Asynchrony in larval development of the pine beauty moth, Panolis flammea, on an introduced host plant may affect parasitoid efficacy

In the United Kingdom, Panolis flammea (Den. and Schiff.) (Lepidoptera: Noctuidae) is an important pest species of the introduced lodgepole pine but not of its natural host Scots pine. The timing of P. flammea larval growth must be synchronized with its host tree if the larvae are to succeed. We collected field data during 1990 which revealed that the phenological window starts earlier in Scots pine and is shorter than that observed in lodgepole pine. The larvae are found in the field earlier and within a narrower time frame within a Scots pine forest than in a lodgepole pine forest. The larval developmental period is significantly longer on lodgepole pine than on Scots pine. The synchrony/asynchrony of P. flammea to its natural host (Scots pine) and an introduced tree (lodgepole pine) results in the parasitoids having a different impact on the larvae of the two hosts. At any one time, the host plant, caterpillars and parasitoids are more synchronous on the ancestral Scots pine than on lodgepole pine, resulting in a higher percentage of larvae in the optimal instar for parasitism at that time. In lodgepole pine, the percentage of suitable instars available to parasitoids is lower at any given time. The information presented here furthers our understanding of the possible mechanisms for the observed differential population dynamics of the insect on Scots pine and lodgepole pine in the UK. Handling editor: Robert Glinwood.     

The effect of previous defoliation of pole-stage lodgepole pine on plant chemistry,and on the growth and survival of pine beauty moth (Panolis flammea) larvae

Summary A study of the effects of defoliation by insects on the chemistry of lodgepole pine (Pinus contorta), and on the performance of Panolis flammea (Lepidoptera; Noctuidae) larvae, was carried out in a forest in northwest Scotland I year after a severe outbreak of P. flammea had caused extensive defoliation. Larval weight and survival were not significantly different on trees that had experienced different levels of defoliation in 1986. The nitrogen and tannin content of current and previous years' pine needles was not significantly affected by defoliation (although both were slightly greater in the foliage of defoliated trees). Phosphorus content of young pine foliage was lower (but not significantly lower except on one occasion) on heavily defoliated trees. On all sampling occasions, however, the nitrogen: phosphorus ratio was significantly higher on heavily defoliated trees. There were large differences in monoterpene composition of the previous year's shoots associated with defoliation intensity, but these differences had largely disappeared in the new growth. The results are discussed in relation to other studies on the effects of insect damage on plant chemistry and insect performance and in relation to the abundance of P. flammea in Scotland.     

The performance of the pine beauty moth on water-stressed lodgepole pine plants: a laboratory experiment

Summary A laboratory experiment was done to see whether artificially induced waterlogging, or water shortage in lodgepole pine (Pinus contorta) would affect the egg laying preference, larval survival and larval growth of Panolis flammea. Female moths showed no egg laying preference between unstressed and stressed plants. Larval survival was greater on unstressed (85%) than on stressed (32%) plants, and the weight of larvae reared on unstressed plants was significantly greater than those reared on stressed plants. These results imply that outbreaks of the pine beauty moth on trees growing in deep unflushed peat are not caused by a stress-induced improvement in the nutritional quality of the host-plant.     

The chemical composition of pine foliage in relation to the population dynamics of the pine beauty moth,Panolis flammea,in Scotland

Summary This paper reports part of a study to determine why damaging outbreaks of the pine beauty moth, Panolis flammea (D & S) (Lepidoptera: Noctuidae), in Scotland are frequent on lodgepole pine but do not occur on Scots pine, and why outbreaks on lodgepole pine are mainly confined to trees growing in deep unflushed peat. The elongation of shoots and the growth of needles of Scots pine occurred later in the season than did those of lodgepole pine. The foliage of Scots pine generally had a higher level of nitrogen, and consistently had a higher level of phosporus, but had a consistently lower level of tannins than that of lodgepole pine during the period when the larvae were feeding each year. The nitrogen content of the foliage of lodgepole pine growing in an iron pan soil was generally higher than that of lodgepole pine growing in deep peat during the same period but there were no general differences in the phosphorus or tannin contents of lodgepole pine in the 2 soil types. These findings suggest that Scots pine is a more suitable host plant than lodgepole pine and that the foliage of lodgepole pine growing in deep peat is not more suitable than lodgepole pine growing in an iron pan soil. On the basis of the chemical analyses used in this study, it is concluded that the abundance of pine beauty moth in Scotland is not strongly influenced by the nutritional suitability of its host plants.     

