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Global change and pine processionary moth: a new challenge for integrated pest management

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The winter pine processionary moth, Thaumetopoea pityocampa, has a geographic range in southern Europe, northern Africa and Middle East but in the last three decades a substantial expansion of the outbreak area has taken place, both northward and upward in elevation. Modelling and mapping of the range of PPM using GIS is therefore a useful tool for estimating the actual and future impact of the range of PPM on forest management and their socio-economic implications. The influence of weather conditions on nest temperatures and on the feeding activity of the nocturnally active larvae was studied in laboratory and outdoor experiments. Feeding activity was estimated under different temperature regimes. Activity was induced only when day-temperatures were above 9°C and night-temperatures above 0°C. Lower lethal temperatures were estimated by freezing experiments and super-cooling point measurements. For a precise estimation of the relation between nest temperature, air temperature and solar radiation, garden settings for simultaneous measurements were done. Minimum temperatures of the nest correspond well with air temperature minimum; nest maximum can be predicted by air temperature maximum and daily sum of solar irradiation. Climatic conditions, actual position of extreme nests and survival of larvae/colonies transplanted outside the actual range were observed in two alpine valleys (Durance Valley; Venosta Valley). Specific alpine conditions for the occurrence of PPM were studied on a local scale model at Venosta Valley, based on fine scale field surveys (air and nest temperatures, solar radiation) on north and south exposed slopes. Differences in feeding activity between the northern and southern slope can mainly be explained by low potential radiation due to shading of the northern slope during midwinter. Regional models were developed to evaluate the potential range of PPM for the alpine regions Trentino-Alto Adige-Tyrol (Italy-Austria) and Durance Valley (France) using modelling procedures similar to those applied on local scale, but with data from meteorological recording stations. Due to limited availability of solar irradiation data, a sub-model for estimation of global solar irradiation was developed using MeteoSat 7 image-analysis and potential solar irradiation derived from a digital elevation model (DEM). In order to reduce model errors caused by macroclimatic effects and climate zones, the modelling area was divided into adjacent sub-regions. Daily multiple regressions were calculated for modelling daily air temperature maxima and minima. Validation of the estimated bioclimatic variables was done with independent sampled data (translocation experiments in 2002/03 and 2003/04). Instead of sharp temperature thresholds of nest temperature for feeding induction (>9°C) and night feeding (>0°C), fuzzy functions were used to calculate the relative potential feeding activity during the winter period. The spatial distribution of the relative potential feeding activity was compared with the geographic range of PPM in Southern Tyrol. The class limit for "very likely occurrence" of PPM was defined as the minimum of the relative potential feeding activity for locations at the edge of the range during the "normal" winter 2003/2004. The climatic conditions for feeding activity would also permit the occurrence of PPM in the northern alpine range, but compared with the Southern Alps the higher frequency of extreme frost events are limiting the occurrence of PPM. Concerning French Alps, the actual range of PPM is for some areas far behind the limit of potential occurrence. Scenarios for climate warming and range expansion at Venosta Valley are based on the climatic conditions during the winter 2003/2004 (deviation of the mean winter temperature from the long-term mean winter at Schlanders: +0.27°C). The scenarios of climate change predict that every increase of 1°C in winter minimum could induce an altitudinal range expansion of ~200 m. A deviation of only +1°C dramatically increases the proportion of infested black pine stands at Venosta Valley. Almost all conifer stands in this area could be affected by PPM-infestations under +4°C-conditions. The model is available at http://ifff-server.boku.ac.at/ with an user-friendly approach and the possibility to test various climate change scenarios on the range expansion of the species. We think that forest managers, land planning staff and the general public of the Alpine area will be interested in the model. We plan also to extend the model to other geographic areas beside the South Tyrol and the Briancon district. For this, we are willing to start collaboration with other institutes and services.
