Does switching the lights off help avoiding mosquitoes?

Question

This Travel Stack Exchange answer states something I long considered for granted (probably because my parents told me so): if you want to avoid mosquitoes, switch off the light.

4. Opening the window only works well if the temperature on the outside is lower than on the inside. To avoid mosquitos, you will need to switch the light off once the sunlight is gone or your room is pretty high up, so mosquitos don't reach your altitude.

Here is an article supporting this, quoting a certain Mike McLean working for the government organization 'Metropolitan Mosquito Control District'.

Nearly all insects are attracted to some form of light. It’s called phototaxis.

...

McLean added that mosquitoes are attracted to light in a certain spectrum.

Insects like UV light, but don’t pick up on yellow or red lights. So, a lot of people put yellow lights on their front porch to keep bugs away.

However, this site states the opposite, and claims they're guided by CO₂ instead:

Artificial light on the other hand (such as those found on our porch and on the streets) is so close that bugs are unable to maintain a good angle for clear navigation and this confuses them!

Put it simply, mosquitoes aren't really attracted to light.

They are just trying to find a logical sense of their environment through it. Mosquitoes are MORE attracted to carbon dioxide because that's what their hosts usually emit, making it easy to find their food source.

I seem to recall a biologist being interviewed on the radio which claimed something similar as well, that it doesn't matter whether you turned off the lights, the insects will find you by your smell. This article would support that:

Female mosquitoes are known to rely on an array of sensory information to find people to bite, picking up on carbon dioxide, body odor, heat, moisture, and visual cues.

Since I like to keep doors and windows open in the summer evening to cool down the house, and this week I had to kill a few mosquitoes already, this claim has a practical side as well. Will it help if I keep the lights off? (I'm based in the Netherlands, if it matters for the type of mosquito.)

Answer 1

Q Does switching the lights off help avoiding mosquitoes?

In short: "yes",
but with so much caveats that ultimately the needed qualifier is "but it's not effective".

The caveats are: not all species at all stages of life-cycle. Even within the same species some inconsistent behaviours regarding light seeking or avoidance have been described. Some are strongly attracted to light (positive phototaxis), some less so, some seem to avoid light (negative phototaxis).

As the most pestering behaviour seems to be blood seeking from hosts: that is indeed not guided by the lights but by aromas and CO₂, which while they orient themselves visually they also find their hosts in a dark night.

Lights at night do attract a range of insects, including some mosquitoes, which then can see you better; it is therefore still a good idea to keep the lights off. But there are additional and better methods available. It's only best to keep the lights off when no barrier prevents the insects from entering a house. Or keeping the lights on on the outside to guide the phototaxis seeking insects to the outside or into traps there.

Physical barriers are the only reliable way to prevent them from entering anyway. These are the tools of choice for keeping a house mosquito-free.

As is noted in

Proofing dwellings against the entry of mosquitoes is one of the oldest techniques used to reduce nuisance biting and disease transmission (Ross 1913). However, although such techniques and details have become part of vernacular architecture around the world, they have received little critical attention and evaluation. _{–– Norbert Becker et al (Eds): "Mosquitoes and their Control", Springer: Heidelberg, Dordrecht, ²2010.}

The above book is very comprehensive and skips over 'lights' almost entirely. But:

The closest resemblance of the body shape is found within the families of slender, long-legged crane flies (Tipulidae) and non-biting midges (Chironomidae), the latter often being mistaken for mosquitoes, especially around artificial lights at night.

