J. A. Pajares

Identification and Field Activity of a Male-Produced Aggregation Pheromone in the Pine Sawyer Beetle, Monochamus galloprovincialis

The pine sawyer beetle, Monochamus galloprovincialis, is a pest of pine trees in Europe and North Africa. Previously considered a secondary pest of stressed and dying trees, it is now receiving considerable attention as a vector of the pine wood nematode, Bursaphelenchus xylophilus, the causal agent of a lethal wilting disease in susceptible species of pines. Adult beetles are attracted to traps baited with a kairomone blend consisting of a host volatile, α-pinene, and two bark beetle pheromone components, ipsenol and 2-methyl-3-buten-2-ol. More recently it has been shown that mature male M. galloprovincialis produce a pheromone that attracts mature females in a laboratory bioassay. Here, volatiles were collected from mature male and female M. galloprovincialis, and a compound produced specifically by mature males was identified as 2-undecyloxy-1-ethanol from its gas chromatographic retention times, its mass spectrum, and by comparison with synthetic standards. The naturally-derived and synthetic compounds elicited electroantennographic responses from both females and males. Sealed polyethylene vials and polyethylene sachets were shown to be effective dispensers with zero-order release, the latter giving a higher release rate than the former. In two field tests, multiple-funnel traps baited with synthetic 2-undecyloxy-1-ethanol caught both female and male M. galloprovincialis, with higher catches at the higher release rate. This compound also synergized the attractiveness of the kairomone blend, the combined mixture catching 80–140% more beetles than the sum of the catches to each bait separately and luring up to two beetles/trap/d in a moderate-density population. We conclude that 2-undecyloxy-1-ethanol is a male-produced aggregation pheromone of M. galloprovincialis. This is the first example of a sex-specific compound in the cerambycid subfamily Lamiinae with significant behavioral activity in the field at a range sufficient to make it a useful trap bait. The possible roles of this pheromone in the chemical ecology of M. galloprovincialis and its potential use in pine wilt disease management are discussed.

Attractive responses by Monochamus galloprovincialis (Col., Cerambycidae) to host and bark beetle semiochemicals

Abstract:  The pine sawyer Monochamus galloprovincialis is the European vector of the recently introduced pine wood nematode. This nematode is the causal organism of pine wilt disease, a serious tree killer in East Asia. Efficacious baits and traps to monitor and control this beetle are now required. The effect of bark beetle (Ips spp.) pheromone components, released individually (ipsenol) or in blends (ipsenol, ipsdienol, cis‐verbenol and methyl‐butenol), together with host volatiles (turpentine or α‐pinene and ethanol) on M. galloprovincialis trap catches has been studied in Spain. A kairomonal response by male and female of M. galloprovincialis to Ips semiochemicals was found. Beetles were more attracted to host blends supplemented with bark beetle pheromones than to host volatiles alone. Ipsenol alone was attractive to pine sawyers, and was synergistic with α‐pinene and ethanol. The full blend of the four Ips semiochemicals and the host compounds was highly attractive. Multiple‐funnel traps were as effective as black cross‐vane traps in capturing this insect when the escape of trapped beetles was prevented. Trapping of non‐target bark beetle predators was also evaluated. The trogossitid Temnochila coerulea and clerid Thanasimus formicarius were kairomonally attracted to and killed in traps baited with bark beetle pheromones. These results suggest that effective monitoring of M. galloprovincialis would be possible by baiting any of these traps with host volatiles and Ips semiochemicals, but reduction of the lure components and trap modification to minimize impact on predators should be considered.

