Re: what is the best way to test the repellency of a live potted plant?

I doubt that a live potted plant will be able to repel mosquitoes because the
chemicals that may repel mosquitoes are still within the plant. There is
research that indicates that a chemical extracted from Euodia spp., also called
Melicope, can kill mosquito larvae. However, that would require that the
chemical be extracted from the plant and sprayed on standing water where the
mosquitoes larvae might be present. 

Plants with mosquito repellant properties include lemon thyme (Thymus X
citriodorus), citronella grass (Cymbopogon nardus), catnip (Nepeta cataria) and
mosquito geranium (Pelargonium ‘Citrosa’). These plants repel mosquitoes but
only if the leaves are crushed or extracted and the juice or extract placed on
the skin. However, few of the plant extracts were as effective as DEET, an
artificial mosquito repellant. Catnip was better than DEET in some tests.

To do an experiment to test a live plant's ability to repel mosquitoes you could
try something like the following: 

1. Build two identical insect-tight chambers each about 1 meter square. 
2. Place a potted plant in one end of the chamber.
4. In the second chamber place an identical pot filled with the same soil but no
plant.
5. Release 100 mosquitoes into each of the two chambers.
6. Watch the mosquitoes to see if any land on the plant. If the plant repels
mosquitoes, they should stay as far away from the plant as possible.

You could also try your arm-in-cage test but that would probably require that
you use leaf extracts on the arm. The last reference mentioned a simple
experiment where leaf extract was rubbed on one side of the interior of a tube.
Mosquitoes were placed in the tube, and it was determined if more mosquitoes
landed on the treated or untreated side.


References


I. Ramli, N.H. Kamarulzaman, K. Shaari, G.C.L. 2004. p-O-Geranylcoumaric Acid
from Melicope Lunu-Ankenda.  Natural Product Research. 18: 289-294.


Mosquito Repellent Plants


Jeyabalan, D., Arul N., and Thangamathi, P. 2003. Studies on effects of
Pelargonium citrosa leaf extracts on malarial vector, Anopheles stephensi
Liston. Bioresource Technol. 89:185-189.


Cymbopogon nardus


Catnip oil may repel mosquitoes better than spray