Pine Looper Research Articles

Retrospective Analysis of Lophodermium seditiosum Epidemics in Estonia

The needle trace method (NTM), created and developed by the Finnish forest pathologists prof. T. Kurkela, dr. R. Jalkanen and T. Aalto during the last decade of the XX century, has been already used by several researchers of different countries for retrospective analysis of needle diseases (Hypodermella sulcigena, by R. Jalkanen et al. in Finland) or herbivorous insect pests of Scots pine (Diprion pini, by T. Kurkela et al. in Finland; Bupalus piniaria, by H. Armour et al. in Scotland), but as well of pests of Sitka spruce (Gilpinia hercyniae, by D.T. Williams et al. in England). Scots pine in forest nurseries and young plantations of Estonia is often but irregularly suffering from the epidemics of the needle cast fungus Lophodermium seditiosum. Current environmental regulations exclude from the regulatory (control) measures all the others except of well-argued prophylactic systems, built up on reliable prognoses. The last is inconceivable without the availability of a reliable, as well, and longlasting retrospective time-series of L. seditiosum epidemics, which, as it is known from the last half of the XX century, are occupying large forest areas, usually not least than a half of (the small) Estonia. An appropriate time-series would be useful, as well, for the more basic understanding of the accelerated mortality processes during the stand formation in early pole-age Scots pine plantations. Methodological principles of the use of NTM in an appropriate investigation together with the preliminary results of our research work, looking back for more than a century, are introduced and discussed in this investigation.

Parasitoid assemblages reared from geometrid defoliators (lepidoptera: geometridae) of larch and fir in the alps

Abstract1 Geometrid larvae were collected from larch and fir in the Swiss Alps in 1991–94. Eight geometrid species were found in sufficient numbers to rear out parasitoids:Agriopis aurantiaria,Bupalus piniarius,Epirrita autumnata,Eupithecia lariciata,Odontopera bidentata,Lycia isabellaeandSemiothisa lituratawere collected from larch, andPuengeleria capreolariawas obtained from fir.2 Parasitoid species belonging to five different guilds and four families were obtained; however, the taxonomic status of some of these is not completely resolved.3 The parasitoid complex of the larch‐feeding species was totally different from that of Tortricidae and Tenthredinidae, which feed on the same host tree. In general, there was little overlap in the parasitoid complexes of the larch geometrids, with the most dominant parasitoid of each species reared from only one host. By contrast, many parasitoid species found during our study are also known to attack the same hosts or closely related hosts on different host tree species in different environments, suggesting that host specificity in geometrid parasitoids is more related to host taxonomy than to host plant or habitat.

POPULATION CYCLES IN THE PINE LOOPER MOTH: DYNAMICAL TESTS OF MECHANISTIC HYPOTHESES

The forest insect pest Bupalus piniarius (pine looper moth) is a classic example of a natural population cycle. As is typical for populations that exhibit regular oscillations in density, there are several biological mechanisms that are hypothesized to be responsible for the cycles; but despite several decades of detailed study there has been no definite conclusion as to which mechanism is most important. We evaluated three hypotheses for which there was direct experimental evidence: (1) food quality (nutritional value of pine needles affected by defoliation); (2) parasitoids (trophic interactions with specialist parasitoids); and (3) maternal effects (maternal body size affects the performance of offspring). We reviewed the empirical evidence for each of these hypotheses and expressed each hypothesis in the form of a mechanistic dynamic model. We used a nonlinear forecasting approach to fit each model to three long‐term population time series in Britain that exhibit some degree of regular cycling, and we used parametric bootstrap to evaluate the significance of differences between models in their goodness of fit to the data. The results differed among the three forests: at Culbin, the parasitoid and maternal effects models fit equally well; at Roseisle, the food quality and maternal effects models fit equally well; and at Tentsmuir, the parasitoid model fit best. However, the best‐fit parasitism models required that the parasitism rate vary between nearly 0 and nearly 1 during a cycle, greatly exceeding the range of parasitism rates that have been observed in the field. In contrast, the required variation in the observable maternal quality variable (pupal mass) was within the range of empirical observations. Under mild constraints on the parasitism rate (though allowing a much wider range than has been measured in B. piniarius at any location), the fit of the parasitism model fell off dramatically. The maternal effects model then had uniformly strong support, outperforming the constrained parasitism model at all three sites and the food quality model at two; it performed slightly better than the food quality model at the remaining site. This represents the first system in which the maternal effects hypothesis for population cycles has been supported by both strong biological and dynamical evidence.

