For. Stud. China, 2012, 14(3): 224-228 DOI 10.1007/s11632-012-0309-9 Host selection behavior and incidence of the bark beetle Scolytus kashmirensis (Coleoptera: Curculionidae: Scolytinae) attacking elm (Ulmus Spp.) trees in Kashmir Abdul A. BUHROO' 卫 G. Department ofZoology, University ofKashmir, Hazratbal, Srinagar 190006, lndia 。 Beijing Forestry University and Springer-飞Terlag Berlin Heidelberg 2012 Abstract The status of the incidence of the bark beetle Scolytus kashmirensis Schedl on elm (Ulmus spp.) trees was determined in four districts of the Kashmir Valley in 2009. The incidence of the borer was higher in the Anantnag (25.93%) and Shopian (22.35%) districts of the Kashmir Valley, followed by the Ganderbal (17.14%) and Baramulla (1 6.67%) districts. The overall infestation re­ corded in these districts was 20.52%. The beetle under study chewed the scars on twigs ofboth the host and tentative non-host plants supplied to them in cages but bored and laid eggs in only one ofthem (the host plant). Both species of elm, Ulmus wallichiana and U. villosa, were susceptible to borer attacks; however, U. villosa showed low susc巳ptibility and high resistance compared to U. wallichi­ ana. Older, taller elms were preferred for feeding by bark be巳tles and are therefore much more susceptible to its infestation compared to younger elms. This bark beetle species also preferred to oviposit in branches ofthe host plants with diameters of9一 12mm. Key words bark beetle, Ulmus spp., host selection, incidence, oviposition 1 Introduction understood. Variation within host species can be especially chal­ The suitability of potential host plants encountered lenging for stem-colonizing scolytid beetles, because by insect herbivores varies widely because of genetic, of their requirement to kill trees to reproduce, the cor­ environmental and phenological factors (Fitt, 1986; responding ability of trees to ki11 beetles which fail Singer and Parmesan, 1993). Variability within plant in their attempts and the requirement to locate new populations has been proposed as a source of co­ hosts by each generation (Cates and Alexander, 1982; Nebeker et a1., 1993; RafIa and Small町" 1995). In ad­ evolutionary changes in host selection behavior and dition, most conifer bark beetles deposit a11 or nearly of genetically based divergence among herbivore a11 of their egg clutches within one host and their populations (Futuyma, 1983; Rausher, 1983; Jaenike progeny develops endophytica11y without the ability and Holt, 1991). Several studies have reported changes to seek a new host (Atkins, 1966; Wood, 1982). With in oviposition and feeding behavior in response to their short life span, high risk of predation outside changes in host plants (Harrison, 1987; Thompson et trees and experiencing decreased lipid reserves during a1., 1990; Singer and Parmesan, 1993). The potential of host searching (Sahota et al., 1987), adult bark beetles an herbivore population to undergo selective changes must make quick and viable host selection decisions. is determined by the extent of phenotypic variation Discrimination between resistant and susceptible hosts in behavior, the genetic basis of this variation and the is typically preferred following landing of tree-ki11ing relationships between selection and fitness (Jaenike, bark beetles (Rudinsky, 1962; Hynum and Berryman, 1990; Via, 1991; Carrière, 1998). However, genetic cor­ 1980; Moeck et al., 1981). Field pa忧ems suggest that relations between parental and offspring responses to the optimum host selection decision is density depen­ different hosts have only been investigated during the dant; colonization of healthy trees is more prevalent at last few decades (Courtney and Hard, 1990; Thompson high than at low beetle densities (Sa企anyik et al., 1975; et a 1., 1990; Via, 1991) and heritable variation in ac­ Wood, 1982). ceptance of plants within a host species is even less The Himalayan elm, Ulmus wallichiana, is a de- 'Author for correspondence. E-maiI: [email protected] Abdu! A. BUHROO: Host se!ection behavior and incidence of the bark beet!e Scolytus kashmirensis... 225 ciduous tree and host of the e1m bark beetle, Scoly­ Infestation of S. kashmirensis in Ulmus popu1ations tus kashmirensis Sched1 (Sched1, 1957; Heybroek, was observed on the basis of species specific symp­ 1963). S. kashmirensis is a common shot-ho1e borer toms. Shape and size ofbore/tunne1, tunne1ing pa忧em ， on e1m trees in the Kashmir Valley and acts as a vec­ niche of the grubs, nature and distance between sub tor of Ophiostoma himal-ulmi, the Dutch e1m disease tunne1s arising from the main feeding tunne1 which pathogen found on1y in the Hima1ayas (Brasier and opens to the outside through which feces and chewed Mehrotra, 1995). The cherry bark elm, Ulmus villosa, wood are expelled and the presence or absence of formerly called U. laevigata Roy1e, is native to the frass in the main feeding tunne1s are species