Essential Oils Effects on Culex Mosquitoes

Statement of Problem

Malaria, West Nile virus, Dengue fever, Zika virus, and Yellow Fever are mosquito-borne diseases that kill thousands of people each year (Figure 1).

Figure 1. Culex Mosquito

Source: Science News

DDT and DEET are chemicals found in most mosquito pesticides or repellents, but both can be harmful to humans (DEET can cause liver damage, and DDT can cause lung cancer). It is important to find an alternative to DEET and DDT, to protect humans from mosquito- borne diseases without additional side effects that can be detrimental to human health.

Introduction

Mosquitoes are not the direct source of death every year. What cause deaths are the parasites that live on them. The diseases they carry vary, for instance Malaria, West Nile virus, Yellow Fever, and Zika virus, and all of which are fatal to humans (Figure 2). Controlling the mosquito population will reduce the number of mosquito-borne diseases.

DDT and DEET are chemicals found in most mosquito repellent and pesticides. They were made to help humans, but both are harmful to humans’ health.DEET can cause birth defects, liver and kidney damage.

DDT, already banned in the US and most western countries, can cause seizures, infant death, lung and breast cancer.

There are 2 sections of the lab, a physical lab and a previous study on another natural pesticide, San Francisco plant oil. The physical lab uses cinnamon, catnip and citronella oil. The same concentrations where DEET is most effective (between 10% and 30%) were used in this experiment. A study by Jerouen Lumabao showed that the active chemical in the San Francisco plant (codiaeum variegatum) could also kill mosquitos.

My hypothesis is that essential oils such as catnip, citronella, cinnamon and San Francisco plant could be used to replace DEET and DDT to control the mosquito population.

Methodology

All equipment was cleaned with dish soap and all mosquitoes were fed to prevent premature death, and set aside. The essential oil's limiters were taken off and poured into their own cups. The oil's cups were labeled then set aside. A total of 9 cups (3 per each oil) plus a control cup were used in the experiment. To achieve the concentrations of 10%, 20% and 30%, see the chart below for each combination of oil and water (Table 1).

The water was measured through a thin syringe (Figure 3) for accuracy. Each container was labeled with their appropriate names.

A netted enclosure for mosquitoes was prepared on a table with a light source from above. Two cameras were added on top of sealed enclosure.

10 larvae were added to each container using a wide nozzle syringe (Figure 3). All 10 containers were added into the enclosure. Using a thinner syringe, oils were added to the containers using the appropriate concentration levels (Table 1). The syringe was washed in between the different oils. Data recorded in 10-minute intervals.

Results

The experiments were recorded in 10-minute intervals (Table 2).

Subjects in the Catnip and the cinnamon showed minor changes to their movements while cinnamon and control showed none.

20 minutes past and most of the small larvae from the catnip and the citronella died. No deaths from the larger larvae, just less movement. Cinnamon had small movement from the smaller larvae, but the rest were healthy. The control has all healthy mosquito larvae.

30 minutes past and the larvae from the catnip 20% and 30% and all the citronella were all dead. In the containers with Cinnamon, all smaller larvae died, but the more developed larvae were still alive. All larvae in control environment remained healthy. (Figure 5).

At one hour, the larvae in all cinnamon containers were killed. All larvae in the experimental containers, except the control, were dead.

On a separate study, JerouenLumabao dripped a small amount of Codiaeumvariegatum (San Francisco plant. See figure 6) extract to water containing mosquito eggs and larvae. Within 24-hours, the substance containing Codiaeumvariegatum killed both mosquito larvae and eggs. The experiment proved that his hypothesis was correct, Codiaeumvariegatum killed the mosquito eggs and larvae within 24-hours.

Discussion/Conclusion

The results from the lab experiment, revealed two important findings:

1. Even with the lowest concentration, all 3 essential oils used in this experiment killed larvae. However, citronella and catnip oil can kill quicker than cinnamon oil. This shows that although all 3 essential oils could be used to kill mosquitoes, the chemicals inside the oils are different.

2. The stage of larvae effects the speed of the mortality. In the first 30 minutes, the smaller larvae died off first before the larger. Then the pupas, the ones closer to becoming flying mosquitoes, were the hardest to kill. This necessitates treating still water in the beginning of mosquito season while most mosquitoes are in their young larvae stage (Figure 7).

The lab experiment and Jerouen Lumabao’s study supported the hypothesis that essential oils derived from plants (catnip, citronella, cinnamon and San Francisco plant) could be used to replace DEET and DDT to control mosquito population. Each of the essential oils above have certain chemicals in them that are different than DEET and DDT that are not harmful for humans but very toxic to mosquitoes.

Future Research

In an article by American Chemical Society, they tested the cinnamon for the chemicals that killed the mosquitoes in their experiment. The chemical, cinnamaldehyde, did not resemble any chemicals in commercial mosquito pesticides. Like cinnamaldehyde, there could be different chemicals found in citronella, catnip and San Francisco plant, that are not harmful to humans but can kill mosquitoes. As a future research, finding different chemicals in the essential oils above have benefits such as:

1. A more effective, natural pesticide can be developed using the exact chemical(s) as opposed to using the plant essential oils

2. The side effects of the chemicals on human health can be further researched

3. Additional essentials oils that share the same chemicals could be found