A reappraisal of the population dynamics of the pine beauty moth, Panolis flammea, on lodgepole pine, Pinus contorta, in Scotland

The pine beauty moth, Panolis flammea, is a defoliating pest of lodgepole pine (Pinus contorta) forests in Scotland. This article reviews early and recent research on the population ecology of Panolis flammea and presents an analysis of pupal survey data collected between 1977 and 1993. Research in the 1980s suggested that natural enemies, although effective in preventing P. flammea outbreaks on Scots pine (Pinus sylvestris), played an insignificant role in the population dynamics of P. flammea on lodgepole pine. However, analysis of pupal survey data showed that delayed density-dependent action of natural enemies, probably parasitoids, was overlooked during the 1970s and 1980s. Recent research suggests that fungal pathogens are responsible for a decline in the frequency and severity of outbreaks of P. flammea on lodgepole pine. This suggestion, together with the overlooked importance of other natural enemies, indicates that the population ecology of P. flammea in Scotland has changed during the past 20 years and requires a full reappraisal. Received: May 31, 1999 / Accepted: August 18, 1999     

Sub-lethal plant defences: the paradox remains

Lodgepole pine (Pinus contorta) trees of two different seed origins, one a poor quality host (Alaskan lodgepole pine), the other a good quality host (south coastal lodgepole pine), were infested with known numbers of eggs of the pine beauty moth, Panolis flammea. Each tree had paired sleeves, one allowing access by invertebrate predators, the other denying this access. When the sleeves were removed, the numbers of larvae surviving, their weights and developmental stages were assessed. Larvae reared on south coastal lodgepole pine (SLP) in the absence of predators were significantly heavier and had significantly better survival rates than larvae reared in comparable conditions on Alaskan lodgepole pine (ALP). However, in the open sleeves, although the larvae reared on SLP were significantly heavier than those on ALP, survival was significantly greater on ALP. Thus predation was greater on the faster developing larvae on the better quality host. These results indicate that slow growth by a herbivore does not necessarily result in greater vulnerability to predators.     

The growth and survival of Panolis flammea larvae in the absence of predators on Scots pine and lodgepole pine

Abstract. 1. The survival, growth and development of larvae of the pine beauty moth, Panolis flammea (D & S) (Lepidoptera: Noctuidae) were examined as part of a study to determine (i) why damaging outbreaks of this insect in Scotland are frequent on lodgepole pine but do not occur on Scots pine, and (ii) why outbreaks are associated with areas of deep un-flushed peat.
2. Larvae were studied inside predator exclusion cages on mature pine trees in Elchies forest where a major infestation occurred in 1978–79.
3. Surprisingly, larval survival was generally greatest on Scots pine and lowest on lodgepole growing in deep peat. Also, larval growth and development were greater on Scots than lodgepole pine and were unaffected by the type of soil in which the lodgepole pine was growing.
4. Larval performance was generally better on lodgepole pine that had been thinned and received fertilizer.
5. Larval survival was affected by pine shoot stage during egg hatch in one of the two years in which this was examined.
6. Observations on P.flammea pupae were confused by disease, parasitism and probably by differences in weight loss caused by differences in larval development. Parasitism by ichneumonid parasitoids was recorded on Scots pine but not on lodgepole pine.
7. It was concluded that (i) the absence of pine beauty moth outbreaks on Scots pine, and (ii) the occurrence of outbreaks on lodgepole pine growing in deep unflushed peat were not the result of lodgepole pine growing in deep peat being a more suitable host plant than lodgepole pine and Scots pine growing elsewhere. It seems more likely that the observed outbreak behaviour of P.flammea in Scotland is associated with differences in predation and parasitism in plantations of difference host plants and in plantations of lodgepole pine growing in different soils.     

