How do sex and sexual maturation influence the response of Monochamus galloprovincialis to host odours?

Abstract

Finding the right host plant for feeding and reproduction is crucial for herbivorous insects. Usually they need both visual and olfactory cues to locate and colonize their host plants, but the respective role of the two types of stimuli is difficult to disentangle. Model plants mimicking the shape and colour of natural hosts, combined with odours dispensers, are relevant tools for this purpose. We used dummy pines and cut branches of natural pines to investigate host attraction in Monochamus galloprovincialis, the insect vector of the pine wood nematode in Europe. We compared the behavioural response of males and females, sexually mature or immature, in a large climatic chamber and in an olfactometer. Immature females were significantly attracted by the sole odours released by pines. Immature males and mature males and females needed a combination of visual and olfactory cues to find the host tree. These findings suggest that beetles use both visual and chemical cues to locate pine trees but that relevant stimuli likely differ between beetles of different sex and sexual maturation status. Our results question the implementation of precautionary clear‐cuts around infested trees for limiting the spread of PWN.

Effectiveness of clear‐cuttings in non‐fragmented pine forests in relation to EU regulations for the eradication of the pine wood nematode

“…In Scenario 1, we distinguish two sub‐cases: the CCZ has no effect on the dispersal behaviour (Scenario 1‐1, ‘strategy of non‐avoidance of the CCZ’; Figure a) or the beetle tends to exit the CCZ and not enter it again (Scenario 1‐2, ‘strategy of avoidance of the CCZ’; Figure b) because Monochamus beetles are known to be attracted by visual and chemical cues emitted by host pines (Giffard, David, Joubard, Piou, & Jactel, ). In Scenario 2, because the clear‐cutting occurs after the beetles have dispersed, CCZ cannot affect the past dispersal behaviour of the insect vector.…”

The Effect of Trap Color on Catches of Monochamus galloprovincialis and Three Most Numerous Non-Target Insect Species

“…The positive response of M. galloprovincialis to green may be explained by the presence of green-sensitive opsins in the eyes of different beetles, including M. alternatus and Anoplophora glabripennis (Motschulsky) [ 33 ]. This may also be a reason why immature males and both mature males and females of M. galloprovincialis are attracted to the green pine plants/branches [ 47 ]. Interestingly, M. alternatus was found to possess only green sensitive opsins [ 33 ], but the beetles were more attracted to black and brown traps than to green traps in the field tests [ 46 ].…”

“…Surprisingly, its eyes are of the apposition type, such as in diurnal species, but they are adapted to low light intensity [ 45 ] and were shown to play an important role in mate finding over short distances [ 46 ]. The importance of visual and/or chemical cues in host tree finding was also shown for M. galloprovincialis , and its response to relevant stimuli appeared to be dependent on sex and sexual maturity [ 47 ].…”

Modelling Monochamus galloprovincialis dispersal trajectories across a heterogeneous landscape to optimize monitoring by trapping networks

“…All the land-use types containing high density of non-host tree species, principally broadleaved trees like oaks, had high friction values for the dispersal of M. galloprovincialis. The avoidance of patches of non-habitat maybe explained by the lack of attractive chemical cues for the beetles, as they are attracted to pine terpenes, particularly during the maturation phase of young adults (Giffard et al 2017). In addition, broadleaved trees might emit non-host volatiles that are commonly used by conifer-specialist insects to identify and avoid non-habitats (Jactel et al 2011), according to the semiochemical diversity hypothesis (Zhang and Schlyter 2004).…”