This post evaluates the claim on the label, “mosquitoes will gather near them”. Per the company, it is the first step in how the device kills mosquitoes. I.e., the device needs to attract mosquitoes if it is going to work.
Evaluating the claim
I used a security camera to record activity around the cap area. Here’s a photograph of how I arranged everything:
Below is a 15-second time-lapse to show that small insects such as ants were easily visible, even at night. I think they are Prenolepis imparis, which are 3-4 mm long —mosquitoes are larger and thus would be detectable even in flight.
On the day that began filming (September 2nd, 2020) I counted over a dozen mosquitoes (all Aedes albopictus) landing on my arms and legs within 30 seconds. According to the instruction sheet, the device begins to work instantly, as soon as water is added, so an hour of remote, video observation should be a sufficient amount of time to evaluate the attraction claim.
I collected continuous footage for over a week, ending observations on September 10th. The mosquitoes were still plentiful on that day.
Aryaprema, V.S., E. Zeszutko, C. Cunningham, E.I.M. Khater, and R.-D. Xue. 2020. Efficacy of commercial toxic sugar bait station (ATSB) against Aedes albopictus. J. Florida Mosquito Control Association 67: 80-83. PDF
Below is a rough reconstruction of the laboratory experiment they conducted. In each of the cages (BugDorm-2120), 100 male and 100 female tiger mosquitoes (Aedes albopictus) were released, then monitored for mortality at 24, 48, and 72 hours.
Below are the cumulative mortality data for the three cages. Result: the Spartan Mosquito Eradicator filled with the provided packet ingredients (treatment) did not result in higher mortality. I.e., there was no evidence the device killed mosquitoes under laboratory conditions.
The researchers also conducted a field experiment using two sites that had large populations of tiger mosquitoes (because of the presence of tires). At each site they deployed five tubes (separated by 4 m), switching whether the tubes were “treatment” or “control” tubes every 2 weeks. A BG-Sentinel trap (without carbon dioxide) was used to quantify mosquito numbers every week.
Below are the weekly numbers of mosquitoes caught in the BG Sentinel traps. Results: there was no evidence that presence of treatment tubes (filled as per company guidelines) reduced the numbers of mosquitoes at the sites.
The scientists concluded that “Both laboratory and field components of our study show that the Spartan Mosquito Eradicator is not effective in reducing abundance of Ae. albopictus.” They speculate that the contents do not attract mosquitoes and that the holes on the device (~3 mm) are too small for mosquitoes to easily reach the fluid inside. They also highlight the need for an experiment to evaluate whether the active ingredient (1% sodium chloride) kills adult mosquitoes. I.e., even if mosquitoes were attracted to Spartan Mosquito Eradicators and could easily get inside, the salt might not be lethal.
Here are instructions for building an indoor mosquito trap using a 2-liter plastic soda bottle. All you do is add some bait (honey, fruit, juice, sugar water, or some nectar-containing flowers) and place in a dark corner of the room. It works because mosquitoes seek out sugar, which they require to fuel themselves. Once inside the bottle they can’t get out.
The above instructions are a modification of a Taiwanese science-fair project that eventually went viral. The differences between the original instructions and mine are that (1) I don’t recommend adding dry active yeast, (2) I suggest sugar sources other than granulated sugar, and (3) I don’t wrap trap in black paper. The omission of yeast is because I don’t think the generation of carbon dioxide is necessary to attract mosquitoes to sugar. In fact, adding yeast likely reduces the attractiveness and causes the trap to fail faster.
The critical part of the original instructions is to deploy the device on the floor in a corner of a room. This is because mosquitoes love to hang out in corners — they are dark and relatively free of desiccating drafts.
The original instructions suggest 50 g (~1/2 cup) sugar and 200 mL (~1 cup) water but the ratio probably doesn’t matter at all. Brown sugar is likely better than granulated (white) sugar because it has more impurities (some of which are volatile). A drop of rose water might make the sugar mixture more attractive.
Make traps with different types of bait to see which ones are most attractive to the species that are local. Anopheles coluzzii, for example, seems to prefer papaya and banana juice over mango juice (Nignan et al. 2020). Other species might prefer oranges. Or, perhaps, durian.
Replace your bait when it stops attracting mosquitoes. Perhaps every four days if you use fruit (Meza et al. 2020).
If you use flowers, opt for ones that have nectar (if you know) and are light-colored. Or stick a small potted orchid inside the bottle — their blooms last for weeks.
So when mosquitoes find themselves trapped inside, they will zero in on whatever you have on the countertops — fruit, puddles of syrup, cut flowers, or even a dirty sponge. I don’t have photographs of mosquitoes eating fruit inside but Justin Yoshida (Thailand) does: on jackfruit, on apple slices, and on eggplant. Mosquitoes indoors are likely not especially picky about fruit type because the option is starving to death. Mosquitoes even fall into juice containers and die, apparently, as one restaurant discovered.
In case you’re skeptical that these traps can actually work, here’s a video by somebody who followed the original (science fair) directions and killed 9-10 mosquitoes in 24 hours:
Why it won’t work outside
Don’t bother using these traps outside (the recommendation of the viral versions). Mosquitoes prefer natural sources of sugar so they will likely ignore anything inside a bottle, regardless of how delectable you think the concoction is. The exception would be if you live in a desert and there are no plants near your house.
The traps will also not work in rooms full of flowering plants or decomposing fruit. Similarly, if your kids spill juice and soda everywhere, the traps won’t work.
Adding toxins to the mix
If you have a house free of small kids and meddlesome pets, you can add bit of boric acid to the solution to create an attractive toxic sugar bait (ATSB) station. Then, when mosquitoes ingest the fluid they will die even if they manage to escape the trap (it can happen). In fact, once you have a toxin in the fluid you can and should just get rid of the funnel part of the trap — its presence is likely a barrier to some mosquitoes even though it’s relatively wide (~2 cm). Instead, cut a 3 cm hole in the side and keep the cap on the bottle. Note that because these devices are indoors you don’t need to worry about the boric acid (or whatever) poisoning the pollinators in your yard.
The above is nicely explained by Andy Lee Graham:
One perk of adding boric acid is that fermentation will likely be slowed down, extending the life of your fruit juice. Note that fermentation will occur even though you haven’t added any yeast. Fungal spores are present everywhere.