An operative kairomonal lure for managing pine sawyer beetle Monochamus galloprovincialis (Coleoptera: Cerymbycidae)

Abstract:  Monochamus galloprovincialis Olivier (Col., Cerambycidae) is a vector of the pine wood nematode, Bursaphelenchus xylophilus, causing the destructive pine wilt disease. An effective lure for monitoring and/or mass‐trapping would be of great interest in the management of this pine sawyer. Males and females of this species show an attractive kairomonal response to blends composed of four pheromone compounds used by Ips spp. bark beetles and two host volatiles from pines. This six‐component lure is highly attractive but may to be too complex and costly for practical use as each component is released from a separate lure. The role of each component, ipsdienol, ipsenol, cis‐verbenol, methyl butenol, α‐pinene and ethanol as attractants for M. galloprovincialis was field tested in Spain to obtain a simpler but equally effective bait. Ipsenol was confirmed as the strongest kairomonal signal to M. galloprovincialis synergizing response to α‐pinene by 95 times. The addition of methyl butenol to this blend doubled the number of males and females trapped. On the other hand, neither ipsdienol, cis‐verbenol nor ethanol improved the results when incorporated into the above three‐component blend. A lure consisting of ipsenol, methyl butenol and α‐pinene may be very cost‐efficient in operational monitoring or mass trapping of M. galloprovincialis. Three potentially repellent candidates, (−)verbenone, methyl cyclohexenone and trans‐conophthorin, were also tested against the attractive three‐component bait. trans‐Conophthorin significantly reduced male catches of M. galloprovincialis; methyl cyclohexenone had no effect. Verbenone significantly enhanced the response of females to the attractive combination of α‐pinene, ipsenol and methyl butenol.

Olfactory Sex Attraction and Mating Behaviour in the Pine Sawyer Monochamus galloprovincialis (Coleoptera: Cerambycidae)

The pine sawyer Monochamus galloprovincialis Olivier (Coleoptera: Cerambycidae) is a vector of the pine wood nematode Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle. Male and females of this species have a kairomonal attraction to host volatiles and Ips semiochemicals. Once on the host tree, males and females copulate and oviposition occurs. Bioassays using Y-tube olfactometry revealed that females were attracted to volatile compounds produced by males, but not to volatiles produced by females. However, immature males did not seem to release attractants for mature females and immature females did not show any attraction for mature males. A experiment designed to know about mating behaviour in this specie revealed that most of the males encountered females while they were walking. In all pairs both sexes contacted with antennae before copulation, however, in some occasions copulation did not proceed just after antennal contact. On the contrary, in all pairs observed, the male licked the elytra of the female with his mouth palpi just before copulation (licking); immediately afterwards, the male grabbed the female with his forelegs and mounted her suggesting a chemically mediated mate recognition by males.

2-(Undecyloxy)-ethanol is a major component of the male-produced aggregation pheromone of Monochamus sutor

The small white‐marmorated longicorn beetle, Monochamus sutor (L.) (Coleoptera: Cerambycidae), is widely distributed throughout Europe and Asia. It is a potential vector of the pine wood nematode, Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle, the causal agent of the devastating pine wilt disease. Volatiles were collected from both male and female beetles after maturation feeding. In analyses of these collections using gas chromatography (GC) coupled to mass spectrometry, a single male‐specific compound was detected and identified as 2‐(undecyloxy)‐ethanol. In analyses by GC coupled to electroantennography the only consistent responses from both female and male antennae were to this compound. Trapping tests were carried out in Spain, Sweden, and China. 2‐(Undecyloxy)‐ethanol was attractive to both male and female M. sutor beetles. A blend of the bark beetle pheromones ipsenol, ipsdienol, and 2‐methyl‐3‐buten‐2‐ol was also attractive to both sexes in Spain and Sweden, and further increased the attractiveness of the 2‐(undecyloxy)‐ethanol. The host plant volatiles α‐pinene, 3‐carene, and ethanol were weakly attractive, if at all, in all three countries and did not significantly increase the attractiveness of the blend of 2‐(undecyloxy)‐ethanol and bark beetle pheromones. 2‐(Undecyloxy)‐ethanol is thus proposed to be the major, if not only, component of the male‐produced aggregation pheromone of M. sutor, and its role is discussed. This compound has been reported as a pheromone of several other Monochamus species and is another example of the parsimony that seems to exist among the pheromones of many of the Cerambycidae. Traps baited with 2‐(undecyloxy)‐ethanol and bark beetle pheromones should be useful for monitoring and control of pine wilt disease, should M. sutor be proven to be a vector of the nematode.

