Variation in parasitoid attraction to herbivore-infested plants and alternative host plant cover mediate tritrophic interactions at the landscape scale

Abstract

Context Tritrophic interactions may be affected by local factors and the broader landscape context. At small spatial scales, carnivorous enemies of herbivorous insects use herbivore-induced plant volatiles (HIPVs) to find herbivores, but it is unknown whether variation in plant attractiveness due to differential HIPV emission can enhance recruitment of carnivores from the wider landscape. Objectives We studied whether parasitism of caterpillars of the butterfly Pieris brassicae on white cabbage was influenced by landscape composition and cover with brassicaceous species that provide hosts for parasitoids of P. brassicae in 19 landscapes in the Netherlands. We also investigated whether differential attraction of parasitoids to herbivore-infested plants affected parasitism of P. brassicae caterpillars by using different accessions as proxies for HIPV emission. Results The cabbage accession that is highly attractive to parasitic wasps recruited more wasps than a less attractive accession, but only when parasitism rates were high. Parasitism rate as proxy of wasp recruitment correlated positively with the cover of brassicaceous plants and area of arable land, suggesting that these habitats support hosts for the wasps and their population growth. In contrast, forest area was negatively associated with parasitism rates. Conclusions Our study shows that the degree of attractiveness of plants to parasitoids, which is probably mediated by HIPVs, can be a useful predictor of parasitism, but needs to be considered within the landscape context. To understand the strength of tritrophic interactions it is crucial to consider localscale processes driven by plant-trait variation in combination with landscape-scale processes that determine carnivore abundance.

Factors influencing the occurrence of fall armyworm parasitoids in Zambia

“…Maize plants of 10 to 21 days old (3-9 leaf stages) emit induced volatiles when Spodoptera exigua or S. littoralis feed on the young leaves and consequently attract more natural enemies compared to undamaged plants (D'Alessandro et al 2009;Turlings et al 1991;Fritzsche-Hoballah and Turlings 2001). While most studies on HIPVs and natural enemies have been conducted under controlled laboratory conditions, some have demonstrated their effects under field environments (Aartsma et al 2019(Aartsma et al , 2020Bernasconi Ockroy et al 2001;De Lange et al 2018;Drukker et al 1995;Poelman et al 2009;Shimoda et al 1997). Furthermore, a recent study using 3-leaves stage (9-12 days old) maize plants confirmed that S. frugiperda has lower HIPVs induction on maize than other Spodoptera species (De Lange et al 2020).…”

Following the pest outbreak: preliminary findings on the landscape effect on Dasineura oleae and its parasitoids in central Italy

“…We do not want to rule out other factors that could mask some important environmental variables, Further analysis over time and space is thus needed to understand better how the effect of the landscape depends on other abiotic factors such as temperature, rainfall, photoperiod or other variables related to the development of the olive tree, in addition to the role of complementary local scale variables that strictly depend on the traits of pest and of the natural enemies community. In fact, some land use variables may not completely capture the specific ecological prerequisites of such organisms (Aartsma et al, 2020).We also found a small-scale crossover effects on the infestation rate but not an overall effect of single variables. The role of the landscape on the olive leaf gall midge needs more investigation.…”

Human-Mediated Land Use Change Drives Intraspecific Plant Trait Variation

“…Although we were not able to find any studies that have directly measured the effect of land use change on plant indirect defenses in natural plant populations, the little evidence we have suggests that there could be differential selection by natural enemies on indirect defense traits. In a study done on cabbage infested with herbivore Pieris brassicae placed in different landscapes, it was found that the induction of plant volatiles in response to herbivory can mediate the effect on parasitism ( Aartsma et al, 2020 ). To test this, two different accessions of cabbage were used.…”