Zinc-tolerant Suillus bovinus improves growth of Zn-exposed Pinus sylvestris seedlings

Scots pine (Pinus sylvestris L.) seedlings inoculated or not (NM) by a Zn-sensitive or a Zn-tolerant isolate of the ectomycorrhizal fungus Suillus bovinus (L. Fr.) Roussel were exposed to 0.1 or 150 μM Zn²⁺ for 9 months. We hypothesized that inoculation with a Zn-tolerant S. bovinus isolate should result in added Zn resistance of the host plant. Plant and fungal growth as well as nutrient profiles and photosynthetic pigments in pine needles were quantified. In NM plants and in plants colonized by the Zn-sensitive isolate, plant growth, N, P, Mg and Fe assimilation were strongly inhibited under Zn stress and concurred with significantly reduced chlorophyll concentrations. In contrast, plants colonized by the Zn-tolerant isolate grew much better and remained physiologically healthier when exposed to elevated Zn. These results provide further evidence for the important role metal-adapted mycorrhizal fungi play as an effective biological barrier against metal toxicity in trees.     

The role of below-ground competition during early stages of secondary succession: the case of 3-year-old Scots pine (Pinus sylvestris L.) seedlings in an abandoned grassland

In abandoned or extensively managed grasslands, the mechanisms involved in pioneer tree species success are not fully explained. Resource competition among plants and microclimate modifications have been emphasised as possible mechanisms to explain variation of survivorship and growth. In this study, we evaluated a number of mechanisms that may lead to successful survival and growth of seedlings of a pioneer tree species (Pinus sylvestris) in a grass-dominated grassland. Three-year-old Scots pines were planted in an extensively managed grassland of the French Massif Central and for 2 years were either maintained in bare soil or subjected to aerial and below-ground interactions induced by grass vegetation. Soil temperatures were slightly higher in bare soil than under the grass vegetation, but not to an extent explaining pine growth differences. The tall grass canopy reduced light transmission by 77% at ground level and by 20% in the upper part of Scots pine seedlings. Grass vegetation presence also significantly decreased soil volumetric water content (Hv) and soil nitrate in spring and in summer. In these conditions, the average tree height was reduced by 5% compared to trees grown in bare soil, and plant biomass was reduced by 85%. Scots pine intrinsic water-use efficiency (A/g), measured by leaf gas-exchange, increased when Hv decreased owing to a rapid decline of stomatal conductance (g). This result was also confirmed by δ ¹³C analyses of needles. A summer ¹⁵N labelling of seedlings and grass vegetation confirmed the higher NO₃ capture capacity of grass vegetation in comparison with Scots pine seedlings. Our results provide evidence that the seedlings' success was linked to tolerance of below-ground resource depletion (particularly water) induced by grass vegetation based on morphological and physiological plasticity as well as to resource conservation.     

Conidia of Trichoderma virens as a phosphorus source for mycorrhizal Pinus sylvestris seedlings

In this study, the mobilization and further translocation of phosphorus from conidia of saprotrophic fungus Trichoderma virens into Pinus sylvestris seedlings by nondestructive measuring of ³²P was assessed. The radioactive phosphorus flux from the conidia to the Scots pine seedlings forming mycorrhiza with Laccaria laccata and Suillus bovinus amounted up to 27.82% and 7.42%, respectively, on the 28th day of the experiment, while at the same time in nonmycorrhizal pine seedlings, the detected radioactivity reached only 0.56%. Our studies revealed that both ectomycorrhizal fungi: L. laccata and S. bovinus, mobilized the phosphorus from radioactive conidia of T. virens. On this basis, we conclude that activities of the mycosymbionts may facilitate absorption and further translocation of phosphorus from organic matter into the host plants.     

Glyphosate-induced changes in the attack success and development of the mountain pine beetle and impact of its natural enemies

Roundup (active ingredient glyphosate) administered into the sapwood around the root collar of lodgepole pine trees, Pinus contorta var. latifolia Engelm., was investigated as a tool for creating trap trees for the mountain pine beetle (MPB), Dendroctonus ponderosae Hopk. MPB's attacked semiochemical-baited, glyphosate-treat trees before attacking baited control trees. Bark samples disclosed an increase in survival of MPB eggs and early instar larvae, enhanced larval development and increased attacks by insect parasites and predators in treated trees. The braconid wasp, Coeloides dendroctoni Cush., parasitized MPB larvae found at high densities in treated trees two months following attack. The dipteran predator, Medetera aldrichii Wh., was only found in treated trees. Increased competition by Ips pini (Say) had a negative impact on MPB survivorship. The enhanced impact of insectan agents apparently offset any glyphosate-induced gains in MPB survival or development, but did not cause a significant reduction in MPB emergence.     

