Hide and seek in forests: colonization by the pine processionary moth is impeded by the presence of nonhost trees

• 1 The disruption of host‐finding cues has been proposed as a key mechanism underlying the lower damage caused by phytophagous insects in mixed forests. We tested this hypothesis by investigating the distribution of pine processionary moth Thaumetopoea pityocampa (Denis & Schiffer‐Müller) (Lepidoptera) infestation at the edges of pure stands of Pinus pinaster (AÏton) at some distance from nonhost trees (Experiment 1) or bordered in part by a broadleaved hedgerow (Experiment 2).
• 2 An ‘edge effect' was demonstrated, with trees at the edge of the stand being more heavily infested than those at the interior of the stand.
• 3 The presence of a nonhost broadleaved hedgerow in front of the edge of the pine stand resulted in lower T. pityocampa infestation. There were significantly fewer T. pityocampa nests behind the hedgerow than on the exposed part of the edge. The presence of the hedgerow did not dilute or repel T. pityocampa infestation further into the pine stand, although it decreased the infestation of T. pityocampa throughout the pine stand. The decrease in T. pityocampa infestation behind the hedgerow was greater when the broadleaved hedgerow was taller than the pine trees.
• 4 These results highlight the benefits of using nonhost tree species on the edge of monospecific forest stands to reduce insect damage. This approach could be promoted as an innovative forest pest management method.

     

Effects of climate on pine processionary moth fecundity and on its egg parasitoids

Climate change may be affecting the fecundity of phytophagous insects as well as impacting their natural enemies. However, temperature impacts these two insect groups differently, disrupting population regulation mechanisms, and ultimately, possibly culminating in an outbreak of the host. The pine processionary moth (PPM) is one of the most harmful insects of the Mediterranean basin. Not only are PPM larvae harmful to plants, but they are also dangerous to humans because of their urticating hairs. Although some information is available on climate change effects on the PPM, little is known about its potential effects on PPM egg parasitoids, especially on their distribution range or on their role in controlling PPM populations. The aim of this article was to verify the effects of climate on PPM fecundity and on its egg parasitoids. Our results show that climate warming may affect the PPM positively, but not its egg parasitoids. Specifically, during our study mild winters directly favored the PPM, while increasing summer temperatures (over 30°C) also favored the PPM indirectly, by decreasing parasitism rates. We predict that ever‐milder winters will not only favor PPM development, but also encourage it to spread in otherwise previously inhospitable environments.     

Needle terpene concentrations and emissions of two coexisting subspecies of Scots pine attacked by the pine processionary moth (Thaumetopoea pityocampa)

Mediterranean pine forests are often attacked by caterpillars of Thaumetopoea pityocampa (Lep., Thaumetopoidae), one of the most important defoliators in the Mediterranean region causing large economic losses and ecological effects. The needle terpene concentrations and emissions may play a key role in the defense of pines. We studied two subspecies of Pinus sylvestris, nevadensis (an endemic and relict subspecies) and iberica , with different levels of caterpillar attack in Sierra Nevada mountains (Spain). GC–MS analyses showed large total concentrations of terpenes (6 to 39 mg g^?1 of dry weight) in the needles of both subspecies under field conditions. Concentrations were 25 % higher in “Non-Attacked Trees” (NATs) of the iberica than in the nevadensis subspecies. The branches of NATs had terpene concentrations 20 % higher than those of “Attacked Branches of attacked trees” (ABs). Within attacked trees, the “Non-Attacked Branches” (NABs) also had terpene concentrations 20 % higher than those of ABs. Mainly α-pinene and germacrene D had higher concentrations in NATs and NABs than in ABs. Some terpenes had higher concentrations in NABs than in NATs, indicating possible systemic reactions. In subsp. nevadensis, the percentage of monoterpenes relative to total terpenes was higher in ABs than in other attack states. The rates of emission in nevadensis (standardized to 30 °C) were ca. three times higher in ABs than in NABs and NATs. These results suggest that the lower terpene concentrations and high percentages of monoterpenes in ABs were produced by a combination of emission losses and terpene induction in response to herbivorous attack.     

