by Michael Keller

A massive screening effort that sifted through more than 1,600 plant species has discovered a handful of compounds that could make the next generation of safe insecticides.

An international research team isolated five metabolites from two types of plant that counteract hormones found only in insects, which they say makes the compounds safe for people and the environment.

The metabolites, naturally produced by a species of shrub called Lindera erythrocarpa and a common herbaceous flowering plant in the aster family named Solidago serotina, are chemical warfare agents the plants have evolved to thwart insect attackers. They work by counteracting a core regulator of development and reproduction in insects called juvenile hormone.

In experiments, mosquitos of the species that typically carries yellow fever were exposed to low doses of the natural insecticides, which are part of a class called juvenile hormone antagonists (JHANs). Researchers watched as larvae died and the ovaries of juvenile females failed to develop fully.

“Our experiments showed that these five JHANs are effective against yellow fever mosquitoes,” said Alexander Raikhel, an entomology professor at the University of California, Riverside who led efforts for the part of the team in the U.S. “These newly discovered natural molecules could lead to the development of a new class of safe and effective pesticides to control mosquitoes and, we expect, other agricultural pests.”



(Compound isolated from L. erythrocarpa [LE3B] and from S. serotina [SS5A] impaired ovarian development in treated female mosquitoes. [Left] Normal development of ovarian follicles from a female mosquito treated with solvent. [Center and Right] Ovaries from a 4-day-old female mosquito after treatment with 0.5 μg LE3B or SS5A per mosquito. Courtesy Raikhel et al./PNAS.)

A contingent of the team in South Korea is now testing to see whether the five metabolites have the same insecticidal qualities in agricultural pests. In their paper, which appeared last month in the journal PNAS, the authors note the importance of finding new ways to control insects, which cause major economic and public health problems.

“Insects cause enormous economic damage and human suffering,” they wrote. “Diseases transmitted by insects result in a million deaths per year, and insect infestation leads to annual losses of agricultural products worth billions of US dollars. The high toxicity of currently available insecticides presents environmental and health risks, and growing resistance and cross-resistance of insects to these existing insecticides gravely complicates the situation. Hence, there is an urgent need to develop novel effective insecticides.”

Top Image: The Asian tiger mosquito is a known vector of viral infections like Dengue and yellow fever. Via Shutterstock.