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The engraver beetle Ips acuminatus in the south-eastern Alps - Life traits and population dynamics
Full text linkIn the last years extensive outbreaks of the pine engraver beetle Ips acuminatus (Gyllenhal) (Coleoptera: Curculionidae, Scolytinae) have been reported in many Scots pine (Pinus sylvestris) forests in the Alps including the valley of Boite (Dolomites).
The beetle has been considered for a long time of minor economic importance, but recently it has been included among the ten most damaging wood boring insect in Europe as a result of the increasing tree mortality caused by this species. Extrinsic factors such as high temperature and drought are known to trigger outbreaks of I. acuminatus and it is likely that climate change may aggravate the threat to pine forests, either with the beetle alone or in combination with secondary pathogens and pests, as the recent infestations seem to confirm.
I. acuminatus is one of the most common bark beetles infesting Scots pine (Pinus sylvestris) in Eurasia. It is a polygamous species with up to 6-12 females joining each male within the gallery systems. The maternal galleries radiate outward from the central nuptial chamber (formed by the male) creating a distinctive star-shaped pattern. Eggs are laid on both sides of the maternal galleries. Larval galleries develop shortly in the phloem as I. acuminatus is a phloemycetophagous species associated with Ophiostoma brunneo-ciliatum and Ambrosiella macrospora. Before emerging, callow adults need a period of maturation feeding that takes place in the phloem close to the galleries where the larvae have developed. The adults infest the upper part of the trunk and the branches, as a bark thickness of 2-3 mm is preferred. Literature reports I. acuminatus as monovoltine in Scandinavia and bivoltine in southern Europe, overwintering as adult mainly under the bark of the infested trees. However, overwintering in the litter has been considered possible in northern populations. Spring emergence begins slowly when air temperature reaches 14°-16°C, but the real mass flight occurs when temperature exceeds 18°C. As many other bark beetle species, I. acuminatus have a very pronounced spatial patterning linked to the cooperative attack strategy it adopts, resulting in a „spot infestation‟.
This dissertation addresses poorly known aspects of the biology of the bark beetle observed during the outbreak that started in 2005 in the south-eastern Alps, with particular focus on:
- voltinism, phenology and breeding performance in relation to both temperature and colonisation density, in order to determine how these factors may affect insect performance and population dynamics in a climate-change perspective;
- spatial-temporal dynamics of the infestations during the different phases of the outbreak,
in order to model bark beetle activity and behaviour;
- effects of a sanitation felling on spot dynamics and damage level, in order to help management decisions making about whether to apply active control measures;
- natural enemy complex associated with I. acuminatus, in order to assess the role of parasitoids and predators on population dynamics.Il Coleottero Scolitide Ips acuminatus (Gyllenhal) (Coleoptera: Curculionidae, Scolytinae) ha recentemente causato estese e gravi infestazioni in diverse zone distribuite sull‟arco alpino e, tra queste, la valle del Boite (Dolomiti).
Lo scolitide, per lungo tempo considerato di scarsa rilevanza economica, è stato recentemente incluso tra le dieci specie di insetti xilofagi più dannose in Europa in quanto sempre più frequentemente associato a fenomeni di elevata mortalità del pino silvestre.
È noto che fattori abiotici quali elevata temperatura e stress idrico possono scatenare gravi infestazioni di I. acuminatus: per questo motivo è probabile che i cambiamenti climatici in atto aumentino i rischi cui possono essere soggette le pinete di pino silvestre, per l‟attività sia dell‟insetto da solo sia in associazione con parassiti opportunisti (secondari). Le gravi infestazioni segnalate negli ultimi anni sia sulle Alpi occidentali che su quelle orientali sembrano confermare tale ipotesi.
I. acuminatus è specie ad areale euroasiatico ed è uno dei più comuni organismi xilofagi legati al pino silvestre (Pinus sylvestris). L‟insetto è poligamo e in un sistema di gallerie si possono trovare fino a 12 femmine associate a un singolo maschio. Le gallerie materne si irradiano da un vestibolo centrale scavato dal maschio, determinando un caratteristico „sistema a stella‟. Le uova sono deposte lungo entrambi i lati della galleria materna e le larve si sviluppano in brevi gallerie scavate nel floema, essendo la specie fleomicetofaga e comunemente associata a specie fungine funghi quali Ophiostoma brunneo-ciliatum e Ambrosiella macrospora. Prima di emergere dal materiale infestato, i giovani adulti necessitano di un periodo di maturazione che svolgono nutrendosi del floema situato nelle immediate vicinanze delle gallerie larvali e delle celle pupali in cui si sono sviluppati. A termine del periodo di maturazione, gli adulti sfarfallano e colonizzano i rami e la parte superiore dei fusti del pino silvestre, in quanto prediligono le parti con corteccia di spessore non superiore a 4-5 mm.