Genetic differentiation of the pine processionary moth at the southern edge of its range: contrasting patterns between mitochondrial and nuclear markers

The pine processionary moth (Thaumetopoea pityocampa) is an important pest of coniferous forests at the southern edge of its range in Maghreb. Based on mitochondrial markers, a strong genetic differentiation was previously found in this species between western (pityocampa clade) and eastern Maghreb populations (ENA clade), with the contact zone between the clades located in Algeria. We focused on the moth range in Algeria, using both mitochondrial (a 648 bp fragment of the tRNA‐cox2) and nuclear (11 microsatellite loci) markers. A further analysis using a shorter mtDNA fragment and the same microsatellite loci was carried out on a transect in the contact zone between the mitochondrial clades. Mitochondrial diversity showed a strong geographical structure and a well‐defined contact zone between the two clades. In particular, in the pityocampa clade, two inner subclades were found whereas ENA did not show any further structure. Microsatellite analysis outlined a different pattern of differentiation, with two main groups not overlapping with the mitochondrial clades. The inconsistency between mitochondrial and nuclear markers is probably explained by sex‐biased dispersal and recent afforestation efforts that have bridged isolated populations.     

Significant mortality of eggs and young larvae of two pine processionary moth species due to the entomopathogenic fungus Metarhizium brunneum

Bioassays were conducted to determine the susceptibility of egg masses and young larvae of two pine processionary moth species, Thaumetopoea pityocampa and Thaumetopoea wilkinsoni, to two strains (ARSEF4556, V275) of the entomopathogenic fungus Metarhizium brunneum. Mortality of treated eggs by both strains ranged from 96% to 99% but not all of this was caused by M. brunneum since control groups also experienced egg mortality due to saprophytic fungi. Still, larvae hatched in the laboratory from eggs treated with M. brunneum were all killed by this fungus, acquiring M. brunneum conidia, whereas larval mortality was 0% in the control groups. Young larvae of both pine processionary moth species were also highly susceptible to ARSEF4556 and V275 with larval mortality ranging between 94% and 100%, 8 days post-inoculation, with the vast majority of larvae being killed within the first 2–4 days. Larval mortality was dose dependent. Results were consistent across the two pine processionary moth species, showing that the pathogenicity of M. brunneum to both eggs and young larvae might be promising for biological control of these insect pests. The study also showed that non-target parasitoids of pine processionary moth eggs were also susceptible to M. brunneum. Further work is required to understand and reduce the M. brunneum effect on non-target insects.     

Similar local,but different systemic,metabolomic responses of closely related pine subspecies to folivory by caterpillars of the processionary moth

Plants respond locally and systemically to herbivore attack. Most of the research conducted on plant–herbivore relationships at element and molecular levels have focused on the elemental composition or/and certain molecular compounds or specific families of defence metabolites showing that herbivores tend to select plant individuals or species with higher nutrient concentrations and avoid those with higher levels of defence compounds. We performed stoichiometric and metabolomics, both local and systemic, analyses in two subspecies of Pinus sylvestris under attack from caterpillars of the pine processionary moth, an important pest in the Mediterranean Basin. Both pine subspecies responded locally to folivory mainly by increasing relative concentrations of terpenes and some phenolics. Systemic responses differed between pine subspecies, and most of the metabolites presented intermediate concentrations between those of the affected parts and unattacked trees. Our results support the hypothesis that foliar nutrient concentrations are not a key factor for plant selection by adult female processionary moths for oviposition, since folivory was not associated with any of the elements analysed. Phenolic compounds generally did not increase in the attacked trees, questioning the suggestion of induction of phenolics following folivory attack and the anti‐feeding properties of phenolics. Herbivory attack produced a general systemic shift in pines, in both primary and secondary metabolism, which was less intense and chemically different from the local responses. Local pine responses were similar between pine subspecies, while systemic responses were more distant.     

Spatial patterns at host and forest stand scale and population regulation of the pine processionary moth Thaumetopoea pityocampa

相似文献   

Host utilisation by moth and larval survival of pine processionary caterpillar Thaumetopoea pityocampa in relation to food quality in three Pinus species

Abstract 1. The work reported here analysed host utilisation by the pine processionary moth Thaumetopoea pityocampa (Lepidoptera: Thaumetopoeidae), the relationship between moth oviposition patterns and larval performance, the chemical characteristics of the plant in relation to the performance of different larval instars, and the role of these factors in the outbreak capacity of the species. In order to do this, a combination of field and laboratory techniques was used to study three pine species differing in nutritional characteristics.
2. Moths oviposited in the three pine species analysed, although cluster pine received a lower number of batches. Late-instar larvae were able to feed on all three pine species, however first-instar larvae developed on Scots and black pine but died on cluster pine. Consequently, oviposition in cluster pine can be considered an oviposition mistake, and indicates that moths are rather unselective when ovipositing on different pine species.
3. Chemical analysis of needles suggested that the quantity of nitrogen was the main factor responsible for the difference in survival of larvae.
4. The oviposition pattern of the moth and the larval susceptibility to food quality in Thaumetopoea pityocampa agree with the theory that unselective oviposition of the moth is a precondition for eruptive dynamics in phytophagous insects.
5. The success of the larvae depends mainly on the probability of the moth finding a suitable host. This probability is determined strongly by the changes of structure and coverage in Mediterranean pine woodlands, due to human management.     

