Second and third trophic level effects of differences in plant species reflect dietary specialisation of herbivores and their endoparasitoids

Abstract

In natural populations, plants demonstrate an array of indirect and direct defence strategies that help to protect them from their herbivores and pathogens. Indirect defences include the release of odours that attract the natural enemies of herbivores, whereas direct defences may include the production of secondary compounds, allelochemicals that impair herbivore development or repel herbivore attack. Although both strategies have been well studied independently, comparatively little attention has been paid to examining the conflict that may arise between indirect and direct defences, such as when the performance of ‘recruited’ parasitoids or predators is negatively affected by plant allelochemicals. Here, we examine the growth and development of polyphagous and oligophagous folivores and their respective endoparasitoids on three crucifer species. One of the species, Brassica oleracea, was recently cultivated, whereas populations of B. nigra and Barbarea vulgaris occur naturally. Additionally, these species possess contrasting life‐history patterns and are also known to exhibit differences in secondary chemistry. The development of the generalist herbivore–parasitoid system was much more variable over the three crucifers than that exhibited by the specialists. Moreover, generalist herbivore and/or parasitoid fitness‐related traits (survival, development time, pupal, or adult size) were much more negatively affected on the wild crucifers than in the specialist association. Our results suggest that the relative importance of direct and indirect defences in plants may rest on the degree of dietary specialisation exhibited by herbivores and their natural enemies, and on the level of toxicity in the plant species under investigation.

Genetic Variation in Defense Chemistry in Wild Cabbages Affects Herbivores and Their Endoparasitoids

“…Most importantly, parasitoid development and survival appeared to closely reflect the effects of plant quality on host development. Various studies have similarly reported that the performance of both herbivores and their natural enemies are negatively affected by plant allelochemicals (Campbell and Duffey 1979, Barbosa et al 1986, Gunasena et al 1990, Sznajder and Harvey 2003, Harvey 2005.…”

Development and reproduction of Podisus nigrispinus (Hemiptera: Pentatomidae) fed with Thyrinteina arnobia (Lepidoptera: Geometridae) reared on guava leaves

“…However, this approach may decrease their efficiency in the field because the stimuli they receive in mass rearing are different from those in natural prey. Therefore, biological aspects of these predators can be adversely affected (Sznajder and Harvey, 2003). The knowledge about the performance of P. nigrispinus reared on natural prey is important not only to obtain the information about this predator on another host, but also to obtain data on its establishment in areas with the culture.…”

Plant-mediated effects in the Brassicaceae on the performance and behaviour of parasitoids

“…Generalist herbivores, which can feed on plant species in several plant families, are usually more sensitive to plant allelochemicals than specialist herbivores, which are adapted to feed on plants containing specific phytotoxins, such as GS (Blau et al 1978). Likewise, parasitoids attacking generalist herbivores have been shown to be more strongly affected by the herbivore's diet than parasitoids that attack hosts only feeding on brassicaceous plant species (Sznajder and Harvey 2003;Gols et al 2008c). Specialist herbivores have evolved efficient GS detoxification mechanisms (Ratzka et al 2002;Wittstock et al 2004;Agerbirk et al 2006).…”

“…Consequently, parasitoids of specialist herbivores may be exposed to only low levels of GS or their breakdown products. However, the development of parasitoids of hosts that are specialised on brassicaceous plant species have also been shown to differ with host plant quality Harvey et al 2003;Sznajder and Harvey 2003;). Negative plant-mediated effects can even affect hyperparasitoids (parasitoids that develop in other parasitoids) in the fourth trophic level Soler et al 2005).…”