During my field study, I observed that I found more mosquito larvae in dirty ditches under an open sky. Based on my observations, for my mosquito traps, the specific variables I chose to control were centered around the quality of water and trap wall materials. I made 3 traps: A deep ceramic pot with mud, water, sticks, and dead and live plants, a cut water bottle with clear water and black electrical tape wrapped around it, and a shallow, wide plastic dish filled with water and dead vegetation but relatively little other particulates.
After 4 days I see a large change in the pot trap (1) but relatively little change in the plastic bottle (3) and plastic dish trap (2).
After 4 days the pot trap shows significant changes in the contents. The water became significantly less clear over time and shows an abundant presence of mosquito larvae. Mosquito eggs are lining the sides of the pot, but interestingly very few on the multiple sticks and leaves in the pot that stick out of it. I was able to identify the mosquito species as Aedes aegypti which does transmit diseases. There were an average of 44 in my mosquito larvae samples.
Mosquito larvae (Aedes Aegypti) under a microscope
The 3 samples taken
Plastic dish trap
The plastic dish trap showed no signs of mosquito presence. The most significant change was a change in the color of the water from relatively clear to a darker color, possibly tinted by dust and vegetation. Despite keeping it in a flower bed where I expected a greater relative abundance of mosquitos than the more desolate area where pot (1) was positioned, there was nearly no evidence of other insects in or around it.
The plastic bottle trap was near identical, with little changes and having slightly less water in it before, likely due to the hotter days going into summer. Otherwise, there were no significant changes to mention.
After 1 week the traps have shown no changes besides water level since the 4-day update. The average number of mosquitos has not changed in the pot trap and the other two traps have shown no changes besides an increase in water level due to rain. There are interestingly no signs of pupae in the pot trap and there seems to be a similar number of adults and eggs in the trap. They are, however, not the same eggs and adults as it seems they are in different positions.
After two weeks there is relatively little change to the plastic bottle and dish traps. However, in the pot trap, there are now no mosquito larvae, pupae, adults, or eggs. A hypothesis for this sudden disappearance is that due to rain the previous day, the mosquitoes left or all became adults. I have noticed in mosquito mapping that there are close to no mosquitoes following days where it rains, even in places I have documented larvae to be there. I will need to observe over the next week if more mosquitoes appear. In addition, the plastic bottle trap, besides fluctuation in water level, has shown other dead insects and debris building up in the water.
Insect (likely a sort of fly) inside the
plastic bottle trap
Comparing the three traps there is an indication that "dirtier" water with mud and vegetation attracts mosquitoes more than the clear water seen in the plastic bottle trap. I have observed in MHM that a common behavior for larvae and pupae is to dive down into the water in response to a disturbance and camouflage themselves against the mud at the bottom of a container. These results may point to mosquitoes searching out containers with a dark bottom, which was only found in the pot trap (1).
The contents of each trap, dead and/or live vegetation, mud, leaves, sticks, and small debris had different effects on mosquito larvae counts. What seemed most indicative was that an environment emulating small, swampy ponds with abundant vegetation, mud, and lots of debris attracted larvae the most. In specific the more "dirty" the water is and the less visibility in the water, the more larvae will be present over time.
Precipitation seems to have an immediate effect on mosquito larvae presence. Immediately after rain, the number of larvae, mosquitoes, and eggs would drop to 0 in the pot trap. The other traps lacked mosquito presence and had no change besides water level.
I am not extremely confident in my predictions as to why precipitation may affect larvae presence but I hope to do more research on it. I am curious to find out the influence of the relationship between water quality, temperature, humidity, and light on the breeding of mosquito larvae. What are your thoughts about this? Please share your views in the comments.
About the author: Ishaan is a high school student in New Jersey. Besides being a robotics enthusiast, he loves playing tennis, following Formula 1 races, and painting. His 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/). Ishaan shared his experience this summer in this blog post.