Biology, Niche And Monitoring Techniques On Main Bark Beetles In Natural Spruce Forests In Qinghai

As one of the main afforestation species in the northwest,Picea crassifolia distributes widely in Qinghai,especially in Maixiu forest farm. Nowadays,bark beetles are damaging more and more spruce in this area. The article studied systematically the biological and ecological characteristics of the main bark beetle species from 2005 to 2007 in the natural spruce forests in Maixiu. Bark beetle pheromone is applied to control and monitor by a series of field tests in Maixiu, having got some good results and providing a theoretical and technical resistance for the sustainable control of the pest.1. There are 10 bark beetle species mainly found in natural spruce forest, including Ips nitidus, Ips shangrila, Polygraphus polygraphus, Tomicus sp., Pseudips orientalis, Dendroctonus micans, Pityogenes saalasi, Trypodendron lineatus, Scolytus sinopiceus and Pityophthorus pini. I. nitidus and I. shangrila are the two pionner secondary species and spread a large range in Maixiu natural forest. They attack weak spruce ordinarily, but also healthy trees when the population is large enough. D. micans as other Dendroctonus bark beetle is a pioneer species that attacks healty spruce.2. Through the study of the biological characteristic of Ips nitidus,it is discovered that the pest can finish two generations per year in Maixiu,the overwintering adults start to fly in the early May and reach the peak fly period since the middle until the late May. larvae stage of the first generation lasts 22-29d, the pupae stage lasts 7-11d,and the new callow emerge from late June to the middle July. The second generation last much shorter than the first one and appears from the early until the late.August. I. shangrila is often present in association with I. nitidus and also finishes two complete generations at Maixiu,but the time of overwinter adults'colonization is normally half a month later than that of I. nitidus. Depending on different elevations, the emergence can start since the middle May until the early June. The period from eggs to callow adults of the first generation takes 38 to 54d generally. And the second emergence time will appear in late August.3. Natural enemies in the natural spruce forests are found as following: the adults and the larvae of Thanasimus substriatus and Thanasimus lewisi.are predators of all the bark beetles. Respectively there are parasitoids Roptrocerus spp. which parasitize I. nitidus or I. shangrila larvae, Meringopus calescens calescens which parasitizes I. shangrila larvae, Cosmophorus sp. which parasitizes P. orientalis adults and Roptrocerus sp. which parasitize P. polygraphus, and also there is Pyemotes sp. which parasitizes bark beetle adults. Thanasimus substriatus is a predominant pradatory ememy, the average rate of bark beetles and Thanasimus substriatus in each trap is 20:1. A Roptrocerus species which parasitizes P. polygraphus is a dominant parasitoid, total collections of this species and other Roptrocerus species which parasitizes I. nitidus or I. shangrila is 74:1:2.4. Niches in 3 cells of spatial resources in spruce of 6 bark beetles species e were studied by using niche theory. The result indicates that the bark beetles achieve the balance and coexistence orders by various choices and utilization of spatial resources. Dentroctonus micans attacks the base of healthy spruce trunk as an initial species. This explores an available colonizing space for other secondary beetles. Then I. nitidus attacks trunk's middle and down parts ordinarily. I. shangrila colonizes from the top and branches of a mature tree, or an entire young tree.5. Studies on the field trapping effects of different ecolures in natural spruce forest showed that IT-Ecolure had little effect on Ips shangrila and a certain trapping ability to Ips nitidus, but lures need to be changed every month to monitor the emergence period because of the fast diffusing speed. The six improved attractants had better trapping ability to Ips nitidus than Ips shangrila, among which, IT-3 and Mountaintype-A were the strongest, with mean capture efficiency both about of 22 individuals in elevation 2800~2900m,30 individuals in 2900~3000m, 110 and 70 individuals above 3000m. These six IT-ecolures can be applied in monitoring Ips nitidus in the forest. Lures of chemical Ipsenol, Ipsdienol and cis-Verbenol has no trapping ability to Ips shangrila or little effect on Ips nitidus. But the combination lures of Ipsenol and cis-Verbenol trapped the most Ips nitidus and the natural enemy Thanassimus individuals. The other three combination lures had activities discreased with chemical Ipsdienol. So it's considered that Ipsdienol has the inhibition in trapping Ips nitidus, but not in trapping Thanasimus.