Freeze-preservation of buds from Scots pine trees

A procedure has been developed for freeze-preservation of buds of the Scots pine (Pinus sylvestris L.). Instead of liquid nitrogen, cold storage in –80°C was used. The partly dormant material used in the experiments was obtained directly from a natural stand in Northern Finland and no prefreezing or cryoprotectants for preconditioning were used. Cooling velocity was 1°C/min up to a terminal freezing temperature of –39°C, after which the buds were immersed in liquid nitrogen at –196°C for 10 minutes. The material was then transferred to a deepfreezer at –80°C and stored up to 6 months. After rapid thawing, the buds were sterilized and their viability was tested by FDA staining and by culturing meristems on 1/2 MS medium for at least two weeks. All the freezing experiments were performed during March and April. The best survival of buds (90–100%) was achieved at the beginning of April, after which a pronounced decline in survival occurred obviously due to a rise in the water content of the buds.     

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

In 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.     

Feast and famine: previous defoliation limiting survival of pine processionary caterpillar Thaumetopoea pityocampa in Scots pine Pinus sylvestris

This study analyses the consequences of previous defoliation on the survival of the larvae of the pine processionary moth Thaumetopoea pityocampa (Denis and Schiffermüller) feeding on relict Scots pine Pinus sylvestris (L.) ssp. nevadensis Christ in the Sierra Nevada mountains (SE Spain). Egg batches of the pine processionary moth were placed on four groups of Scots pines that underwent different periods of herbivory. The larval survival was related to the nitrogen content, fibre, phenolics and terpenes in the needles. Larval survival was higher in undefoliated pines, lower in pines defoliated two consecutive years, and intermediate in pines defoliated only one year, suggesting a direct relationship between previous defoliation and larval survival. In contrast, none of the characteristics of the needles showed a clear relationship with larval survival. The resulting reduction in larval number also affects the capacity of the larvae to develop during winter, because it hampered nest warming. Thus, previous defoliation limits, although it does not impede, the possibility of repeated defoliation on Scots pine.     

Radiation and soil temperature interactions on the growth and physiology of eastern white pine ( Pinus strobus L.) seedlings

A greenhouse experiment was set up during one growing season to test the hypothesis that soil temperature controls a significant part of the light response of eastern white pine (Pinus strobus L.) seedlings that is observed in the field. The experimental design was a three by three factorial split-plot design, with three levels of light availability: 10%, 40% and 80% of full light; and three levels of soil temperature: 16 °C, 21 °C, and 26 °C in the soil at midday. The results show significant interactions between light and soil temperature factors on several variables (gas exchange, root growth, leaf-mass ratio and leaf–mass per unit area), but not on shoot dry mass. These interactions indicate that, in the field, a significant proportion of the light response of young eastern white pine could result from changes in soil temperature, especially under conditions of limiting water availability. Our results suggest that soil temperature must be taken explicitly into account as a driving variable when relating the growth of young eastern white pine to photosynthetic radiation.     

The history and control of the pine beauty moth, Panolis flammea (D. & S.) (Lepidoptera: Noctuidae), in Scotland from 1976 to 2000

1 The pine beauty moth, Panolis flammea, has been a serious pest of lodgepole pine plantations in Scotland since 1976. It historically feeds on native Scots pine throughout Europe but population levels of P. flammea on this host have never been high enough to cause tree mortality in the U.K. 2 This paper reviews recent advances in the biology of the pest and documents control programmes from 1976 to 1999. 3 There has been practically uninterrupted population monitoring of P. flammea from 1977 to the present day in Scottish lodgepole pine plantations. Intervention with chemical spraying has often been necessary. 4 The population data suggest that populations of P. flammea may have had a cyclic pattern over the monitoring period, with outbreaks occurring at regular intervals of between 6 and 7 years. 5 The amplitude of population cycles was large during the 1970s and 1980s, but has dampened in recent years. Natural enemies are believed to contribute to this trend. Fungal disease, specifically, appears to have had a greater effect on pest populations in recent years than in the past and is suggested to have contributed significantly to the population dynamics observed since 1990.     

