Monochamus alternatus Hope (Coleoptera: Cerambycidae) is a major vector pest insect to spread pine wood nematode, Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle in eastern Asia. The control and treatment of M. alternatus Hope is difficult because it develops hidden under bark and therefore is not accessible to chemical agents for natural enemies. Allison et al. [1] note that various species of Monochamus (Coleoptera: Cerambycidae) respond to conifer volatiles and bark beetle pheromones. As one efficient and eco-friendly way to control species' population, trapping M. alternatus with an attractant is useful in the treatment of harmful species with no detriment to environment. This method has been widely utilized in forestry areas [2-4]. In Texas, Billings and Cameron [5] and Billings [6] found a kairomonal response by Monochamus titillator (F.) to a blend of Ips spp. pheromones (ipsenol, ipsdienol and cis-verbenol). In recent years, a variety of attractants have been developed from volatiles of host plants, which are crucial for monitoring, prevention and control of M. alternatus and to control the spread of B. xylophilus and break cycle pathways [7-13]. In southeastern United State, M. titillator is attracted to traps baited with ipsenol or ipsenol and ipsdienol [14]. Raffa [15] reported that M. carolinensis (Olivier were captured in ipsdienol- baited traps in Wisconsin). In British Columbia, Miller and Borden [16] found that trap catches of M. clamator (LeConte) increased as the combined release rates of ipsdienol and (-) – ß - phellandrene increased. Allison et al. [17] found that four Monochamus spp. In Northwestern North America respond to the pheromones of sympatric bark beetle, likely a mechanism for optimal foraging by adults for oviposition sites [18]. However, recent field tests in China showed that two bark beetle attractants had a negative attractiveness to M. alternatus. Therefore, this study was designed to screen and optimize the more effective substances of M. alternatus attractants to enhance their utility. A novel field test was carried out to investigate the attractiveness to M. alternatus of six bark beetle attractants combined with a Chinese longicorn beetle attractant. The results provide a theoretical basis for monitoring and controlling M. alternatus as well as inhibiting the spread of pine wilt disease.

In this paper, effect of European Hylesinus beetle attractants on M. alternatus Hope were firstly studied and compared in eastern China, to find efficient products for treatment of M. alternatus and prevention of the spread of B. xylophilus.

Experimental site

The study was conducted in the forest at Fuyang, Zhejiang Province, China (30°03’N, 119°57’E). The dominant species in the forest was Pinus massoniana, P. elliotii and P. taeda. Twenty to thirty percent trees of all species were infected by the pine wood nematode disease, but chemical pesticides were not used in the experimental site for a long time. For P. massoniana, it has an area of 301 hm², an average age of 23 years, an average height of 6 m and an average density of 800 trees/hm².

Attractants

All of the attractants used in this experiment are listed in the Table 1. M. alternatus attractant M-99 was provided by the Forest Pest Control and Quarantine Bureau of Zhejiang Province, China, and bark beetle attractants were provided by the French National Institute for Agricultural Research (INRA) in France.

Table 1: Chemical lures and enantiomeric purity of chemicals tested in the field assay

Experimental design

The experiment was carried out from May 1st to July 15th, 2010, which includes pre- and post-peaks of M. alternatus adult populations. Pine trees with a distance of 3 m or more between each other and located on the roadside, hillside and ridge where air circulation was good were selected. The cross vanes type trap was used for beetle collection. Traps were fixed with iron wire on the trees and 1.5-2.0 m above the ground as well as at least 50 m apart from each other.

The experiments had 6 treatments (Table 2), each with 5 replications. When a trap was set, the attractants were fixed in the middle of the column inside the trap without a cap or with an opening in the sack for slow release of volatile compounds. M-99 was replaced every 15 days and the rest had no replacement. All insects trapped were collected and recorded every 3-7 days, which was depending on weather conditions. After each collection, each trap was changed the position with the next trap. The insects captured were taken back to the laboratory for counting and identification. Meanwhile, the number of M. alternatus Hope adults, eggs and nematodes carried were observed with microscopes and statistically calculated.

Table 2: Comparison of effects among five attractants for M. alternatus Hope

Statistical analysis

Statistic analysis of the experimental data was performed using Microsoft Office Excel 2007. One way ANOVA in SPSS13.0 was performed for the attractive effects between different lures. In addition, Duncan’s method was used to analyze the differences between various treatments (P<0.05).

