Annie Yart

Induced Responses in Phenolic Metabolism in Two Norway Spruce Clones after Wounding and Inoculations with Ophiostoma polonicum, a Bark Beetle-Associated Fungus.

Two Norway spruce (Picea abies Karst.) clones, one resistant and the other susceptible to mass inoculation with Ophiostoma polonicum Siem., were compared with regard to their phenolic compositions and chalcone synthase (CHS) and stilbene synthase activities of their phloem before and at 6 and 12 d after artificial inoculation with sterile malt agar or O. polonicum. In unwounded phloem, the resistant clone differed from the susceptible clone by the presence of taxifolin glycoside, lower concentrations of stilbene glycosides, and higher CHS activity. After inoculation, (+)-catechin concentration and CHS activity dramatically increased around the wound, particularly in the resistant clone. Stilbene synthase activity also increased, but more slowly and to a lower level, whereas the concentrations of stilbenes remained stable. Tanning ability decreased in the susceptible clone, whereas it remained stable in the resistant one. It is proposed that the induced phenolic response of Norway spruce phloem consists of an activation of the phenolic pathway, finally leading to tannins and insoluble polymers. It is suggested that resistance to O. polonicum depends on the ability of the tree to easily activate the flavonoid pathway.

Stimulation of tree defenses by Ophiostomatoid fungi can explain attack success of bark beetles on conifers