Comparison of methods for estimation of needle losses in Scots pine following defoliation by Bupalus piniaria

In 1996, ca. 7000 hectares of pine forests at Hökensås in SW Sweden were defoliated by the pine looper, Bupalus piniara (L.) (Lepidoptera. Geometridae). Following an aerial damage survey using CIR (colour infra red) photography, and estimation of pupal densities in the soil, ca 4000 ha of the most defoliated pine stands were sprayed in early August 1997 with Bacillus thuringiensis var. kurstaki. The control operation was succeessful but probably redundant, as no further defoliation occurred in unsprayed reference areas. In order to assess defoliation levels in different damage classes for later growth loss studies, 47 circular study plots were laid out in pine stands representing different damage and age classes. The remaining foliage was recorded for each tree using the following classes: 0, 10, 30, 50, 70, 90 and 100%. The defoliation levels in 1996 were estimated by disregarding the 1997 needle age class. Thirteen ca. 40-year-old sample trees representing different damage classes were felled, and the remaining foliage of all branches was estimated by needle age class using the above-mentioned scale. One branch in each of the whorls 1996, 1991, 1986 and 1981 was sampled and its needle dry weight was determined. The sample branch data confirmed the field observations that virtually no additional defoliation took place in 1997. The damage classes estimated from the CIR-pictures only agreed with the field damage estimates at the higher end of the damage scale. In contrast, the field estimate correlated well with plot means derived from tree-wise estimates (R2 = 0.93), and with with the calculated needle biomasses per tree (R2 = 0.90). Thus, the field damage classification was supported by the more detailed defoliation estimates, and hence forms a relevant basis for later growth loss studies.

Tree Mortality, Foliage Recovery and Top-kill in Stands of Scots Pine (Pinus sylvestris) Subsequent to Defoliation by the Pine Looper (Bupalus piniaria)

In 1996, the pine looper (Bupalus piniaria) (L.) defoliated 7000 ha of Scots pine (Pinus sylvestris L.) forest at Hökensås, in southern Sweden. To study tree mortality, foliage recovery and top-kill, plots were laid out in stands with varying levels of defoliation in autumn 1997. Tree mortality peaked 2 yrs after defoliation, and amounted to 25% in stands suffering from 90–100% defoliation. Suppressed trees suffered higher mortality than intermediate and dominant trees. In stands suffering <90% defoliation, tree mortality did not exceed 8%. Foliage recovery in moderately and severely defoliated stands was not complete at the end of the 4 yr study period, whereas slightly defoliated stands had regained full foliage in 1998. Top-kill was most frequent in severely defoliated stands, and 50% of all trees in these stands suffered from top-kill at the end of the study period in spring 2001.

Attack dynamics of the pine shoot beetle, Tomicus piniperda (Col.; Scolytinae) in Scots pine stands defoliated by Bupalus piniaria (Lep.; Geometridae)

Abstract 1 After a 1‐year, extensive pine looper (Bupalus piniaria) outbreak, plots were laid out to study tree susceptibility to attack, and performance of Tomicus piniperda in pine trees suffering from varying levels of defoliation.2 Tomicus piniperda was the dominating stem‐attacking species among the primary stem colonizers, and 82% of all trees that died had been colonized by T. piniperda.3 Beetle attacks primarily struck severely defoliated trees, i.e. trees that suffered from 90% to 100% defoliation.4 Beetle attacks peaked in the second year after cessation of the outbreak, and suppressed trees were both more frequently attacked and more susceptible to beetle attack than intermediate and dominant trees.5 Trees surviving beetle attacks carried more foliage than trees that did not survive the attacks.6 A single year of severe defoliation is enough to render pine trees susceptible to secondary pests, such as T. piniperda.

