Modulação das defesas químicas de plantas contra dois artrópodes herbívoros moldam as interações ecológicas subsequentes

Abstract

Plants under herbivory have their induced defenses activated, which act directly on the development and survival of the herbivore by the production of toxic or antinutritive compounds. Plants reallocate energy to synthesize these defenses, which can lead to changes in their primary metabolism. However, herbivores from different feeding guilds have developed strategies to overcome these host defenses, which may or may not facilitate attacks by subsequent herbivores. Hence, this thesis aims to investigate the effect of herbivory of the southern red mite (Oligonychus ilicis) and the coffee leaf miner (Leucoptera coffeella) on the induced defenses of coffee plants (Coffea arabica) and its ecological consequences for conspecifics and heterospecifics. Behavioral tests with herbivores were carried out in the laboratory, and targeted and untargeted analysis of the primary and secondary metabolism of coffee plants, as well as analysis of the phytohormonal profile. In the first chapter, it was shown that plants infested by the mite were more attractive and increased oviposition of conspecifics than non-infested plants. Apparently, the alkaloids caffeine, theophylline, and trigonelline did not appear to exert a defense function in C. arabica plants against the mite. However the phenolic compound, chlorogenic acid was a strong candidate for that role. Although it was not possible to affirm that the mite suppresses coffee plant defenses, its feeding increased the concentrations of salicylic acid (SA) and 12-oxophytodienoic acid (OPDA), but not jasmonic acid (JA) and jasmonic acid-isoleucine (JA-Ile). We suggest that the conversion of the precursor, OPDA, into jasmonates, JA, and JA-Ile, is not successful in plants infested with the mite, which could be related to the greater susceptibility of these plants. In the second chapter, the coffee leaf miner infestation made the coffee plant a better host for the subsequent infestation of conspecifics, but not heterospecifics. On the other hand, L. coffeella did not discriminated between mite-infested and non-infested, however the leaf miner was negatively affected and consumed less leaf tissue, compared to non-infested ones. The results of the chemical analysis showed that herbivores induced distinct responses in the metabolic profile (primary and secondary) of plants under single infestations and simultaneously (multiple infestation). Furthermore, while the single infestation upregulated the concentrations of greater number of features (unidentified compounds), the multiple infestation triggered suppressed them. These results seem to reflect the different phytohormonal regulation of plant defenses by herbivores. Leaf miner-infested plants showed accumulation of SA and abscisic acid (ABA), but not JA. Mite-infested plants showed accumulation of SA and OPDA, but not JA and JA-Ile. Our results suggest that the southern red mite and the coffee leaf miner suppress coffee plant defenses that favor the establishment and development of conspecifics, but not heterospecifics. Although both herbivores reduce the defenses modulated by JA, the mechanism by which this suppression occurs seems to be different between the two and has not yet been reported in the literature.