Ripe coffee berry volatiles repel second instar nymphs of Antestia bugs (Heteroptera: Pentatomidae: Antestiopsis thunbergii)

Abstract

Understanding the roles of volatile organic compounds (VOCs) in insect–plant interactions is a key component towards the development of safe pest management strategies and sustainable agriculture. Kairomones in unripe berries of Coffea arabica mediate host recognition of second instar nymphs of Antestia bugs, Antestiopsis thunbergii Gmelin, and are good candidates for the pest management. In the current study, we investigated the VOCs that contribute to deterring the pest from ripe berries. Behavioral assays showed that headspace volatiles collected from ripe berries were significantly avoided by second instar nymphs. A mixture of the ripe berry volatiles and unripe berries (known preferred diet) was also significantly avoided when tested against blank or unripe berries, thereby confirming that VOCs from ripe berries had altered the host recognition process and had an odor masking effect. Coupled gas chromatography/mass spectrometric (GC/MS) analysis of the headspace volatiles revealed a blend of chemicals of which ten elicited electrophysiological activity in antennae of second instar nymphs. Five of these compounds including; 3-hydroxy-2-butanone, 2-heptanone, 2-isopropyl-3-methoxypyrazine [IPMP], 2-isobutyl-3-methoxypyrazine [IBMP] and (E)-β-caryophyllene were identified as unique to the volatiles of ripe berries and they elicited avoidance behavior in second instar nymphs when tested singly and in a blend. In addition, their blend also inhibited responses of nymphs to a synthetic attractant blend (kairomone). Our results suggest that the blend of the five compounds can be exploited as repellents in the management of A. thunbergii by pushing the pest away from coffee plantations or interfering with the pest–host recognition process through masking of suitable host odors.