Genetic differentiation in the winter pine processionary moth (Thaumetopoea pityocampa--wilkinsoni complex), inferred by AFLP and mitochondrial DNA markers

The winter pine processionary moth has become an important pine pest in the last century, as a consequence of the spread of pine cultivation in the Mediterranean region. The pattern of genetic differentiation of this group, that includes two sibling species (Thaumetopoea pityocampa and Th. wilkinsoni), has been studied in nine populations using amplified fragment length polymorphism (AFLP) and single strand conformation polymorphism-sequence analysis (SSCP) of the mitochondrial cytochrome oxidase 1 (COI) and cytochrome oxydase 2 (COII). Results indicate the existence of strong genetic differentiation between the two species that became separated before the Quaternary ice ages. Moreover data indicate that Th. pityocampa has a strong geographical structure, particularly evident at the nuclear level, where all pairwise phiST resulted to be highly significant and individuals from the same population resulted to be strongly clustered when an individual tree was reconstructed. The estimates of the absolute number of migrants between populations (Nm), obtained from mitochondrial and nuclear DNA markers, suggest that gene flow is low and that a gender-related dispersal could occur in this species. The males appear to disperse more than females, contributing to the genetic diversity of populations on a relatively wide range, reducing the risks of inbreeding and the genetic loss associated with bottlenecks occurring in isolated populations.     

Tree species identity and forest composition affect the number of oak processionary moth captured in pheromone traps and the intensity of larval defoliation

1. Pure forests are often seen as being more prone to damage by specialist pest insects than mixed forests, and particularly mixed forests associating host and nonhost species. We addressed the effect of tree diversity on oak colonization and defoliation by a major specialist pest, the oak processionary moth (OPM)
2. We quantified the number of male OPM moths captured and larval defoliation in pure stands of two oak host species (Quercus robur and Quercus petraea) and in mixed stands associating the two oak species or each oak species with another nonhost broadleaved species. We conducted two complementary studies to test the effect of host species and stand composition: (i) we used pheromone trapping to compare the number of males OPM captured throughout the distribution of oak hosts in France and (ii) we noted the presence of OPM nests and estimated defoliation in mature forests of north‐eastern France.
3. Oak species and stand composition significantly influenced the number of male OPM captured and defoliation by OPM larvae. Quercus petraea was consistently more attractive to and more defoliated by OPM than Q. robur. Both oak trees were attacked more in pure stands than in mixed stands, in particular mixed stands associating oaks with another (nonhost) broadleaved species.
4. The results of the present study support the view that mixed forests are more resistant to specialist pest insects than pure stands, and also indicate that this trend depends on forest composition. Our study provides new insights into OPM ecology and has potential implications for forest management, including the management of urban forests where OPM causes serious human health issues.

     

Low temperature tolerance and starvation ability of the oak processionary moth: implications in a context of increasing epidemics

• 1 We investigated how modifications in winter and spring temperature conditions may affect the survival of a spring‐hatching Lepidoptera, the oak processionary moth Thaumetopoea processionea.
• 2 Supercooling and chilling injury experiments indicate that eggs are especially cold hardy at the start of the winter period, although this ability is reduced later in the season. In the spring, young larvae are sufficiently cold hardy to ensure no direct mortality as a result of late frosts.
• 3 A comparison of phenological models shows that neonate larvae may await the unfolding of new oak leaves for relatively long periods (e.g. 1–30 days). Under both low (4°C after 5 days at 16°C) and high temperature experimental scenarios (constant 16°C), the majority of neonate larvae can survive starvation for more than 2 weeks.
• 4 Larvae may also suffer from food depletion once their development has been initiated (e.g. during cold springs) if the threshold temperature for feeding is not reached for several consecutive days, or in the case of late frosts affecting foliage availability. When temperature is reduced to 4°C, developing larvae become inactive and do not feed anymore; their starvation survival capability is reduced to approximately 2 weeks (cold spring hypothesis). At 16°C, developing larvae that are deprived of food can only survive for 10 days (late frost hypothesis).
• 5 We conclude that, in the oak processionary moth, neonate larvae are relatively well adapted to early hatching relative to budburst, ensuring them the highest foliage quality for development. In some years, however, phenological asynchrony or cold spring conditions may affect the persistence of populations at the limits of the species' range.

