In continuing to explore the crystal structure of insecticides, the research team began studying fluorinated forms of DDT, swapping out chlorine atoms for fluorine. They prepared two solid forms of the compound—a monofluoro and a difluoro analog—and tested them on fruit flies and mosquitoes, including mosquito species that carry malaria, yellow fever, Dengue, and Zika. The solid forms of fluorinated DDT killed insects more quickly than did DDT; the difluoro analog, known as DFDT, killed mosquitoes two to four times faster. The researchers also made a detailed analysis of the relative activities of the solid-state forms of fluorinated DDT, noting...