Survey Methods on Insect Forest Pests in the Aosta Valley Forest
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Forster, B.; Knifek, M.; Grodzki, W. (eds.) 1999: Methodology of Forest Insect and Disease Survey in Central Europe. Proceedings of the Second Workshop of the JUFRO WP 7.03.10, Apri120-23, 1999, Sion-Chateauneuf, Switzerland. Birmensdorf, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) 231-233. Survey methods on insect forest pests in the Aosta Valley Mario Negro e Luca Dovigo Regione Autonoma Valle d' Aosta- Direzione forestazione Loc. Gr. Charriere, 6/a 1-11020 Saint-Christophe (Aosta) ltalia Phone: 0039/0165/36'12'57 Fax: 0039/0165/23'56'69 E-Mail: d-Forestazione@regione. vda.it Italo Currado e Peter John Mazzoglio Universita degli Studi di Torino, DiVa. P. R. A.- Entomologia e Zoologia applicate all'Ambiente ViaL. da Vinci 44 1-10095 Grugliasco (Torino) ltalia Phone: 0039/011/670'85'35 Fax: 0039/011/670'85'86 E-Mail: [email protected] Forest pest monitoring in the Aosta V alley generally follows the first record of an outbreak; in order to check the evolution of a propagation, sometimes it is enough to observe a certain phenologic .phase of the pest, in other cases the use of pheromone traps is necessary, provided that .the costs for the personnel and the material employed are justified by the need of a control_intervention. In the last decade, several insect pests . have been studied so to forecast their outbreak dynamics and check their impact on the forests: Lymantri.a monacha L. (Lepidoptera Lymantriidae) After the outbreak, which ended in 1991 and involved about 6,800 ha of forests the Aosta Valley, another anomalous infestation ·of this tussock moth took place in the locality Sue of Saint Marcel, far from the first outbreak area. The attack began in 1994 on a surface of 2.28 ha and continued in 1995 (Fig. ) covering an area of 3.38 ha. In 1996 the attack spread downstream and occupied a surface of 3.9 ha. Periodic surveys in the search of eggs were carried out from 1995 to 1997 to monitor the extension and seriousness of the outbreak; then samples of larvae were taken and reared in the laboratory. The rearings gave a mortality of larvae and pupae caused by parasitoids, viral polyhedrosis, and undetermined factors, which permitted only 28-32% of the larvae to reach the adult stage, thus revealing a situation normally found in declining outbreaks. Zeiraphera diniana Gn. (Lepidoptera Tortricidae) The appearance of this larch moth was expected. in the Aosta V alley in 1990 Pheromone traps were placed in different sites from 1989 to 1994, but they did not giv11 relevant captures. The typical outbreak every 10 years, documeated for over 150 years 231 had been interrupted. So this monitoring was stopped, awaiting the outbreak of the year 2000. Instead, the moth made a heavy attack in the Valley in 1996; the infestation interested above all the V al di Cogne, where about 330 ha of woods were involved. In some areas the of the attack was so high that the trees were completely defoliated. This infestation had a much lower intensity and extension in the V al di Rhemes and Valgrisenche. In 1997 the outbreak involved again the Val di Cogne, more or less 300 ha in the same area of the previous year. This time the defoliation reached lower levels than in 1996. In the V al di Rhemes the area attacked increased considerably (270 ha), but the plants were not seriously defoliated; .in the V algrisenche the extension and the intensity of the infestation were almost the same. z. diniana also appeared in other localities of the Aosta Valley (La Thuile: 200 ha, Pre S.Didier: 20 ha, Morgex: 75 ha e Avise: 7 ha) with slight defolations .. In 1998 the outbreak moved particularly towards the northeastern part of the Valley. In these new areas the larch moth attacked about 600 ha pf woods. Instead in the localities involved in 1996 and 1997 only some small areas were infested Acantholyda posticalis Mats. (Hymenoptera Pamphiliidae) Since 1973 this sawfly is carrying outran outbreak iri the Aosta Valley·on scotch pine in more and more extended areas. In 1997 it attacked 800 ha of pine woods, causing heavy defoliations (Fig. ). In the years following the attacks; dead pine trees had to be cut and conveyed, because of the propagation of bark beetles. For various the diapausing larvae were sampled · to monitor the infestation intensity of the involved areas, fmding population densities similar to those checked in 1976, therefore showiqg a constantevolution of the outbreak during the years with a low incidence of insect parasitoids and microbial diseases. Tomicus minor tH.) and Tomicus piniperda, (L.) (Coleoptera Scolitidae) As a consequence of numerous snow-broken trees caused by the exceptional snowfall of April 1989, since 1990 there was an outbreak of these pine shoot beetles which interested hundreds of hectares of pine woods. Besides these pests, other bark beetles, such as Ips sexdentatus and Ips acuminatus, caused damage, even if of lesser seriousness. The infestation of the pine shoot beetles was studied observing the bored shoots and controlled by placing trap timber and cutting and conveying the infested trees. Mter three years of interventions, the outbreak decreased and only isolated and incidental attacks were observed. 232 Thaumetopoea pityocampa D. & S. (Lepidoptera Thaumetopoeidae) The controJ of the pine processionary, which has been infesting the Aosta Valley fo ages, is restricted to the manual collection of nests. Since 1995 these interventions wen carried in. all attacked sites, whereas lately, both for the increase of the outbreak ii areas re-forested with. scotch and black pines, and for the reduction of costs, nes collecting was carried out only in these plantations. The observations made on natural woods, in spite of an increase of the number of nests did not show an increase of damage; only some branches and, sometimes, some had dried up. However, the fluctuation of the infestations do not seem to depend or nest collecting; in fact infestations have increased considerably (Fig. ), probably because of a climatic influence. This year, in small isolated areas, a coritrol attempt by sexual confusion and mass trapping will be made; this may be a solution for small pine woods intensively visited by tourists and isolated from other infested areas. lps typographus L. (Coleoptera Scolitidae) Starting from 1991, this bark beetle showed to be the worst pest for the Norway spruce woods of the AostaValley. Following the outbreak of Lymantria monacha from 1984 to 1991 and the hurricane Vivien of February 1990, in several sites of the Valley, a great number of mass-propagation centres arose. At the beginning they involved groups of 10-20 spruce trees, then the attacks worsened and in some cases groups of hundreds of trees were brought to death. The cutting and conveying operations of these dead trees ended only in 1997, employing a considerable number of forestal personnel. Against the bark beetle, besides the clearing of mass-propagation centres, .since 1991 the infested forests were controlled by means of hundreds of pheromone traps (Fig. ). At the beginning pheromones were used only for monitoring purposes, but since 1994 they were employed mainly for mass trapping (generally the traps were placed in pairs). In some cases also trap timber was used. From the {Fig. ) it is clear that after a rather regular triennium there is an abrupt increase of captures; which is obvious in the mean of captures per trap (Fig. ). In the last every new mass-propagation centre was rapidly checked, both in areas previously attacked .and in new areas. A complete version with figures can be obtained by the authors. 233 .