Why a Bed Net Protects Against Malaria, But Not Against Dengue

"Mosquito" gets treated as one insect with one set of habits, but the species that actually spread disease don't even agree on what time of day to bite. That mismatch has a real, practical consequence: a bed net, one of the most effective public health tools ever deployed against malaria, does comparatively little against dengue — not because nets don't work, but because the mosquito spreading dengue is rarely active at the hours anyone is actually using one.

A daytime biter and two nighttime biters

Aedes aegypti, the primary vector for dengue and chikungunya, is a daytime biter by habit. The US CDC's dengue fact sheet is specific about this: Aedes aegypti bites primarily during the day, with activity peaking roughly two hours after sunrise and continuing through several hours before sunset. It can bite at night too, but mainly in artificially lit areas — a 2020 study found that exposure to light at night roughly doubled the mosquito's nighttime feeding rate compared to fully dark conditions, meaning the day-biting pattern is strong but not absolute, especially indoors where lights stay on after dark.

Anopheles mosquitoes, the genus responsible for malaria transmission, run on close to the opposite schedule. Public health guidance is built around the fact that most Anopheles species are crepuscular or nocturnal feeders, biting mainly from dusk to dawn — which is precisely why insecticide-treated bed nets are such an effective malaria intervention: they intercept the mosquito during exactly the hours it's most active and most likely to be feeding on someone asleep indoors. A field study in Goa, India, using human-bait landing catches across 85 nights and 14 localities, tracked this directly in Anopheles stephensi and found the exact nighttime pattern shifted with the season — a distinct early-morning peak in the pre-monsoon months, versus a more bimodal pattern concentrated in the 8pm-to-midnight and 3am-to-6am windows during the monsoon. Either way, the activity stayed solidly nocturnal, well after most households are asleep for the night.

Culex mosquitoes, the vector for West Nile virus and (outside the Americas) Japanese encephalitis, follow a broadly similar dusk-to-dawn pattern to Anopheles, with the CDC noting adult Culex mosquitoes are most active from dusk to dawn. Some regional studies on Culex-borne disease have found secondary biting peaks later in the night rather than a single dusk-only spike, but the broad distinction from Aedes's daytime habit holds consistently across sources.

Why this actually changes what protection works

The practical upshot is a genuine mismatch between a very effective malaria tool and dengue prevention. This doesn't mean a bed net offers zero protection against dengue — but the core rationale for why nets work so well against malaria (catching a nocturnal mosquito while a person is asleep and stationary) simply doesn't transfer to a mosquito that's mostly done biting hours before anyone goes to bed. A household that treats a bed net as its main defense against mosquito-borne disease is well protected against a nighttime biter and comparatively exposed to a daytime one.

That's also why dengue-prevention messaging looks so different from malaria-prevention messaging at the household level. Covering water storage containers, clearing standing water in flowerpot saucers and discarded containers, using repellent during the day rather than only at bedtime, and screening windows and doors all target a mosquito that's active during normal waking hours and breeds in small amounts of clean water close to where people live — a genuinely different set of habits than the swamp-adjacent, dusk-active malaria vector that bed nets were designed around.

• Aedes aegypti (dengue, chikungunya) bites mainly during the day, peaking roughly two hours after sunrise through several hours before sunset — though artificial light can meaningfully increase nighttime biting.
• Anopheles mosquitoes (malaria) are predominantly dusk-to-dawn or nocturnal feeders, which is exactly why insecticide-treated bed nets are such an effective malaria intervention.
• A Goa, India field study tracking Anopheles stephensi across 85 nights found a consistently nocturnal pattern — an early-morning peak before the monsoon, shifting to late-evening and pre-dawn peaks during it — well into the time most households are asleep.
• Culex mosquitoes (West Nile virus, Japanese encephalitis) are also mainly dusk-to-dawn biters, broadly grouping with Anopheles rather than Aedes on timing.
• Because of this mismatch, daytime-focused measures — repellent, covering water storage, screening — matter more for dengue prevention specifically than nighttime tools like bed nets do.

None of this changes the basic logic of mosquito control that applies across every species: eliminate standing water, and reduce the places mosquitoes can breed near a home. What changes is which hours of the day are actually worth the extra vigilance, depending on which disease is the real concern in a given area. Sevacorp offers a free inspection for anyone wanting a closer look at what's actually breeding mosquitoes on a property, regardless of which species is involved.

• Sources:
• US Centers for Disease Control and Prevention — Aedes aegypti fact sheet — https://stacks.cdc.gov/view/cdc/31032/cdc_31032_DS1.pdf
• US Centers for Disease Control and Prevention — "Culex Mosquitoes" — https://www.cdc.gov/mosquitoes/about/culex-mosquitoes.html
• World Health Organization — "Malaria" fact sheet, on vector control measures including insecticide-treated nets — https://www.who.int/news-room/fact-sheets/detail/malaria
• Korgaonkar, N.S. et al. (2012) — "Mosquito biting activity on humans & detection of Plasmodium falciparum infection in Anopheles stephensi in Goa, India", Indian Journal of Medical Research, 135:120-126 — https://ijmr.org.in/mosquito-biting-activity-on-humans-detection-of-plasmodium-falciparum-infection-in-anopheles-stephensi-in-goa-india/
• Rund, S.S.C. et al. (2020) — American Journal of Tropical Medicine and Hygiene, on artificial light and Aedes aegypti nighttime biting — https://pmc.ncbi.nlm.nih.gov/articles/PMC7695055