Báo cáo khoa học: "Scots pine susceptibility to attack by Tomicus piniperda (L) as related to pruning date and attack density"

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Original article Scots pine susceptibility to attack by Tomicus piniperda (L) as related to pruning date and attack density B C Långström Hellqvist Swedish University of Agricultural Sciences, Division of Forest Entomology, S-776 98 Garpenberg, Sweden (Received 25 May 1992; accepted 23 November 1992) Summary — The susceptibility of young Scots pine to bark beetle attack was increased by pruning similar size 10, 7 and 1 month(s) prior to beetle flight. Beetle population in the trees to a crown = study area was high, and spontaneous attacks were expected to occur on the pruned trees. Half of the trees were baited with split pine bolts in order to attract more beetles to attack these trees. Thus, experimental trees carrying one-third of their original foliage and with different vigour indices due to = the pruning history were exposed to 2 levels of beetle attack. The pine shoot beetles preferentially attacked baited trees, whereas attack rates did not differ between pruning dates. Six wk after attack, beetle performance was better in trees pruned shortly before attack than in trees pruned earlier. Vig- our indices differed between the 2 treatments, but phloem starch, secondary resinosis (expressed as lesion size and resin acid content) and tree survival did not. Trees that eventually survived were sig- nificantly less attacked than those that died. but the 2 groups did not differ in tree characteristics (ex- cept in cambial electrical resistance). pine shoot beetles / Pinus sylvestris / beetle performance / defence reactions / host vitality Résumé — Susceptibilité du pin sylvestre aux attaques de Tomicus piniperda L en fonction de la date d’élagage et de la densité d’attaque. La susceptibilité de jeunes pins sylvestre aux atta- ques de scolytides a été accrue en élagant les arbres, de façon à ce que la taille de leur couronne soit comparable. Les élagages ont eu lieu environ 10, 7 et 1 mois avant le vol des insectes. Les ni- veaux de population dans la zone d’étude étaient élevés et des attaques spontanées étaient prévi- sibles sur les arbres élagués. Pour augmenter leur attractivité, la moitié des arbres ont été appâtés avec des rondins de pin. Ainsi, des arbres portant environ un tiers de leur feuillage d’origine, et ayant différents indices de vigueur à cause de l’élagage (tableau 1) ont été soumis à 2 niveaux d’atta- que. La moitié des arbres ont été coupés début juin, les autres fin août. T piniperda a attaqué de préférence les arbres appâtés (figs 1, 2) mais le taux d’attaque a été le même pour les différentes dates d’élagage (fig 1). Six semaines après les attaques, les arbres élagués le plus tardivement ren- fermaient plus d’insectes parents et plus de galeries contenant des larves que les arbres élagués précocement (tableau II). Les galeries maternelles étaient aussi significativement plus longues dans le premier cas (fig 1). Les arbres élagués environ 1 an avant l’attaque représentaient donc un maté- riel moins favorable pour les insectes. Les indices de vigueur différaient également entre les 2 traite-
ments (tableau I), mais l’amidon présent dans le liber, la réaction secondaire (mesurée par la taille de la zone réactionnelle et son contenu en acides résiniques) et le taux de survie des arbres étaient semblables (fig 1, tableau III). La réaction de défense induite a avorté sur certains des arbres qui sup- portait une densité d’attaque supérieure à 200 galeries maternelles par m (fig 3). La longueur 2 moyenne des galeries dépassait 40 mm (fig 4). Cependant, des arbres plus densément attaqués ont survécu. Chez les arbres résistants, les lésions occupaient au maximum 30% de la surface du phloème dans la partie basse du tronc (fig 5). Les arbres supposés survivants étaient significative- ment moins attaqués que les morts, mais leur taille, leur croissance et leur indice de vigueur étaient les mêmes (tableau IV). Cependant, la résistance électrique du cambium mesurée à la date de l’atta- que était significativement différente dans les 2 groupes, ce qui paraît illogique (tableau IV). Une des- cendance a été observée uniquement sur les arbres tués, avec un taux de multiplication inférieur à l’unité (tableau IV). Un début d’occlusion de l’aubier a été remarqué sur quelques arbres (potentielle- ment mourants ?) après 6 sem. L’aubier des arbres morts était fortement bleui, mais pas celui des arbres survivants. Tomicus piniperda / Pinus sylvestris / performance des insectes / réactions de défense / vitali- té de l’hôte INTRODUCTION references therein). Thus, trees or stands may become susceptible to bark beetles as a result of reduced vitality and/or in- In contrast to herbivores in general, most creased beetle populations, as exemplified bark beetles attacking live trees need to by the concept of epidemic threshold (Ber- kill their hosts in order to reproduce suc- ryman, 1982). cessfully. Consequently, host trees have In Europe, Tomicus piniperda (L) (Col evolved strong defence systems against Scolytidae) is the most important bark bee- bark beetles. Conifers counteract attacking tle attacking Scots pine (for references, bark beetles and their associated blue- see eg Escherich, 1923; Postner, 1974; stain fungi by a dual defence system Långström, 1983). In northern Europe, based on primary resin which is exuded however, T piniperda is seldom capable of when resin ducts are severed, and by an successfully attacking living pine mass induced secondary resinosis containing trees, whereas in southerly areas it more the aggressor in resin-soaked lesions (for has been kill trees from time to reported to an overview, see Christiansen et al, 1987). time (for references, see Långström and Successful colonisation by bark beetles This difference in beetle Hellqvist, 1991). occurs when the beetles can exhaust the aggressiveness or host susceptibility trig- defence system of the host trees by mas- gered our interest in studying this pest- sive synchronized attacks (Berryman et al, host relation under our conditions. 