A plant-destroying virus farmers call one of their worst enemies may soon be an ally in the fight against crop pests and mosquitoes, say University of Florida researchers. Scientists genetically modified tobacco mosaic virus so that it produces a natural, environmentally friendly insecticide, turning the pathogen into a microscopic chemical factory, said Dov Borovsky, an entomologist with UF’s Institute of Food and Agricultural Sciences. The modified virus is almost completely harmless to plants and simply produces the insecticide.