Massimo Faccoli

Effect of weather on Ips typographus (Coleoptera Curculionidae) phenology, voltinism, and associated spruce mortality in the southeastern Alps.

ABSTRACT Summer drought associated with high temperatures recorded in the last few years has given rise to outbreaks of bark beetles developing in weakened host trees. The aim of this study was to investigate the possible weather effect on the biology of and damage caused by Ips typographus L. in the southeastern Alps. The study was carried out recording temperature (1962–2007), precipitation (1922–2007), and the damage caused by I. typographus (1993–2007). In addition, data from pheromone-baited traps (1996–2005) provided information on the main periods of flight activity of I. typographus. From 1922 to 2007, precipitation during March-July has decreased ≈200 mm (-22%), whereas since 1962–2007, mean temperatures during March-July increased ≈2°C (+13%). Damage caused by I. typographus was inversely correlated with March-July precipitation from the previous year but not correlated with temperature. Increases in spring temperature did not affect the development timing of the first generation, but only changed its onset. Earlier swarming of both over-wintering beetles and first-generation offspring (≈20 d sooner over 10 yr), and the early start of the second generation permitted more complete development of the second brood. Voltinism in this species is discussed in relation to thermal and photoperiodic thresholds, indicating that the occurrence of a third generation is limited by the summer photoperiod rather than by temperature. In conclusion, results suggest that spring drought increases damage caused by I. typographus in the following year, whereas warmer spring affects insect phenology.

Climate affects severity and altitudinal distribution of outbreaks in an eruptive bark beetle

Temperature warming and the increased frequency of climatic anomalies are expected to trigger bark beetle outbreaks with potential severe consequences on forest ecosystems. We characterized the combined effects of climatic factors and density-dependent feedbacks on forest damage caused by Ips typographus (L.), one of the most destructive pests of European spruce forests, and tested whether climate modified the interannual variation in the altitudinal outbreak range of the species. We analyzed a 16-year time-series from the European Alps of timber loss in Picea abies Karsten forests due to I. typographus attacks and used a discrete population model and an information theoretic approach to compare multiple competing hypotheses. The occurrence of dry summers combined with warm temperatures appeared as the main abiotic triggers of severity of outbreaks. We also found an endogenous negative feedback with a 2-year lag suggesting a potential important role of natural enemies. Forest damage per hectare averaged 7-fold higher where spruce was planted in sites warmer than those within its historical climatic range. Dry summers, but not temperature, was related to upward shifts in the altitudinal outbreak range. Considering the potential increased susceptibility of spruce forests to insect outbreaks due to climate change, there is growing value in mitigating these effects through sustainable forest management, which includes avoiding the promotion of spruce outside its historical climatic range.

Conifer phenolic resistance markers are bark beetle antifeedant semiochemicals

1 Phenols are important in conifer resistance to fungi associated with bark beetles and as markers for resistance to beetle mass‐attacks. However, the mechanism of phenolic activity in conifer resistance to Ips typographus bark beetle remains unclear.

Winter mortality in sub-corticolous populations of Ips typographus (Coleoptera, Scolytidae) and its parasitoids in the south-eastern Alps

A study concerning the winter mortality of a sub-corticolous population of Ips typographus and its parasitoids has been carried out in the south-eastern Alps (Italy) during the winter 1997/98. Three attacked spruce trees were sampled three times (November, February and April) by collecting infested bark disks (1 dm2 each). All insects that emerged from the bark or died in the samples before emergence were counted. The mean number of living Ips typographus occurring under the bark decreases by 49 % from November to April. Winter mortality mainly affects larval stages and young adults. The same trend was observed for the parasitoids Coeloides bostrychorum (48.5 %) and Roptrocerus xylophagorum (47.5 %).

A Suite of Models to Support the Quantitative Assessment of Spread in Pest Risk Analysis

Pest Risk Analyses (PRAs) are conducted worldwide to decide whether and how exotic plant pests should be regulated to prevent invasion. There is an increasing demand for science-based risk mapping in PRA. Spread plays a key role in determining the potential distribution of pests, but there is no suitable spread modelling tool available for pest risk analysts. Existing models are species specific, biologically and technically complex, and data hungry. Here we present a set of four simple and generic spread models that can be parameterised with limited data. Simulations with these models generate maps of the potential expansion of an invasive species at continental scale. The models have one to three biological parameters. They differ in whether they treat spatial processes implicitly or explicitly, and in whether they consider pest density or pest presence/absence only. The four models represent four complementary perspectives on the process of invasion and, because they have different initial conditions, they can be considered as alternative scenarios. All models take into account habitat distribution and climate. We present an application of each of the four models to the western corn rootworm, Diabrotica virgifera virgifera, using historic data on its spread in Europe. Further tests as proof of concept were conducted with a broad range of taxa (insects, nematodes, plants, and plant pathogens). Pest risk analysts, the intended model users, found the model outputs to be generally credible and useful. The estimation of parameters from data requires insights into population dynamics theory, and this requires guidance. If used appropriately, these generic spread models provide a transparent and objective tool for evaluating the potential spread of pests in PRAs. Further work is needed to validate models, build familiarity in the user community and create a database of species parameters to help realize their potential in PRA practice.

