The egg parasitoid complex of the pine processionary moth (
Thaumetopoea pityocampa
) was surveyed for the first time on the Thasos Island, Greece. A total of 96 egg batches containing 20391 eggs ...were collected between 06 and 10 of September, 2017 from Aleppo pines (
Pinus halepensis
) at four sites (Skidia, Thimonia, Alyki and Panagia). Four primary parasitoids were identified (
Ooencyrtus pityocampae
,
Baryscapus servadeii
,
Anastatus bifasciatus
and
Trichogramma
sp.), as well as the hyperparasitoid
B. transversalis
. Among the parasitoids groups,
O. pityocampae
was the most common, followed by
B. servadeii
, whilst the number of other species was low. The highest survival rate was reported for three species:
O. pityocampae
,
B. servadeii
and
A. bifasciatus
, while the highest was the mortality in
Trichogramma
sp. All emerged adults of
O. pityocampae
and
B. servadeii
were female specimens and in
A. bifasciatus
- males. The number of females of
B. transversalis
was three times higher than the one of males.
Ooencyrtus pityocampae
and
B. servadeii
were the most important parasitoids of
T. pityocampa
, destroying respectively 27.1% and 9.9% of the host eggs.
Global warming modulates the spatial and temporal occurrence of insect outbreaks, leading to as-yet-unknown effects on forests ecosystems. Warmer trends may favour the upward and northward expansion ...of pests, albeit increased exposure to heat events and droughts may also hamper insect growth and development. Thus far, further research is needed about the balance of climate warming on pine processionary moth (PPM) (Thaumetopoea pityocampa) development stages, especially at broader scales, despite being the main conifer-defoliating insect in the Mediterranean area. This research analyses the relationships of PPM with the climatic conditions during its most vulnerable development phases in Spain to provide base-information for forest managers. We hypothesize that warmer winter temperatures will increase PPM growth at their larval feeding stage, whereas summer-heat events will reduce PPM rates from egg and early larval stages, leading to counterbalanced effects of climate warming. Furthermore, we expect dry springs will allow an earlier development of PPM and higher incidence of outbreaks. To analyse climate effects on PPM populations in Andalusia, Castilla-La Mancha, and Navarre (37 to 42°N), we compiled information from the Regional Forest Services comprising up to 26 years of monitoring data from 2465 forest stands dominated by Pinus nigra and Pinus sylvestris. We fitted Cumulative Link Mixed Models (CLMM) to test the climate effects on four PPM defoliation severity levels. Our results support higher PPM larvae survival and incidence due to warmer winter conditions, but also the reduction of PPM population size under summer heat conditions. Particularly, the increasing incidence associated to warmer winters during the larval defoliating stage is counterbalanced by the decreasing population at earlier life stages during summer heat events. Spring drought also plays an important role on PPM incidence rates, but its effect is idiosyncratic to each region, suggesting an adaptation of PPM populations to regional conditions, claiming to tailor-made forest management endeavours. This study reveals that a better comprehension of abiotic effects along the whole PPM life cycle is paramount to understand the impact of climate warming on insect outbreaks which shorten wood production and carbon sequestration of Mediterranean forests.
•Understanding novel environmental conditions on pest outbreaks is paramount to forecast their future incidence.•Positive effects of warmer winters for PPM populations is counterbalanced by the negative impacts of summer heat events.•Spring drought plays an important role on PPM incidence rates, but its effect is idiosyncratic to each region.
Climatic warming is assumed to expand the geographic range of insect pests whose distribution is mainly constrained by low temperatures. This is the case of the pine processionary moth (Thaumetopoea ...pityocampa), which is one of the main conifer defoliators in the Mediterranean Basin. Warmer winters may lead to a northward/upward expansion of this insect, as short-term studies have shown. However, no long-term data, i.e. spanning at least one century, has been used to examine these projections. We test the hypotheses that climatic warming (i) has caused an upward shift of the pine processionary moth, and (ii) has increased the frequency of severe defoliations. We used dendrochronological methods to reconstruct defoliations over the period 1900–2006 in 14 sites spanning a wide altitudinal range (1070–1675 m) in Teruel, eastern Spain. We built local ring-width chronologies for four co-occurring pine species with different degree of susceptibility against the moth defoliations, from highly suitable or palatable species (Pinus nigra) to moderately (Pinus sylvestris, Pinus halepensis) or rarely defoliated species (Pinus pinaster). We validated the tree-ring reconstructions of outbreaks using a field record of stand defoliations spanning the period 1971–2006. Outbreaks in the most affected P. nigra stands corresponded to abrupt one- to two-year growth reductions (70–90% growth loss). Reconstructed outbreaks occurred on average every 9–14 years. The growth memory of outbreaks was weaker but lasted longer (1–6 years) than that due to droughts (1–3 years). Neither an upward expansion nor an increase in outbreak frequency was observed. Severe PPM defoliations did not increase as climate warmed, rather they were positively related to the winter North Atlantic Oscillation.
