7F Ch4 Cheat Sheet: Mosquito and Disease Surveillance

🎯 Top 5 Traps

1

Surveys measure RELATIVE abundance, not absolute population. The manual is explicit: "These surveys cannot determine the absolute population of mosquitoes." Distractor on the exam is the absolute-numbers framing — surveys show fluctuations and trends, not headcounts.

2

Landing collections measure BITING ACTIVITY — not flight range, not disease activity. The collector exposes skin for 5 to 10 minutes around sundown; mosquitoes are aspirated as they land. Same person/animal/duration/exposure across stations to make trends comparable.

3

NJ light trap = STATIONARY (110V household current, 25W bulb). CDC light trap = PORTABLE (6V battery) — the right answer for REMOTE sites. Easy power-and-portability flip. NJ trap is mounted 5 to 6 feet up, 30+ feet from buildings. CDC trap goes anywhere.

4

Gravid traps target Culex (poorly caught by light/CO2) using WATER WITH ORGANIC INFUSION as the attractant. Distractors include "low-wattage infrared bulb" and "wing-beat frequency transmitter" — both wrong. The female approaches to lay eggs and gets sucked up alive, ideal for virus isolation studies.

5

Dead corvids (crows, ravens, blue jays) are a key WNV surveillance signal. Corvids are highly sensitive to WNV and experience high mortality. Citizen reports of dead corvids and laboratory testing of carcasses indicate active WNV transmission in an area. Live sentinel birds measure seroconversion (antibodies); dead corvids indicate current viral activity.

🔢 Numbers You Must Know

Number

What It Represents

5 to 10 minutes

Designated landing-collection sit period (with skin exposed)

110 volts / 25 watts

NJ light trap power requirement and bulb wattage (stationary, household current)

5 to 6 feet

Mounting height of NJ light trap above the ground

30+ feet

Minimum distance from buildings for NJ light trap placement

1 to 5 nights/week

Operating schedule for NJ light trap

6 volts

CDC miniature light trap and gravid trap battery pack — enables remote use

3 to 6 feet

Standard CDC light trap height (with motorized fan drawing mosquitoes into collection net)

20 to 25 feet

Late-summer canopy height for CDC traps targeting Culex (for WNV testing in bird-feeding mosquitoes)

400 to 500 percent

Increase in overall trap catch when CDC trap is baited with both CO2 and light

20 to 25 percent

Increase in number of species captured when CO2 is added as an attractant

350 ml

Capacity of standard white plastic dipper for larval surveillance

3 to 5 dips

Minimum number of dips at each larval sampling site or station

1 to 2 weeks

Larval inspection interval during the mosquito breeding season

24 per trap per night

Historical New Jersey general-annoyance threshold (NJ light trap, all female species combined)

1 inch

Distance below the gravid trap intake pipe at which water level should be brought

🔀 Easily Confused

Pair / Group

Distinguishing Feature

Initial vs Operational survey

Initial: planning — species ID, breeding sources, habitats, flight range, vector status, recommendations. Operational: continuing evaluation of control effectiveness, population fluctuations, and arbovirus activity throughout the season and across years.

NJ light trap vs CDC light trap

NJ: 110V household current, stationary, 25W bulb, 5-6 ft up, 30+ ft from buildings, fixed-site seasonal data. CDC: 6V battery, portable, 3-6 ft (or 20-25 ft canopy late summer), used in remote areas without power.

Light trap vs Gravid trap

Light trap: light/CO2 attractant, broad species mix, mostly females. Gravid trap: water-infusion attractant, captures gravid Culex females alive — designed because Culex is poorly caught with light/CO2.

Landing collection vs Resting collection

Landing: active sampling — collector exposes skin, sits 5-10 minutes, biting activity index. Resting: daytime inspection of dark/cool/humid shelters where most adults rest — population density index.

Natural vs Artificial resting stations

Natural: houses, stables, privies, culverts, under bridges, hollow trees, overhanging banks, overgrown fields. Artificial: wooden boxes (historically black-out/red-in) or fiber pots — best for species like Culiseta melanura that other methods miss.

Sentinel birds vs Dead corvid reporting

Sentinel birds: live test flock systematically bled to measure viral antibody seroconversion over time. Dead corvid reporting: citizen reports + carcass testing — corvids' WNV sensitivity makes their deaths a real-time activity indicator.

Oviposition trap vs Egg sod sampling

Oviposition trap: container with water and substrate (muslin, balsa wood) — eggs laid just above water line; collects container Culex and tree-hole Aedes. Sod sampling: collect sod from suspected breeding habitat, run through egg separation machine — for Aedes/Psorophora damp-soil eggs.

🪤 Adult Mosquito Trap Quick Reference

Trap Type

Power & Setup

Attractant & Best Use

NJ light trap

110V household current; stationary; 25W bulb; 5-6 ft above ground; 30+ ft from buildings; 1-5 nights/week; photo sensor or 7-day timer

Light. Standardized seasonal density and species composition. Avoid competing light sources and windy areas.

CDC miniature light trap

6V battery; portable; 3-6 ft height (20-25 ft canopy late summer for Culex)

Light, CO2, or both. CO2-only collects almost exclusively females (ideal for virus studies). CO2+light = +400 to 500% catch, +20 to 25% species. Best for remote sites.

Gravid trap

6V battery; lightweight; water level 1 in below intake pipe; dark-colored tray

Water with organic enrichment (infusion). Captures live Culex females approaching to oviposit — ideal for virus isolation and WNV testing.

Oviposition trap

Container (drinking glass to 5-gal bucket); water + substrate (muslin or balsa); drain holes mandatory

Water. Collects eggs of container Culex and tree-hole Aedes (Ae. triseriatus, Ae. japonicus). Substrate replaced weekly (or daily for Culex egg rafts).

📊 Disease Surveillance Components

A complete program monitors all five — each measures a different signal.

Component

What It Measures

Sentinel bird seroconversion

Viral antibody buildup over time within a test flock or wild bird population — systematic bleeding and testing reveals when and where viral activity is emerging.

Vector mosquito infection rate

Pooled mosquito samples (especially Culex) tested for virus. Increases or decreases in infection rate reveal threats.

Dead bird reporting

Especially relevant for WNV. Corvids (ravens, crows, blue jays) are highly sensitive and die from infection — high mortality is a real-time signal of active virus.

Weather patterns

Precipitation and temperatures dictate mosquito populations and shape arbovirus transmission cycles. Higher temps + larger vector populations = more viral amplification.

Human and animal disease incidence

Confirmed clinical cases reveal obvious threats and demands for control. The endpoint of the surveillance pyramid.

💡 Memory Hooks

NJ vs CDC: "NJ for Neighborhood, CDC for Country." NJ light trap is plugged in (stationary). CDC light trap runs on a battery (portable) — for remote sites without power.

Surveys: "Relative, not absolute." You can't count every mosquito. You measure trends, comparing the same trap at the same place over time.

Landing = Biting: Landing collections measure biting activity, not flight range or disease. Same person, same time, same exposure across stations.

Gravid = Culex = WNV: Gravid traps catch what light/CO2 misses. Culex is the WNV vector. Gravid trap pulls live females for virus testing.

Dead corvids: "Crow death = WNV alert." Corvids' high WNV mortality makes their carcasses an active-transmission signal.