Exploring associations between international trade and environmental factors with establishment patterns of exotic Scolytinae

Although invasion of exotic ambrosia beetles (fungus feeders) and bark beetles (phloem feeders) (Coleoptera: Curculionidae: Scolytinae) is considered a major threat to forest health worldwide, no studies have quantitatively investigated the anthropogenic and environmental factors shaping the biogeographical patterns of invasion by these insects across large spatial scales. The primary aim of this study was to assess the relative importance of international trade and several environmental variables of the recipient region on species richness of established exotic Scolytinae. As a reference, we also evaluated the relationships between the same environmental variables and species richness of native Scolytinae. Using an information-theoretic framework for model selection and hierarchical partitioning, we evaluated the relative importance of the potential drivers of species richness of native and exotic Scolytinae in 20 European countries and the 48 contiguous continental US states. Analyses were conducted separately for ambrosia and bark beetle species. Value of imports was a strong predictor of the number of exotic Scolytinae species in both regions. In addition, in the USA, warmer and wetter climate was positively linked to increased numbers of both native and exotic ambrosia beetles. Forest heterogeneity and climatic heterogeneity and secondarily forest area were key drivers in explaining patterns of species richness for native bark beetles but not for exotic species in both regions. Our findings suggest that if current infestation levels continue on imported plants and wood packaging material, increasing international trade will likely lead to more establishments of exotic Scolytinae with concomitant negative effects on forest health in both Europe and the USA. Compared to Europe the risk of invasion appears higher in the USA, especially for ambrosia beetles in the southeastern USA where the climate appears highly suitable for exotic establishment.

Improving the early detection of alien wood-boring beetles in ports and surrounding forests

Summary 1. International ports are generally considered the most likely points of entry for alien woodboring beetles. A better understanding of the factors affecting their arrival and establishment at ports and their surrounding areas is of utmost importance to improve the efficacy and the cost-effectiveness of early detection programmes. Our work aimed at understanding how port size and the characteristics of the landscape surrounding the port, in terms of forest cover and forest composition, influence the occurrence of alien wood-boring beetles. 2. From May to September 2012, 15 Italian international ports and the surrounding forests were monitored with multi-funnel traps baited with a multi-lure blend (a-pinene, ethanol, ipsdienol, ipsenol, methyl-butenol), three in each port and three in forests located 3–5 km away from the port. We identified both alien and native Scolytinae, Cerambycidae and Buprestidae beetles. 3. Fourteen alien species, among which four are new to Italy, were trapped. Alien species richness was positively related to the amount of imported commodities at the port scale. Broadleaf forests surrounding ports received larger number of alien species than conifer forests. By contrast, total forest cover in the landscape surrounding ports was positively related to the occurrence of native but not alien species. The alien and native species richness was higher in the surrounding forests than in the ports. 4. Synthesis and applications. The simultaneous use of traps in ports with large volume of imported commodities and in their surrounding broadleaf forests can strongly increase the probability of alien wood-boring beetle interceptions. The identification of sites where the arrival and establishment of alien species is more probable, combined with an efficient trapping protocol, can substantially improve the efficacy of early detection. Similar approaches may be used in other countries as early warning systems to implement timely measures to eradicate or contain alien invasions at the European scale.

Damage reduction and performance of mass trapping devices for forest protection against the spruce bark beetle, Ips typographus (Coleoptera Curculionidae Scolytinae)

Abstract• The spruce bark beetle, Ips typographus, is one of the main European forest pests, and mass trapping is probably the most common strategy applied to reduce its population density. However, the results concerning the effectiveness of this control system are often controversal, and many studies consider only the trapping performance with no attention to the damage reduction.• During spring-summer 2005, a control program against I. typographus outbreaks was set up in NE Italy. Twenty-four spruce forests heavily infested by I. typographus were studied: six protected by pheromone slot-traps, six by horizontal trap-logs and six by standing trap-logs; six untreated stands were kept as controls. Trap-logs were baited with a pheromone specific to I. typographus and treated with insecticide. Each type of device was tested at high, medium and low density in relation to the number of trees infested during the previous year. New damage occurring in the investigated stands was later monitored for one year.• Protected forests showed mean damage about 80% lower in 2005 than in 2004, with no statistical difference among traps, trap-logs or standing trap-logs. Instead, unprotected forests (controls) suffered damage to a similar extent in both years. Trapping devices showed no statistical differences among mean captures. Device densities showed similar results in damage reduction and insect trapping.• The results support the hypothesis that intensive trapping performed at stand level may be useful for protecting forests against I. typographus, locally reducing population density and tree mortality.Résumé• Le coléoptère scolytide, Ips typographus, est l’un des principaux ravageurs des forêts européennes d’épicéa, et le piégeage phéromonal est probablement le procédé de lutte le plus utilisé pour réduire la densité de ses populations. Cependant, l’efficacité de ce système de contrôle n’est souvent pas très claire, et beaucoup d’études considèrent seulement les performances du piégeage et non la réduction des dégâts.• En 2005, un programme de lutte contre I. typographus a été appliqué dans le Nord-Ouest de l’Italie. Une étude a été conduite dans 24 forêts d’épicéa lourdement infestées par le typographe : six protégées par pièges à phéromones, six par arbres-pièges abattus, six par arbres-pièges sur pied, et six laissées sans protection (témoins). Les arbres-pièges ont été appâtés avec une phéromone spécifique d’ I. typographus et traités avec un insecticide. Chaque type de dispositif a été testé à haute, moyenne et basse densité en se basant sur le nombre d’arbres infestés l’année précédente. Les dégâts nouveaux causés par le typographe ont été suivis pendant un an.• En 2005, toutes les forêts protégées ont montré un niveau moyen de dégâts d’environ 80 % inférieur à celui de 2004, sans différence significative entre les dispositifs, alors que les forêts témoins ont souffert de dégâts similaires les deux années. Le nombre moyen de captures ne différait pas significativement entre les dispositifs de piégeage. La diminution des dégâts et du nombre d’insectes piégés a été comparable à toutes les densités de traitement.• Ces résultats confortent l’hypothèse selon laquelle le piégeage de masse au niveau du peuplement peut être utile pour la protection des forêts contre le typographe, en diminuant la densité de population du ravageur et ses dégâts.