1989; and references therein). Possession of aggregation pheromones as well as as- So far, we have found that even low- sociation with pathogenic blue-stain fungi vigour Scots pines that were additionally seem to be typical features of tree-killing weakened by pruning have a remarkable bark beetles (Christiansen et al, 1987; and resistance to induced attacks by T piniper- references therein). As the resistance var- da (Långström and Hellqvist, 1988). Trees ies with host vitality, more beetles are responded with vigourous induced defence needed to overwhelm the resistance of reactions, enclosing the beetles in resin- vigourous and fast-growing trees than less soaked lesions. Typically, trees that failed vital ones (Christiansen et al, 1987; and to resist attacks accumulated less resin ac-
ids in the lesions and depleted their starch MATERIAL AND METHODS reserves in the phloem (Långström et al, 1992). Two species of blue-stain fungi, Leptographium wingfieldii Morelet and Field work Ophiostoma minus (Hedgc) H et P Syd, were frequently isolated from the sapwood The experimental site was a 30-yr-old pure = of killed trees (Solheim and Långström, stand at Norrsundet in Gästrikland, Central pine 1991).The same species have been found Sweden (= 61 °N lat, 16 °C long). The pine trees to be associated with T piniperda in France displayed misshapen crowns due to intensive (Lieutier et al, 1989b). Thus, the interaction shoot-feeding by pine shoot beetles over many years, and were obviously not in good condition between the beetle, its fungi and Scots (see also Långström and Hellqvist, 1988; pine seems to be similar in Sweden and in Långström et al, 1992). France (Lieutier et al, 1988; 1989a; Lieuti- In order to create a tree population with re- er, in press). duced but similar capacity for carbohydrate pro- The physiological mechanisms underly- duction despite different vigour indices, trees ing host resistance to bark beetles are were pruned to similar needle biomass on 3 oc- poorly understood. Carbohydrates, being casions prior to beetle attack. In June 1988, 60 similar-looking (diameter, height and crown size) both an energy source and raw material for pine trees were selected for this pruning experi- the defence chemistry, may be important ment in the low-vigour stand described above. (Christiansen et al, 1987; and references Twenty of these trees were pruned on 21 June therein); especially the tree’s capacity to (after beetle flight in 1988), 9 September 1988 translocate carbohydrates to the area un- and 9 March (prior to beetle flight in 1989), re- der attack (Christiansen and Ericsson, spectively, leaving the 7-8 uppermost whorls in- 1986; Miller and Berryman, 1986; tact (table I). Långström al, 1992). Hence, manipula- et As the beetle population was high in the tion of needle biomass and tree vitality (de- area, beetle attacks were expected to occur on the pruned trees (cf Långström and Hellqvist, fined as vigour index sensu Waring and 1988). In order to induce a higher level of beetle Pitman, 1985) should affect the tree’s de- attack, half of the trees (10 in each treatment) fence capacity in a predictable way. Our furnished with split bolts of fresh pine were previous studies also showed that pruned wood to enhance host attraction to the beetles trees succumbed more frequently to beetle (Långström and Hellqvist, 1988). This baiting attack than unpruned trees, but as the for- was carried out on 9 March 1989, but as beetle mer were also subject to more attacks, we flight started later than expected, all bait-bolts were replaced with new bolts on 13 April, when could not separate the effect of attack den- flying beetles were observed in the stand. Judg- sity on the induced defence reaction from ing from meteorological data, that day was prob- that of host tree vigour. ably the first day of Tomicus flight in the area. Thus, in the present study, we com- In an attempt to measure tree vitality at the pared the susceptibility of weakened trees time of beetle attack, we measured the cambial similar needle biomass but different with a electrical resistance (CER) of the inner bark with vigour indices (ie a similar capacity to pro- a Shigometer, especially developed for this pur- pose (for a technical description and references, duce carbohydrates, but different growth see Lindberg and Johansson, 1989). This tech- efficiency) to induced attacks by pine shoot nique has been used in different contexts for de- beetles. By relating beetle performance scribing tree vitality (see eg Piene et al, 1984a, and defence reactions to tree characteris- 1984b; Matson et al, 1987), and also in bark tics, we attempted to identify factors typical beetle studies, but with contradictory results for resistant trees, as well as critical attack (Christiansen, 1981; Lieutier and Ferrell, 1988). levels for trees of different vitality. CER readings were taken from experimental