The susceptibilities of Thaumetopoea pityocampa/wilkinsoni larvae to Bacillus thuringiensis formulations were screened in 2003 and 2004. Eggs and larvae were collected from pine forests in Israel, Italy and France. Larval mortality bioassays were conducted with formulations of Delfin, Dipel DF and Foray 48B at concentrations ranging from 0.001 to 0.1%. Significant differences in susceptibility to Bt were recorded among populations that were either regularly treated, often treated, or never treated with Bt. The mortality recorded in a population that was never treated with Bt was twice that in a regularly Bt-treated population. The mortality bioassay was optimised with regard to the patterns of larval hatching and age. The correlation between susceptibility to Bt and the possible resistance to the microbe is discussed. The reported decreasing susceptibility of Thaumetopoea to Bt in the intensive Bt IPM that was revealed in the present study must be taken into account in adopting guidelines for the use of Bt to control this pest. Factors to be considered include records of persistence of Bt in the forest during the insect season. The outcome of the result has been already applied to the Integrated Pest Management in the above countries, mainly by avoiding to repeat applications on the same areas. The monitoring plan of another results of this TIP (Pheromone 32691) has been applied to identify the areas. We expect that other countries where IPM is currently carried out will adopt the same procedure. The information will be spread by the publication of scientific and technical papers and on the project web site. For this reason, we think that the public Forest Health Services of all the countries where the pest is present can be interested, as well as a few SME involved in the production and trading of the bio control preparations. Research and extension institutes can be interested as well. In the calculation of the potential follow-up, we included only the qualified technical staff involved in decision-making but not the end-users of the forest resources (citizens). The expected benefits consist of a reduction of the whole area annually treated against the moth in the core areas. However, we are observing that the range expansion associated with the global change is requiring the pest control in new areas (e.g. the Alps), thus increasing the money invested by private and public forest owners. This will require an increase of the qualified jobs related to the survey work and the organization of the IPM in each country.
Climatic anomalies may produce, or accelerate, geographic range expansions of species limited by temperature or other climatic variables. Most such expansions are only temporary, before the prevailing climatic conditions drive the founder populations extinct. In contrast, here we report a recent rapid shift of the range limit during the record hot summer of 2003 in southern Europe that has the potential to be both permanent, and to have important implications on species range dynamics in general. The winter pine processionary moth (Thaumetopoea pityocampa), an important pine defoliator whose larvae feed in colonies during the winter, is limited in its distribution by winter temperatures. In the last three decades, warmer winters have led to a gradual but substantial expansion of its range both latitudinally and altitudinally. In the summer of 2003, T. pityocampa underwent an extraordinary expansion to high elevation pine stands in the Italian Alps; its altitudinal range limit increased by one third of the total altitudinal expansion over the previous three decades. In an experiment, we found flight activity of newly emerged females to increase with temperature. By determining a threshold temperature for flight take-offs under controlled conditions, we calculated that the nights above the threshold temperature were over five times more frequent, and considerably warmer, at the range limit in 2003 than in an average year. We therefore attribute the colonization of extreme, high-elevation sites to increased nocturnal dispersal of females during the unusually warm night temperatures in June-August 2003. Importantly, the colonies established at extreme sites survived the winter and produced offspring in 2004, although the range did not expand further due to low night temperatures that year.. We discuss several life history characteristics of T. pityocampa that maximize the likelihood of population persistence at the new range limit. As global warming continues and climatic anomalies are predicted to become more frequent, our results draw attention to the importance of extreme climatic events in the range formation of phytophagous insects. The result adds more understanding about the spatial expansion of the moths, unifying the dispersal phase as an adult with the survival during the larval development (result 32991). We have now a general model able to predict the expansion of the moth at range edge, and taking into account the role of extreme climatic events. This is an almost unique case in pest science and could serve as a reference model for a number of studies. A paper has been recently accepted by the journal Global Change Biology, with enthusiastic comments by reviewers and the editor. A great follow-up in both scientific and applied topics is expected.
