Importance of primary metabolites in canola in mediating interactions between a specialist leaf-feeding insect and its specialist solitary endoparasitoid

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.

Genetically manipulated Brassica genotypes affect demography and performance of Diadegma semiclausum parasitizing Plutella xylostella

“…Also, pupal weight is a good indicator of offspring fitness as heavier pupae are known to produce larger and more fecund adults than their smaller counterparts (Soufbaf et al. ). Further, smaller size resulting in lower fecundity would decrease the rate of population increase.…”

“…High value of the intrinsic rate of increase ( r ) of arthropods indicates susceptibility of a host plant (Soufbaf et al. ,b, ). However, to measure the efficiency of a parasitoid, we should consider not only its intrinsic rate of increase but also its parasitism capacity (Nikooei et al.…”

“…However, several studies have suggested that body size/weight often affect reproductive success through variation in fecundity, dispersal, searching efficacy and host handling strategies (Price et al 1980;Visser 1994;Kazmer and Luck 1995;Ebon et al 2000). Also, pupal weight is a good indicator of offspring fitness as heavier pupae are known to produce larger and more fecund adults than their smaller counterparts (Soufbaf et al 2012). Further, smaller size resulting in lower fecundity would decrease the rate of population increase.…”

“…Ten pairs of two-d-old mated D. semiclausum were introduced into the cage. The wasps were provided with a diet of 10% honey solution (Soufbaf et al 2012). After 24 h, the exposed larvae were removed and placed in ventilated plastic containers (20 9 15 9 7 cm).…”

Finish line plant–insect interactions mediated by insect feeding mode and plant interference: a case study of Brassica interactions with diamondback moth and turnip aphid

“…These compounds are usually carbon (C)‐based or nitrogen (N)‐based defensive compounds which also vary with season, soil properties, plant age and the herbivores’ feeding damage (Gols et al ., ). Plant organs with high turnover rates such as leaves generally contain higher N concentrations than the relatively dormant phloem saps and this N content influences insects that feed on it (Mattson, ; Karley et al ., ; Soufbaf et al ., ). Tolerance of a plant to herbivory is a genetic trait and is defined as a compensatory response by which a plant decreases the influences of the herbivores attack (Kessler & Baldwin, ; Fornoni, ).…”