Behavioral disruption of two orchard hemipteran pests by garlic essential oil

Essential oils (EOs) are promising sources of effective bioactive compounds for insect pest control, especially in heavily treated agrosystems like orchards. Plants belonging to the Amaryllidaceae family - onion, garlic (Allium sativum L.), and others - present an interesting potential in apple (Malus domestica Borkh.) and pear (Pyrus communis L., both Rosaceae) tree integrated pest management due to the repellent and deterrent properties of their chemical compounds. This study explores the potential disruption by garlic EOs of the behavior of two hemipteran pests towards their host trees: rosy apple aphid, Dysaphis plantaginea (Passerini) (Aphididae), on cultivated apple, and pear psyllid, Cacopsylla pyri (L.) (Psyllidae), on pear. Effects on orientation and feeding behavior were evaluated using choice tests and the electropenetrography (EPG) technique. The results revealed that garlic EOs delivered through rubber dispensers were intrinsically repellent, but when combined with the attractive host plant, the repellents and attractants canceled each other out for the two studied hemipterans. Garlic EOs caused disruptions in the feeding behavior of the two insects, particularly the psyllids, which showed a decrease in phloem sap intake. This study highlights the mechanisms disrupting the process of host-plant colonization, in particular the possible masking of host-locating cues or the involvement of confusing chemical stimuli due to EO volatiles.