Fonti bibliografiche riportano la specie come monovoltina in Scandinavia e bivoltina in Europa meridionale. I. acuminatus sverna allo stadio adulto principalmente nel materiale infestato in cui si è sviluppato; per le popolazioni nordiche la lettiera sembra costituire un ulteriore sito di svernamento. I primi voli primaverili hanno luogo quando la temperatura dell‟aria raggiunge i 14 -16°C, ma il picco dei voli si verifica quando questa supera i 18°C. Come molti altri scolitidi che adottano la strategia dell‟attacco massale al fine di vincere le difese dell‟ospite, le infestazioni di I. acuminatus si manifestano con attacchi diffusi e concentrati su un numero variabile di piante vicine tra loro, dando luogo a tipiche infestazioni definite a „macchia di leopardo‟.
Durante il lavoro di ricerca, condotto in concomitanza al verificarsi di una grave pullulazione dello scolitide nelle Alpi sud-orientali, si è cercato di chiarire diversi aspetti poco noti della biologia dell‟insetto, dedicando particolare attenzione a:
- voltinismo, fenologia e performance riproduttiva considerate in relazione a temperatura e densità di colonizzazione, allo scopo di determinare come questi fattori possano influire sulla performance e sulla dinamica di popolazione dell‟insetto nel quadro del cambiamento climatico;
- dinamiche spazio-temporali dei nuclei di infestazione di I. acuminatus durante le diverse fasi della pullulazione, al fine di prevedere il grado di attività e il possibile comportamento futuro dell‟insetto;
- impatto di tagli fitosanitari sulle dinamiche di popolazione ed effetti nel limitare i danni arrecati alle pinete, allo scopo di stabilire criteri di valutazione utili nella gestione dei boschi infestati;
- complesso di nemici naturali associati a I. acuminatus, al fine di determinare quale ruolo e importanza possano avere parassitoidi e predatori sulla dinamica delle infestazioni
Spread of the introduced biocontrol agent Torymus sinensis in north-eastern Italy: dispersal through active flight or assisted by wind?
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Effectiveness of different trapping protocols for outbreak management of the engraver pine beetle Ips acuminatus (Curculionidae, Scolytinae)
No full textA population of Ips acuminatus was monitored from 2007 to 2009 by multi-funnel pheromone-baited traps in a Scots pine forest of the southeastern Alps of Europe. We compared the captures obtained with two different lures (Austrian and Spanish pheromones, commercially available) in five infested types of forest. Although captures showed a similar trend among sites, with no significant interaction between lures and sites, the Spanish pheromone was on average eight times more attractive than the Austrian one. The mean number of trapped insects was lower in healthy stands (control) and old clearcuts (more than 1 year old) than in sites suffering recent infestation (standing or felled infested trees and recent clearcuts). Total captures were significantly correlated with tree mortality recorded annually within a 500 m radius around the traps. This pattern may be a useful input for establishing the timing of application of the best monitoring program of I. acuminatus populations. © 2012 Copyright Taylor and Francis Group, LLC
Spatial - temporal dynamics of an Ips acuminatus outbreak - implications for management.
No full textSpatio-temporal dynamics of an Ips acuminatus outbreak and implications for management
No full text1 Understanding spatio-temporal processes of bark beetle infestations is crucial for predicting beetle behaviour and aiding management decisions aiming to prevent or mitigate tree mortality. We recorded the spatial and temporal distribution of killed trees during the 5-year period of an Ips acuminatus outbreak. 2 Killed trees were always grouped in well-defined patches (infestation spots). In years of high population density, infestation spots were large and aggregated, whereas, in years of low density, infestation spots were small and weakly aggregated or randomly distributed within the study area. 3 Most trees were killed in the spring by beetles that had hibernated but, in some years, trees were also killed in the summer by new-generation beetles originating from spring attacks. Spring-killed trees always formed new infestation spots at new locations (i.e. spot proliferation). By contrast, summer-killed trees always occurred at the edge of active spots established in the spring, thus resulting in spot growth. 4 With regard to management strategies, the results obtained in the present study suggest that areas located in close proximity to infestations of the previous year should be prioritized for risk assessment. Because large spots account for most of the observed tree mortality, the cut-and-remove method should be focused on these spots as soon as crown discoloration appears in the summer. If applied timely, this strategy will remove the new-generation beetles originating from the spring attacks before they emerge and also reduce the risk of spot growth. © 2012 The Royal Entomological Society
Life history traits promoting outbreaks of the pine bark beetle Ips acuminatus (Coleoptera: Curculionidae, Scolytinae) in the south-eastern Alps.