Interactions between growth, herbivory and long-term foliar dynamics of Scots pine

It is generally thought that carbon-limited conifers with low priority stem growth investment will suffer significantly reduced wood formation following defoliation by insects, as long as resource sinks (apical buds and young needles) are unaffected compared to sources (mature needles). We examined the long-term consequences of periodic defoliation by a moth (Bupalus piniaria L.) on the growth of Scots pine (Pinus sylvestris L.), by retrospectively determining annual rates of needle retention using the needle trace method, and comparing these rates with patterns of radial growth obtained by tree-ring analysis. Cumulative moth densities in the current and previous year had the strongest negative influence on subsequent tree growth. Radial and volume increments were reduced substantially (by up to 50%) for 2–3 years after peaks in the moth population. In turn, tree growth was positively correlated with needle retention, with better growth promoting better retention in the following two seasons. This dominant relationship masked the more subtle impact of B. piniaria on needle retention. However, when each needle cohort was examined separately, it was possible to detect the immediate effects of B. piniaria on the loss of the youngest (0 to 1-year-old) needle cohort. Needle budgeting differed for trees in two study compartments, where the rate of tree growth was evidently different. In the compartment where trees grew more slowly they retained a greater number of needle sets over time by shedding fewer of the older needles, but they responded more quickly to the negative effects of the defoliator by losing needles more rapidly in years when the defoliator was abundant.

Performance of pine looper Bupalus piniarius larvae under population build‐up conditions

AbstractIn the first year of an outbreak, Bupalus piniarius larvae, encounter intense crowding. In the later stages of larval development, they are forced to feed on the non‐preferred current‐year needles of Scots pine or even on alternative hosts. It was hypothesized that larval feeding on a non‐preferred resource (current‐year needles) will negatively affect B. piniarius performance. It was also hypothesized that larval mutual interference (crowding without competition for food) will have negative additive effects. These hypotheses were tested in laboratory and field experiments. Fourth instar larvae were reared singly and under crowded conditions in cohorts of ten. Larvae in both situations were reared on control branches (containing both mature and current‐year shoots) and branches containing only current‐year shoots. Crowded larvae were reared also on Norway spruce, an alternative host. Crowding and feeding on a non‐preferred resource had opposite effects on B. piniarius larval performance. Crowding in the late larval instars enhanced larval performance while absence of the preferred resource had negative effects. Larval growth rate was higher and development time was shorter for larvae exposed to crowded conditions than for solitary larvae. There was, however, no difference between the groups in final pupal weights or survival. Survival was 25% lower for larvae feeding on non‐preferred current‐year needles and pupal weights 9% lower, compared with results for larvae feeding on mature needles. Larvae feeding on Norway spruce suffered greatly extended development time, 82% lower survival, and resulted in 60% lighter pupae compared with conspecifics on Scots pine. It was concluded that not only quantity but also quality of the available food resource is critical for B. piniarius development.

The financial costs of defoliation of Scots pine (Pinus sylvestris) by pine looper moth (Bupalus piniaria)

The financial costs of defoliation of Scots pine by the pine looper moth (Bupalus piniaria L.) were evaluated for three pine stands in Tentsmuir Forest, Scotland, by comparing observed tree growth with estimates of the growth that would have been expected if the moth had not been present. It was calculated that five or seven periods of partial defoliation, caused by successive peaks in the moth population, had reduced the total volume of marketable timber available in thinnings and at final harvest by 26-35 m(3) ha(-1). Nearly all of this loss occurred in the sawlog category of timber. Total discounted income over the rotation, based on long-term (1984-2001) average timber prices and a 3.5 per cent discount rate, was reduced by 5.8-7.5 per cent when the same rotation length was used for both observed and expected growth. At a discount rate of 6 per cent, total income was reduced by 4.4-5.2 per cent. Extending the rotation by 3 or 4 years to allow the mean final tree size to reach that expected in the absence of defoliation, or by 4 or 6 years to allow the same total volume of timber to be extracted, increased total revenue but did not increase gross discounted income because of the effect of discounting over a greater number of years.

Asymmetric synthesis of all stereoisomers of 7,11-dimethylheptadecane and 7-methylheptadecane, the female pheromone components of the spring hemlock looper and the pitch pine looper

The asymmetric synthesis of the stereoisomers of 7,11-dimethylheptadecane ( 1 ) and 7-methylheptadecane ( 2 ) via α-alkylation employing the SAMP/RAMP hydrazone method with high asymmetric induction and good overall yields is described. A mixture of (7 S,11 R)- 1 and ( S)- 2 is the female-produced sex pheromone of the spring hemlock looper moth ( Lambdina athasaria) and the pitch pine looper moth ( Lambdina pellucidaria). They are both forest pests in northeastern North America.

