumes, or tobacco during duty hours.
- Capture each mosquito the instant it lands on the exposed skin, using a mouth aspirator or an inverted collection tube, before the mosquito is able to take a blood meal.
- Follow an hourly duty cycle of 45 to 50 minutes of active catching followed by a 10 to 15 minute rest break; two collectors per station should alternate shifts to minimize fatigue-related bias.
- At the end of each hour, transfer all captured mosquitoes into a labeled paper cup; the label must record the date, site, station type, hour interval, and collector identity.
- Provide cotton pads moistened with a 10 percent sugar solution to keep live specimens viable for subsequent infection assays, or freeze cups on dry ice when specimens are destined for morphological or molecular analysis.
- Record temperature, humidity, and weather conditions at each hourly interval throughout the session.
Specimen Processing and Identification
The post-collection processing steps include:
- Euthanize specimens by freezing or brief chloroform exposure and sort them by sex and hour of capture.
- Identify females to species or species complex level using standard morphological taxonomic keys, and confirm members of cryptic complexes, such as the Anopheles gambiae or Anopheles dirus complexes, by PCR assays.
- Grade physiological status as unfed, fed, half-gravid, or gravid, and perform parity determination by examining ovarian tracheole coiling or by the Polovodova dilatation method.
- Store specimen subsets appropriately: desiccated on silica gel for sporozoite ELISA and blood meal PCR, in RNAlater or at minus 80 degrees Celsius for arbovirus detection, and in 70 to 80 percent ethanol for the reference morphological collection.
Data Recording and Analysis
Calculate the human landing rate for each station as the total number of female mosquitoes of each species divided by the number of person-nights or person-hours of collection. Tabulate hourly counts to construct biting rhythm curves, compare indoor and outdoor landing densities, and derive the entomological inoculation rate by combining landing rates with sporozoite prevalence. Report species composition as percentages and apply appropriate statistical models, such as negative binomial regression, when comparing intervention arms, seasons, or sites.
Applications
- Malaria vector surveillance and identification of primary and secondary vector species in endemic regions.
- Evaluation of vector control interventions, including long-lasting insecticidal nets and indoor residual spraying, where changes in landing rates quantify protective efficacy.
- Efficacy testing of topical repellents, spatial repellents, and insecticide-treated clothing following WHO pesticide evaluation scheme guidelines.
- Arbovirus vector studies measuring Aedes and Culex biting pressure in urban and rural settings.
- Vector bionomics research, including host preference, biting time characterization, and assessment of outdoor and residual malaria transmission.
- Calibration and validation of alternative sampling tools such as CDC light traps, human-baited double net traps, and odor-baited traps.
- Practical training in medical entomology, vector biology, and public health field courses.
FAQ
Why is the human landing catch method considered the gold standard?
Because the human volunteer is the actual host, the HLC directly measures the mosquitoes that would bite a person under natural conditions. No mechanical trap fully reproduces human odor, body heat, and visual cues, so HLC-derived landing rates remain the benchmark for measuring human–vector contact and for validating every alternative sampling device.
What are the main risks and how are they controlled?
The principal risk is disease transmission through mosquito bites sustained during collection. Established controls include institutional ethics approval, informed consent, malaria chemoprophylaxis, vaccination where vaccines exist, limiting the exposed skin surface, strict hourly rotation and rest periods, exclusion of collectors with allergies or health conditions, continuous medical supervision, and guaranteed access to prompt diagnosis and treatment.
What equipment is required for a standard HLC session?
Essential items include HEPA-filtered mouth aspirators or battery aspirators, mesh-covered paper cups, pre-printed labels, red-filter torches, timers, field data sheets, sugar solution supplies, secure transport boxes, and cold-chain storage for molecular samples.
When should collections be scheduled?
Nocturnal Anopheles and Culex populations are typically sampled from 18:00 to 06:00, whereas diurnal Aedes species are collected during the two activity peaks shortly after sunrise and before sunset. Local pilot observations should be used to refine the exact sampling window for each target species.
Are there alternatives when HLC is not ethically feasible?
Yes. Human-baited double net traps, CDC light traps positioned beside occupied bed nets, BG-Sentinel traps, tent traps, and odor-baited traps can reduce or eliminate direct biting exposure. However, each alternative must first be calibrated against HLC because catch efficiency varies by species, season, and setting.
How are the results reported?
Results are reported as human landing rates in females per person per hour or per night, species composition percentages, biting rhythm curves, parity and infection rates, and, when combined, entomological inoculation rates. All outputs should be presented with site identifiers, station type, sample sizes, and appropriate confidence intervals.