(up to the first living whorl at 3 m height) on 2 occasions: 11 April (all trees) and 13 stems trees = transported to the laboratory within 24 h, April (baited trees only). Readings were taken in were and cold-stored at +2 °C until the next day. early afternoon, and the ambient temperature recorded every 30 min. From each tree, 2 was were taken with the probes inserted readings into the bark at opposite sides of the vertically Laboratory procedures stem at breast height. Uncorrected readings were used since ambient temperature was stable during the procedure and close to the On the day after felling, the stems were cut at standard 15 °C. 20 and 30 cm stem height. The lower sections Half of the pruned trees were felled on 1 were discarded, and the upper 10-cm pieces were placed in trays with a few cm of a water June (when beetle tunelling was still in progress suspension of Fast Green (0.25 g per 1 I water; and developed lesions were expected to be Parmeter et al, 1989) and were allowed to take found; cf Långström et al, 1992), and the re- up the dye for 24 h at room temperature. Then maining pruned trees on 24 August 1989 (when new surfaces were cut 5 cm above the lower the brood had emerged and trees had either = end of the bolts and the presence of unstained died or survived). After felling, tree length, crown length, annual height growth back to non-conducting sapwood and heartwood was 1983, crown fresh weight (ie all live branches), delineated. and the number of live whorls were recorded. After cutting the stem in sections, the bolts The trees were classified as surviving, survival between 30-80 and 130-180 cm stem heights uncertain, dying or dead, according to the ap- were immediately frozen, the 80-130-cm sec- pearance of the foliage and the inner bark. tion taken for isolation of fungi from beetle gal- A stem disc was sawn at breast height, and leries and sapwood (Solheim and Långström, the border between the translucent sapwood 1991),and the remaining sections up to live and opaque heartwood marked immediately. All crown were cold-stored until analysed.
Before removing the bark on the 30-80-cm net lesion area was obtained by subtracting the stem section (and section 130-180 cm, if T mi- gallery (calculated as gallery length x area egg nor (Hart) was present), all exit holes of the 2 mm average egg gallery width). Knowing the emerging new brood of pine shoot beetles were attack density and the mean lesion area, the to- per m inner bark could be calcu- 2 counted (not applicable for June-felled trees). If tal lesion area galleries of T minor were present under the lated. bark, the exit holes of this species were counted on the wood surface, the difference between the 2 counts then being attributable to T piniperda. Chemical analyses As the bark was relatively thin, no correction was made for the few beetles emerging through old exit holes (cf Salonen, 1973). The presence Inner bark samples were pooled within each of blue-stain on the cut bolt ends was noted in pruning date into 3 attack density classes (see 10% area classes. below) prior to analysing resin acids and starch as previously described by Långström et al For the first 20 galleries encountered of each (1992). beetle species after bark removal, the following were recorded: total gallery length, length of le- sion tip ahead of the gallery tip, total lesion length, presence of parent beetle(s), eggs, lar- Statistics vae or pupae in the gallery; then the lesions sur- rounding the galleries were delineated on trans- analysed using the SAS statistical Data parent film; finally, the lesions were cut out were package (SAS, 1987). Treatment along the lesion periphery and refrozen for later program were compared by analyses of variance chemical analyses (June-felled tree only). All ad- means followed by Tukey’s test for multiple compari- ditional galleries as well as those found on the by 2-way ANOVAs (Zar, 1984). Pairs of sons, or other stem sections (including that taken for iso- tested with Student’s t-test, correct- means were lation of fungi) were counted, separating beetle ing for unequal variances when appropriate species and attack attempts (< 1 cm in gallery (Zar, 1984). The resin acid composition in the length) from longer egg galleries (> 1 cm in samples was analysed by principal component length). analysis (PCA). Relationships between vari- For trees felled in June, additional phloem ables were analysed using correlation coeffi- were taken from an unaffected part of samples cients and stepwise linear regressions were the stem (> 10 cm from the nearest lesion) for computed in order to explain the variation. later analyses of resin acids and starch, and from phloem adjoining lesions for starch analy- ses; all samples were refrozen as the lesion RESULTS samples mentioned above. The discs taken at breast height pol- were ished, and annual ring widths measured were with 0.01 mm accuracy along 2 opposite radii. Tree vigour Radial growth, basal area growth, vigour index (ie the cross-sectional