Oviposition preference and larval survival of Diprion pini on Scots pine clones in relation to foliage characteristics

1 When laying eggs, adult female Diprion pini discriminated between clones of Scots pine, Pinus sylvestris. 2 Larval survival was affected by Scots pine clone but was not correlated with oviposition preference. 3 Diprion pini laid most eggs on tougher needles of Scots pine. 4 There was no evidence to suggest that D. pini is responding to the monoterpene composition of the foliage.     

Variation in the suitability of Pinus contorta (lodgepole pine) to feeding by three pine defoliators, Panolis flammea, Neodiprion sertifer and Zeiraphera diniana

A series of experiments were carried out on Pinus contorta Dougl. in Scotland to establish if there were any inter-provenance differences in suitability to three major forest pests: the pine beauty moth, Panolis flammea (D and S) (Lep., Noctuidae), the European pine sawfly, Neodiprion sertifer (Geoff.) (Hym., Diprionidae), and the larch bud moth Zeiraphera diniana Guennée (Lep., Tortricidae). There were significant differences in the survival, weight, and development time of P. flammea on different provenances of seedling logepole pine. Southern interior lodgepole pine (ILP) proved to be the most resistant provenance. Larvae performed significantly better on Alaskan lodgepole pine (ALP) and Skeena River lodgepole pine (ELP). Panolis flammea larvae showed significant feeding preference for certain provenances of mature lodgepole pine, with ILP being preferred to ALP, north coastal lodgepole pine, and Scots pine. There were significant differences in the mean relative growth rate of N. sertifer on different provenances of seedling and mature trees. ALP was the most resistant provenance among seedling trees, but the least resistant among mature trees. There were also significant differences in survival on foliage from mature provenances. There were no significant differences in survival of second instar Z. diniana on different provenances of mature lodgepole pine.     

Relationship between respiratory depletion of sugars and loss of cold hardiness in coniferous seedlings over-wintering at raised temperatures: indications of different sensitivities of spruce and pine

Long-term effects of elevated winter temperatures on cold hardiness were investigated for Norway spruce (Picea abies L. Karst.), lodgepole pine (Pinus contorta Dougl.) and Scots pine (Pinus sylvestris L.). Two-year-old seedlings with the same pre-history of growth and cold hardening in the field were maintained from early December to late March at two field sites in northern Sweden and in a cold room. The temperatures at these locations averaged –13·5, –8·9 and 5·5°C, respectively. Following treatments, carbohydrate contents and cold tolerances were assessed. Needle respiration was also analysed during the 5·5°C treatment. Cold tolerance of lodgepole pine and Scots pine was much reduced following the 5·5°C treatment. Cold tolerance was somewhat reduced in lodgepole pine following the –8·9 °C treatment, but was essentially maintained in spruce throughout all treatments. The cold tolerance of needles was strongly correlated with their soluble sugar contents. Spruce maintained cold hardiness by having larger reserves of sugars and lower rates of respiration which decreased more rapidly as sugars were depleted. Tolerance of lodgepole pine to frost desiccation was also much reduced following the 5·5°C treatment.     

Changing dynamics of the pine beauty moth (Panolis flammea) in Britain: the loss of enemy free space?

1 The pine beauty moth Panolis flammea has two main host plants in Britain: Pinus sylvestris (Scots pine), which is the ancestral food plant where the insect is never abundant enough to cause tree mortality, and Pinus contorta (lodgepole pine), an introduced host tree that has experienced periodic widespread tree mortality due to this pest.
2 We review the recent literature, published mostly after the year 2000, regarding the impact of natural enemies on the population dynamics of P. flammea in Britain.
3 The natural enemies of P. flammea are more diverse and abundant in Scots pine habitat than in lodgepole pine habitat and some of them show differential selection for P. flammea larvae in Scots pine habitat over those located in lodgepole pine habitat.
4 It is concluded that the difference in the population dynamics of this insect in the two different habitats was probably the result of the P. flammea finding enemy-free space in lodgepole pine habitat.
5 Recent evidence on the diversity and impact of natural enemies on lodgepole pine has demonstrated that they currently have a much more significant impact on this pest than they did in the 1970s and 1980s, when outbreaks were frequent.