Brightly coloured insects feeding on tropical plants may be a signal that the plant contains chemicals useful in fighting cancer or tropical diseases, researchers suggest in a recently published paper.

"The results of this study could have direct and positive impacts on the future of medical treatment for many diseases around the world," said project director Todd Capson, a research chemist with the Smithsonian's Tropical Research Institute in Panama.

A colorful beetle may indicate that the plant it's eating contains useful chemicals. (Don Windsor/Smithsonian Tropical Research Institute)

Five scientists — including three affiliated with McGill University — tested the idea that certain tropical beetles or butterfly larvae were more likely to be found on plants that contain useful chemicals.

Brightly coloured species were found on nine of the 10 plant species that can be used to fight breast cancer or malaria, but on only four of 10 medicinally inactive plants, an abstract of the article published in Frontiers in Ecology and the Environment said.

There was no significant difference between the numbers of plain-coloured insects found on active and inactive plants.

The researchers used the coloured bugs to find out whether their bad taste or toxicity to predators is because of the chemicals they got from the plants.

"We put two and two together," Julie Helson, from the Department of Plant Science at McGill, said in a release Tuesday. "We knew that brightly coloured insects advertise to their predators that they taste bad and that some get their toxins from their host plants."

The idea that colourful insects could point to medicinal plants has been frequently discussed but never been rigorously tested before, the Smithsonian research institute said.

"I am hopeful that other investigators will follow our lead and test our theory that insects can lead us to plants with disease-fighting properties," Capson said.

Helson, Capson and Timothy Johns are all affiliated with McGill. The other two scientists, Annette Aiello and Donald M. Windsor, are with the Tropical Research Institute.

Funding for the study came from U.S. National Institutes of Health, the U.S. National Science Foundation, the U.S. Department of Agriculture, the National Science and Engineering Research Council of Canada and a fellowship.