Direct and indirect effects of herbivores influencing plant invasions.

Non-native plants rarely escape damage by herbivores. Instead, upon arrival in a new region, they begin to acquire new enemies, replacing those they have lost during their migration. These herbivores can include both natives to the new region and species that have themselves been accidentally or deliberately introduced from elsewhere, potentially including examples originating from the invader's original range. Shifts of new enemies from other hosts can occur over a range of timescales, depending in part on whether evolutionary change is required, but are likely to be faster for plants that are widespread and phylogenetically related to a herbivore's original host, and faster for generalist herbivores than for specialists. The occurrence of herbivores is not necessarily uniform across an invader's range; instead, they may be less diverse or abundant in host populations that are geographically or ecologically marginal, though existing evidence is mixed. Collectively, these new suites of herbivores can affect the growth and fitness of invaders, both directly by damaging them and indirectly by attacking their competitors. Studies comparing the demographic consequences of herbivory for successful vs unsuccessful invaders may help to clarify how often such impacts limit invasiveness. The view that an invader enters 'enemy-free' space is inaccurate; instead, persistence and spread of non-native plants often may be affected by the novel and changing assemblage of herbivores that they acquire within their new distribution.

Caterpillar-induced rice volatiles provide enemy-free space for the offspring of the brown planthopper

Plants typically release large quantities of volatiles in response to herbivory by insects. This benefits the plants by, for instance, attracting the natural enemies of the herbivores. We show that the brown planthopper (BPH) has cleverly turned this around by exploiting herbivore-induced plant volatiles (HIPVs) that provide safe havens for its offspring. BPH females preferentially oviposit on rice plants already infested by the rice striped stem borer (SSB), which are avoided by the egg parasitoid Anagrus nilaparvatae, the most important natural enemy of BPH. Using synthetic versions of volatiles identified from plants infested by BPH and/or SSB, we demonstrate the role of HIPVs in these interactions. Moreover, greenhouse and field cage experiments confirm the adaptiveness of the BPH oviposition strategy, resulting in 80% lower parasitism rates of its eggs. Besides revealing a novel exploitation of HIPVs, these findings may lead to novel control strategies against an exceedingly important rice pest.

Direct and indirect effects of herbivores influencing plant invasions.

Non-native plants rarely escape damage by herbivores. Instead, upon arrival in a new region, they begin to acquire new enemies, replacing those they have lost during their migration. These herbivores can include both natives to the new region and species that have themselves been accidentally or deliberately introduced from elsewhere, potentially including examples originating from the invader's original range. Shifts of new enemies from other hosts can occur over a range of timescales, depending in part on whether evolutionary change is required, but are likely to be faster for plants that are widespread and phylogenetically related to a herbivore's original host, and faster for generalist herbivores than for specialists. The occurrence of herbivores is not necessarily uniform across an invader's range; instead, they may be less diverse or abundant in host populations that are geographically or ecologically marginal, though existing evidence is mixed. Collectively, these new suites of herbivores can affect the growth and fitness of invaders, both directly by damaging them and indirectly by attacking their competitors. Studies comparing the demographic consequences of herbivory for successful vs unsuccessful invaders may help to clarify how often such impacts limit invasiveness. The view that an invader enters 'enemy-free' space is inaccurate; instead, persistence and spread of non-native plants often may be affected by the novel and changing assemblage of herbivores that they acquire within their new distribution.