Years ago, we had four dogs infested with ticks and fleas. When two of them were caged under the Yellow Oleander (Cascabela thevetia) the pests disappeared after about a week. But the dogs inside our house remained infested.
I have repeated this experiment by giving a friend a pot of this shrub. He placed it near the cage of his German Shepherd and claimed the ticks and fleas also vanished. A neighbor who transferred the pot in her garden reported to me the same result on her puppy.
I would be glad to know if the same effect can be seen elsewhere. There is no need to boil any part of this plant and apply the concoction on any animal or people, or to rub the parts on the same. The plant appears to exude a chemical harmful to ticks and fleas. I wonder if it can also kill the chigoe flea (also known as jigger), the parasite that is afflicting millions of people in Kenya.
I have made another experiment by putting bottles of water under the shrub, and placed two other bottles of water 20-30 meters away from the Yellow Oleander. For three months, I didn't find any mosquito larva in the bottles, including in the bromeliads in my mother's garden. Bowls with water in the garden also do not have mosquito larva for years now.
But mosquito larvas have recently been found in flower pots filled with water inside my mother's house; the large Cascabela thevetia outside the house had been destroyed although a young one grows in the garden. This phenomenon appears to be consistent with the presence of ticks on dogs inside the house, but not of dogs outside, near the plant.
I would be excited to know if the same result of my experiments, albeit simple, can be duplicated elsewhere under controlled conditions, because of the threat of dengue in many parts of the world. Two things to consider, one possibly trivial: The flowers of our plant are orange, not yellow, and the fruit is round, not elongated. It is either similar or the same as this. There are other Oleander varieties but what I've seen so far in Cagayan de Oro is yellow and orange. I have made experiments only on the orange.
Also, be aware that the Yellow Oleander is highly toxic. The Queensland Poisons Information Center states: "All parts of the plant are toxic if eaten, particularly the fruit and seeds. This species has been responsible for the deaths of several children ...." Supply or sale of this plant is prohibited in Queensland. Petco.com also gives this warning: "Animals and humans can also be hurt by oleander, even without touching the plant. Breathing the smoke or burning branches can cause poisoning, and merely smelling the flowers may be harmful."
But if it can be proven that the Yellow Oleander prevents the development of mosquito larvas without coming in physical contact with them, it might still be useful to propagate the plant in human communities. One way to keep it safe is to raise it inside a cage partly made of chicken wire or similar material. The plant will then continue to receive sufficient sunlight to grow, with minimal chance of harming people and animals.
The Yellow Oleander was among six toxic plants examined by researchers of Gauhati University of India. Experiments on crude seed oil of the plants revealed larvicidal effect on Aedes aegypti and Culex
quinquefasciatus mosquitoes. The result of the experiments was published in Biofertilizers and Pesticides in 2012. The Yellow Oleander was found to be least effective, however: "Among these
six crude oil extracts, P. pinnata exhibited the highest larvicidal activity ...
The seeds oil of C. thevetia showed the lowest toxicity against Ae.
aegypti and C. quinquefasciatus."
Ae. aegypti is the carrier of the dengue virus. C. quinquefasciatus is responsible for malaria, West Nile virus, and the parasitic roundworm that causes lymphatic filariasis.
I have contacted two researchers of Gauhati University and suggested placing bottles of water under and near the Yellow Oleander, and observe if mosquito larva will thrive in those bottles -- without putting any part of the Yellow Oleander in the bottles. Also informed the Ahadi Kenya Trust, and posted a message about the shrub in the World Health Organization Facebook. In the Philippines, I have informed the Department of Science and Technology, a group in Xavier University, and the head of a Manila firm that conducts research on chemicals and insects.
The experiment can, of course, be done also using other toxic plants.
Whatever the result of the experiment, one can always come up with other hyphotheses. The current spread of the Ebola virus is an opportunity to discover if the Yellow Oleander and other toxic plants can offer a cure. How will patients of Ebola and other diseases respond when placed near these plants? Is the Ebola virus present in fruit bats and other animals living near the Yellow Oleander?
Yellow Oleander at the main gate of Xavier Estates, Cagayan de Oro.