Interações multitróficas envolvendo Coffea arabica, dois herbívoros e um inimigo natural

Abstract

Plants upon herbivory damage activate induced defense mechanisms that trigger the production of chemical compounds, which act directly by affecting the herbivore itself, or indirectly through recruitment of herbivore natural enemies. In contrast, herbivores developed strategies for escaping or manipulating host defenses and therefore settling on the host. As a result of herbivory by a particular species, plants can become more susceptible to the colonization of a second herbivore, facilitating multiple herbivory, which is a very common scenario in natural environments, but still poorly studied. Multiple herbivory, particularly by herbivores from different feeding guilds, induces in the plant a different defensive response from that upon attack of only one species, in a way that it is difficult to predict the consequences on tritrophic interactions. Thus, we investigated whether previous infestation in Coffea arabica L. by Planococcus minor (Maskell) (Hemiptera: Pseudococcidae), a sapsucking insect that potentially manipulates plant defences, facilitates infestation by Oligonychus ilicis McGregor) (Acari: Tetranychidae); and whether multiple herbivory by these arthropods (phloem-sucking and cell-content feeder) alters the attractiveness of herbivore-induced plant volatiles to the predatory mite Euseius concordis (Chant) (Acari: Phytoseiidae). Preference of O. ilicis females to non-infested and P. minor-infested plants was evaluated in arena choice tests. Results showed no preference of the mite for one of the hosts and females deposited similar numbers of eggs in both treatments. However, in performance assays, in which the numbers of eggs, larvae, nymphs and adults of each plant were counted, O. ilicis did better in non-infested plants compared to P. minor-infested plants. In regard to the third trophic level, in arena tests where mites were exposed only to olfactory cues, the predator E. concordis oriented to volatiles emitted by plants infested with its prey O. ilicis, but was not attracted to volatiles emitted by plants infested with the mealybug, which is not considered their prey. Finally, volatiles released by multiple infested plants (O. ilicis + P. minor) were as attractive as those emitted by plant infested with only O. ilicis. Thus, contrary to our initial hypothesis, our study showed that infestation by the mealybug did not alter host preference of the phytophagous mite and impacted its population growth. Despite this, multiple herbivory by herbivores from distinct feeding guilds exerted a neutral effect on the natural enemy's response compared to indirect defences of prey-infested plants. This study provides initial information about multitrophic interactions in coffee involving two pests and an important biological control agent of phytophagous mites, that can be explored for developing more sustainable management tactics. Therefore, future studies will be carried out in order to characterize volatile blend and phytohormone levels of coffee plants upon single and multiple herbivory.