Attraction of different lures for M. alternatus Hope

A total of 147 M. alternatus adults (71 males and 76 females; sex ratio of 0.93) were captured by the five attractants from May 1st to July 15th. The quantity of M. alternatus Hope attracted by each lure, the quantity of the nematodes they carried, and the number of eggs were shown in Table 2.

*The differences between various treatments were analyzed by Duncan method (P < 0.05).

Based on their attractive effects, M-99 and exo-brevicomin are best, Seudenol is second, and then 2-Methyl-3-buten-2-ol and Ipsenol, ipsdienol and cis-verbenol. M-99 and exo-brevicomin attracted the largest amount of adult M. alternatus Hope is 35, which also showed high quantity of nematodes and eggs. The control group (water) was worst.

ANOVA results show that there is no significant difference between M-99, Exo-brevicomin, Seudenol, and Ipsenol, ipsdienol and cis-verbenol. However, these four lures showed distinctly better attraction than 2-Methyl-3-buten-2-ol which only trapped 4.2 adults on average. The control group again showed the worst effect.

Quantities of captured M. alternatus adult-carried nematodes and female-carried eggs

Microscopic examination of M. alternatus adults trapped by the five attractants revealed that the percentages of adults carrying pine wood nematodes trapped by M-99, Exo-brevicomin, 2-Methyl-3-buten-2-ol, Seudenol and Ipsenol, ipsdienol and cis-verbenol were 82%, 79%, 71%, 68%, and 56%, respectively. The adult females trapped by the five attractants had deep yellow mature eggs and white immature eggs in their ovaries. As shown in Table 2, the number of eggs per females trapped in different treatments had no significant difference.

Attractiveness of different attractant combinations to other wood-boring beetles

The species and number of other wood-boring beetles trapped by M-99 and four attractant combinations are listed in Table 3. As for the species, a large number of insects belong to coleopteran. There are also insects from Homoptera and Orthoptera. In addition, borer pests, such as Spondylis buprestoides and M. bimaculatus Gahan, are in large quantities, which are close to that of M. alternatus Hope. This indicates that these five lures not only show attraction to M. alternatus Hope, but also have the attractive effect on borer pests like S. buprestoides and M. bimaculatus Gahan.

Table 3: The species and number of individuals of wood-boring insects trapped by different attractants

Based on the number of trapped M. alternatus Hope, Exo-brevicomin showed the best effect. M-99 is relatively more stable and attracts more female insects compared to Exo-brevicomin, which can effectively prevent breeding of M. alternatus Hope and spread of B. xylophilus. On the other hand, Exo-brevicomin has better an attractive effect on the M. alternatus Hope in the period of nutrition supplement.

As for the species and quantity of the trapped insects, Seudenol captured the highest number of species, especially Coleoptera. Among them, S. buprestoides and M. bimaculatus Gahan have the largest quantities. These results show that Seudenol can be widely applied to various insects. However, the volatilization of M-99 is great and difficult to control. Therefore, M-99 can only be used in a short time and has to be replaced frequently, which limits its practical application. In contrast, Hylesinus beetle attractants are used in a sustained release manner, which can effectively control the volatilization and thus prolong the cycle time and reduce the cost. Therefore, these lures have broad applications.

In this study, we found that there was no significant difference among Exo-brevicomin, Seudenol, Ipsenol, Ipsdienol and Cis-verbenol, and M-99, whereas these four lures showed significant improved effects compared to 2-Methyl-3-buten-2-ol. This could be caused by many factors, such as the lure composition, natural environment, host plant, geographical difference, and geographical isolation of M. alternatus Hope. Among them, the lure composition is the most important factor. The preference to host plants from the insects can also cause different attractive effects. For M. alternatus Hope, M-99 has the best attraction, because that the plant-sourced volatile substance from M-99 matches well with M. alternatus Hope, while the volatile substances in other lures mainly target Hylesinus beetle. Moreover, the attractive effects are influenced by the environment, the installation technique, volatilization control, and weather condition. Therefore, appropriate attractants should be selected to achieve an optimal effect based on the practical condition and requirement.

The project was jointly supported by funds from the National 948 (No. 2009-4-36) and international cooperational program of science and technology (No. 2006DFA31790).