In fact some mosquitoes seem to prefer a 'no light at all' situation when feeding, although they still exhibit certain aspects of positive phototactic behaviour in an experimental setting:

We expected to see attraction to LEDs during this stage. That mosquitoes did not exhibit higher preference for LEDs than for the unlit control is surprising and suggests that light alone is a poor attractor or that our experimental design needs to be refined.[…]
These observations suggest previtellogenic An. quadrimaculatus prefer no light to all other wavelengths during host location, or when feeding. Our findings differed from Burkett and Butler (2005) in that mean contact seconds were highest with green diodes than all other treatments.[…]
In all trials, mosquito contact seconds for vitellogenic An. quadrimaculatus were never higher for the unlit control than lit LEDs. These findings suggest a possible phototactic association with parous mosquitoes.[…]
Significantly more parous An. subpictus were captured in light traps (86.6%) than cattle-baited samples (69.6%).[…]
Utilizing exact wavelengths would enhance the attraction of gravid traps to specific mosquito species from longer distances, while the oviposition site of the trap remains unlit. This application could improve population monitoring methods for medically important species known to exhibit photophilic behavior, while maintaining dark oviposition sites.[…]
Few significant differences in wavelength preference were observed among previtellogenic and vitellogenic An. quadrimaculatus. Previtellogenic mosquitoes were in contact with red LEDs significantly longer than vitellogenic mosquitoes, while vitellogenic mosquitoes contacted blue LED significantly longer than previtellogenic mosquitoes. These findings demonstrate the effects of physiological development on mosquito wavelength preference. During the previtellogenic stage mosquitoes are host seeking, thus utilizing specific visual parameters to locate a blood meal (Bidlingmayer 1994). However, in the vitellogenic stage, mosquitoes are in search of an oviposition site and are possibly sensitive to alternative visual cues (Allan and Kline 2004). Our results offer additional evidence of behavioral differences between reproductive stages.
_{–– Michael Thomas Bentley: "Behavioral Phototaxis Of Previtellogenic And Vitellogenic Mosquitoes (Diptera: Culicidae) To Light Emitting Diodes", Dissertation, University Of Florida, 2008. (PDF)}

Asking for 'lights and mosquitoes' is really broad. Guessing that Aedes vexans is most common pest in the Netherlands as well, it still leaves room for quite a number of different species and resulting different behaviours. What is the goal here? Only avoid being bitten, not seeing them swarming? The sound can be nuisance as well, as can be providing them a non-blood food, resting or oviposition sites.

Mosquitoes can be a nuisance in quite a few ways other than stinging for blood. Only females about to lay eggs do that anyway, so CO₂ seeking is not the only behaviour to control and blood not their only food source. In fact sugar water (nectar, etc.) is the meal of choice for both sexes, most of the time.

Different species at different stages of their life-cycle exhibit different attraction or avoidance behaviour regarding light sources. Some adult mosquitoes prefer different wavelengths, but that is almost irrelevant for indoor living space lighting, which usually includes a broader range of wavelengths.

What to employ in traps would be

Alanine, Ammonia, Beef Boullion, Cholesterol, Cystine, Glutamic Acid, Glycerin, Hemoglobin, Oleic Acid and Benzoic Acid, Peptone, Phenylalanine, Sugar solution, Tyrosine, Urine, Vaseline, CO2, Lactic acid, Octenol, Sweat and other skin emanations

To repel them:

penny royal, pipe smoke, chloroform

from: John VanDyk: "Mosquito Hostseeking Bibliography", Iowa State University. and Mosquito Host-Seeking: a partial review

But the list of plant-derived essential oils is quite long. Those either really repel the insects or just interfere with their sensory system for target acquisition is quite long; smelly, and even nice smelling plants, seem to be a plus:

