Citrosa

A plant I bought at Cameron Highlands for RM6. The nice Malay lady at Kea Farm mentioned that it can repel "nyamuk" (mosquitoes) and so, it was only natural that I would get two (2) units for my humble abode. Of course the scientific name was never going to be "pokok halau nyamuk" (mosquito repelling plant) so upon some searching online I discovered that the plant is called "Citrosa". 

However, a certain study has noted that the plant in its natural state may not in reality be so effective in chasing mosquitoes away.

What about the claims of 'Citrosa' as a mosquito fighter? Dr. G.A. Surgeoner and J. Heal at the University of Guelph in Ontario tested the effect of 'Citrosa' and lemon thyme (Thymus x citriodorus) against the biting activity of Aedes aegypti mosquitoes. They found that the whole plant of 'Citrosa' geranium DID NOT provide significant protection against mosquito bites (yet the ads state "The chemicals act to block the mosquito's sensory apparatus so that it can not detect mammals. Mosquitoes may be in the area around the plant but they can't detect you.") Crushing of 'Citrosa' leaves on the hand and wiping one's hand through the 'Citrosa' plant appeared to provide about 30-40% repellency. However, Surgeoner and Heal found that crushed lemon thyme produced 62% repellency! Compare this with commercial Deep Woods Off, which produced 90.4% reduction in biting activity.

Source: http://www.richters.com/newdisplay.cgi?page=OttoRichter/1993.html