The effects of 10 commercial canola, Brassica napus L., cultivars widely grown in Iran--'SLM(046),' 'Opera,' 'Okapi,' 'RGS(003),' 'Modena,' 'Sarigol,' 'Zarfam,' 'Licord,' 'Hayula(420),' and 'Talaye'--on the demographic parameters of diamondback moth, Plutella xylostella L. (Lepidoptera-Plutellidae), were determined. The experiments were conducted in a growth chamber at 25 +/- 1 degrees C, 65 +/- 2% RH, and a photoperiod of 16:8 (L:D) h. The comparison of intrinsic rate of natural increase (r(m)), net reproductive rate (R0), and the survival rate of adult stage of P. xylostella on 10 canola cultivars suggested that this pest performed best on SLM(046). The r(m) value of P. xylostella ranged between 0.241 on RGS(003) and 0.304 on SLM(046). The R0, finite rate of increase (lambda), mean generation time (T), and doubling time (DT) values of P. xylostella on SLM(046) were 52, 1.35, 13.4, and 2.35 and on RGS(003) were 31, 1.27, 14.4, and 2.94, respectively. The Weibull model adequately described the shape of the survivorship curve of adult P. xylostella from life-table data. A significant fit was obtained with the Weibull model for P. xylostella in all experimental canola cultivars. As a result, SLM(046), Opera, and Hayula(420) were the most suitable hosts and had least negative impact on life-history statistics of the pest.

No abstract

No abstract

The role of primary plant chemistry on trophic interactions is not well studied. We examined the effect of primary plant metabolites, focusing on nitrogen, on several biological indices of second and third trophic level insects in a model tritrophic system, consisting of two strains of the crucifer, Brassica napus (canola) (SLM 046 and RGS 003 ), the specialist insect herbivore Plutella xylostella (L.) (Lepidoptera: Plutellidae), and its specialist koinobiont larval-pupal parasitoid Diadegma semiclausum (Hellén) (Hymenoptera: Ichneumonidae). In particular, we measured relative growth rate of the herbivore in relation to an index for plant quality (nitrogen content of leaf tissues), developmental time of the herbivore (sum of second, third, and fourth larval instars durations), and intrinsic rate of increase (r m ) of the herbivore and the parasitoid. Tritrophic studies were conducted on development, survivorship curve analysis, reproductive potential, life history, parasitism, and several other fitness correlates of the parasitoid. The life table parameters of D. semiclausum were determined under laboratory conditions. The intrinsic rate of increase (r m ) of the parasitoid was significantly higher on RGS 003 than SLM 046 . In this tritrophic model, the results indicated that the bottom-up direct effect on the herbivore population growth rate was marginally as strong as the direct effect of top-down force due to the parasitoid population growth rate; but it was higher than its indirect counterpoint mediated with the parasitoid population growth rate. Consequently, D. semiclausum performed better on RGS 003 , which was the most inferior host to P. xylostella in comparison with another plant cultivar and had the lowest content of nitrogen in its leaves.

No abstract