Reduced realised fecundity in the pine looper Bupalus piniarius caused by host plant defoliation

Summary1. Whether the potential fecundity of herbivorous insects is realised or not may depend on female behaviour, which in turn may be influenced by host plant acceptability. Female Bupalus piniarius were observed to discriminate against needles growing out the year following defoliation (current‐year needles) of its host plant Pinus sylvestris.2. It was hypothesised that the discriminatory behaviour was due to current‐year needles being less secure as a substrate. Field and laboratory experiments were designed to test this hypothesis and to estimate the discrepancy between potential and realised fecundity when females were offered defoliated branches.3. In a laboratory oviposition experiment, B. piniarius females were exposed to branches bearing either current‐year needles only or both mature and current‐year needles. Daily oviposition rate, egg batch size, longevity, and mature eggs and fat retained at death were recorded for each female. In field experiments, the rate at which eggs dropped from expanding needles and the capacity of neonate larvae hatching from the dropped eggs to colonise a tree were assessed.4. Significantly fewer eggs were laid when females were exposed to defoliated branches.5. Twenty‐six and 16% of the eggs laid on current‐year needles dropped from the needles in 1998 and 1999 respectively, whereas no eggs dropped from mature needles in 1998 and only one egg (&lt; 1%) dropped in 1999.6. A very small proportion of larvae hatching on the forest floor (simulated egg drop) was able to recolonise host trees.7. These results emphasise the importance of oviposition behaviour on realised fecundity when analysing insect population dynamics. In the case of B. piniarius, egg placement, although a minor detail during the normal course of events, became of key importance when defoliation deprived females of their preferred egg attachment site.

Host resistance in defoliated pine: effects of single and mass inoculations using bark beetle‐associated blue‐stain fungi

Abstract1 In 1996, 7000 ha of pine forests were defoliated by the pine looper Bupalus piniaria in south‐western Sweden.2 The susceptibility of trees of different defoliation classes (0, 30, 60, 90 and 100% defoliation) to beetle‐vectored blue‐stain fungi was tested in inoculation experiments. Forty and 120‐year‐old Scots pine trees were inoculated with ‘single’, i.e. a few inoculations of Leptographium wingfieldii and Ophiostoma minus, two blue‐stain fungi associated with the pine shoot beetle Tomicus piniperda. The young trees were also ‘mass’ inoculated with L. wingfieldii at a density of 400 inoculation points per m2 over a 60 cm stem belt.3 Host tree symptoms indicated that only trees with 90–100% defoliation were susceptible to the mass inoculation.4 Single inoculations did not result in any consistent differences in fungal performance between trees of different defoliation classes, regardless of inoculated species or tree age class.5 Leptographium wingfieldii produced larger reaction zones than O. minus, and both species produced larger lesions in old than in young trees.6 As beetle‐induced tree mortality in the study area occurred only in totally defoliated stands, mass inoculations seem to mimic beetle‐attacks fairly well, and thus seem to be a useful tool for assessing host resistance.7 As even severely defoliated pine trees were quite resistant, host defence reactions in Scots pine seem to be less dependent on carbon allocation than predicted by carbon‐based defence hypotheses.

Does pheromone biology of Lambdina athasaria and L. pellucidaria contribute to their reproductive isolation?

Recently, 7-methylheptadecane and 7,11-dimethylheptadecane have been reported as sex pheromone components of both spring hemlock looper (SHL), Lambdina athasaria, and pitch pine looper (PPL), Lambdina pellucidaria. Our objective was to test the hypothesis that SHL and PPL are reproductively isolated, in part, through species specificity in: (1) absolute configuration of pheromone components, (2) diel periodicity of pheromonal communication, and/or (3) seasonal flight period. In coupled gas chromatographic-electroantennographic detection (GC-EAD) analyses of stereoselectively synthesized (7S)- and (7R)-7-methylheptadecane [7S; 7R] as well as (7S,11S)-, (7R,11R)-, and (meso-7,11)-7,11-dimethylheptadecane [7S,11S; 7R,11R; meso-7,11], only 7S and meso-7,11 elicited responses by male SHL and PPL antennae. In field experiments, male SHL and PPL were attracted only to lures containing 7S plus meso-7,11. In hourly recordings of trap-captured males, SHL and PPL in their respective habitats were trapped between 24:00 and 03:00 hr. Capture of both SHL and PPL in pheromone-baited traps throughout June indicated overlapping seasonal flight periods. These findings of identical absolute configuration of pheromoal components, diel periodicity of pheromonal communication, and overlap of seasonal flight periods support synonymy of SHL and PPL. Finite taxonomic classification of PPL and SHL must await careful assessment of further criteria, such as morphometrics, molecular comparisons and ecological analyses.