Abstract• Our aim is to present why the hypothesis, that Ophiostomatoid fungi play an important role in the establishment of most bark beetle species on living conifers, is valuable.• After summarizing knowledge about the relationships of bark beetles with conifers and fungi, we conclude that controversy results from misinterpretations when using fungal pathogenicity to demonstrate the role of Ophiostomatoid fungi in beetle establishment on host trees.• We demonstrate that fungal pathogenicity is not the right parameter to appreciate the role of fungus in beetle establishment on host trees. We argue that artificial low density inoculations that allow the appreciation of fungus ability to stimulate tree defenses and thus to help beetles in overcoming tree resistance must be used in complement to mass inoculations. In both cases, results must be expressed in terms of tree defense stimulation rather than in terms of tree killing.(i)Fungal species stimulating tree defenses are generally not those that grow the best in the sapwood.(ii)We argue that beetle development in the phloem, fungal invasion of the sapwood and phloem, and tree death, occur after tree defenses are exhausted, and that any fungus present in the beetle gallery could thus potentially invade the sapwood after defense exhaustion.• We conclude that stimulation of the tree defense reactions in both the phloem and the superficial sapwood is a real benefit brought by fungi to the beetles during the first phase of establishment (overcoming tree resistance).• Considering the origin of the bark beetle fungus associations attacking living trees and their general functioning based on stimulation of tree defenses, we develop three hypotheses:(i)any beetle species would be helped in its establishment in a given tree species by developing an association, even loosely, with a fungus species belonging to the Ophiostomatoid flora of that tree species;(ii)the necessity of a considerably low level of tree resistance for fungus extension into the tree is the selection pressure that has led fungi to develop their intrinsic ability to stimulate tree defenses, through their ability to grow into the phloem. This association can be completed by antagonistic fungal species controlling extension of the previous fungal species in the tree tissues;(iii)Beetle species using the strategy of overcoming tree resistance are associated with a fungal complex, of which species could assume three roles regarding relationships between beetles and trees: 1- to stimulate tree defenses in the phloem and superficial sapwood, 2- to grow into the sapwood after tree resistance is overcome, and 3- to control phloem extension of the first other two categories. Bringing nutrients to the beetle progeny can be a fourth role.• We propose that bark beetle — Ophiostomatoid associations can be categorized, based on associations’ frequency and complexity while taking into account beetle aggressiveness. We show that a close correspondence exists between beetles’ aggressiveness and the ability of their main associated fungal species to stimulate the defenses of their host tree.• We conclude with suggesting that most sapwood invading fungi might be “cheaters” which have taken advantage of the efficiency of the relationship between beetles and fungi that stimulate tree defenses.Résumé• Notre objectif est de présenter les raisons de la validité de l’hypothèse selon laquelle les champignons jouent un rôle important dans l’installation de la plupart des espèces de Scolytes sur conifères vivants.• Après avoir résumé les connaissances sur les relations des Scolytes avec les conifères et les champignons, nous concluons que la controverse résulte d’interprétations erronées lorsque l’on utilise le pouvoir pathogène des champignons pour démontrer le rôle des Ophiostomatoïdes dans l’installation des insectes sur les arbres hôtes.• Nous démontrons que le pouvoir pathogène n’est pas le paramètre correct pour apprécier le rôle du champignon dans l’installation des Scolytes sur les arbres hôtes. Nous soutenons que des inoculations artificielles à faible densité, qui permettent d’apprécier la capacité du champignon à stimuler les défenses de l’arbre et à ainsi aider le Scolyte à surmonter la résistance de celui-ci, doivent être utilisées en complément des inoculations massives. Dans les deux cas, les résultats doivent être exprimés en termes de stimulation des défenses de l’arbre plutôt qu’en termes de mortalité de l’arbre.(i)les espèces de champignons qui stimulent les défenses de l’arbre ne sont généralement pas celles qui présentent la meilleure croissance dans l’aubier.(ii)nous soutenons que le développement de l’insecte dans le phloème, l’invasion de l’aubier et du phloème par le champignon, et la mort de l’arbre, interviennent après épuisement des défenses de l’arbre, et que tout champignon présent dans les galeries de l’insecte pourrait donc potentiellement envahir l’aubier après épuisement de ces défenses.• Nous concluons que la stimulation des réactions de défense de l’arbre à la fois dans le phloème et l’aubier superficiel représente un bénéfice réel apporté par les champignons aux Scolytes pendant la première phase de leur installation (surmonter la résistance de l’arbre).• En ce qui concerne l’origine des associations Scolytes — champignons attaquant les arbres vivants et considérant leur fonctionnement général basé sur une stimulation des défenses de l’arbre, nous développons trois hypothèses :(i)toute espèce de Scolyte serait aidée dans son installation sur une espèce d’arbre donnée en développant une association, même lâche, avec une espèce de champignon appartenant à la flore Ophiostomatoïde de cette espèce d’arbre ;(ii)la nécessité d’un très faible niveau de résistance de l’arbre pour autoriser l’extension fongique dans le végétal est la pression de sélection qui a conduit les champignons à développer leur capacité intrinsèque de stimulation des défenses de l’arbre, à travers leur capacité à croître dans le phloème. Cette association peut être complétée par des espèces fongiques antagonistes contrôlant l’extension des espèces précédentes dans les tissus de l’arbre ;(iii)les espèces de Scolytes utilisant la stratégie de surmonter la résistance de l’arbre sont associées à un complexe fongique dont les espèces assurent trois fonctions eu égard aux relations entre les Scolytes et les arbres : 1— stimuler les défenses de l’arbre dans le phloème et l’aubier superficiel, 2— croître dans l’aubier après que la résistance de l’arbre ait été vaincue, and 3— contrôler l’extension des deux catégories précédentes dans le phloème. L’apport de nutriments à la progéniture du Scolyte peut représenter une quatrième fonction.• Nous proposons que les associations Scolytes — Ophiostomatoïdes puissent être classées, en se basant sur la fréquence et la complexité de l’association et en prenant en compte l’agressivité de l’insecte. Nous montrons qu’il existe une étroite correspondance entre l’agressivité des insectes et la capacité de leur principale espèce fongique associée à stimuler les défenses de l’arbre hôte.• Nous concluons en suggérant que la plupart des espèces de champignons envahissant l’aubier pourraient être des “tricheurs” qui ont profité de l’efficacité des relations entre les Scolytes et les espèces fongiques stimulatrices des défenses de l’arbre.

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.

High intercontinental migration rates and population admixture in the sapstain fungus Ophiostoma ips

Ophiostoma ips is a common fungal associate of various conifer‐infesting bark beetles in their native ranges and has been introduced into non‐native pine plantations in the Southern Hemisphere. In this study, we used 10 microsatellite markers to investigate the population biology of O. ips in native (Cuba, France, Morocco and USA) and non‐native (Australia, Chile and South Africa) areas to characterize host specificity, reproductive behaviour, and the potential origin as well as patterns of spread of the fungus and its insect vectors. The markers resolved a total of 41 alleles and 75 haplotypes. Higher genetic diversity was found in the native populations than in the introduced populations. Based on the origin of the insect vectors, the populations of O. ips in Australia would be expected to reflect a North American origin, and those in Chile and South Africa to reflect a European origin. However, most alleles observed in the native European population were also found in the native North American population; only the allele frequencies among the populations varied. This admixture made it impossible to confirm the origin of the introduced Southern Hemisphere (SH) populations of O. ips. There was also no evidence for specificity of the fungus to particular bark beetle vectors or hosts. Although O. ips is thought to be mainly self‐fertilizing, evidence for recombination was found in the four native populations surveyed. The higher genetic diversity in the North American than in the European population suggests that North America could be the possible source region of O. ips.

