•The percentage of PPM infested trees is higher in stands with fewer trees.•PPM concentrates on more apparent trees, i.e., taller or at stand edge.•Stand edges with westerly aspect are more at risk ...of PPM infestation.•Attack patterns within and between stands may be due to female moth preference.
The pine processionary moth (PPM, Thaumetopoea pityocampa) is the main defoliator of pines in the Mediterranean area, necessitating constant surveillance and regular pest management. A sound understanding of the spatial distribution of infested trees, both within and between stands, is required to increase management efficiency. We hypothesized that both host tree density at stand scale and tree apparency at individual tree scale were responsible for between- and within-stand patterns of PPM infestation. We tested these hypotheses on a sample of 171 maritime pine stands in the Landes de Gascogne, the largest plantation forest in Europe. We showed that PPM infestation (percentage of infested trees) decreased significantly with stand density, and was therefore greater in older than in younger stands. The probability of a pine tree being attacked increased significantly with tree height and proximity to the edge of the stand. Mortality rates of exposed sentinel egg batches did not differ with distance from the stand edge. We discuss three likely explanations for higher infestation of taller trees at stand edges: better survival of larvae on sun-exposed trees, and random interception vs. active host selection by gravid females. Our findings suggest that stand management could be adapted in order to decrease the risk of damage by the pine processionary moth, and that predictive tools for infestation dynamics can be based on forest growth models.
Context
Development and survival vary across a species’ geographic range and are also affected by local conditions like urban warming, which may drive changes in biology that magnify or reduce the ...risks of hazardous organisms to people. Larvae of the pine processionary moth (
Thaumetopoea pityocampa
Schiff; PPM) are covered with setae (hair-like structures) that cause allergic reactions in warm-blooded vertebrates upon contact with the skin, eyes, or respiratory tract.
Objectives
Our objective was to determine whether PPM larva development, phenology, and survival change with urban warming in ways that affect the risks of this organism to people.
Methods
In Orléans, France, we conducted a field study of PPM larvae across a gradient of urbanization from forests to city center to measure winter survival and the timing and duration of the life stage that poses the greatest risk to people.
Results
Larvae in the city spent more time in the fifth, most dangerous, instar than larvae in the forest. Urban warming indirectly increased larva survival by advancing phenology of urban larvae to a more cold-tolerant life stage prior to the winter cold period. Our results indicate that local urban warming drives changes in larva biology that increase the risks the organisms pose to people.
Conclusions
In recent decades, the PPM has expanded its geographic range to higher latitudes with rising temperatures. Our study highlights that local landscape variation, such as a mosaic of warmer and cooler temperatures in cities, can alter the effects of this type of range expansion for people.
An increasing body of evidence indicates that the association between different plant species may lead to a reduction in insect herbivory, i.e. associational resistance. This might be due to a ...top-down regulation of herbivores by increased numbers of natural enemies or to a disruptive bottom-up influence of lower host plant accessibility. In particular, the richer plant communities release more diverse plant odours that may disturb olfactory-guided host choice and mating behaviour of insect herbivores, i.e. the "semiochemical diversity hypothesis". However, this hypothesis has been rarely tested experimentally in natural habitats, notably forest ecosystems. We tested the effects of non-host volatiles (NHV) on mate and host location by the pine processionary moth (PPM) at the scale of individual pine trees with branches of non-host tree (birch) at their base. Pheromone trap catches and the numbers of larval nests were both reduced by non-host presence under treated pine trees, confirming an associational resistance mediated by NHV. In both males and females, the antenna could detect several birch volatiles, including methyl salicylate (MeSa). MeSa inhibited the attraction of the PPM male to pheromone traps, as did bark and leaf chips from birch trees. Our test of three doses of MeSa at the habitat scale (50 m forest edges) showed that the reduction in the numbers of male PPM captured in traps and in larval nests was MeSa dose-dependent. These results show that odours released by deciduous non-host trees can reduce herbivory by a forest defoliator in conifers, providing support to the "semiochemical diversity hypothesis" as a mechanism of associational resistance.