Synthesis of All the Stereoisomers of 7-Methylheptadecane and 7,11-Dimethylheptadecane, the Female Sex Pheromone Components of the Spring Hemlock Looper and the Pitch Pine Looper

All the stereoisomers of 7-methylheptadecane (1) and 7,11-dimethylheptadecane (2) were synthesized by starting from the enantiomers of citronellol (3) and methyl 3-hydroxy-2-methylpropanonate (8), respectively. A short synthesis of meso-7,11-dimethylheptadecane [(7R,11S)-2] was achieved starting from meso-2,6-dimethylheptanedioic acid [(2R,6S)-21]. A mixture of (S)-1 and (7R,11S)-2 is the pheromone of the spring hemlock looper moth (Lambdina athasaria) and the pitch pine looper moth (L. pellucidaria).

Effects of previous defoliation on pine looper larval performance

Summary1 During outbreaks of the pine looper, Bupalus piniarius, its host, Pinus sylvestris, is severely defoliated. The larvae of this geometrid normally feed on mature needles. However, because trees are totally defoliated during outbreaks, the next generation is forced to feed on current‐year needles.2 Bupalus piniarius larvae feeding on previously defoliated trees may show lower performance either because of induced resistance or because larvae have to feed on needles not normally fed upon (current instead of mature).3 These hypotheses were tested in an experiment where larvae were reared on (i) shoots naturally defoliated the previous year, and thus, bearing only current‐year needles, (ii) non‐defoliated shoots where larvae had access only to current‐year needles, and (iii) control shoots with access to both current and mature needles.4 There was no support for the induction hypothesis. Survival was lower on naturally defoliated shoots than on control shoots (81.3 vs. 90.9%), but survival was lower also on non‐defoliated shoots where larvae had access only to current‐year needles (78.8%). Data on larval feeding distribution showed a strong preference for mature needles.5 Needle nitrogen concentration of current‐year needles was 38% higher on defoliated trees than on non‐defoliated trees.6 It is concluded that defoliation affected larval performance primarily through the removal of the preferred type of needles and not because of an induced resistance. Effects of increased concentrations of allelochemicals in defoliated shoots, if present, were probably cancelled out by increased nitrogen concentrations.

SEX PHEROMONE COMPONENTS OF PITCH PINE LOOPER, Lambdina pellucidaria

Two methylated hydrocarbons, 7-methylheptadecane (7) and 7,11-dimethylheptadecane (7,11), are sex pheromone components of female pitch pine looper (PPL), Lambdina pellucidaria. Compounds extracted from the pheromone glands of female moths were identified by coupled gas chromatographic–electroantennographic detection (GC-EAD) and coupled GC–mass spectrometry (GC-MS) in selected ion monitoring mode. In field-trapping experiments, 7 and 7,11 in combination, but not singly, attracted numerous male moths. 5,11-Dimethylheptadecane (5,11) was detected by GC-EAD in female PPL pheromone gland extract, but did not significantly increase attraction of PPL males to 7 plus 7,11. Although 7 was > 10 times more abundant than 7,11 in pheromone gland extracts, traps baited with synthetic 7 plus 7,11 at a blend ratio of 1:1, rather than 1:0.1 or 1:0.01, captured the most PPL males. The chemical communication of PPL and spring hemlock looper (SHL), Lambdina athasaria, is strikingly similar. Both species employ 7 plus 7,11 as sex pheromone. Restriction of SHL to forests with eastern hemlock or balsam fir and PPL to forests with pitch or other hard pines contributes to their reproductive isolation. PPL and SHL may also use different optical isomers of enantiomeric 7 and stereoisomeric 7,11 to maintain specificity of their chemical communication.

