Effect of nitrogen fertilization level applied to tomato on the greenhouse whitefly

The greenhouse whitefly, Trialeurodes vaporariorum (Westwood), was studied on tomato plants, Lycopersicon esculentum (Miller) treated with three different nitrogen levels [308, 140 and 84 ppm] within the normal range for tomato fertilisation in Spain. Nitrogen affected the thickness of the leaflet lamina and of the abaxial epidermal cuticle; plants supplied with 308 ppm of N had the thinnest leaf. High nitrogen fertilization increased egg survival, size of pupal exuviae and female tibial length. Females that had been reared on plants fertilized with 84 ppm of N showed the lowest oviposition frequency, when allowed to oviposit on plants fertilized with 140 ppm of nitrogen, but the development time of immatures and the longevity and fecundity of the next generation of females were not significantly different. T. vaporariorum populations that developed on plants fertilized with high nitrogen level showed a higher intrinsic rate of increase, making its control more difficult. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.