SEES 2022: Effect of Alkalinity on Mosquito Abundance

Background: I live in a suburban area around 30 miles south of San Francisco in the West Bay, near the wetlands/the bay. Our county regularly treats the wetland trails for mosquitoes, and they also do aerial treatment, especially in the spring when mosquitoes like to breed.

Many previous literature papers concluded that mosquitoes prefer to oviposit in slightly alkaline water; as such, I predicted that there would be a higher abundance of mosquito larvae in the alkaline water.

To make an alkaline solution, I added baking soda to water; to make an acidic solution, I added aspirin powder. I also tried different baits: liquid fish food, yeast (& brown sugar), and no bait (discussed below).

Previous Attempts & Challenges: 

Attempt 1 (~2 weeks): For the first two weeks, I filled five 5 oz glass Oui yogurt jars 2/3 full with tap water. I filled three containers with 2, 3, and 4 pinches of baking soda (lowest, medium, and high alkalinity, respectively); I filled one jar with one pinch of aspirin powder. Finally, I added two drops of liquid fish food to each and placed the box in the bushes for shade.

Results: In both weeks, I found no larvae and no egg rafts, but there were other small bugs.

Observations @ end:

• I think some of the leftover yogurt merged with the water and created some icky water.
• The jars had different levels of water, with the cleaner water levels lower and yogurt-water higher. It is possible that some animals drank the water or water evaporated since it was pretty hot during those weeks.

Possible Errors & Adaptations:

• Container Size: jars were too small! Many papers show that mosquitoes prefer to oviposit in larger volumes of water/containers.
  • Adaptation: In the second attempt, I increased the bucket size to five gallons
• Yogurt Water: in the fermentation process of yogurt, lactose in yogurt is fermented by bacteria and converted to lactic acid. Mosquitoes are supposedly attracted to lactic acid on humans, but I'm not sure if it's a good breeding condition.
  • Adaptation: did not use yogurt jars in future iterations
• Liquid Fish Food: there isn't much online about whether mosquitoes are attracted to liquid fish food
  • Adaptation: switched baits in future iterations

After two weeks, I eliminated the experiment and began a second one...

Attempt 2 (~2 weeks): I took two five-gallon buckets (one neon orange and one white) and filled each with around one gallon of rainwater. Next, I added one plastic spoonful of baking soda to the white bucket. Then, I added one plastic spoonful of yeast and a stick to each. I placed the containers on different sides of my yard.

Results: 0 larvae, 0 egg rafts; some small bugs in the control/orange bucket

Observations @ end:

• The control water turned dark brown and had a lot of dirt in it since I put it under a tree; the alkaline water turned milky.

Possible Errors & Adaptation:

• Didn't do bait correctly: A few days after I added the yeast, I noticed I forgot to add brown sugar as well, and the fermentation process never started
  • Adaptation: when I noticed this, I added the brown sugar immediately and waited one and a half weeks, but figured nothing was likely to happen; so, I started another experiment (my current one)
• Bait (why I chose nothing for my current experiment): Around a week before we started mosquito trapping, I found mosquito larvae in a black, half gallon plastic container in the bushes in my backyard while looking for a table tennis ball. The container was accidentally filled with water when the sprinklers turned on; therefore, I didn't use bait in my current experiment since I figured it would do fine without (which it did!), and bait was too much of a hassle before.

Current Experiment (~2 weeks, ongoing): Using the same two classic five-gallon buckets from Attempt 2, I filled each with one gallon of hose water, and I did not use bait. In the white bucket, I added one spoonful of baking soda to make the water more alkaline. In the orange bucket, I did not add anything (control). I then placed the buckets in the bushes with one metre separating them.

Results: In the white bucket, there were around 200 larvae and seven egg rafts. In the orange bucket, there were around 100 larvae and two egg rafts.

Assuming that each egg raft had 100 larvae, there was a threefold increase in larvae in the alkaline water (300 vs 900)!

I also found a dead, big bug that looked like a tick (I hope and believe it wasn't actually though), a dead fly, and a young, still transparent rat-tailed maggot (which I found terrifying).

Pictures:
One of the egg rafts.

A mosquito larva-- GLOBE app identified it as Aedes albopictus, but I think it looks more similar to Aedes aegypti (both are invasive).

Their mother died in the water.

Close up of mosquito head and tail. I think I broke its tracheal trunk but oh well it would've died someway 😅. I couldn't see the tail too well while trying to identify the species because the camera quality wasn't high enough. I also forgot optical zoom existed, so I saved some larvae in the control water, which I will look at again tomorrow and use another phone with optical zoom for pictures.

Observations, Possible Error, & Future:

• (O) General Habitat: some dirt got in the water and settled at the bottom of the buckets. Other than that, the water seemed to be pretty clean.
• (PE) Bucket Color: since the buckets were different colors, mosquitoes might have preferred one color over the other.
• (PE) Bucket Location: though they were only one meter apart, the orange (control) one was slightly more hidden. The mosquitoes could've seen the alkaline bucket first and just decided to oviposit there before noticing the orange bucket.
• (F) Third Bucket: I also wanted to test whether mosquitoes would oviposit in slightly acidic water, but I wasn't able to find a third bucket of the same size @ home. After I finish the last pictures, I will probably use the same buckets and do control water vs. slightly acidic water to see what happens.

​​​​ ​​​​​​​About the author: Haley O, is a junior at Palo Alto High School, Palo Alto, CA. This blog describes a mosquito trapping experiment conducted as part of the NASA STEM Enhancement in the Earth Sciences (SEES) summer high school research internship. Her virtual internship is part of a collaboration between the Institute for Global Environmental Strategies (IGES) and the NASA  Texas Space Grant Consortium (TSGC) to extend the TSGC Summer Enhancement in Earth Science (SEES) internship for US high school (http://www.tsgc.utexas.edu/sees-internship/). Haley shared her experience this summer in this blog post