Full text linkThe pine bark beetle Ips acuminatus has recently increased frequency and intensity of outbreaks in Pinus sylvestris stands in the Alps. During a 3-year period, we investigated life-history traits of the species that may have adaptive value. In the south-eastern Alps,
I. acuminatus becomes active in early spring when the air temperature reaches 14C, suggesting the presence of a local population adapted to low temperature. Such an early emergence allows the complete development of a second generation, even if only a portion of the population is truly bivoltine. As a consequence, there are two main attack periods, the first in early spring and the second in summer, resulting in different trees being colonised each time. Irrespective of the generation, a large part of the beetles leaves the breeding substrate before hibernation, and this is interpreted as an escape from natural enemies associated with the bark. These findings suggest that the populations of I. acuminatus of the south-eastern Alps may benefit from climate warming as they have more opportunities to complete the second generation and to escape from mortality factors associated with a long permanence in the bark. In addition, the extended period of tree colonisation offers more possibilities to locate suitable hosts and to build up outbreak densities
Integrated pest management approaches against Drosophila suzukii
No full textThe appearance of Drosophila suzukii in 2009 has strongly affected cherry fruit production. Prior to its invasion, Italian cherry orchards were treated with only two insecticide applications, the first against aphids (Myzus cerasi Sulz.) before flowering and the second against Rhagoletis cerasi, about 20-30 days before harvest. After D. suzukii invasion, an additional two-three pre-harvest (close to harvest) insecticide treatments are required, but the number of insecticide applications can increase to five-eight depending on pest abundance, crop susceptibility and other environmental factors. The intensive use of insecticides poses serious concerns about the presence of residues on fruits exceeding maximum residue limits (MRLs), the development of resistance, and negative impacts on the environment beyond beneficials. To obtain a good and sustainable control of D. suzukii the chemical strategies should be coupled with cultural management the use of nets and parasitoids. To achieve good control of the carpophagus larvae it is essential to monitor, both the adults with trap lured with blends of fruit juices and the oviposition on the ripening fruit, since the percentage of infestation is not related to the number of catches in the food traps. Considering the viability of D. suzukii eggs and larvae, it is lower under dry, warm conditions. Therefore, cool humid microhabitats should be avoided by pruning to open up the canopy to increase airflow in the trees and reduce shading. In addition, the use of mulches by reducing standing water in the orchard can further contribute to the reduction of humidity. Precision irrigation should also be incorporated to reduce pooling of water on the ground. Mass trapping, placing numerous traps around the perimeter outside fruit tree fields, is a suitable and cost-effective method only for cultivations where the pest pressure is considerably low, if necessary insecticides could be applied to the surface of the traps to function as an attract-and-kill strategy. Among the sustainable protection techniques for the control of D. suzukii, the use of insect-proof nets has proved effective, reducing or completely replacing the use of insecticides in some instances, and providing high levels of exclusion of D. suzukii from the crop. During the ripening season, sanitary measures such as removal of dropped, infested and over-ripe fruits is suggested. The collection and treatment of infested fruit through sun exposure, disposal in closed containers, crushing, low temperature treatments, bagging and burying, to destroy D. suzukii eggs and larvae are essential IPM procedures to limit the infestation of healthy fruit. The augmentative release of parasitoids and conservation biocontrol of generalist predators, potentially, could contribute to the integrated management of D. suzukii populations, especially in natural habitats close to commercial crops, however further work on the effectiveness of native parasitoids and generalist predators in Europe and the USA, in the field, is required. In this paper, the integration of different tools for D. suzukii control will be discussed, in order to develop effective, eco-friendly and practical strategies for the management of the pest on cherry
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