area of a given annual Tree diameter, height and number of re- ring (or rings) in percent of the total sapwood area; see Waring and Pitman, 1980; for a dis- maining whorls after pruning were similar cussion of the underlying physiological assump- for experimental trees of the 3 pruning tions, see Waring and Pitman, 1985), and sap- dates (table I; ANOVA followed by Tukey’s wood percentage were calculated and used as test for multiple comparisons). Height expressions of tree vitality prior to beetle attack growth, crown length, ring widths and sev- (table I). eral other expressions of tree vigour were Lesion calculated lesion areas were as significantly lower for the trees pruned in lesion width (obtained from length by mean June 1988 than for trees pruned in April measurements of lesion widths for every cm in 1989, and intermediate for trees pruned in transparent film). A length from the drawings on
1 cm, ie failed attack attempts there was August 1988 (table I). However, galleries < difference in cambial electrical resis- rather than true galleries, differed clearly no between tree groups (fig 1). tance. At attack densities < 200 egg galleries per m mean egg gallery length remained , 2 Beetle performance short, indicating failure in establishing a brood (fig 3). This was true for both batch- es of trees, ie trees felled in June as well Beetle attack as in August. At higher attack densities, gallery lengths were also similar between of the 60 trees included in the All but one the 2 groups of trees, indicating that full attacked by T piniperda and 13 study were gallery length had been reached by 1 trees were also attacked by T minor. The June. It is noteworthy that some of the sur- attack density of the latter species was viving trees had gallery lengths similar to negligible (maximum of 5 galleries on the those that eventually died. tree attacked most); hence no further at- tention will be paid to T minor in this study. Since no other bark-living insects were Beetle behaviour and brood found on the stem sections in any num- development bers, T piniperda (and its associated blue- stain fungi) was the major challenge of the Since attack densities on baited and un- tree’s defensive capacity. baited trees were overlapping (cf fig 2), The attack density of T piniperda on the trees were regrouped in 3 attack density lower stem (0.3-0.8 m) did not differ signif- classes within each pruning date (< 150, icantly between pruning dates (fig 1; 2-way 151-300, > 300 egg galleries per m re- , 2 ANOVA; data for the 2 sampling dates spectively) regardless of whether they had were pooled, as they did not differ). As ex- been baited or not, before further analyses pected, the attack density was higher on of beetle behaviour and defence chemistry baited trees than on unbaited ones (see were made. also figure 2). all trees with a low attack By 1 June, The attack density on the lower stem abandoned by the parent density were was well correlated with the total number beetles and no larvae had hatched in the of egg galleries on the whole trunk ex- galleries (table II), regardless of pruning ploited by the beetles (fig 2). Although date. Presence of parent beetles as well baited trees were clearly more attacked, as the percentage of galleries with devel- there was a great overlap between the 2 oping brood was higher in severely than in groups. intermediately attacked trees. For the trees attacked most, these percentages in- creased from the oldest to the latest prun- Gallery construction ing date. Thus, attack density had a large influence on the probability for successful Egg galleries were significantly shorter in colonisation, and the beetles seemed to do pruned in June 1988 than in those trees better on trees pruned shortly before than pruned in March 1989 (fig 1; ANOVA fol- long before attack (successful brood devel- lowed by Tukey’s test for multiple compari- opment occurred only in trees that were sons), indicating more persistent oviposi- tion attempts in the latter than the former eventually killed by the attacks; see be- trees. Correspondingly, the percentage of low).
Defence reactions In the surviving trees, the defensive le- sions covered an increasing proportion of the inner bark with increasing attack densi- Induced defence reaction ty, occupying at the most 30% of the in- = ner bark area on the lower stem (fig 5). None of the several variables used to de- scribe the size of the lesion developing around the egg gallery differed significantly Defence chemistry between treatments (fig 1, right column). Plotting the lesion tip length against the Starch mean gallery length revealed a strongly Starch levels did not differ systematically non-linear relationship (fig 4), indicating between pruning dates or attack density that the induced defence reaction culminat- levels (table III). However, means (control ed at 20 mm gallery length, and thereaf- = phloem) for the attack density classes dis- ter failed to contain an increasing propor- played decreasing levels: 13.0, 11.9 and tion of the galleries within the lesions. This 10.3% with increasing attack density. In 8 result was valid for both batches of trees, cases out of 9, starch levels of control demonstrating that gallery expansion and samples were somewhat higher than for lesion formation was, in fact, finished by 1 samples taken close to a lesion. June.
