Spatial scale, neighbouring plants and variation in plant volatiles interactively determine the strength of host–parasitoid relationships

Abstract

Species‐specific responses to the environment can moderate the strength of interactions between plants, herbivores and parasitoids. However, the ways in which characteristics of plants, such as genotypic variation in herbivore induced volatiles (HIPVs) that attract parasitoids, affect trophic interactions in different contexts of plant patch size and plant neighbourhood is not well understood. We conducted a factorial field experiment with white cabbage Brassica oleracea accessions that differ in the attractiveness of their HIPVs for parasitoids, in the context of different patch sizes and presence or absence of surrounding Brassica nigra plants. Parasitism rates of experimentally introduced Pieris brassicae caterpillars and the presence of naturally occurring Pieris spp. caterpillars in the plots were assessed throughout the growing season. The abundance of Pieris caterpillars was neither affected by cabbage accession nor plot size. Later in the season, when B. nigra plants had senesced, fewer caterpillars were found on cabbage plants in plots with a B. nigra border. Parasitism rates fluctuated over the season, and were not affected by plot size. However, the B. nigra border negatively affected parasitism rates on the accession that is less attractive to the parasitoid Cotesia glomerata, but not on the more attractive accession. Our results show that plant variation in HIPVs can differentially influence herbivores and parasitoids depending on characteristics of the surrounding vegetation context. These findings underscore the importance of considering the interaction between focal plant traits and neighbourhood context to reliably predict trophic cascades.

Crop species diversity levels with attract and reward strategies to enhance Pieris brassicae parasitism rate by Cotesia glomerata in strip intercropping

“…To assess field parasitism rates in different cropping systems, we used an existing protocol of release and recapture (Aartsma, Hao, et al., 2020; Aartsma, Pappagallo, et al., 2020; Poelman, Oduor, et al., 2009). Ten caterpillars were released on one (in 2019) or two (in 2020 and 2021) Rivera plants per experimental strip.…”

“…Furthermore, we tested if the inclusion of leguminous plants with extrafloral nectaries within a strip‐cropping system could further enhance parasitism rate by the nectar reward to adult parasitoids (Bugg et al., 1989). We employed a novel strategy of incorporating an attractive plant cultivar within the strip‐cropping system that is known to be attractive to parasitoids on a landscape scale (Aartsma, Hao, et al., 2020; Aartsma, Pappagallo, et al., 2020). We expected this cultivar to recruit parasitoids from a further distance (Aartsma, Leroy, et al., 2019), which in turn would aid the parasitism rate of caterpillars in the cash cultivar included in this cropping scheme.…”

“…Furthermore, we tested if the inclusion of leguminous plants with extrafloral nectaries within a strip-cropping system could further enhance parasitism rate by the nectar reward to adult parasitoids (Bugg et al, 1989). We employed a novel strategy of incorporating an attractive plant cultivar within the strip-cropping system that is known to be attractive to parasitoids on a landscape scale (Aartsma, Hao, et al, 2020;Aartsma, Pappagallo, et al, 2020).…”

Advances in the Biosynthesis of Terpenoids and Their Ecological Functions in Plant Resistance

“…Terpenoids can also participate in the induced defense responses of plants. For example, (E)-β-farnesene repels aphids, and caryophyllene and linalool attract rice lice wasps [37][38][39][40] (Figure 1).…”

Options for diversifying agricultural systems to reduce pesticide use: Can we learn from nature?

“…Companion plants of crop species may offer alternate prey or hosts, pollen, nectar, refugia, and microhabitats that may not be offered by monocultures (Landis et al, 2000). On the other hand, the more complex vegetation and olfactory composition of intercrops may influence the ability of natural enemies to find their prey or hosts on the crop plants (Aartsma et al, 2020).…”