Compartilhando a planta hospedeira com um ácaro fitófago: efeitos bottom-up e top-down beneficiam a cochonilhabranca Planococcus minor

Abstract

Plants are able to defend themselves from herbivore attack in several ways, one of which is through chemical substances that can affect herbivore arthropods directly, or indirectly by recruiting natural enemies. Although it has been poorly studied, herbivory by multiple herbivore species deserves more attention, as induced response of plants upon multiple herbivory generally differs from those upon simple herbivory, in ways that can impact tritrophic interaction. In addition to the ecological context, stud ying multiple herbivory at the applied perspective is necessary because of the implications for the attraction of natural enemies and the perspective of developing integrated pest management strategies. The coffee Coffea arabica L. (Rubiaceae) is one of the most important crops for the country's economy, whose production is limited by the attack of several pests, among them the passionvine mealybug and the southern red mite. Considering the lack of information on multiple herbivory in the coffee system, the aim of this study was to evaluate whether previous infestation with Oligonychus ilicis (McGregor) (Acari: Tetranychidae) in coffee plants influences colonization and establishment of Planococcus minor (Maskell) (Hemiptera: Pseudococcidae); and, whether multiple herbivory by the two pests influences the behavioral response of the predatory ladybug, Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae) to the herbivore-induced plant volatiles. In order to evaluate host preference between mite-infested plant and uninfested plant, choice tests were conducted in an arena using 3 rd -instar mealybug nymphs at 24, 48 and 72 h. In order to evaluate P. minor performance, 50 1 st -instar nymphs were transferred to a plant (mite-infested or uninfested) and, after 15 days, numbers of nymphs and adults were counted. Ladybug olfactory preference to volatiles emitted from uninfested and infested coffee plants with one or two of the herbivores were evaluated using a Y-tube olfactometer. Data showed that the mealybugs preferred mite-infested plants as a host over uninfested plant. Population growth of P. minor was higher in mite-infested plant than uninfested plant, indicating to be a better host. Olfactometer assays showed that the ladybug preferred volatiles emitted by plants infested with its prey, P. minor, but it was not attracted to volatiles mite-infested plants. Plants infested with both mealybug and mite emitted repellent volatiles to the ladybug that preferred clean air over the mealybug + mite-infested plants. Thus, previous infestation with mites induce changes in coffee plants that comprise in better hosts to passionvine mealybug than uninfested plants, favoring multiple herbivory. In addition, the mealybug choice for miteinfested plants should also favor the mealybug because of the emission of volatiles that repel the ladybird, being a strategy to escape predation. Future studies should focus on the manipulative mechanisms of coffee plant defenses by mite herbivory, phytohormone quantification, gene expression and chemical characterization of volatile profiles emitted by coffee plants upon simple and multiple herbivory.