I decided to test the impacts of fertilizer on mosquito breeding habitats.
Background:
I live in the Tampa Bay Area in Florida, and a major issue facing our ecosystems is fertilizer entering our waterways from runoff after people fertilize their lawns before it rains. This can lead to major algae blooms, like red tide, which are harmful to the rest of our marine organisms. Just last year, there was a particularly dangerous bloom that led to a fish kill where our waterways were littered with millions of dead fish.
However, the Tampa Bay Area contains more than just marine ecosystems. We have plenty of freshwater lakes, creeks, and puddles along with brackish water, estuaries, and mangrove swamps. What these places all have in common is that they are much better mosquito breeding habitats than the Tampa Bay. I wanted to know more about how fertilizer surface runoff effects our mosquito habitats.
Hypothesis:
I think there will be more mosquito larvae in habitats with more fertilizer. Other organisms, like algae, will grow better in habitats with more fertilizer, and mosquito larvae will eat them!
Experiment, take one:
I took four plastic cups and added 0, 1/8, 1/4, and 3/8 tsp of fertilizer to each one. Then, I added 1/2 tsp sugar to each one as bait (BAD IDEA). I filled all the cups so they each held 3/2 cup of solution. I refilled the cups to the fill line every day to maintain the concentrations, keeping them under the shade of my front porch.
After two weeks, I had zero mosquito larvae.
I did, however, find about 10 or so of these guys in the cup with 1/8 tsp fertilizer:
[I apologize for the poor camera quality. I have the old iPhone SE.] If anyone knows what these are, please let me know. I think they're freaky and ugly and yucky, but if someone knows what they are, I'd like to know.
They were each about 5-6 mm long and very squirmy. They liked to gather up around the popsicle stick.
Problems with this experiment:
After a while, a film had built up on top of the traps with fertilizer. There was mold and algae and it was really icky. I think this had to do with the sugar and the fertilizer concentrations.
The concentrations of fertilizer were just not realistic. On the box, the directions said to mix a couple teaspoons with a gallon of water. I was using concentrations that were stronger than the intended concentration of regular fertilizer! This was not a good representation of water impacted by runoff, which would be far more diluted.
The volume of water was also way too low. Mosquitoes were not interested in my traps whatsoever. A few days before I started my experiment, I emptied out our fountain (a couple meters to the Northeast of where I set up my traps) which held a few gallons of water and had hundreds of mosquito larvae in it. I couldn't move my traps to this spot because it isn't in the shade and it rains like crazy here.
Experiment, take two:
I got four buckets and added 0, 1, 2, and 3 tsp [not metric :(] of fertilizer to each one. I filled them each up with 10 L [metric!!! :)] of tap water from a garden hose. I did NOT add sugar this time. I just set this up yesterday, so I haven't seen any mosquito larvae yet.
If anyone has any suggestions for me, please tell me!!! I want larvae :(
UPDATE: 7/6/22
I forgot to mention that I cut up some pieces of palm frons into mostly-even 50ish cm chunks and put one in each bucket to give the mosquitos somewhere to lay their eggs.
After a week, I found 250 mosquito larvae in the bucket with two teaspoons of fertilizer!!! Yay science!!!
I was unable to classify the larvae through the GLOBE Observer App because I couldn't tell if there were any teeth, but they all looked like this (I put them in alcohol to kill them):
I dumped the buckets - at an appropriate time so as to not cause fertilizer runoff - to kill the larva :) I refilled them all and set them all back out.
I also noticed that the water with fertilizer had turned from blue to greenish in color. I wish I took a picture. I'm guessing that some algae grew. If my hypothesis was correct, the larvae were feeding off this algae. To keep my experiment consistent, I am completely resetting the buckets each week with new water and fertilizer.
So far, I've had 0 larvae in the buckets with 0, 1, and 3 tsp of fertilizer and 250 in the bucket with 2 tsp of fertilizer after one week. While this data doesn't definitively show a correlation between fertilizer pollution and mosquito population, it tells me that my experiment is working!! In the coming weeks, I might get more data to establish a correlation.
Also, if anyone knows what type of mosquito larvae I got, please tell me!
UPDATE: 7/13/22
I got a lot of more data this week! Three of the buckets had larvae. The experiment seems to be running quite smoothly, and we may even use my data in our group project!