EOs are good candidates as repellent agents since they are capable to deter mosquitoes from flying to and landing on skin and sucking blood by acting locally or at a distance. This property is related to the chemico-physical characteristics of EO constituents such as their high volatility. For long time, the only repellent available on the market was DEET (N,N-diethyl-m-toluamide), but in the last decades, several EO-based repellents for applications to human skin have been introduced. One of the first EOs used for this scope was that of lemongrass (Cymbopogon citratus (DC.) Stapf) often mixed with that of peppermint (M. x piperita). Generally, the repellency of EO constituents increases as the number of methyl groups in the side chain of the molecule increases. As an example, peppermint EO protected from An. annularis, An. culicifacies, Ae. albopictus and Cx. quinquefasciatus with efficacy comparable to that of Mylol, a commercial mosquito repellent. M. spicata L. EO provided protection against flights of An. stephensi. Repellent effects may be given by either major or minor con- stituents of EOs.
_{–– Filippo Maggi & Giovanni Benelli: "Essential Oils from Aromatic and Medicinal Plants as Effective Weapons Against Mosquito Vectors of Public Health Importance", (p69–129), in: Giovanni Benelli & Heinz Mehlhorn (Eds): "Mosquito-borne Diseases Implications for Public Health", Parasitology Research Monographs 10, Springer Nature: Cham, 2018. (DOI)}

S. J. Holmes: "The Reactions Of Mosquitoes To Light In Different Periods Of Their Life History", Journal of Animal Behavior, 1(1), 29-32, 1911.

Masami Shimoda & Ken-ichiro Honda: "Insect reactions to light and its applications to pest management", Appl Entomol Zool, 2013. DOI 10.1007/s13355-013-0219-x

M. W. Service: "Mosquito (Diptera: Culicidae) Dispersal – The Long and Short of It", J. Med. Entomol. 34(6): 579–588, 1997.

Frédéric Baldacchino et al.: "Control methods against invasive Aedes mosquitoes in Europe: a review", Pest Manag Sci 2015; 71: 1471–1485. DOI 10.1002/ps.4044

Michael T. Bentley et al.: "Response Of Adult Mosquitoes To Light-Emitting Diodes Placed In Resting Boxes And In The Field", Publications from USDA-ARS / UNL Faculty. 997, 2009.

Daniel L. Kline: "Traps and Trapping Techniques for Adult Mosquito Control", Journal of the American Mosquito Control Association, 22(3):490.-496, 2006

As mosquitoes use all their senses to acquire their targets it is difficult to highlight just one input system as "that's it". As a general outline for 'mosquitoes', without focus on a particular species:

An elemental aspect of mosquito vectorial capacity is the blood meal, during which pathogen transmission occurs and which is required by all anautogenous mosquitoes in order to obtain a rich source of protein and other essential components to complete oogenesis. To accomplish this, females (males do not blood feed) have developed a suite of complex host-seeking behaviours to locate and select a potential blood meal host. Primarily, the location of the host is based on olfactory, visual and thermal stimuli (Fig. 2). Females possess numerous classes of antennal and other types of chemosensory receptors that respond to host odours. The host-seeking process may differ within species depending on the season and the availability of certain hosts. However, it can usually be divided into several distinct phases:

1. Nonoriented ranging flight behaviour that enhances the likelihood of the female coming into contact with stimuli derived from a potential host. These stimuli are typically volatile host-derived odorants that are known as kairomones (as they benefit only the blood meal seeking mosquito receiving these signals), which are detected by the female mosquito’s olfactory system.
2. Oriented host location behaviour resulting from long-distance, olfactory-based contact with host stimuli. Typically, the concentration of these stimuli increases as the mosquito and host come closer together. Interaction or synergism of the components of the host odour in attracting a given species is a very complex process that developed in the course of evolution between the insect and the target organisms. The female mosquito flies upwind in a zigzag pattern that holds the mosquito within the plume and brings it closer to the odour source (Dekker and Card e, 2011).
3. Selection and directed attraction to a suitable candidate host, once the female has identified it in her immediate vicinity. While still largely olfactory driven, as distance to host diminishes, the role of visual, thermosensory and other stimuli increases. The compound eyes serve to discriminate between form, movement, light intensity, contrast and colour. Mosquitoes respond particularly to blue, black and red colours, whereas least attraction is caused by white and yellow; they can easily detect temperature differences of 0.2°C, and water vapour in short-range orientation–attraction may also play a role (Lehane, 1991).
4. Alighting upon the potential host provides still higher concentrations of volatile kairomone, as access to low volatile odorants that can only be received at close range, direct contact to gustatory cues as well as heightened thermal and visual signalling.
5. Probing involves direct contact by the labellum, stylets and other mouthparts of female mosquitoes to activate mechanosensory as well as chemosensory pathways that play critical roles in the successful completion of the blood meal.