specific Indian Hima1ayas (Santamour, 1979). All parts of an and serve to characterize the infested p1ants. e1m tree, from roots to twigs, buds, 1eaves, fl.owers and Infestation rates were recorded separate1y for two heartwood, are susceptib1e to insect attack. E1m trees Ulmus species at the marked study site and ana1yzed in poor physio1ogica1 conditions are often attacked by statistically. species of the genus Scolytus which, although they are seconda可 pests ， are a major cause of tree decay. Dutch e1m disease caused by the fungus Ophiostoma 2.2 Host selection and oviposition preference ulmi (= Ceratocystis ulmi), is one of the most destruc­ tive p1ant diseases to affect e1m trees in temperate re­ E1m 10gs, infested with the shot-ho1e borer, were cut gions of the world (Gibbs and Brasier, 1973; Brasier, into pieces of about 30 cm in 1ength, sea1ed at both 1991). The incidence of bark beet1es is 1argely deter­ ends with melted paraffin wax to avoid moisture 10ss mined by the distribution and abundance of their host and transported to the 1aboratory. These cut 10gs were tree species and climate (Lekander et al., 1977). Older, put in jars covered with mus1in cloth to ensure that taller e1ms are preferred for feeding by bark beetles grubs wou1d emerge as adults. Fresh 10gs of both host and therefore much more 1ike1y to become diseased trees (Ulmus spp.) and non-host trees (Salix sp.) were compared with younger trees (Sengonca and Leisse, tied to the borer infested 10gs to see the oviposition 1984). The trees infested by bark beetles may be rec­ preference and host specificity. Adu1ts were allowed to ognized at a distance by fading fo1iage of the tree, ini­ emerge naturally and craw1 or fl.y to begin searching tially a 1ight green then changing to a 1ight straw co1or for a new host. in a few weeks, eventually changing to yellowish­ Observations made during the study were statisti­ brown. C10se inspection may show a fine reddish­ cally ana1yzed. The per cent va1ues were ana1yzed by brown boring dust in bark crevices at the base of these Z-tests for differences between two proportions and trees (Webber, 1990). the va1ues were considered significant at p 三 0.05. For an insect to se1ect a new p1ant species as a host, the p1ant must support the reproduction of the insect (host suitabi1ity) and the insect must undergo 3 Results severa1 behaviora1 steps that 1ead to sustained feeding or oviposition (host acceptance) (Walter et 址， 2010). 3.1 Incidence and infestation Therefore, the objective of the present study was to test the incidence and host acceptance of the e1m borer A tota1 of 975 e1m trees were observed in 32 nurseries 丘 kashmirensis from the four districts in the Kashmir Valley. Out of these 975 trees, 203 were found infested with the shot­ ho1e borer，丘 kashmirensis. According to the survey 2 Materials and methods results (Tab1e 1), the incidence of the borer was high­ est in the Anantnag and Shopian districts, i.e., 25.93% 2.1 Incidence and distribution of S. kashmirensis and 22.35%, respective1y, followed by the Ganderba1 and Baramulla districts, i.e., 17.14% and 16.67%, re­ In order to study the incidence and distribution of 丘 spective1y. The overall infestation recorded in these kashmirensis on Ulmus, i.e., Ulmus wallichiana and districts was 20.52%. U. villosa, in the Kashmir Valley, a month1y survey was conducted in unmanaged e1m nursery p10ts in 2009. Four districts were se1ected, i.e., Anantnag, 3.2 Host selection and oviposition preference Shopian, Ganderba1 and Baramulla. The rate of borer infestation was calcu1ated by the following formu1a: E1m shot-ho1e borers perceive the odor of their host Per cent infested = Tota1- -.-- ---------number oftrees-- .---- ------.--infested x 100 Tota1 number oftrees observed 226 Forestry Studies in China, Vo1.l4, No.3, 2012 plants by biting, chewing and boring into the bark. ι villosa (cher可 bark elm) andι wallichiana (Hi­ This has been confirmed by supplying primary malayan elm) to the shot-ho1e borer, S. kashmirensis, branches of elm and willow as oviposition material to was revealed by the feeding and infestation rates. Ta­ ovipositing females. Females made bores on both elm ble 4 shows that the shot-hole borer preferred U. wal­ and willow branches, but oviposited only on the elm /ichiana twigs (diameter 8一 11 mm) compared to U. branches (Table 2). Difference in the number of bores villosa twigs (diameter 8-11 mm). The data in Table made on elm and willow was insignificant (p > 0.0 匀， 4 depict low susceptibility and high resistance in the while the difference in the number of oviposited eggs case of U. villosa. was highly significant (p < 0.0001), which confirmed host specificity of the shot-hole borer under investiga­ tíon. 4 Discussion Gravid females scurried over host plants, bore the primary branches, 6-15 mm in diameter, severed bark Bark beetles have been reported as potential or regular and phloem completely and xylem partially.