In the Atlas cedar forests located on the northern massifs of the Blidean Atlas and at the eastern extension of the Saharan Atlas, 79 egg batches of processionary moth Thaumetopoea pityocampa (Denis ...& Schiffermuller, 1775) were collected during the summer period from two sites: Chrea National park (46), and Ouled Yagoub forest (33). To assess the effect of the egg batches characteristics on the parasitism, the eggs were monitored after the hatching of the larvae and/or the emergence of the parasitoids. The average number of eggs/batches in the Ouled Yagoub site (184 eggs) was significantly higher than of the population of Chrea (151). Data analysis showed that the means comparisons of the hatched and unhatched number of eggs between the two sites were significant. In the case of the population of Chrea, the egg mass was laid in the form of a cylinder on twigs of relatively small diameters while for the population of Ouled Yagoub eggs were laid in the form of plates on twigs of larger diameter, thus more exposed to parasitoids. For the two populations, three active egg parasitoids were identified: Ooencyrtus pityocampae (Mercet, 1921) (Encyrtidae), Baryscapus servadeii (Domenichini,1965) (Eulophidae), and Trichogramma embryophagum (Hartig, 1838) (Trichogrammatidae), the most dominant. These parasitoids were heterogeneously distributed on the egg batches collected in the cedar’s plantation of the Chrea, but homogeneously on the egg batches collected in the Ouled Yagoub cedar forest. The activity and distribution of parasitoids on the egg-laying surface are influenced by the form on the branch chosen by the female.
•Diapause of Thaumetopoea pityocampa prolonged at least 7years in our study area.•Length of prolonged diapause generally increased with increasing elevation.•Prolonged diapausing individuals emerged ...in advance of simple diapausing ones.•Emergence from prolonged diapause sustained density when biocontrol was done.•Prolonged diapause is an important component of population dynamics.
Due to its negative impact on tree growth and human health, pine processionary moth is a major concern for forest managers, especially in recent outbreak expansion areas. As some individuals have prolonged diapause for more than a single year, population dynamics of this species is hard to understand. To decipher the mechanism of prolonged diapause and its role in population dynamics, we started a pest surveillance program in 1999 in a pine processionary population in the southern-central Alps of northern Italy, a recent range expansion zone for the species. The 16-year study used a pheromone trap network and four large rearing cages. We found some individuals could diapause for up to a maximum of seven years. With few exceptions, prolonged pupal diapause increased and retrieval rate of moth in cages decreased with increasing elevation. Moreover, we found prolonged diapausing individuals to emerge in advance of non-diapausing individuals. This trait allowed us to infer the proportion of prolonged diapausing individuals caught in the pheromone traps. Prolonged diapause was responsible for maintaining high population density for eight years in spite of annual applications of the biocontrol agent Bacillus thuringiensis kurstaki. This sustained density relied on individuals from cohorts before the application of insecticide started, and from cohorts not completely suppressed by the insecticide applications.