Responses of the Mediterranean Pine Shoot Beetle Tomicus destruens (Wollaston) to Pine Shoot and Bark Volatiles

The pine shoot beetle Tomicus destruens has two dispersal phases per generation. In the first, mature adults move toward trunks of dying pines to lay eggs; in the second, callow adults move toward the shoots of healthy pines for maturation feeding. However, there is no information on the chemical stimuli that govern host selection by T. destruens adults. The aims of this study were: (1) to identify the volatiles released by shoots and bark of stone pine that are behaviorally and electrophysiologically active on T. destruens; (2) to verify which blends and concentrations of such volatiles are differently active on males and females, as well as on callow and mature adults, during the two host search phases (breeding and feeding). A four-arm olfactometer was used to test the behavior of walking T. destruens adults toward various sources of volatiles including fresh shoots and bark, their collected volatiles, and two synthetic blends. For each odor, the behavior of both callow and mature males and females was recorded individually. Shoot and bark extracts were analyzed by coupled gas chromatography and mass spectrometry (GC–MS), and tested by gas chromatography coupled with electroantennography (GC–EAD) on T. destruens males and females. Two blends of two (α-pinene and β-myrcene; blend A) and three (α-pinene, β- myrcene, and α-terpinolene; blend B) synthetic compounds, chosen among those that induce EAD responses and known to be attractive for other bark beetle species, were tested in the olfactometer at five concentrations. Insect behavior was affected by the degree of sexual maturation but not by sex. Callow insects were attracted by shoots and their extracts, while mature individuals by bark and its extracts. Six extracted compounds were active on T. destruens antennae: limonene, (Z)-3-hexen-1-ol and β-caryophyllene, α-pinene, β-myrcene, and α-terpinolene. α-Terpinolene, released only by bark, was active only on mature insects, whereas (Z)-3-hexen-1-ol, released only by shoots, was active only on callows. Males and females showed similar EAD responses. Of the six extracted volatiles, two were attractive for callow adults (blend A) and three for matures (blend B). In both cases, responses were positively correlated with blend concentration, although a repellent effect was noted at the highest concentrations.

Testing phenotypic trade-offs in the chemical defence strategy of Scots pine under growth-limiting field conditions

Plants protect themselves from pathogens and herbivores through fine-tuned resource allocation, including trade-offs among resource investments to support constitutive and inducible defences. However, empirical research, especially concerning conifers growing under natural conditions, is still scarce. We investigated the complexity of constitutive and induced defences in a natural Scots pine (Pinus sylvestris L.) stand under growth-limiting conditions typical of alpine environments. Phenotypic trade-offs at three hierarchical levels were tested by investigating the behaviour of phenolic compounds and terpenoids of outer bark and phloem. We tested resource-derived phenotypic correlations between (i) constitutive and inducible defences vs tree ring growth, (ii) different constitutive defence metabolites and (iii) constitutive concentration and inducible variation of individual metabolites. Tree ring growth was positively correlated only with constitutive concentration of total terpenoids, and no overall phenotypic trade-offs between different constitutive defensive metabolites were found. At the lowest hierarchical level tested, i.e., at the level of relationship between constitutive and inducible variation of individual metabolites, we found that different compounds displayed different behaviours; we identified five different defensive metabolite response types, based on direction and strength of the response, regardless of tree age and growth rate. Therefore, under growth-limiting field conditions, Scots pine appears to utilize varied and complex outer bark and phloem defence chemistry, in which only part of the constitutive specialized metabolism is influenced by tree growth, and individual components do not appear to be expressed in a mutually exclusive manner in either constitutive or inducible metabolism.