Alien interference: disruption of infochemical networks by invasive insect herbivores

Abstract

Insect herbivores trigger various biochemical changes in plants, and as a consequence, affect other organisms that are associated with these plants. Such plant-mediated indirect effects often involve herbivore-induced plant volatiles (HIPVs) that can be used as cues for foraging herbivores and their natural enemies, and are also known to affect pollinator attraction. In tightly co-evolved systems, the different trophic levels are expected to display adaptive response to changes in HIPVs caused by native herbivores. But what if a new herbivore invades such a system? Current literature suggests that exotic herbivores have the potential to affect HIPV production, and that plant responses to novel herbivores are likely to depend on phylogenetic relatedness between the invader and the native species. Here we review the different ways exotic herbivores can disrupt chemically mediated interactions between plants and the key users of HIPVs: herbivores, pollinators, and members of the third (i.e. predators and parasitoids) and fourth (i.e. hyperparasitoids) trophic levels. Current theory on insect invasions needs to consider that disruptive effects of invaders on infochemical networks can have a short-term impact on the population dynamics of native insects and plants, as well as exerting potentially negative consequences for the functioning of native ecosystems.

Beetle feeding induces a different volatile emission pattern from black poplar foliage than caterpillar herbivory

“…9 The total emission rate of beetledamaged foliage was »40% lower than that of caterpillar-damaged foliage. However, in our experiments beetle feeding caused »65% less leaf area loss (3.42 § 0.52% vs. 9.85 § 1.40%), so beetle feeding may be considered more volatileinducing.…”

“…[6][7][8] These differential plant responses are thought to be due to differences in the elicitors present in insect oral secretions, in the mode of feeding, or in the host specificity of the insects or the timing of attack. 9 However, most evidence for herbivore species-specific volatile emission comes from short lived herbaceous species. Woody perennials are barely studied in this context.…”

“…4,[16][17][18] In this study, beetles created more numerous and smaller lesions in poplar leaves than the gypsy moth caterpillars did in our previous work. 9 Thus the overall area affected by beetle damage might be bigger even though the actual area removed is smaller. For this reason, it is difficult to directly compare the amount of volatile emission caused by insects with very different feeding modes.…”

Plant-modified trophic interactions

“…An alternative perspective of essentially the same effect is that invasive herbivores may affect the infochemical network and reduce the search efficiency of native parasitoids for their native hosts [41]. It is interesting to note here that the same effect (interference) can be regarded as a good thing (population persistence) or a bad thing (reduced impact of natural enemy of herbivore), depending on the time scales of the perspectives: multi-generational population dynamics versus single generation effects.…”

Climate Change, Range Shifts and Multitrophic Interactions

“…Many other insects are known to be expanding into new habitats as a result of climate warming [7,97,98]. As they do so, they interact with native plants and their associated arthropod communities.…”