The pine processionary moth Thaumetopoea pityocampa (Lepidoptera: Notodontidae) is the main pine defoliator in the Mediterranean region. Its urticating larvae cause severe human and animal health ...concerns in the invaded areas. This species shows a high phenotypic variability for various traits, such as phenology, fecundity and tolerance to extreme temperatures. This study presents the construction and analysis of extensive genomic and transcriptomic resources, which are an obligate prerequisite to understand their underlying genetic architecture. Using a well‐studied population from Portugal with peculiar phenological characteristics, the karyotype was first determined and a first draft genome of 537 Mb total length was assembled into 68,292 scaffolds (N50 = 164 kb). From this genome assembly, 29,415 coding genes were predicted. To circumvent some limitations for fine‐scale physical mapping of genomic regions of interest, a 3X coverage BAC library was also developed. In particular, 11 BACs from this library were individually sequenced to assess the assembly quality. Additionally, de novo transcriptomic resources were generated from various developmental stages sequenced with HiSeq and MiSeq Illumina technologies. The reads were de novo assembled into 62,376 and 63,175 transcripts, respectively. Then, a robust subset of the genome‐predicted coding genes, the de novo transcriptome assemblies and previously published 454/Sanger data were clustered to obtain a high‐quality and comprehensive reference transcriptome consisting of 29,701 bona fide unigenes. These sequences covered 99% of the cegma and 88% of the busco highly conserved eukaryotic genes and 84% of the busco arthropod gene set. Moreover, 90% of these transcripts could be localized on the draft genome. The described information is available via a genome annotation portal (http://bipaa.genouest.org/sp/thaumetopoea_pityocampa/).
The pine processionary moth, Thaumetopoea pityocampa (Denis and Schiffermüller), is an important insect in the Mediterranean region, as it defoliates pines and its urticating hairs can cause allergic ...reactions in humans and animals. Moreover, this species exhibits an interesting genetic structure as recently a distinct East-North African mtDNA lineage (‘ENA clade’) has been described.This clade has been recently detected in Greek populations where it has currently expanded its range by replacing the ‘endemic’ T. pityocampa lineages. Here, we report new data on the rapid spread of ‘ENA clade’ in the Greek island Evoia in only a few years. As the underlying mechanisms of the ‘ENA clade’ range expansion has not been studied so far, we screened T. pityocampa for an infection with the heritable bacterial endosymbionts Wolbachia (Bacteria: Anaplasmataceae), Cardinium (Bacteria: Bacteroidaceae), Rickettsia (Bacteria: Rickettsiaceae) and Spiroplasma (Bacteria: Spiroplasmataceae). These bacteria can manipulate the reproduction of infected hosts, something that could potentially explain the rapid spread of ‘ENA clade’ lineage. Therefore, we screened 28 individuals that exhibited T. pityocampa ‘ENA clade’ and ‘endemic’ T. pityocampa haplotypes from nine populations scattered all over Greece. None of them was infected with any of the four endosymbionts, suggesting that these bacteria do not cause reproductive manipulations in T. pityocampa lineages and, thus, other factors should be explored in future research efforts.
Background: Moths of the genus Thaumetopoea are widespread pests in the coniferous and deciduous forests in Bulgaria. Contact with the caterpillars, larval form of different Thaumetopoea species, ...causes a series of complaints in humans: mainly contact dermatitis (erucism), but also IgE-mediated allergic reactions. The aim of the present pilot study is to investigate the skin reaction after prick tests with allergens from different Thaumetopoea species in a group of people who have frequent contacts with the processionary caterpillars. Material and methods: A group of 42 subjects were surveyed - 37 men and 5 women between the ages of 18 and 87. Specific sensitization to caterpillars of three Thaumetopoea species: Thaumetopoea pityocampa (pine processionary); Thaumetopoea processionea (oak processionary) and Thaumetopoea solitaria (pistachio processionary) was assessed by allergy skin prick tests (SPT) with specially designed caterpillar allergens. Results: Positive allergy skin tests to one or more caterpillar’s allergens were measured in 18 (43%) participants. A simultaneous test with the three allergens from the different Thaumetopoea species showed that in 5 (31%) of the cases, skin hypersensitivity only to allergen from T. pityocampa was present. Monosensitization to T. processionea observed in 2 (12%). The rest 9 (57%) participants with positive skin test show different profiles of polysensitization to Thaumetopoea allergens under study. Conclusions: The evaluation of skin reactivity after SPT with different caterpillar’s allergens outlined the important role of processionary allergens, especially this from T. pityocampa, in the development of IgE-mediated allergic complaints in different groups of forestry professionals. In view of these results, it seems that IgE-mediated hypersensitivity allergic reactions to Thaumetopoea caterpillars are at least as important as those with no allergic mechanism.
