Coffee Berry Borer Joins Bark Beetles in Coffee Klatch

Juliana Jaramillo,Christian Borgemeister,Armin Troeger,Hans-Michael Poehling,Baldwyn Torto,Dickson Mwenda,Wittko Francke,Frederic Marion-Poll

doi:10.1371/journal.pone.0074277

Abstract

Unanswered key questions in bark beetle-plant interactions concern host finding in species attacking angiosperms in tropical zones and whether management strategies based on chemical signaling used for their conifer-attacking temperate relatives may also be applied in the tropics. We hypothesized that there should be a common link in chemical signaling mediating host location by these Scolytids. Using laboratory behavioral assays and chemical analysis we demonstrate that the yellow-orange exocarp stage of coffee berries, which attracts the coffee berry borer, releases relatively high amounts of volatiles including conophthorin, chalcogran, frontalin and sulcatone that are typically associated with Scolytinae chemical ecology. The green stage of the berry produces a much less complex bouquet containing small amounts of conophthorin but no other compounds known as bark beetle semiochemicals. In behavioral assays, the coffee berry borer was attracted to the spiroacetals conophthorin and chalcogran, but avoided the monoterpenes verbenone and α-pinene, demonstrating that, as in their conifer-attacking relatives in temperate zones, the use of host and non-host volatiles is also critical in host finding by tropical species. We speculate that microorganisms formed a common basis for the establishment of crucial chemical signals comprising inter- and intraspecific communication systems in both temperate- and tropical-occurring bark beetles attacking gymnosperms and angiosperms.

Highlights

Phytophagous insects recognize specific olfactory signals in order to find their hosts against the ‘background noise’ caused by environmental odours This specificity in olfactory signaling is typically defined by its quantity and/or quality, which in turn is governed by relative proportions of components in the signal [1]
Identified coffee berry volatile organic compounds (VOCs) associated with Scolytinae chemical ecology were chalcogran and frontalin (Table 1)
We found that coffee berries (C. arabica) produce compounds identical with pheromones of coniferous Scolytinae which attack coniferous trees and which serve as kairomones for host location by the tropical relative, the coffee berry borer

Summary

Introduction

Phytophagous insects recognize specific olfactory signals in order to find their hosts against the ‘background noise’ caused by environmental odours This specificity in olfactory signaling is typically defined by its quantity and/or quality, which in turn is governed by relative proportions of components in the signal [1]. As a result of these interactions, some plants have evolved to mimic the odor bouquet of certain insects to cause avoidance behaviour in herbivores [2], as demonstrated for bark beetles whose sensory detection system allows them to detect host volatiles, and to avoid non-host volatiles [3,4,5,6]. Within Scolytinae, bark beetles mainly feed on bark and phloem, occasionally on seeds, acquiring most of their nutrients from dead plant tissue [7,8]. Ambrosia beetles (Scolytinae and Platypodinae), on the other hand, attack xylem tissue of their hosts and are typically associated with symbiotic microorganisms, with fungi and with bacteria. Ambrosia beetles are found largely in wet tropical forests [9]

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Conclusion