Plants release volatile chemicals when attacked by caterpillars. In the 29 March Nature, Consuelo De Moraes and colleagues of the USDA Agricultural Research Service, Gainesville, Florida, report that some of these chemicals — five were identified by gas chromatography and mass spectrometry — are released by tobacco plants exclusively at night (Nature 2001, 410:577-580).

De Moraes et al observed that nocturnal female moths spend a greater proportion of their time — 80% of the observed hour — in an area with only undamaged plants than in an area with both damaged and undamaged plants. The moths selected only non-infested plants (that is, undamaged plants) on which to lay their eggs (p<0.0001) and tended to avoid non-infested plants that were close to infested ones. The moths also avoided non-infested plants to which were attached a small rubber device that released volatiles in approximately the same...