The impact of pine looper moth, Bupalus piniaria L. (Lepidoptera; Geometridae) on the growth of Scots pine in Tentsmuir Forest, Scotland

Pine looper moth ( Bupalus piniaria) is an autumn defoliator of pines in Europe, but its impact on tree growth is not well established. Full stem analysis of 40 Scots pine trees felled close to their harvest date in Tentsmuir Forest, Scotland, was used to relate annual growth increments to cyclic fluctuations in B. piniaria densities as recorded by Forestry Commission pupal surveys. Between 1954 and 1989, five peaks in the moth population occurred at Tentsmuir, and radial, cross-sectional area (CA) and volume increments were reduced significantly 1–2 years following each peak. Height increments were reduced after a delay of 3 years. These reductions in increment occurred even though defoliation in the stand was light and B. piniaria densities never exceeded 33 pupae m −2, a density below that normally considered damaging. Temperature variables had some influence on radial, CA and volume increments, and rainfall had an effect on height growth, but the role of climatic factors was small and largely overridden by the greater effect of defoliation. Radial, CA and volume increments were reduced by 17–28% for 2–3 years after peak moth densities, but height growth showed only a small and variable response. Final diameter at breast height, CA, volume and height of the trees at felling were reduced on average by 3.1%, 4.6%, 5.6% and 1.5%, respectively. Wood production at the final crop spacing of 513 stems ha −1 was reduced by 28.3 m 3 ha −1, a loss which would have required a further 2.2 years of unaffected growth at the end of the rotation to have been replaced.

Common Mechanisms Underlying Contrasting Dynamics in Two Populations of the Pine Looper Moth

Census data from an outbreaking population of the pine looper moth, Bupalus piniaria L. (Lepidoptera: Geometridae) are used to derive a life-table for the population. A comparative analysis is made of this life-table with one published for a non-outbreaking population of the moth. The stage-specific survival rates are found to exhibit qualitatively similar patterns, though the absolute survival rates differ substantially in some cases. There is evidence for the operation of density-dependent processes at several points in the moth's life-cycle. The results of published experimental studies are used in deriving proposals for the mechanisms underlying the patterns of stage-specific survival. Finally, it is suggested that the underlying mechanisms are fundamentally similar in both populations and that differing environmental conditions modulate the differential expression of these mechanisms in the two populations, so generating the observed differences in their population dynamics

Site Characteristics and the Population Dynamics of the Pine Looper Moth

Data from 27 populations of Bupalus piniaria L. (Lepidoptera, Geometridae) spanning a minimum of 22 years are used to estimate the parameters of a simple difference model of the moth's population dynamics. The resulting parameter estimates are compared with the «site characteristics» of the forest in which each population exists. The per capita net rate of increase is found to be positively correlated with latitude, while the shape parameter in the function describing immediately density-dependent mortality is inversely related to local rainfall. Possible physiological and behavioural mechanisms underlying these correlations are discussed

Heavy-Metal Contents in Pupae of Bupalus piniarius (Lepidoptera: Geometridae) and Panolis flammea (Lepidoptera: Noctuidae) near an Industrial Source

The concentrations of copper (Cu), iron (Fe), nickel (Ni), and cadmium (Cd) were analyzed in the pupae of Bupalus piniarius (L.) and Panolis flammea (Denis and Schiffermuller) reared on needles collected from the same sites with different heavy-metal levels. Metal analysis on an individual basis revealed specific differences between the two common defoliators of the Scots pine ( Pinus sylvestris L.). The highest heavy-metal concentrations in B. piniarius (Cu 137, Fe 83, Ni 2.1, Cd 0.9 μgg−1)and P. flammea (Cu 89, Fe 59, Ni 5.3, Cd 2.9 μgg−1)were recorded in those reared on needles from the vicinity of the emission source in Finland. The decreasing trend of the log-transformed metal concentrations followed a linear regression model with increasing distance from the factories. The ratio between the concentration of copper and iron in the insects and that in the needles was proportionally lower in heavily polluted areas. Cadmium bioaccumulation was observed in P. flammea but not in B. piniarius .