Tag Archives: nectar

DIY mosquito trap using a plastic soda bottle

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.

Tips

  1. 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.
  2. 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.
  3. Replace your bait when it stops attracting mosquitoes. Perhaps every four days if you use fruit (Meza et al. 2020).
  4. 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.
  5. If you happen to have a plant with extrafloral nectaries, that’s a great bait that will likely last for a long time (when you’re on vacation, for example). Try a bunch of wild cherry leaves, for example.

Why it works

Mosquitoes are famous for sucking blood, but like many insects they spend most of their lives quietly ingesting sugar from flowers and rotting fruit. For example, here are some mosquitoes nectaring in the middle of the day:

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.

© 2020 COLIN PURRINGTON

Theobroma cacao flower

Here are some close-ups of Theobroma cacao flowers at Longwood Gardens in Kennett Square. The plant is economically important (because chocolate) so people fuss over pollination a lot, but its bizarre floral anatomy is noteworthy regardless of the species’ value. First, here’s a photograph of a stem bearing a developing fruit and a flower:

Longwood Gardens’ meadow, Kennett Square, PA.

The catchiest structures are the pointy red staminodes, stamens that became neutered over evolutionary time, which probably have roles in visual attraction of pollinators (ceratopogonid midges) and in preventing self pollination. The real stamens are enclosed in translucent petal pouches.

According to one scenario I read, the flies first land on the exterior of the pouch, then crawl inside to lap up nectar from minute glands on the adaxial surface near the anthers. During their foraging they get coated with pollen, and some of the pollen gets deposited on the style (small white structure encircled by the staminodes) when they exit the pouch. Here’s a close-up that shows the translucent pouches:

Theobroma cacao anther sacs

Presumably some of transferred pollen is from previous visits at different trees (because most types are self-incompatible). These flies do such a terrible job pollinating that farmers often just do it themselves with paintbrushes and forceps. There’s even speculation that the domestication of T. cacao some 1500 years ago slowly changed the plant enough that the original pollinator(s) (bees?) were lost, with the midges being the only insects still interested in the meager nectar rewards.

The photograph below the “parallel staminodes” variant of the flower.

Theobroma cacao (chocolate tree) flower with parallel staminodes. Longwood Gardens, Kennett Square, PA.

Using mosquitoes’ sweet tooth to control Zika transmission

Now that everyone wants to kill mosquitoes that transmit Zika virus, can somebody please make a transgenic plant that expresses mosquitocidal Bti (Bacillus thuringiensis subsp. israelensis) toxins? Just stick the Bti gene behind a phloem-specific promoter so that the protein gets pumped into the nectar. Then when males and female mosquitoes drink (and almost all do), they die.

White-footed woods mosquito (Psorophora ferox) nectaring on goldenrod flowers.

You could then plant acres of the modified plant nearby towns to protect people from Zika (and anything else transmitted by mosquitoes). The beauty of this method is that you could reduce populations of mosquitoes from an area without spraying, and do so for generations if you modified nectar-producing perennials. I know it’s trendy to dislike GMOs (like vaccines), but I think many people would support them under these circumstances.

And yes, apparently Bti toxins can kill adult mosquitoes (including Aedes aegypti), not just larvae. Klowden and Bulla 1984 demonstrated it, for example. And yes, Aedes aegypti drinks nectar (and probably fruit juice).

Of course, even if somebody had the incentive to make such a plant, it could take a decade to wade through the red tape involved in getting non-regulated status from governments. So if you want to do something today, leave out containers of sugar water (10%) that is laced with Bti (e.g., Mosquito Dunks, which you can buy online or at hardware stores). Maybe add something floral to attract them, too. (A review of olfactory cues suggests that imitation cherry and apple can work. If you don’t have those sitting around, I’d wager a few drops of jasmine flavoring or rose water would work, and those are easily found at local stores.) Even if the Bti doesn’t immediately kill the adult, adults sucking up a big sugar meal can transfer the bacteria to water where they lay eggs, and thus eventually cause the death of any larvae that develop. Note that bees and ants might get interested in your sugar water, but the Bti is completely harmless to them.

And if you don’t want to use Bti, there are plenty of articles on using sugar baits laced with insecticides (e.g., Qualis et al. 2013, Junilla et al. 2015). They really can work: mosquitoes absolutely love sugar and will drink up poisons in the process. These are great if you don’t want to use crop dusters to destroy all insects in the area.

If you have kids and want to entertain them, add food dyes to the sugar bait and then challenge them to find mosquitoes with bellies full of sugar water. For older kids that might be amused by actual science, use two dyes to test attractiveness of two different volatiles (or different sugars). It’s probably rare to recapture one right after a nectar meal, but when distended they reveal gut contents nicely.

FYI, white-footed woods mosquito (Psorophora ferox) doesn’t transmit Zika, but illustrates to the unbelieving that mosquitoes do drink nectar.