Is climate warming leading to an upwards shift of severe pine processionary moth (PPM) defoliations in Mediterranean pine forests? Field records of stand defoliation and tree-ring reconstructions of outbreaks did not support an upward shift, but allowed detecting a positive link between PPM defoliations and the winter North Atlantic Oscillation. Display omitted
•We tested if warmer winters increased pine processionary moth (PPM) defoliations.•PPM defoliation negatively impacted longer but weaker growth than drought.•Neither an upward expansion nor an increase in outbreak frequency was observed.•PPM defoliations were positively related to the winter North Atlantic Oscillation.
•Pine-birch forests were more resistant to primary pests than pine monocultures.•Associational resistance was due to direct and indirect, growth-mediated, effects of birch.•Growth-mediated effects ...occurred independently of drought conditions.
Tree species diversity generally has positive effects on forest primary productivity and resistance to natural perturbations, but diversity-function relationships can vary with site conditions. Recently, studies in forest diversity experiments have shown that tree diversity and local climate, in particular drought intensity, interactively affect insect herbivory. On the other hand, many studies focused on the response of forests to drought in terms of tree growth but without analysing the concomitant effects on susceptibility to pests. It is of particular interest to understand the combined effects of drought and tree diversity on the growth of the host tree, since host resource concentration is a determining factor of a pest’s host choice.
We used a tree diversity experiment where tree species diversity and drought conditions were both manipulated to evaluate their interactive effects on the susceptibility of maritime pine (Pinus pinaster Aït.) forests to two primary pests (i.e. infesting healthy trees): the pine stem borer (PSB) Dioryctria sylvestrella, and the pine processionary moth (PPM; a leaf chewer), Thaumetopoea pityocampa. Using structural equation models, we investigated the direct and indirect effects (i.e. mediated by host resources) of the presence of birch and drought on the total number of attacks of PPM and PSB, in the same plots and in the same year.
We showed that pine-birch plots were more resistant to both PPM and PSB attacks than pine monocultures. Furthermore, we found that this associational resistance pattern was due to direct effects of birch trees on attacks, possibly related to disrupting non-host volatiles (NHVs), but also to indirect, resource-mediated effects whereby the presence of birch trees reduced the amount of host pine resources available to the pests. Drought conditions modulated birch mediated effects on resistance of maritime pine forests only for PSB attacks. Overall, our work improves our understanding of tree diversity-herbivory relationships and helps explain how climate might modulate such relationships.
Studies on egg parasitoids of the pine processionary moth (Thaumetopoea pityocampa) were conducted during the period 1991-2018 in native localities of the pest on the Balkan Peninsula and in Asia ...Minor. In Bulgaria the biological material (2510 egg batches and 579273 eggs) was collected in 48 host localities. A number of 650 egg batches and 135611 eggs were studied from the Balkan countries (North Macedonia, Bosnia and Herzegovina, Albania and Greece), and in the Asian part of Turkey (Asia Minor), the biological material was examined from nine habitats. Eight species of egg parasitoids (Ooencyrtus pityocampae, Baryscapus servadeii, B. transversalis, Pediobius bruchicida, Anastatus bifasciatus, Eupelmus vesicularis, E. vladimiri and Trichogramma sp.) were found. The total regulating effect of egg parasitoids in Bulgaria was on average 17.6%, and in the other Balkan countries – 24.9%. Trichogramma sp. was found in 63.1% of the analysed samples in Bulgaria and in 55.6% from the neighboring countries. The percent of parasitism of T. pityocampa eggs by Trichogramma sp. was low - on average 0.39% for Bulgaria and 0.73% for the other Balkan countries. The relative share of the species in the total percentage of parasitised eggs for Bulgaria and the other countries was 2.2% and 2.9%, respectively.
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•Pine stand colonization by PPM increases with pine density.•The proportion of attacked pines decreases with pine density.•Birch provides pure associational resistance by reducing ...pine apparency.•Apparency effects occur within and between stands.•Associational resistance fades with time.
Mixed forests are thought to be less prone to pest insect damage than monocultures. This may result from reduced host availability (i.e., density effect) or from non-host trees reducing the physical or chemical apparency of host trees (i.e., associational resistance, AR). However, associational and density effects are often confounded in mixed forests. We aimed to disentangle their relative contribution to attacks of pine trees by a specialist pest, the pine processionary moth (PPM, Thaumetopoea pityocampa). We assessed pine infestation by PPM by counting the number of winter nests during three consecutive years along an experimental gradient of pine density in presence or absence of a fast growing species, namely birch. The total number of PPM nests per plot increased with pine density (maximum in high density monocultures), while the proportion of attacked pine trees decreased along the same gradient. Birch provided associational resistance via reduced pine apparency due to their greatest higher. This mechanism occurred at two spatial scales, whenever birch was planted within pine plots or in adjacent plots. Associational resistance was stronger in dense stands, probably due to reduced distance between pines and neighboring birches. But AR faded with time, pines becoming taller than birches, making density effects preeminent over apparency effects. Our findings suggest that mixing tree species to trigger resistance to pest insects requires taking into account the relative growth rate of associated species together with the relative proportion of associated species, both within and between stands.
