Genetic Engineering Offers New Way to Combat Insect Pests (web article)

In the ongoing battle against insects and the diseases they transmit, scientists are learning to shift from sterilizing mosquitoes and other bugs to manipulating their genes, according to Oxford University researcher Luke Alphey, PhD.

Until recently, the sterile insect technique (SIT) has been used to control insect pests, said Alphey in a March 30 presentation at the Johns Hopkins Bloomberg School of Public Health. In SIT, large numbers of male insects are bred, sterilized with radiation, and released. These sterile males then mate with wild females, but no offspring result. Ideally, the population collapses in time.

Successful SIT programs have been conducted against the screw worm fly, the Mediterranean fruit fly (medfly), and the tsetse fly. Half a billion medflies, for example, were released over Los Angeles during the 1990s, quelling the insect invasion. (A facility in Central America produces 2 billion sterile medflies per week for distribution.)

If SIT works, why pursue the genetic manipulation of insects at all? "For one thing," says Alphey, "irradiating these insects damages their chromosomes, rendering them not as fit as their wild cousins" and making them less effective agents for SIT. A significant zap of radiation is required to sterilize the males ("They better be sterile," he says), yet it often leaves them so weakened that they're unable to compete in the wild.

To get around these problems with SIT, Alphey and his group are researching a genetic approach they call RIDL (Release of Insects carrying a Dominant Lethal [gene]). RIDL (pronounced “riddle”) involves genetically engineering a lethal gene into the males. This death-causing gene, passed on to all the progeny of the males, works by allowing an innocuous protein to control its own expression, thereby causing the protein to overproduce itself explosively. So much of the protein is produced that cells are disrupted and the insect is killed. The genetically modified RIDL females, on the other hand, die out before reaching adulthood—a nifty benefit when one is battling mosquitos, since the female is the one that does the damage.

RIDL, Alphey says, should be acceptable to a public that largely hates insect vectors and the pathogens they carry. But the method also has its negatives:

• With SIT, all the insects die after release; with RIDL, however, successive generations continue to breed in the environment.
• Mosquitos bite and are scary to people, especially GM mosquitoes. Communities are apt to say, “Don't release them in our neighborhood!”

Alphey's next steps? “Working through the political and regulation processes. We must gather evidence that will prove to regulators that the RIDL insects are safe for the environment and effective.” --Rod Graham