Up to date, Cost Benefit Analysis (CBA) has a rather long history of applications to the forest field. Since the issuing of Gregersen and Contreras' manual in 1979, which only followed of five years Little and Mirrlees' Project Appraisal and Planning (1974), the profitability of many forest projects, especially in developing countries, has been assessed through this technique. Five levels of costs and benefits, including externalities and distributional effects, are identified, each corresponding to a step forward towards the TEV of natural resources, as well as a more reliable approximation of the 'true' social costs and benefits, that is the welfare gain of the investments: 1. Financial Analysis (FA): only monetary flows of expenditures and revenues are taken into account; prices are those observed in the market and market profit is the only objective 2. Conventional Economic Analysis (CEA): market prices of costs and benefits are adjusted by means of conversion factors to reflect the true value of resources, therefore eliminating distortions and market failures (monopolies, etc.) and transfer payments (taxes, subsidies, etc) 3. Extended Economic Analysis 1 (EEA1): off-site market effects are taken into account, namely those external to the areas of IPM but internal to the market; economic valuation techniques used are based on indirect market effects, such as productivity changes outside the area of intervention, effects on real estates market values, possible off-site damages and so on 4. Extended Economic Analysis 2 (EEA2): effects external to the market (intangibles, externalities, public goods/bads, etc, on-site and off-site) enter the CBA; non-market values have to be estimated using Consumer Surplus measures, e.g. Travel Cost and/or Contingent Valuation (CVM); environmental variations in and outside the area are considered and the objective-function is open to include people welfare 5. Socio-Economic Analysis (SEA): costs and benefits are assigned to the various social groups and weighted according to 'utilities'; this is the most critical and controversial step both from the theoretical and practical point of view, a way of attempting a 'social' analysis of the projects' gains and losses that could be done at each step of the CBA; the objective is again welfare taken into account utilities weighted according to people income and benefits and costs accruing to low income people (e.g. costs and benefits of villagers nearby the forest are given a higher weight). For our purpose we will only carry out FA, EAA1 and EAA2. The following methods for estimating benefits and costs have been applied throughout the five case-study areas: (i)market revenues include timber sales, both from thinning and final fellings (when the market for wood is active), valued with reference to stumpage values, roadside and/or market according to situations and a figurative (i.e. implicit) value of the fixed asset of the forest, which has been accounted for in terms on an annual land rent. This value remains stable in a well-managed forest, while on the contrary it decreases if the forest estate is not properly managed, as it is in the case of pest attacks. (ii)market costs include a overhead cost linked to land tax, surveillance and management and project costs in the with-analysis, including purchase of specific products - Btk or other products - of equipment (rent or purchase) and labour costs of personnel involved (iii) Off site market benefits (accounted for in EA1) refer to protection from erosion and Carbon sequestration. The first one is estimated based on data provided by a recent publication on the estimated provided by Mediterranean Forests (Croitoru and Merlo, 2005). Carbon sequestration has been estimated on the basis of the net annual increment of the forest given a value of 13 euros per ton of C fixed (Croitoru and Merlo, 2005). (iv) Off-site market costs (accounted for in EA1) are estimated through the daily costs of hospital treatment for a person struck by dermatitis after having being in contact with the pine moth. (v) Off-site non-market benefits (accounted for in EA2) include externalities such as recreation and landscape. These have been estimated through values taken from literature when available and judged reliable, or from ad hoc surveys in some cases. (vi) Analysis has been performed using a discount rate of 2%, while a sensitive analysis has been carried out to assess more precisely the effects of discount rates on the cash flow values. The model is suggested for application in any situation requiring a careful evaluation of pest control. It gives to managers, forest service staff and administrators a valuable tool for the assessment of the profitability of the control by taking into account all costs and benefits for the society, including the costs related to the medical treatment of people showing allergic reactions.
Six microsatellite markers were developed for the lepidopteran species Thaumetopoea pityocampa using an enrichment protocol before cloning. Five of them are already used in routine for population genetic studies on T. pityocampa, and four are also usable for T. wilkinsoni. The six markers are unlinked and show different polymorphism levels (from low to high). Development method and needed minimum technical details for use are described in an international journal of genetics (Molecular Ecology Notes). Information for synthesis and use of the needed PCR primers is also freely available from the associated international database (MENotes Database ID: 12587730, 12587732, 12587733, 12587735, 12587737). The original clone sequences (as references) are deposited in an international free database (Genbank, accession numbers: AY520912, AY520913, AY520914, AY520915, AY520916). These molecular markers are of interest for population and ecological studies on pine processionary moths at different space and time scales (from broad to fine). They are excellent markers for studying: (i) genetic diversity and population genetic structure, (ii) gene flow, dispersal and migration related issues, (iii) effective population size and demographic events, (iv) parentage and relatedness. The result allows to study recent population history and to infer some factors acting on it. Consequently, they could constitute a tool to address other applied questions related to PPM in the Mediterranean area, such as the origin of the expanding populations. The result could support the development of studies at a local scale in order to help forest managers or public authorities (e.g. regional councils) to deal with tree or public health concerns (colonization pathways, assessment of possible barriers to the expansion, identification of factors promoting the dispersal, risk of host plant shift and choice of planted tree species).
