Trees attacked by herbivores do not cry for help uselessly
Publication in Ecography focuses on question whether trees attacked by herbivores are able to call effectively for predators who could help them from herbivores.
Recently, it was shown that plants can cry for help when attacked by herbivorous insect. The phenomenon known as „crying for help“ was originally described as interactions between herbivore damaged plants, insect herbivores and parasitic wasps attacking larvae of the herbivore. Parasitoids and parasites were proved to be attracted to plant tissues damaged by herbivores significantly more than to undamaged plant tissue.
It starts to be clear that also predators of herbivorous insect can be preferentially attracted to infested plants. Our recent experiments in forest of Papua New Guinea showed that models of caterpillars (made under strict scientific protocols from plasticine) exposed on leaves with herbivorous damage were always attacked more than caterpillar models exposed on undamaged leaves. We observed this pattern in lowland forests, where wasps and ants are the most important predators, as well as in forests at higher elevations, where birds are the most important predators. It seems that both chemically (e.g. ants) and visually (e.g. birds) prefer to search for food at trees crying for help, and they may use chemical signals from damaged plant tissues as well as visual appearance of damaged leaves (possibly with excrements of herbivorous insect) as a clue. It seems to be also more efficient to call for help predators who remove the herbivorous insect immediately rather than parasites that tend to leave host insect larvae alive for certain time.
Sam K., Koane B., Novotný V. (2014) Herbivore damage increases avian and ant predation of caterpillars on trees along a complete elevational forest gradient in Papua New Guinea. Ecography. Published online: 31 July 2014. DOI: 10.1111/ecog.00979