Geometrid outbreak waves travel across Europe

We show that the population ecology of the 9- to 10-year cyclic, broadleaf-defoliating winter moth (Operophtera brumata) and other early-season geometrids cannot be fully understood on a local scale unless population behaviour is known on a European scale. Qualitative and quantitative data on O. brumata outbreaks were obtained from published sources and previously unpublished material provided by authors of this article. Data cover six decades from the 1950s to the first decade of twenty-first century and most European countries, giving new information fundamental for the understanding of the population ecology of O. brumata. Analyses on epicentral, regional and continental scales show that in each decade, a wave of O. brumata outbreaks travelled across Europe. On average, the waves moved unidirectionally ESE-WNW, that is, toward the Scandes and the Atlantic. When one wave reached the Atlantic coast after 9-10 years, the next one started in East Europe to travel the same c. 3000 km distance. The average wave speed and wavelength was 330 km year(-1) and 3135 km, respectively, the high speed being incongruous with sedentary geometrid populations. A mapping of the wave of the 1990s revealed that this wave travelled in a straight E-W direction. It therefore passed the Scandes diagonally first in the north on its way westward. Within the frame of the Scandes, this caused the illusion that the wave moved N-S. In analogy, outbreaks described previously as moving S-N or occurring contemporaneously along the Scandes were probably the result of continental-scale waves meeting the Scandes obliquely from the south or in parallel. In the steppe zone of eastern-most and south-east Europe, outbreaks of the winter moth did not participate in the waves. Here, broadleaved stands are small and widely separated. This makes the zone hostile to short-distance dispersal between O. brumata subpopulations and prevents synchronization within meta-populations. We hypothesize that hostile boundary models, involving reciprocal host-herbivore-enemy reactions at the transition between the steppe and the broadleaved forest zones, offer the best explanation to the origin of outbreak waves. These results have theoretical and practical implications and indicate that multidisciplinary, continentally coordinated studies are essential for an understanding of the spatio-temporal behaviour of cyclic animal populations.

Kairomonal responses of Tomicus destruens (Col., Scolytidae) to host volatiles α‐pinene and ethanol

The Mediterranean pine shoot beetle Tomicus destruens is one of the most damaging bark beetles attacking Mediterranean pine forests in southern Europe and north Africa. We studied the attractiveness of the host volatiles α‐pinene and ethanol at a range of release rates, alone or in combination, to T. destruens, in order to develop an attractive lure for the management of this beetle. T. destruens was attracted slightly to the host volatile α‐pinene, but a strong synergistic effect was found in the attraction towards monoterpene when ethanol was added to the bait. The highest catches of T. destruens were obtained by the optimal blend releasing 300 mg/day of α‐pinene and 900 mg/day of ethanol. In contrast to data reported for the related species T. piniperda, Mediterranean pine shoot beetles were clearly attracted to baits releasing ethanol alone (1350 mg/day). trans‐Verbenol, which was also added to host volatiles in some tests, did not affect the response. The use of the attractive blend proposed would have a low impact on the natural enemy population of Thanasimus formicarius because of asynchronies in flight periods. Other non‐target insects, such as the facultative predator or competitor Oxipleurus nodieri, were also significantly attracted. These results allow the development of an operative lure for the effective monitoring of T. destruens, although improvements by the addition of other host volatiles should be studied.

