The Human Landing Catch (HLC) field test is the internationally recognized gold-standard technique for directly measuring human–mosquito contact, mosquito landing density, and the field efficacy of repellents and vector control products. By capturing host-seeking mosquitoes as they land on human bait under standardized conditions, this method generates biologically relevant data essential for vector surveillance, disease risk assessment, and product registration. This article presents the technical principles, test items, operating procedures, quality controls, and applications of professional human landing catch field testing services.
Technical Overview
The Human Landing Catch (HLC) method, also referred to as human-bait mosquito collection or the human landing counting technique, is an entomological field procedure in which trained collectors capture or count mosquitoes as they land on exposed human skin. The method exploits the natural host-seeking behavior of female mosquitoes, which locate blood-meal sources through carbon dioxide, lactic acid and other skin volatiles, body heat, moisture, and visual cues.
Because the human volunteer serves simultaneously as the attractant and the measurement reference, HLC provides a direct estimate of the human–vector contact rate, which is the epidemiological parameter most closely linked to pathogen transmission risk. For this reason, HLC is widely regarded as the reference standard against which alternative sampling tools, such as CDC light traps and BG-Sentinel traps, are calibrated. In product efficacy studies, the method allows precise quantification of landing suppression achieved by topical repellents, spatial repellents, mosquito coils, vaporizer devices, and insecticide-treated materials under true field conditions.
Testing Samples
Target Mosquito Species
Field testing can be designed around the ecology and activity rhythms of the dominant local vector species, including:
- Aedes albopictus (Asian tiger mosquito) and Aedes aegypti, the principal vectors of dengue, Zika, and chikungunya viruses, which exhibit diurnal and crepuscular biting activity.
- Culex pipiens complex species and Culex quinquefasciatus, night-biting vectors of filariasis and Japanese encephalitis.
- Anopheles sinensis and related Anopheles species, malaria vectors with dusk-to-dawn host-seeking behavior.
- Armigeres subalbatus and other secondary pest species common in urban and suburban habitats.
Test Products and Formulations
Client-submitted test articles suitable for HLC-based field evaluation include:
- Topical skin repellents containing DEET, icaridin (picaridin), IR3535, para-menthane-3,8-diol (PMD), or oil of lemon eucalyptus.
- Spatial repellent products, including mosquito coils, vaporizer mats, liquid vaporizers, and passive emanator devices.
- Insecticide-treated textiles, clothing, wristbands, and stickers.
- Residual surface treatments and space spray formulations applied within the test environment.
Test Environments
Representative field sites are selected on the basis of documented mosquito activity and study objectives, typically including residential communities, urban parks, schools, construction sites, wetlands and vegetated margins, livestock sheds, waste transfer stations, and international port and border quarantine zones.
Testing Items
Standard HLC field study designs support the following measurement endpoints:
- Landing density index: the number of mosquitoes landing per person per hour, calculated separately by species, sex, and time interval.
- Species composition and population structure of collected adult mosquitoes.
- Physiological age grading of female specimens, including unfed, blood-fed, half-gravid, and gravid categories.
- Diurnal and nocturnal landing activity rhythms across defined observation windows.
- Complete Protection Time (CPT) for repellent products, defined as the elapsed time from product application until the first confirmed landing or bite event that meets the failure criterion.
- Percentage landing inhibition and repellency rate relative to paired untreated controls.
- Effective duration and residual performance of treated materials under field exposure.
- Knockdown and 24-hour mortality of captured specimens for products with toxic modes of action.
- Optional laboratory follow-up, including pathogen screening of collected mosquitoes for dengue virus, malaria parasites, or Japanese encephalitis virus.
Testing Methods
Study Design and Site Preparation
Test sites are screened during a pre-study survey to confirm adequate baseline landing pressure, and sampling stations are positioned with standardized distances from larval habitats, vegetation, and competing human or animal hosts. Environmental parameters, including temperature, relative humidity, wind speed, and illuminance, are recorded at every observation interval to support interpretation.
Human Bait and Volunteer Management
All protocols are reviewed by an ethics committee and executed under documented informed consent. Volunteers undergo health screening, abstain from alcohol, tobacco, perfumed products, and other confounding substances for a defined period before testing, and wear standardized clothing. In repellent efficacy studies, a defined skin area, commonly the forearm from wrist to elbow, is treated at the labeled application dose while the remaining skin remains protected. Collection staff use mechanical aspirators or shielded mouth aspirators to remove mosquitoes immediately upon landing and before blood feeding, minimizing bite exposure.
Standard Collection Procedure
Observations are scheduled within the peak activity windows of the target species, for example early morning and late afternoon periods for Aedes surveillance and the first hours after sunset for Culex and Anopheles studies. A common protocol consists of 15-minute collection intervals alternating with 15-minute rest periods, sustained for two to four hours per session and replicated across multiple days and stations to satisfy statistical power requirements. For repellent trials, treated and untreated limbs or volunteers are exposed in rotation to cancel positional bias, and exposure continues until the protection failure criterion, such as two confirmed landings or the first bite, is reached.
Data Processing and Statistical Analysis
Landing density is expressed as mosquitoes per person-hour, and treatment effects are quantified as CPT medians with confidence intervals or as percent reduction against the concurrent control using Abbott-style correction where appropriate. Species-level identifications are confirmed in the laboratory using standard morphological keys, and results are analyzed with appropriate parametric or non-parametric tests, survival analysis for protection time, and documented quality assurance records.
Applications
- Routine vector density surveillance supporting dengue, malaria, and Japanese encephalitis prevention and control programs.
- Field efficacy substantiation for repellent and household insecticide registration, label claims, and market entry across regulatory jurisdictions.
- Post-outbreak evaluation of emergency vector control interventions such as space spraying and larval source management.
- Performance benchmarking of commercial products under realistic climatic and mosquito-pressure conditions.
- Calibration of passive sampling tools, including light traps, gravid traps, and BG-Sentinel traps, against the human landing reference.
- Port health and border quarantine vector monitoring in accordance with international health regulation requirements.
- Academic and public health research on host-seeking behavior, biting rhythms, and vectorial capacity.
FAQ
Q: Is the human landing catch method safe for volunteers?
A: Safety is managed through ethics-approved protocols, pre-exposure health screening, immediate capture of mosquitoes before biting, protective coverage of untreated skin, session duration limits, medical supervision, and, in endemic settings, vaccination or chemoprophylaxis as medically indicated.
Q: How does HLC differ from trap-based surveillance?
A: Traps estimate relative mosquito abundance, whereas HLC directly measures landing on a human host, the parameter most relevant to disease transmission and personal protection product performance. HLC is therefore used as the reference method for validating trap performance.
Q: What is Complete Protection Time and why does it matter?
A: Complete Protection Time is the duration after product application during which no confirmed landing or bite occurs. It is the core efficacy claim for topical repellents and is determined through timed HLC exposure against untreated controls.
Q: Which standards and guidelines govern HLC field testing?
A: Studies are designed in accordance with WHO guidelines for efficacy testing of topical and spatial repellents, WHO vector surveillance manuals, applicable national vector density surveillance standards, and regional pesticide registration data requirements.
Q: How long does a typical field study take?
A: A surveillance landing survey typically requires several consecutive evenings or activity windows per site, while a repellent efficacy study generally involves multiple treatment and control replicates conducted over one to two weeks to capture full protection time distributions.
Q: Are ethical alternatives available when bite risk is unacceptable?
A: Yes. In high-transmission settings, the human-baited double-net trap and other barrier configurations can separate the volunteer from direct mosquito access while preserving human odor attraction, and these variants can be offered as a risk-mitigated modification of the standard protocol.