A series of studies were carried out to design pheromone-based monitoring of the Pine Processionary Moth (PPM), Thaumetopoea pityocampa. In a dose - response field test the number of male captures significantly increased with the dosage of pityolure to a plateau around 10mg. The activity of pheromone dispensers lasted at least 11 weeks, enough to cover the whole flight period of T. pityocampa. In a comparison of several saturating and non-saturating trap designs, plate sticky traps always showed the best trapping efficiency. Captures were significantly higher in regularly cleaned traps and at tree canopy height but catches of males PPM were positively correlated with those obtained at human breast height. The relationship between the numbers of males PPM captured in pheromone traps and the density of winter nests was investigated using ten traps baited with low doses of pityolure in fourteen maritime pine stands. Mean trap captures calculated from ten to three traps were significantly correlated with nest density, indicating that four plate sticky traps baited with 0.2mg of pityolure per hectare could provide a cost effective tool for monitoring densities of PPM population. The reliability of this design was tested in a total of 33 pine stands of different age and species across three countries, France, Italy and Portugal and in the core and expansion areas of the pest. Results were remarkably consistent showing significant and positive correlations between mean male captures per day and total number of winter nests per hectare irrespective of the regions. The correlations with the level of infestation in the following generation was also positive for all regions although slightly less significant. These results suggest that pheromone-baited traps provide a suitable tool to monitor T. pityocampa populations. The method is already in use in France, in collaboration with a SME from Spain (SEDQ Barcelona) involved in the production of the baits. We plan to extend the system to the other countries interested by the moth within two years by the project end. New jobs in national forest health services will be created by forming people involved in the monitoring and in the selection of the areas where biocontrol is carried out (see Result Btk 32524). The result is targeted to the main representative of forest IPM in each of the interested countries.
Range shifts have been reported recently for a number of species, but few studies have attempted to explain range shifts in mechanistic terms. In this study we sought a mechanistic understanding of the range expansion in T. pityocampa. We studied larval performance during the winter at two expansion areas: one occurring at a latitudinal (central France) and the other at altitudinal scale (northern Italy). In each area we explored natural temperature gradients as spatial analogues for climate change by rearing cohorts of larvae in three zones along each gradient: the core zone (where the moth has been present for over 30 years), the expansion zone (where recent colonization has occurred), and the external zone (outside its 2003 distribution). This approach allowed us to test a mechanistic model for winter-feeding that was developed from laboratory data, and to assess the importance of feeding in winter survival. The model is based on the combined effect of daytime nest temperature, which induces feeding, and minimum temperature for night feeding. The observed patterns in feeding and survival confirm the model's ability to explain the trends in temperature-linked range expansion, and highlight the potential of similar approaches in improving our understanding of species range shifts. In the coldest months, our model was consistent with the observed patterns of feeding activity: feeding was progressively reduced with increasing latitude or elevation, as predicted by the lower number of hours when the feeding threshold was reached, and negatively affected final survival. Insolation raised nest temperature and increased feeding activity on the south but not the north aspect. Prolonged temperature drops below the feeding thresholds occurred at all sites, leading to starvation and partial mortality. Nonetheless, even the most extreme sites still allowed some feeding, and, consequently, up to 20% colony survival and successful pupation. Given that the present distribution of the oligophagous T. pityocampa is not constrained by the distribution of its actual or potential hosts, and that warmer winters will cause the number of hours of feeding to increase and the probability of the lower lethal temperature to decrease, we expect the trend of improved survival in previously prohibitive environments to continue, causing further latitudinal and altitudinal expansion. This work highlights the need to develop temperature-based predictive models for future range shifts of winter-limited species, with potential applications in management. It addresses scientists and managers with a simple tool, based on the measurement of temperature, to assess the potential survival of the pest in the expansion area. A follow-up paper relating the survival to generally available climatic indexes (mean temperature, rainfall) will allow to extend the prediction over a wide geographic scale.