This is the data for this week:
Fertilizer: Larvae Count: 0 tsp 13 1 tsp 0 2 tsp 19 3 tsp 112
This is the total larvae count for both weeks combined:
Fertilizer: Larvae Count: 0 tsp 13 1 tsp 0 2 tsp 269 3 tsp 112
While this doesn't show a definitive linear correlation between fertilizer levels and mosquito population, it still looks like there were more larvae in general in the buckets with a higher concentration of fertilizer. That being said, for more confident results, I should wait a couple more weeks to really make sure this is an actual trend.
The larvae in the buckets with 0 and 2 tsp fertilizer had tail sections that looked like this:
The larvae in the bucket with 3 tsp fertilizer had tail sections that looked like this:
I could classify neither species through the GLOBE Observer App because I didn't see any teeth on the syphons.
This time, I did photograph a sample of the water before and after a week went by for the 3 tsp fertilizer so you could see the difference:
Before:
After:
The water is noticeably greener, and I believe this is a result of algae growth. Because mosquito larvae feed on algae, I think that, after more trials, the shape of my larva data will look more linear.
Final Update: 7/21/22
This will be my final blog update, but my experiment is still up and running for our team research project. We are trying to establish a connection between fertilizer runoff and West Nile virus cases, and my experiment will be used to show an increase in mosquito populations in areas with greater fertilizer pollution.
I sat down for my second-to-last larvae count in front of my garage with my buckets, isopropyl alcohol, a sour cream container, its lid, a pipette, my microscope, and some chicken and honey and collected some data.
I scooped out water from the bucket into the sour cream container and used the pipette to move the larvae from there onto the lid until the bucket was empty. I poured some alcohol in the lid and looked at the larvae under the microscope.
I was finally able to sort the larvae into Aedes, Anopheles, and Culex because apparently there WERE teeth on the syphons (Thank you, Dr. Low!). Here's the data I've gathered so far:
RESULTS:
The table at the top is the total larvae count for both Culex and Aedes, and the two tables below it show the count of just those types. I didn't find any Anopheles, so I didn't include a table for that.
Anyways, here's some graphs I made on Desmos:
Total Larvae Count vs. Tsp Fertilizer per 10 L Tap Water
Larvae Count
Tsp Fertilizer per 10 L Tap Water
The line of best fit clearly shows a positive correlation between fertilizer and mosquito larvae (m = 69.6), but the r value was only 0.6582 (thank you, Desmos!). This is to be expected, as I didn't have a ton of data to throw at it.
Here are the graphs for just Culex and just Aedes:
Culex Larvae vs. Tsp Fertilizer per 10 L Tap Water:
Culex Larvae Count
r = 0.6372
m = 58.6
Aedes Larvae vs. Tsp Fertilizer per 10 L Tap Water:
Aedes Larvae Count
r = 0.7705
m = 11
The data for Culex larvae had a steeper slope, indicating more larvae per unit of fertilizer. However, the data was more spread out, making r smaller and decreasing the certainty of this correlation. On the other hand, the Aedes data had a lower slope value (although still positive) and a higher r value.
CONCLUSIONS:
The fertilizer is definitely increasing the mosquito larvae count for the Aedes and Culex genera, although I have no data on the Anopheles genus. As I've said before, I believe this is because the buckets with more fertilizer grew more algae. This caused more larvae to survive due to less competition for food. That being said, I did end up with small leaves falling into a couple of the buckets at times and had slightly different palm frons in each one, so there was room for error within the consumable nutrients in each bucket.
Some good next steps for this would be more controlled experiments (ie ones that use duplicate wooden planks and have means of keeping out fallen leaves). More data in general would be really helpful in increasing certainty. In further experiments, if there are more steps between fertilizer concentrations, that would also be quite helpful. I'm also interested in measuring the algae content of the buckets after different lengths of time and seeing how this impacts mosquito larvae on a temporal scale.
Further research on this is absolutely necessary because fertilizer runoff is potentially increasing the capacity of vector-borne diseases like Dengue and West Nile virus. This is important when dealing with anything from fertilizing your lawn before a rainstorm to larger industrial nutrient leaks. If more light can be shed on this issue, people can be made more aware about how their actions can affect public health, and maybe more people will be inclined to take action by minimizing their fertilizer/nutrient waste.
About the author: Sarah is from, St. Petersburg, FL. This blog describes a mosquito trapping experiment conducted as part of the NASA STEM Enhancement in the Earth Sciences (SEES) summe r 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/). Sarah shared her experience this summer in this blog post.