Speciation is nowadays recognized as a dynamic process in which the respective roles of forces driving ecological differentiation and reproductive isolation can change through time and space. ...Incipient speciation events are particularly useful to follow such processes that are not tractable when considering well-differentiated taxa. A promising case study was discovered in the pine processionary moth,
Thaumetopoea pityocampa
, a Mediterranean defoliator of
Pinus
species, for which allochrony acting as an automatic magic trait was recognized as the major driver of an incipient speciation process. In Portugal, a unique population with a shifted phenology, known as the summer population (SP), co-occurs with a population following the typical life cycle, known as the winter population (WP). We monitored male activity of both populations in the Leiria region, i.e. over the whole SP distribution range using a systematic sampling along two transects, and studied Portuguese WPs at a larger geographical scale to explore their genetic diversity and spatial pattern of differentiation. Results showed that the WPs were genetically more diverse than the SP, with a strong pattern of isolation by distance both at large and small spatial scales, while the SP was very homogeneous over its whole range, without signature of its recent spatial expansion. Contrary to our expectations, no F1 hybrids were identified, even though we found an extended flight period of the SP, overlapping with the beginning of the WP reproductive period. Interestingly, the SP was found to be mostly limited to the sea shore where the WP is now scarce or absent, which could suggest competitive exclusion. Once clearly occurring in a sympatric context, the allochronic differentiation tends to develop nowadays in parapatry.
We collected 2297 egg batches of the pine processionary moth (Thaumetopoea pityocampa) during the period 1991-2018 from 44 sites in Bulgaria. The sampling sites were classified into three groups ...according to T. pityocampa phenological form (early, late and both forms) as well as in two groups of its range (historical and newly colonized areas). Seven primary egg parasitoids were identified: Ooencyrtus pityocampae, Baryscapus servadeii, Pediobius bruchicida, Anastatus bifasciatus, Eupelmus (Macroneura) vesicularis, Eupelmus (Macroneura) vladimiri and Trichogramma sp., and one hyperparasitoid, Baryscapus transversalis. The average impact of egg parasitoids (the percentage of parasitized host eggs) on T. pityocampa in Bulgaria was 13.8%. The two main parasitoids, O. pityocampae and B. servadeii, parasitized about 90% of the host eggs. The remaining parasitoids were of insignificant consequence to the parasitism of the T. pityocampa eggs, but in areas recently colonized by the pest, A. bifasciatus and Trichogramma sp. had a noticeable share (up to 33% of the impact). In old habitats of the host (areas colonized more than 10 years), the impact was almost two times higher than in new ones (15.3% vs. 8.6%). This could be attributed to B. servadeii, which was rare in newly colonized areas of T. pityocampa (impact 0.5%), but strongly dominant in old habitats (impact 7.2%). In contrast, O. pityocampae had a significant impact in new habitats (4.9%), which increased only slightly over time, reaching 6.0% in old habitats. There was no significant difference between the percentage of parasitism of the early and late form of the pine processionary moth (14.8% vs. 15.9%). However, there was a significant difference in the share of separate species in the parasitoid complex: in the early form, B. servadeii definitely dominated (63% of the infested eggs), while in the late form O. pityocampae dominated, although not so strongly (52% of the infested eggs). This difference is most likely due to the phenological characteristics of the parasitoids and the two forms of T. pityocampa. B. transversalis secondarily infested about 5% of the eggs of O. pityocampae and B. servadeii. This percentage was slightly lower for new habitats and habitats of the early form of pine processionary moth (3% and 4%, respectively). The impacts of the main parasitoids O. pityocampae and B. servadeii as well as the total impact of the parasitoid complex as a whole decreased with altitude. Conversely, the impacts of A. bifasciatus and Trichogramma sp. slightly increased with altitude probably due to the reduced competition of the main parasitoids.
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