Abstract
Wood-boring insects, such as Cerambyx welensii Küster, are involved in oak decline in Mediterranean areas. To advance our understanding of the olfactory perception of C. welensii, we recorded electroantennographic (EAG) responses from male and female antennae to 32 tree volatile organic compounds typical of emissions from its main Quercus L. hosts, and also analysed the dose-dependent response. Cerambyx welensii antennae responded to 24 chemicals. Eight odorants elicited the highest EAG responses (normalized values of over 98%): 1,8-cineole, limonene-type blend, β-pinene, pinene-type blend, sabinene, α-pinene, turpentine and (E)-2-hexenal. Cerambyx welensii exhibits a broad sensitivity to common tree volatiles. The high EAG responses to both limonene- and pinene-type blends suggest the detection of specific blends of the main foliar monoterpenes emitted by Q. suber L. and Q. ilex L. (limonene, α- and β-pinene, sabinene and myrcene), which could influence the intraspecific host choice by C. welensii, and in particular, females may be able to detect oak trees with a limonene-type chemotype. In addition, C. welensii showed high antennal activity to some odorants that characterize emissions from non-host tree species (1,8-cineole, β-pinene, α-pinene, turpentine, δ3-carene and camphene). The results obtained may be applicable to optimize monitoring and mass-trapping programmes in an integrated pest management context.
Highlights
Mediterranean Quercus suber L. and Quercus ilex L. open woodlands have a high ecological, economic and cultural importance in Western Europe and Northern Africa. Tree decline in these Mediterranean Quercus stands is significantly influenced by wood-boring insects, such as Cerambyx welensii Küster (Coleoptera, Cerambycidae), as these beetles act as an aggravating factor [1,2,3]
Taking into account differences we found between sexes, EAG data from males and females were treated separately for six odorants (1,8-cineole, (E)-β-ocimene, β-pinene, α-pinene, α-terpinene and the limonene-type blend), but pooled for the others
Yuen’s bootstrap tests revealed significant differences between sexes only for two compounds, 1,8-cineole (t = 3.66, p = 0.011) and (E)-βocimene (t = 2.05, p = 0.038), while marginally significant differences between sexes were observed for another four odorants: β-pinene, α-pinene, α-terpinene and the limonenetype blend (EAG responses to this blend were compared by using a Mann-Whitney U-test) (1.64 ≤ t ≤ 2.16; 0.056 ≤ p ≤ 0.080, with the limonene-type blend and α-pinene at the lowest and highest ends of the range, respectively). (E)-2-hexenal elicited moderate responses (0.6 ± 0.07 mV, Mean0.2 ± Error0.2, n = 32), and responses to the hexane control were very weak (0.08 ± 0.03 mV, n = 32)
Summary
Mediterranean Quercus suber L. and Quercus ilex L. open woodlands (called montados in Portugal and dehesas in Spain) have a high ecological, economic and cultural importance in Western Europe and Northern Africa. Tree decline in these Mediterranean Quercus stands is significantly influenced by wood-boring insects, such as Cerambyx welensii Küster (Coleoptera, Cerambycidae), as these beetles act as an aggravating factor [1,2,3]. Adults have crepuscular and early nocturnal habits; the larvae bore into wood, mainly in weakened trees, causing tree branches and trunks to break [1] These insects facilitate infection by both plant pathogens and wood-decaying fungi [5]. To understand the olfactory sensitivity of C. welensii to plant volatiles, we analysed EAG responses of adult females and males to tree VOCs, namely, host-related odours
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