Diverse landscapes consisting of mixed crops are expected to support higher biological control, while also contributing to maintain farmland biodiversity. Although bats are known as predators of many ...farming pests, few studies to date have investigated how their foraging activity may enhance natural pest control.
Here, we tested the hypothesis that crop mosaics would provide a temporal continuity in prey availability for bats, ultimately resulting in higher biological control. We sampled bat activity and diversity, and the abundance and damage of three major pests of vineyards, maize, and pine plantations, in both simple and diverse landscapes mixing the three production types. Bat species richness and total activity were higher in vineyards and pine plantations located within diverse landscapes. Bat foraging activity also peaked within diverse landscapes. In vineyards, moth abundance decreased with bat species richness. In pine plantations, pest damage decreased with bat foraging activity. In maize fields, pest abundance and damage increased with bat richness and activity longer-term investigations would be necessary to assess their actual effectiveness. Our study advocates for promoting a diversity of coexisting crops within agricultural landscapes to enhance bat activity and diversity, which in turn would sustain higher biological control and bolster biodiversity conservation in farmland.
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•Diverse agricultural landscapes promote bat activity and diversity.•Landscapes combining annual (maize fields) and perennial crops (vineyards and pine plantations) support higher activity of bat species of conservation concern.•Diverse agricultural landscapes increase bat biological control of Thaumetopoea pityocampa but not of Sesamia nonagrioides.
This study presents results for the dynamic of the populations of the pine processionary moth (
Thaumetopoea pityocampa
) during the period 2007-2017 and the impact of reducing factors in the ...Repub-lic of North Macedonia. The population density was determined by the number of larval nests both per tree and per hectare that varied during the research period. The number of individuals went up between 2007 and 2010, while during the following years it rapidly decreased. Since 2011, an overall prograding trend has been recorded in the several subsequent years. This could be explained by the huge number of individuals from the previous years that were in a diapause. The abundance of pest populations continued to grow in 2016 as no measures were taken. During the winter of 2016/2017, the impact of the extremely low temperatures on pest mortality was monitored in 2016-2017 generation. The density of the populations came to latency due to the very large number of dead larvae of second and third larval stages. We recorded a 100% mortality of larvae in plantations of
Pinus nigra
in the regions near Prilep, Sveti Nikole, Shtip, Kochani and Negotino Villages.
Mapping species spatial distribution using spatial inference and prediction requires a lot of data. Occurrence data are generally not easily available from the literature and are very time-consuming ...to collect in the field. For that reason, we designed a survey to explore to which extent large-scale databases such as Google maps and Google street view could be used to derive valid occurrence data. We worked with the Pine Processionary Moth (PPM) Thaumetopoea pityocampa because the larvae of that moth build silk nests that are easily visible. The presence of the species at one location can therefore be inferred from visual records derived from the panoramic views available from Google street view. We designed a standardized procedure allowing evaluating the presence of the PPM on a sampling grid covering the landscape under study. The outputs were compared to field data. We investigated two landscapes using grids of different extent and mesh size. Data derived from Google street view were highly similar to field data in the large-scale analysis based on a square grid with a mesh of 16 km (96% of matching records). Using a 2 km mesh size led to a strong divergence between field and Google-derived data (46% of matching records). We conclude that Google database might provide useful occurrence data for mapping the distribution of species which presence can be visually evaluated such as the PPM. However, the accuracy of the output strongly depends on the spatial scales considered and on the sampling grid used. Other factors such as the coverage of Google street view network with regards to sampling grid size and the spatial distribution of host trees with regards to road network may also be determinant.
The pine processionary moth (
Dennis and Schiff.), one of the major defoliating insects in Mediterranean forests, has become an increasing threat to the forest health of the region over the past two ...decades. After a recent outbreak of
in Catalonia, Spain, we attempted to estimate the damage severity by capturing the maximum defoliation period over winter between pre-outbreak and post-outbreak images. The difference in vegetation index (dVI) derived from Landsat 8 was used as the change detection indicator and was further calibrated with Unmanned Aerial Vehicle (UAV) imagery. Regression models between predicted dVIs and observed defoliation degrees by UAV were compared among five selected dVIs for the coefficient of determination. Our results found the highest R-squared value (0.815) using Moisture Stress Index (MSI), with an overall accuracy of 72%, as a promising approach for estimating the severity of defoliation in affected areas where ground-truth data is limited. We concluded with the high potential of using UAVs as an alternative method to obtain ground-truth data for cost-effectively monitoring forest health. In future studies, combining UAV images with satellite data may be considered to validate model predictions of the forest condition for developing ecosystem service tools.
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