     

Characterization and cross-amplification of 13 microsatellite loci in the northern pine processionary moth, Thaumetopoea pinivora (Lepidoptera: Notodontidae)

Thirteen polymorphic microsatellite loci were developed for the northern pine processionary moth (Thaumetopoea pinivora) and tested for cross-amplification in seven other species within the Thaumetopoea family. Number of alleles ranged from two to 10 when at least 28 individuals from one population were screened and one locus, Thapin06, appears to be sex linked. Expected heterozygosity ranged from 0.094 to 0.856 and observed heterozygosity ranged from 0.097 to 0.806. Amplification success varied between sister species, with two up to seven loci being successfully amplified. The described loci will be valuable for studying the population genetic structure and dispersal behaviour of this forest pest.     

Response of the egg parasitoids of the pine processionary moth to host density and forest cover at the southern edge of the range

1. Thaumetopoea pityocampa is the most important pine defoliator in the Mediterranean basin. Despite being attacked by a number of natural enemies, populations occur frequently at high density in several areas.
2. Egg parasitism was studied in 27 pine and cedar forests in Algeria, in relation to the host density (tents per tree) and the proportion of forest cover in the landscape.
3. Egg parasitism varied from 2% to 25%, accounted by two parasitoid species, the specialist Baryscapus servadeii and the generalist Ooencyrtus pityocampae.
4. Tent density was negatively correlated with parasitism by B. servadeii but not with that of O. pityocampae. Conversely, parasitism by O. pityocampae increased with the proportion of forest and agricultural cover, but not in the case of B. servadeii.
5. Maximum summer temperature showed no correlation with parasitism rates. Still, temperature frequently exceeded 40 °C during the period of adult parasitoid activity.
6. The low performance of the egg parasitoids at the southern edge of the host range could be explained by the reduced fecundity of the host, climate effects, and phenological mismatching between the parasitoids and the egg development. These and other factors potentially involved the need to be further explored with a long-term study of population dynamics.

     

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.     

Toxicity of essential oils extracted from Origanum onites L. and Citrus aurentium L. against the pine processionary moth, Thaumetopoea wilkinsoni Tams

The pine processionary moth (PPM), Thaumetopoea wilkinsoni Tams. (Lepidoptera: Thaumetopoeidae), is an important forest pest in the Mediterranean area, additionally urticating hairs of the caterpillars of this species cause strong allergic reactions on skin of humans and animals. In the present study, essential oils extracted from aerial parts of Origanum onites L. and fruit peels of Citrus aurentium L. were tested at three doses (0.1, 0.5 and 1%) against 4th and 5th instar larvae of the pest. The results showed that the activities were concentration dependent. The LD50 and LD90 values were 0.288 and 0.926% for O. onites, 0.530 and 2.306% for C. aurentium, respectively.     

Theoretical analysis of the electronic properties of the sex pheromone and its analogue derivatives in the female processionary moth Thaumetopoea pytiocampa

In the present work, the distribution of the electronic charge density of the natural sex pheromone, the (Z)-13-hexadecen-11-ynyl acetate, in the female processionary moth, Thaumetopoea pytiocampa, and its nine analogue derivatives was studied within the framework of the Density Functional Theory and the Atoms in Molecules (AIM) Theory at B3LYP/6-31G *//B3LYP/6-31++G * * level. Additionally, molecular electrostatic potential (MEP) maps of the previously mentioned compounds were computed and compared. Furthermore, the substitution of hydrogen atoms from the methyl group in the acetate group by electron withdrawing substituents (i.e., halogen atoms) as well as the replacement effect of hydrogen by electron donor substituents (+I effect) as methyl group, were explored. The key feature of the topological distribution of the charge density in analogue compounds, such as the variations of the topological properties encountered in the region formed by neighbouring atoms from the substitution site were presented and discussed. Using topological parameters, such as electronic charge density, Laplacian, kinetic energy density, and potential energy density evaluated at bond critical points (BCP), we provide here a detailed analysis of the nature of the chemical bonding of these molecules. In addition, the atomic properties (population, charge, energy, volume, and dipole moment) were determined on selected atoms. These properties were analyzed at the substitution site (with respect to the natural sex pheromone) and related to the biological activity and to the possible binding site with the pheromone binding protein, (PBP). Moreover, the Laplacian function of the electronic density was used to locate electrophilic regions susceptible to be attacked (by deficient electron atoms or donor hydrogen). Our results indicate that the change in the atomic properties, such as electronic population and atomic volume, are sensitive indicators of the loss of the biological activity in the analogues studied here. The crucial interaction between the acetate group of the natural sex pheromone and the PBP is most likely to be a hydrogen bonding and the substitution of hydrogen atoms by electronegative atoms in the pheromone molecule reduces the hydrogen acceptor capacity. This situation is mirrored by the diminish of the electronic population on carbon and oxygen atoms at the carbonylic group in the halo-acetate group. Additionally, the modified acetate group (with electronegative atoms) shows new charge concentration critical points or regions of concentration of charge density in which an electrophilic attack can also occur. Finally, the use of the topological analysis based in the charge density distribution and its Laplacian function, in conjunction with MEP maps provides valuable information about the steric volume and electronic requirement of the sex pheromone for binding to the PBP.     