Mosquitoes differ in many aspects of their feeding and resting (the period during which blood meals are digested and oogenesis is completed) behav- iour due to species-specific sensory adaptations. These characteristics include those that mainly feed/rest indoors (endophagic/endophilic) or out- doors (exophagic/exophilic). Ornithophily is expressed when females prefer to feed on birds, zoophily is used when they feed on other animals (zoophilic species) and the term anthropophily is used when they prefer to feed on humans (anthropophilic species). It is altogether reasonable to speculate that, along with visual cues, a broad range of chemo-, thermo- and mechanosensory inputs provide salient information to shape many, if not, all aspects of these critically important characteristics of the mosquito lifecycle. More importantly:

^{Graphic illustrating the sensory cues used by mosquito vectors to target human hosts depicting visual cues, CO2, odours, body heat and nonvolatiles.}

The visual system comes into play once the mosquitoes are within 5–15 m of humans. Interestingly, visual-guided movement is heightened by the detection of CO2, but only in females. This odour-driven modulation takes place even if the CO2 precedes exposure to the visual cues by several seconds. It appears that the CO2-induced increase in attractive to visual cues provides a mechanism to enhance the likelihood of approaching warm objects, such as human skin. Thus, visual, olfactory and thermal stimuli derived from human hosts all appear to operate synergistically.

_{–– C. Montell & L.J. Zwiebel: "Mosquito Sensory Systems" (p 293–332) in: Alexander S. Raikhel (Eds.): "Progress in Mosquito Research", Advances in Insect Physiology 51, Academic Press: London, Oxford, 2016. (archive.org)}

Curiously, Culex pipiens is generally repelled by light when winter is coming, but that is only of use for denying them shelter, not bites.

One species with opposite behaviour is Ochlerotatus (Ochlerotatus) caspius

They often bite during the day and night, but usually most actively search for a blood meal at dusk. Females are repelled by the lights of standard CDC miniature light traps.
_{(–– Becker, 2010.)}

But whether it's positive or negative phototaxis for this species seems to be a problematic goal to generalise:

Culex p. pipiens showed the greatest attraction, and Cx. p. quinquefasciatus the least. Hybrids were attracted more than quinquefasciatus but less than pipiens. […]
The results point to what may characteristic behavior, but since the mosquitoes were of uniform age (5-6 days) and only nulliparous females were tested, further observations will be required to determine whether members of the complex of other ages and physiological states exhibit similar response patterns. The frequency with which differences in attraction to light characterize different populations of the same mosquito species is not known, but the phenomenon is certainly not unique to Cx. pipiens. In tests in village huts in Nigeria, for example, Service (1970) found that an ultraviolet fluorescent light source was more attractive to Anopheles gambiae sensu lato and An. funestus Giles than a white fluorescent lamp of the same wattage. In Kenya, however, the superiority of the UV lamp for collection of these species was not evident in similar tests. Another example is provided by Anopheles albimanus Wiedemann. In laboratory tests females of this species from Panama and Colombia were more strongly attracted to a white fluorescent lamp than to an ultraviolet lamp of equal wattage, but the same species from El Salvador and Haiti reacted more positively to the UV source (D. P. Wilton, unpubl. data).
_{–– Donald P. Wilton: "Light trap Response and the DV/D Ratio in the Culex Pipiens Complex (Diptera: Culicidae)", J. Med. Entomol. Vol. 18, no. 4: 284-288 31 July 1981.}