Optimization of traps for live trapping of Pine Wood Nematode vector Monochamus galloprovincialis

The pine sawyer beetle Monochamus galloprovincialis, a secondary pest of pines in Europe and North Africa, has become important as it was identified as the vector in Europe of Bursaphelenchus xylophilus, the causal agent of pine wilt disease (PWD). An effective trapping system is needed, not only for monitoring the insect vector but also for direct control of its population. Trapping may also provide key information on the nematode load carried by the beetles, allowing early detection of infections, provided that captured beetles remain alive within the trap. Highly effective attractants have been developed in recent years that are commonly used in combination with diverse standard trap designs. In this study, several trap designs were developed and compared to commercial standard models in order to determine which designs maximized the number of attracted insects actually caught and the proportion of them remaining alive. In total, 12 trap designs were evaluated in five field experiments carried out in France, Spain and Portugal. Teflon coating applied to the whole trap and extended, ventilated collecting cups resulted in a significant improvement of trap performance. These modifications led to significant increases of pine sawyer catches, up to 275%, when applied to multiple‐funnel or black cross‐vane traps, compared to standard designs. Furthermore, a significant proportion of the captured beetles remained alive within the trap. These findings have been used to develop new commercial traps (Econex Multifunnel‐12® and Crosstrap®; Econex, Murcia, Spain) available to forest managers. A model for insect survival within the trap was also fitted. Elapsed time between consecutive samplings, mean relative humidity and maximum radiation were the three most significant variables. Thus, traps should provide a suitable sample of live insects if sun exposure of the trap is minimized and a reasonable sampling schedule is implemented.

Verbenone protects pine trees from colonization by the six‐toothed pine bark beetle, Ips sexdentatus Boern. (Col.: Scolytinae)

Verbenone and trans‐conophthorin were tested against the aggregation pheromone of the six‐toothed bark beetle (Ips sexdentatus Boern.) on two trapping bioassays. Two different release rates of verbenone (2 mg/24 h and 40 mg/24 h) gave similar significant catch reductions (by 73% and 82%, respectively), whereas trans‐conophthorin lowered the catch by 45%. Joint release of both compounds reduced trap catches by 90%. Furthermore, the effect of these semiochemicals on Thanasimus formicarius L. and Temnoscheila coerulea Olivier, two important natural enemies of I. sexdentatus, as well as Hylurgus ligniperda Fabricius, a native associated scolytid, was evaluated. Both predators were significantly affected by verbenone, whereas the effect on H. ligniperda could not be concluded. Based on these results, verbenone was used in a third experiment to protect standing healthy Pinus nigra salzmannii J. F. Arnold trees from induced I. sexdentatus attack. The experiment consisted of two treatments and 20 paired‐tree replicates. Treatments were pheromone‐baited control trees and baited trees treated with verbenone (60 mg/24 h). These trees served as centres of 10 m radius plots from where a number of plot variables was recorded for local stand description. After the experimental period, all control trees had suffered attacks by I. sexdentatus, whereas trees treated with verbenone were significantly less attacked. Among other stand variables considered in the study, the following characterized the variation among plots most efficiently: (i) plot density, (ii) dominant height and (iii) the proportion of suppressed or (iv) intermediate dominance level trees in the plot. However, these variables did not significantly affect the repellent effect by verbenone. Further research should evaluate the use of verbenone on management strategies of ongoing attacks of I. sexdentatus.

Female recognition and sexual dimorphism of cuticular hydrocarbons in Monochamus galloprovincialis (Coleoptera: Cerambycidae).

ABSTRACT Monochamus galloprovincialis Olivier (Coleoptera: Cerambycidae) is the European vector of the pine wilt nematode, Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle, which causes the pine wilt disease. A series of experiments were carried out to determine the existence of a contact pheromone on the females cuticle. All males tested tried to copulate with freshly killed females, but none tried to copulate with the same females after they had been washed with hexane. When the hexane extract was reapplied to the extracted females, 50% of the males tried to copulate with them. This shows that females have a contact pheromone on their cuticle that stimulates male copulatory behavior. Cuticular compounds (mainly hydrocarbons) were sampled with solid phase microextraction and solvent extraction. No marked differences between sampling methods were observed. Individual peak analysis revealed that 23 compounds were significantly more abundant in females and eight were more abundant in males. Correspondence analysis found significant differences between the global hydrocarbon profile of male and female M. galloprovincialis. Individually, these compounds represented a small percentage of the total blend. This suggest that males of M. galloprovincialis may distinguish females by a blend of several, not very abundant, compounds that are present in both sexes but in different proportions.