Resin acids Comparison between surviving and dead trees On 1 June, the content of resin acids were 10-fold in the lesion phloem as com- > pared to unaffected control bark samples Tree mortality and characteristics (table III). No clear differences could be seen in the total amounts of resin acids ei- Ten of the 30 trees felled in August 1989 ther between pruning dates or attack den- were classified as dead, and of these 4, 2 sity classes. and 4 trees had been pruned in June 1988, September 1988 and March 1989, As the resin acid composition did not respectively. As 6 of the dead trees had differ between trees of different pruning been baited and 4 not, tree mortality was dates and attack density classes, data are not clearly linked to either baiting or prun- not shown. The principal component analy- ing date. Six of the dead trees had been sis of lesion and control samples only con- attacked by T piniperda alone, and 4 trees firmed the quantitative effects shown in by both Tomicus species. table III, but did not reveal any consistent The surviving trees did not differ from qualitative patterns between sample groups (data not shown). Thus, the de- the dead ones in tree size, radial growth, fence reaction seems to be mainly quanti- or in vigour index, but the CER readings were significantly different between the 2 tative.
(potentially dying?) trees (fig 6B). In (table IV). Furthermore, the 2 CER some groups readings taken 2 d apart were highly inter- other (surviving?) trees, all sapwood was related (r= 0.895; P 0.0001), and thus stained by the dye and was hence func- = reproducible. CER readings also correlat- tional (fig 6A). In August, surviving trees ed with vigour indices, the best correlation still had all or most of the sapwood fully being that between first CER measure- functional, albeit with deep occluded wed- ment and the vigour index for the period ges in some cases (fig 6C), whereas irreg- 1986-1988 (r = -0.63; P 0.012). How- ular patches of stained sapwood were typi- = ever, this negative correlation is not con- cal for dead trees (fig 6D). Whether the sistent with the larger CER reading for sur- staining of the dead trees was a result of active transportation of dye in the dying viving trees. sapwood, or a passive absorption by des- iccated wood, remains unclear. Beetle performance All dead trees displayed a high percent- age of blue-stain in the sapwood of the cut The attack density of T piniperda, as well ends at the lower and upper stem sections, as the total number of attacks per tree whereas the blue-staining of the sapwood were significantly higher on trees that was negligible on both stem sections of eventually died than on surviving trees surviving trees (table IV; see also Solheim (table IV), whereas T minor occurred in and Långström, 1991). low numbers on both groups of trees (< 1 gallery per tree on average). Thus, T mi- nor obviously had a negligible influence on the outcome of the beetle attack as com- pared T piniperda. to Mean and total gallery lengths were also significantly higher on the trees suc- cessfully attacked by T piniperda than on (table IV). Furthermore, surviving trees no successful brood development occurred on the surviving trees, while exit holes of T piniperda occurred in all dead trees on the lower stem covered with rough bark. How- ever, the brood production per m was low 2 even in the successfully colonised trees, and the average rate of reproduction was less than unity, ie the number of emerging beetles was less than the ovipositing par- ent beetles (table IV). Occlusion and blue-staining of sapwood At felling on 1 June, the treatment with Fast Green disclosed wedge-shaped sec- tions of non-functional sapwood on cut discs immediately below beetle galleries in
DISCUSSION the mean attack den- 1992). Furthermore, baited and unbaited trees were, sities on respectively, above and below 300 egg According to Larsson (1989), phloem- galleries per m a level found to be critical , 2 feeders like bark beetles should be more for successful colonisation in the studies favoured by changes in host vigour than mentioned above. In these small trees, the other guilds of herbivores. In several stud- critical attack density corresponded ≈ 50 ies, conifer susceptibility to bark beetles galleries/tree. egg has been found to be correlate with tree Judging from trees felled on 1 June, the vigour, expressed as the efficiency of the parent beetles stayed longer in galleries of foliage to produce stemwood (Waring and densely attacked trees than on trees of low Pitman, 1980, 1985; Larsson et al, 1983; attack density. A similar pattern could be Mulock and Christiansen, 1986). It has seen for the frequency of galleries contain- been postulated that stress factors like de- ing developing brood. For the densely at- foliation or drought mainly interfere with tacked trees, parent beetle presence as the tree’s ability to allocate carbohydrates well as brood development was lower in for defence and thus render them suscepti- trees pruned in June 1988 than in other ble to beetle attack (Christiansen et al, trees. Correspondingly the frequencies of 1987). Similarly, the concept of growth dif- failed attacks (ie short galleries) tended to ferentiation balance suggests that trees be higher and mean gallery lengths shorter are prone to beetle attack during periods of in trees pruned in June 1988 than in trees intensive growth when less carbohydrates pruned closer to the beetle attack, despite are available for defence (Lorio, 1988). similar attack densities (both felling dates; In the present study, we succeeded in cf fig 1).Thus, the trees pruned 1 yr prior = population with