Oviposition patterns ofHeliothis zea,Manducaspp.,Spodoptera exigua, andTrichoplusia niwere studied in processing-tomato fields of northern California. The initiation of egg laying appears to be related to flower formation, with peak egg deposition occurring in relation to the peak number of open flowers per plant forH. zea, S. exigua, andT. ni. Oviposition byManducaspp. increases as the season progresses. All species deposit most of their eggs on leaves of the terminal half of the branch. The majority of eggs are located on the ventral leaf surface, within one leaf of the inflorescence. From these data, it is possible to estimate the number of plants that would have to be sampled to find an egg of one species at a given egg density.