Natural biological control of the pine processionary moth Thaumetopoea pityocampa (Den. & Schiff.) by the Argentine ant Linepithema humile (Mayr) in Portugal

1 Defoliation by larvae of the pine processionary moth, Thaumetopoea pityocampa, is negligible in stands of Pinus pinaster colonized by the Argentine ant Linepithema humile which preys fiercely on the young moth larvae. In contrast, such damage is widespread where pine plantations are colonized by native ants, predominantly Tapinoma nigerrimum and Lasius niger, which seemingly disregard the larvae. 2 Where L. humile- and native ant-occupied sectors adjoin, there is a 20–50 m overlap in the transition area between L. humile- and native ant-occupied pines. This was most evident in a > 500 ha plantation where there was severe or very severe T. pityocampa attack in native ant sectors contrasting with none in adjoining L. humile sectors. 3 Predation by L. humile is no doubt enhanced by its existence as super-colonies over very large areas, by its foraging activity and recruitment on trees throughout the time when T. pityocampa and other prey are present, and by honeydew- producing Homoptera which help retain foraging L. humile workers in pine tree crowns. 4 The role of L. humile could be enhanced by cultivations that disturb the soil and restrain ground vegetation.     

Carbon reserves and canopy defoliation determine the recovery of Scots pine 4 yr after a drought episode

? Severe drought may increase physiological stress on long-lived woody vegetation, occasionally leading to mortality of overstory trees. Little is known about the factors determining tree survival and subsequent recovery after drought. ? We used structural equation modeling to analyse the recovery of Scots pine (Pinus sylvestris) trees 4 yr after an extreme drought episode occurred in 2004-2005 in north-east Spain. Measured variables included the amount of green foliage, carbon reserves in the stem, mistletoe (Viscum album) infection, needle physiological performance and stem radial growth before, during and after the drought event. ? The amount of green leaves and the levels of carbon reserves were related to the impact of drought on radial growth, and mutually correlated. However, our most likely path model indicated that current depletion of carbon reserves was a result of reduced photosynthetic tissue. This relationship potentially constitutes a feedback limiting tree recovery. In addition, mistletoe infection reduced leaf nitrogen content, negatively affecting growth. Finally, successive surveys in 2009-2010 showed a direct association between carbon reserves depletion and drought-induced mortality. ? Severe drought events may induce long-term physiological disorders associated with canopy defoliation and depletion of carbon reserves, leading to prolonged recovery of surviving individuals and, eventually, to delayed tree death.     

Insect-induced chemical changes in young lodgepole pine (Pinus contorta): the effect of previous defoliation on oviposition, growth and survival of the pine beauty moth, Panolis flammea

ABSTRACT. 1. Significantly more eggs were laid by adult female pine beauty moths ( Panolis flammea (D&S)) on previously undefoliated lodgepole pine ( Pinus contorta Douglas) saplings than on those which had been partially defoliated the year before.
2. The larval weights, mean relative growth rates and survival rates of P.flammea were lower on defoliated trees than on undefoliated trees.
3. Marked and significant differences between the monoterpene profiles of the shoot cortical oleoresin of defoliated and undefoliated trees were linked to oviposition preferences in P.flammea.
4. Differences occurred between the levels of soluble tannins in previously defoliated and undefoliated trees.
5. The results are discussed in relation to earlier work on insect-induced changes in plants, and the significance of inter-provenance differences in lodgepole pine response is assessed.