a similarly creating a tree to beetle attack were less suitable brood reduced needle biomass but different vig- material than those pruned 1 month before our indices, representing a similar photo- beetle flight. Obviously, attacking beetles synthetic capacity but different growth effi- responded to some (chemical or physiolog- ciencies (sensu Waring and Pitman, 1985). ical) cues, and abandoned the former trees Furthermore, the vigour index at the time sooner than the latter. of attack should have been in the critical The observed differences in parent bee- range for successful colonisation, which in tle behaviour and gallery development, several conifer species have been found to could not, however, be related to any cor- be < 10% in annual sapwood area growth responding differences in the extent of the (equalling 100 g stem wood per m needle 2 induced defence reaction, ie the size of the area/yr; cf Waring and Pitman, 1980, 1985; lesion formed in response to the attack. Larsson et al, 1983; Mulock and Christian- This lack of relationship can, however, be sen, 1986). Needle biomass was also suffi- understood when considering the strong ciently reduced to render some of the trees non-linear relation between lesion expan- to attack (Långström al, susceptible et sion and gallery length. Thus, the linear re- 1992). lationship between gallery expansion and We also managed to get the trees with lesion formation observed by Lieutier et al different pruning history attacked in a simi- (1988), was valid only until the defence lar way. The attack density of T piniperda system started to collapse when an in- creasing number of beetles succeeded in was comparable to that found in other breaking out from the lesions. In our data, studies in the same area (Långström and this occurred when galleries, on average, Hellqvist, 1988, (1993); Långström et al,
≈ 25 mm long, and such galleries those obtained These results, well were as as started to occur when attack density ex- for drought-stressed Norway spruce (Chris- ceeded 200 egg galleries/m In surviving . 2 tiansen, 1992), lead to the conclusion that trees, lesions covered a maximum of the momentary vigour, ie the physiological ≈ 30% of the phloem area on lower stem; condition of the tree at the very moment of thus at least two-thirds of the phloem was beetle attack is much more important than still fully functional. the historical vigour which is usually meas- As neither phloem starch nor lesion res- ured. If so, the observed significant differ- in acid content displayed variation that in cambial electrical resistance, ence could be linked to the above pattern in par- measured at the time of attack, between ent beetle behaviour and gallery develop- trees that were going to survive and those ment, other factors must have been in- that eventually died, indicates some impor- volved. For example, primary resin flow tant difference between the 2 batches of (Schroeder, 1990), oleoresin pressure trees. However, the observed result show- (Vité and Wood, 1961) or phloem thick- ing higher CER for surviving trees is illogi- ness may have played a role (Amman, cal since CER was also negatively corre- 1972; Lieutier and Ferrell, 1988). Other de- lated with tree vigour (Christiansen, 1981; fence components such as phenolics may Lieutier and Ferrel, 1988; Filip et al, 1989). also be involved (Lieutier et al, 1991).The Other studies indicate that CER may re- observed resin acid accumulation in the le- flect differences in tree vitality due to fac- sions was similar to that found by tors such as defoliation (Piene et al, Långström et al (1992), and is hence not 1984a), thinning (Piene et al, 1984b; Mat- discussed here. son et al, 1987) and root rot (Lindberg and Altogether, the above results indicate Johansson, 1989). that pruning on different occasions prior to in The poor beetle performance beetle attack had not, after all, differential- even in full successfully colonised trees is ly altered the trees’ susceptibility to bark beetles. Similar results have been ob- agreement with our earlier results in the tained for drought-stressed or pruned Nor- area, and hence is not discussed here way spruce (Picea abies L (Karst)) (Chris- (Långström and Hellqvist, 1988, 1993; tiansen, 1992; Christiansen and Fjone, Långström et al, 1992). The same applies 1993). On the other hand, removal of = to the observation that the sapwood of two-thirds of the foliage resulted in one- dead trees was heavily blue-stained, indi- third of the trees left to grow over the sum- cating that these trees may have been mer being killed by beetle attack. This killed by the beetle-vectored blue-stain fun- would hardly have happened with trees gi rather than the beetles (Solheim and carrying intact foliage (cf Långström et al, Solheim et al, 1993). On Långström, 1991; 1992; and references therein). Thus, the sapwood occlusion (indi- the other hand, pruning treatment substantially increased cating fungal growth) had barely started on the susceptibility of the trees to beetle at- 1 June when egg galleries were fully tack. The reduced defence capacity was grown. It is also worth noting that sapwood also reflected in the comparatively low below all beetle occlusion did not occur starch levels of the inner bark in trees galleries (cf fig 6B). This is consistent with felled on 1 June (cf Långström et al, the findings that only a fraction of the bee- 1992). Similar results have been obtained tle galleries contain blue-stain fungi (Lieuti- for Norway spruce, Picea abies, when 1989b; Solheim and al, 1988, et pruned and inoculated with blue-stain fun- er gi (Christiansen and Fjone, 1993). Långström, 1991).
