none Entered Field experiments were conducted at two locations; Sidi Salem, Kafr El-Sheikh and Kotor, Al-Gharbiya Governorates, Egypt in the growing season 2013/14 to study the population fluctuations of the cabbage white butterfly, Pieris rapae (L.) and its associated parasitoid and predatory species in cabbage plantations. Effects of certain compounds; Neomyl, Bermectine, Biofly and BioGuard on reducing the population density of P. rapae were evaluated. Also, the side effect of those compounds on predators' populations was assessed. Population density P. rapae reached maximal abundance in October, November and January in the two locations. Surveyed true spiders were found belonging to nine families; Araneidae, Dyctinidae, Lycosidae, Linyphiidae, Miturigidae, Philodromidae, Salticidae, Theridiidae and Thomisidae. Five primary parasitoid species; Trichogramma buesi Voegele, Cotesia glomerata (L.), Hyposoter sp., Pteromalus puparum L. and Brachymeria femorata (Panzer) were found parasitizing developmental stages of the pest. Highest abundance of Paederus alfierii was found in December, January and April at Kafr El-Sheikh and in December, March and April at Al-Gharbiya. Highest abundance of Chrysoperla carnea was recorded in October and April in the first location and in January and March in the second one. Maximum number of spiders was recorded in October at Kafr El-Sheikh and in September at Al-Gharbiya. Combined effect of weather factors and predators on the density of P. rapae was higher in the first location than in the second one. Under field conditions, all tested compounds caused reduction in of P. rapae larval infestation in both locations. Neomyl and Bermectine were the most effective ones in reducing P. rapae larvae and eggs hatchability, followed by Biofly. BioGuard was the one. Side effects of these compounds on the predators revealed that Neomyl was moderately effective, while Bermectine, Biofly and BioGuard had slight effects. 2014