Can pheromone trapping predict Ips typographus outbreaks? - Unipd.it

Faccoli, M. and Stergulc, F.: Can pheromone trapping...

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Oral presentation

Can pheromone trapping predict Ips typographus outbreaks?An example from the Southern Alps

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Massimo Faccoli1 and Fabio Stergulc2 Department of Environmental Agronomy and Crop Productions - University of Padua Viale dell’Università, 16/a – 35020 Legnaro (PD) – Italy. e-mail: [email protected] 2 Department of Plant Protection - University of Udine, Italy. Via delle Scienze, 208 – 33100 Udine, Italy. e-mail: [email protected]

Abstract Ips typographus is the main forest pest of Italian spruce forests. Beginning in 1996, the populations of I. typographus occurring in NE Italy have been annually monitored by using pheromone traps. Monitoring lasts about 18 weeks (May – August), with replacement of pheromone dispensers after 810 weeks. Traps are checked and emptied weekly. Insects trapped before dispenser changing are called “spring captures” (May-June), whereas beetles caught after dispenser changing are “summer captures” (July-August). Preliminary analysis of the data (1996-2004) reveals a strong correlation between the ratio of spring and summer captures of the year x (springx/summerx), and the ratio of total captures of the following year (Y(x+1)) and those of the current year (Yx) (Yx+1/Yx). This relationship shows that: - Springx/summerx ratios lower than 1.5 indicate increasing populations in the following year; - Springx/summerx ratios around 1.5-2 indicate stable populations in the following year; - Springx/summerx ratios higher than 2 indicate decreasing populations in the following year. The correlation allows us to estimate the captures of the following year. In this respect, high summer captures mean high risk of outbreak in the next year. The risk of outbreak is affected by the breeding performance of the spring generation (summer captures). Keywords:

monitoring, traps, spruce pest, bark beetle, pheromone, outbreak, forecasting, Italy, Ips typographus.

Introduction The spruce bark beetle Ips typographus (Linnaeus) (Coleoptera Scolytidae) is one of the most destructive pests attacking European spruce forests (Christiansen and Bakke 1988). The beetle also causes great damage to Italian stands growing in the southern Alps (Lozzia 1993; Faccoli 1999; Frigimelica et al 2000; Stergulc et al 2000). In Italy I. typographus attacks host trees early in spring (end of April), when the mean air temperature reaches 18°C. Adults of the parental generation emerge

Csóka, Gy.; Hirka, A. and Koltay, A. (eds.) 2006: Biotic damage in forests. Proceedings of the IUFRO (WP 7.03.10) Symposium held in Mátrafüred, Hungary, September 12-16, 2004


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from over-wintering sites and look for a suitable host to begin the first generation. Then, at the beginning of July, the offspring emerge and start a second generation, which will conclude in September (Faccoli 1999; Netherer 2003). Modern strategies for I. typographus control include the use of traps baited with aggregation pheromones (Bakke et al 1977). Traps are useful both in control by mass-trapping (Raty et al., 1995), and in population monitoring (Lindelöw and Schroeder 2001). Preliminary results concerning I. typographus monitoring were recently presented for some Italian populations (Faccoli and Stergulc 1999; Marchetti et al 1999; Frigimelica et al 2000; Stergulc et al 2000). In general, data from multiyear monitoring give indications about the population trend over time (Bakke 1985). However, no prediction about the population density is given for the following year, which could show either low or high captures. In this paper we summarize data obtained from an I. typographus monitoring carried out over a period of nine years, and discuss how pheromone trapping could forecast the mean captures of the following year. Materials and Methods Monitoring network Since 1994, a monitoring network called “BAUSINVE – Forest Phytopathologic Inventory” is checking the main forest pests and diseases occurring in Friuli – Venezia Giulia, north-eastern Italy (Stergulc and Frigimelica 1997). The forest health is monitored daily by about 60 foresters working for the Regional Forest Service and supervised by a team of entomologists and pathologists in collaboration with many scientific institutes. Data concerning pest and disease outbreaks (species, instar development, density of population), and their damage (number of attacked/killed trees, volume of wood lost, extension of defoliated areas) are recorded in a database, which includes both climatic (temperature and rainfall) and sylvicultural (forest composition, tree age, stand origin...) information. Monitoring of Ips typographus populations Beginning in 1996, populations of I. typographus are monitored permanently in some spruce forests of the region by using ca 30 pheromone traps per year (Theysohn® slot-trap) baited with pheromone dispensers containing 80 mg of cis-verbenol, 1,8 mg of 2-metil-3-butin-2-ol and 8 mg of ipsdienol. The monitored stands are about 70-80 years old, growing at altitudes between 800 and 1200 m a.s.l. The traps are set up and baited at the end of April, checked weekly, and all captured beetles are collected and counted. In accordance with manufacturer recommendations, the pheromone dispensers are replaced after 8-10 weeks (end of June) in order to cover the whole activity period of I. typographus. Monitoring lasts until September (about 18 weeks) and data are reported in the BAUSINVE database as mean captures per trap. Previous investigations carried out in the study area report the development of the first generation as taking 7-9 weeks depending on weather conditions (Faccoli, 1999). Therefore, beetles captured before the end of June, when the dispensers are changing, are only parental adults coming from overwintering (“spring captures”), whereas later catches (“summer captures”) are their offspring. The total captures per year (Yx) are reported as mean number of insects per trap. Statistical analysis Correlations between the ratio of spring and summer captures of the current year (x) (springx/summerx), with the ratio of total captures of the following year (Yx+1) and the captures of the

Csóka, Gy.; Hirka, A. and Koltay, A. (eds.) 2006: Biotic damage in forests. Proceedings of the IUFRO (WP 7.03.10) Symposium held in Mátrafüred, Hungary, September 12-16, 2004


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current year (Yx) were analysed by using a multiple regression procedure giving an R2-value, adjusted for the number of parameters (Zar 1999). A confidence level of 0.05 was considered significant. Results

Flight phenology of I. typographus in SE Alps The flight activity of I. typographus is very extended and occurs over a period of about four months (May - August) (Fig. 1). During the monitoring it is possible to detect two main peaks of Ips typographus captures, the first occurring in the middle of May and the second at the beginning of July (Fig. 1). Spring captures include both overwintering and re-emerging adults, which fly around searching for suitable spruces on which to start the first generation, whereas summer captures are the emerging adults of both first and sister-generations. Spring captures may be higher than summer ones (Fig. 2), but in other cases, sometimes the opposite can be observed (Fig. 3). Mean annual captures are very variable (Fig. 4), indicating either epidemic or endemic Ips typographus populations. Data correlations There are two different significant correlations between springx/summerx ratios and Yx+1/Yx ratios, when the springx/summerx ratios are respectively higher (d.f.= 1; 20, F=17.15, P