Inst Skogforsk 2/81, 1-20 (in Norwegian with In conclusion, the present study con- English summary) firmed earlier observations on beetle per- formance and induced defence reactions Christiansen E (1992) Prolonged drought did not predispose young Norway spruce trees to in- in young Scots pine. It also yielded new fection by the bark beetle transmitted blue- data regarding beetle attack and behavi- stain fungus Ophiostoma polonicum. Scand J our, lesion formation and sapwood occlu- For Res 7, 557-569 sion. However, we failed to demonstrate (1986) Starch Christiansen E, Ericsson A re- differences in resistance between trees of in Picea abies in relation to defence serves different vigour indices, nor did we find val- reaction against a bark beetle transmitted id criteria for describing host resistance. blue-stain fungus, Ceratocystis polonica. Can Hence, further studies are needed to de- J For Res 16, 78-83 velop methods of identifying and measur- Fjone G (1992) Effect of pruning Christiansen E, ing even short-term changes in host sus- susceptibility of Picea abies to infection by on ceptibility to bark beetles. The physical or the bark beetle transmitted blue-stain fungus Ophiostoma polonicum. Scand J For Res 8, chemical properties of the phloem could be 235-242 trait to pursue, as indicated by the meas- a Christiansen E, Waring RH, Berryman AA urements of cambial electrical resistance, (1987) Resistance of conifers to bark beetle despite conflicting results. attack: searching for general relationships. For Ecol Manage 22, 89-106 Escherich K (1923) Die Forstinsekten Mitteleuro- ACKNOWLEDGMENTS pas II. Paul Parey, Berlin, pp 663 Filip GM, Christiansen E, Parks CA (1989) Sec- We thank Stora AB for permission to work on ondary resin production increases with vigor their premises, KSLA for financial support, A of Abies grandis inoculated with Trichospor- Ericsson and R Gref for respectively carrying um symbioticum in northeastern Oregon. US out the starch and resin acid analyses, T Gus- Dept Agric, For Serv, Pacific Northwest Res tafsson for field assistance, E Christiansen and Stat, Res Note. PNW-RN-489, pp 12 H Solheim for field assistance during their visit Långström B (1983) Life cycles and shoot- to Sweden and comments on the manuscript, N feeding of pine shoot beetles. Stud For Suec Rollison for revising the English, and F Lieutier 163,29 for translating the summary into French. Långström B, Hellqvist C (1988) Scots pine re- sistance against Tomicus piniperda as relat- ed to tree vitality and attack density. In: Inte- REFERENCES grated Control of Scolytid Bark Beetles (Payne TL, Saarenmaa H, eds) Proc IUFRO Working Party and XVII Int Congr Entomol (1972) Mountain pine beetle brood Amman GD Symp, Vancouver, BC, Canada, July 4 1988, production in relation to thickness of lodge- 121-133 pole pine phloem. J Econ Entomol 65, 138- 140 Långström B, Hellqvist C, Ericsson A, Gref R (1992) Induced defence reaction in Scots Berryman AA (1982) Biological control, thresh- pine following stem attacks by Tomicus pini- olds, and pest outbreaks. Environ Entomol perda. Ecography 15, 318-327 11, 544-549 Långström B, Hellqvist C (1993) Induced and Berryman AA, Raffa KF, Millstein JA, Stenseth spontaneous attacks by Tomicus piniperda NC (1989) Interaction dynamics of bark and T minor on young Scots pine trees. J beetle aggregation and conifer defense rates. Appl Entomol 115, 25-36 Oikos 56, 256-263 Larsson S (1989) Stressful times for the plant Christiansen E (1981) Infestation ability of epi- stress-insect performance hypothesis. Oikos demic lps typographus in relation to vitality and increment of Norway spruce. Rapp Nor 56, 277-283
