William Wood, a geneticist from the University of Colorado at Boulder, US, has found a method for controlling crop-decimating nematode (roundworm) populations. A gene, isolated from another small worm - Caenorhabditis elegans - can determine whether a fertilised egg will become a male worm. This gene has been named Her-I and is responsive only in mates. In certain nematods, only the females damage crops - so the sex of the worm is crucial. If a crop can he engineered to produce Her-1, the gene can move from plant cells to the worm eggs producing harmless males (Discover, October 1995).