Larsson S, Oren R, Waring RH, Barrett JW (Mattson WJ, Levieux J, Bernard-Dagan C, (1983) Attacks of mountain pine beetle as re- eds) Springer Verlag, New York, 73-92 lated to tree vigour of ponderosa pine. For Matson PA, Hain FP, Mawby W (1987) Indices Sci 29, 395-402 of tree susceptibility to bark beetles vary with Lieutier F (1993) Hypothetical working mecha- silvicultural treatment in a loblolly pine planta- nisms of the induced defence reaction of tion. For Ecol Manage 22, 107-118 conifers to bark beetles and their associated Miller RH, Berryman AA (1986) Carbohydrate al- Ophiostoma. In: Int Symp Taxonoy and Biol- location and mountain pine beetle attack in ogy of the Ophiostomales. Bad Windshein, girdled lodgepole pines. Can J For Res 16, Germany, 21-24 August 1990 (in press) 1036-1040 Lieutier F, Ferrell G (1988) Relationships be- Mulock P, Christiansen E (1986) The threshold tween indexes of tree vigour and the induced of successful attack by lps typographus on defense reaction of Scots pine to a fungus Picea abies: a field experiment. For Ecol associated with lps sexdentatus (Coleoptera: Scolytidae). In: Integrated Control of Scolytid Manage 14, 125-132 Bark Beetles (Payne TL, Saarenmaa H, eds) Parmeter Jr JR, Slaughter GW, Chen MM, Proc IUFRO Working Party and XVII Int Wood DI, Stubbs HA (1989) Single and Congr Entomol Symp, Vancouver, BC, Cana- mixed inoculations of ponderosa pine with da, July 4 1988, 163-178 fungal associates of Dendroctonus spp. Phy- Lieutier F, Yart A, Garcia J, Poupinel B, Levieux topathology 70, 768-772 J (1988) Do fungi influence the establish- Piene H, Thompson RG, Mclsaac JE, Fensom ment of bark beetles in Scots pine? In: Mech- DS (1984a) Electrical resistance measure- anisms of Woody Plant Defenses Against In- ments on young balsam fir trees to specific sects: Search for Pattern (Mattson WJ, volume increment, foliar biomass, and ion Levieux J, Bernard-Dagan C, eds) Springer content of bark and wood. Can J For Res 14, New York, 321-334 Verlag, 177-180 Lieutier F, Cheniclet C, Garcia J (1989a) Com- Piene H, Fensom DS, Mclsaac JE, Thomson parison of the defense reactions of Pinus pi- RG, Alexander KG (1984b) Electrical resis- naster and Pinus sylvestris to attacks by two bark beetles (Coleoptera: Scolytidae) and tance and capitance measurements on their associated fungi. Environ Entomol 18, young, spaced and unspaced, defoliated and 228-234 protected, balsam fir trees. Can J For Res 14, 811-817 Lieutier F, Yart A, Garcia J, Ham MC, Morelet M, Levieux J (1989b) Champignons phytopa- Postner M (1974) Scolytidae (= lpidae), Bor- thogènes associés à deux coléoptères Scoly- kenkafer. In: Die Forstschidlinge Europas. 2. tidae du pin sylvestre (Pinus sylvestris L) et Band. Käfer (Schwenke W, ed) Paul Parey étude préliminaire de leur aggressivité en- Hamburg, Berlin, pp 500 vers l’hôte. Ann Sci For 46, 201-216 Salonen K (1973) On the life cycle, especially Lieutier F, Yart A, Jay-Allemand C, Delorme L on the reproduction biology of Blastophagus (1991) Preliminary investigations phenol- on piniperda L (Col, Scolytidae). Acta For Fenn ics as a response of Scots pine phloem to at- 127,72 tacks by bark beetles and associated fungi. SAS Institute Inc (1987) SAS/STAT Guide for Eur J For Pathol 21, 354-364 Personal Computers. Version 6 ed, pp 1028 Johansson M (1989) The use of Lindberg M, electrical resistance of cambium and phloem Schroeder LM (1990) Duct resin flow in Scots as a measure of tree vigor. Scand J For Res pine in relation to the attack of the bark 4, 175-185 beetle Tomicus piniperda (L) (Col, Scolyti- dae). J Appl Entomol 109, 105-112 Lorio Jr PL (1988) Growth differentiation- balance relationships in pines affect their re- Solheim H, Långström B (1991) Blue-stain fungi sistance to bark beetles (Coleoptera: Scolyti- associated with Tomicus piniperda in Swe- den and preliminary observations on their pa- dae). In: Mechanisms of Woody Plant De- thogenicity. Ann Sci For 48, 149-156 fenses Against Insects: Search for Pattern
Solheim H, Långström B, Hellqvist C (1993) Pa- tion pressure in determining the susceptibility thogenicity of the blue-stain fungi Lepto- of second growth ponderosa pine to bark graphium wingfieldii and Ophiostoma minus beetle infestation. Contrib Boyce Thomps to Scots pine: effect of tree pruning and inoc- Inst 21, 67-78 ulum density. Can J For Res 23 (in press) Pitman GB (1980) A simple model Waring RH, Vité JP, Wood DL (1961) A study of the applica- of host resistance to bark beetles. Oreg State bility of the measurement of oleoresin exuda- Univ For Res Lab Res Note 65, pp 2