Inter-tree variability in the induced defense reaction of Scots pine to single inoculations by Ophiostoma brunneo-ciliatum, a bark-beetle-associated fungus

Abstract In 1987 and 1988, 100 trees year −1 were characterized by their age, height, diameter, area of sapwood section at breast height and growth efficiency indices. At different periods in the year, they were each inoculated with Ophiostoma brunneo-ciliatum at two diametrically opposite locations on the bole. The characteristics of the induced defense reactions (length of reaction zone and total resin quantity) were read in the phloem. The defense reaction zones of old trees (75–115 years old) always contained a greater total quantity of induced resin than the young trees (27–40 years old). They were also longer than in the young trees in 1987. The length of the reaction zone was smaller in June than later in the year, but the quantity of resin remained the same. Growth efficiency was always negatively correlated with the length of the reaction zone, but its correlation with the total quantity of resin in the young trees varied according to the year. In the young trees, total resin quantity was always positively correlated with tree diameter and area of sapwood section. The results are discussed in relation to the resources involved in the trees induced response and with the levels of attack density thresholds above which the trees defense is overcome. It is suggested that these resources are mainly current photosynthates in the case of young trees, while they could be otherwise in the case of old trees. It is pointed out that whilst there is undoubtedly a relationship between single reactions to individual attacks and growth efficiency, the low correlation coefficients do not allow the conclusion that lesion length or total resin from this reaction can be used as indices of the trees defense capability.

Shoot damage by Tomicus sp. (Coleoptera: Scolytidae) and effect on Pinus yunnanensis resistance to subsequent reproductive attacks in the stem

Abstract  1 In South‐western China, Yunnan pines Pinus yunnanensis, suffer considerable damage from an undescribed Tomicus sp. previously thought to be T. piniperda.

Planting Sentinel European Trees in Eastern Asia as a Novel Method to Identify Potential Insect Pest Invaders

Quarantine measures to prevent insect invasions tend to focus on well-known pests but a large proportion of the recent invaders were not known to cause significant damage in their native range, or were not even known to science before their introduction. A novel method is proposed to detect new potential pests of woody plants in their region of origin before they are introduced to a new continent. Since Asia is currently considered to be the main supplier of insect invaders to Europe, sentinel trees were planted in China during 2007-2011 as an early warning tool to identify the potential for additional Asian insect species to colonize European trees. Seedlings (1-1.5 m tall) of five broadleaved (Quercus petraea, Q. suber, Q. ilex, Fagus sylvatica, and Carpinus betulus) and two conifer species (Abies alba and Cupressus sempervirens) were planted in blocks of 100 seedlings at two widely separated sites (one in a nursery near Beijing and the other in a forest environment near Fuyang in eastern China), and then regularly surveyed for colonization by insects. A total of 104 insect species, mostly defoliators, were observed on these new hosts, and at least six species were capable of larval development. Although a number of the insects observed were probably incidental feeders, 38 species had more than five colonization events, mostly infesting Q. petraea, and could be considered as being capable of switching to European trees if introduced to Europe. Three years was shown to be an appropriate duration for the experiment, since the rate of colonization then tended to plateau. A majority of the identified species appeared to have switched from agricultural crops and fruit trees rather than from forest trees. Although these results are promising, the method is not appropriate for xylophagous pests and other groups developing on larger trees. Apart from the logistical problems, the identification to species level of the specimens collected was a major difficulty. This situation could be improved by the development of molecular databases.

Bioassays on Leptographium wingfieldii, a Bark Beetle Associated Fungus, with Phenolic Compounds of Scots Pine Phloem

The fungicidal activity of five phenolic metabolites occurring in Scots pine phloem (Cat, Tax, PS, PC and PSM) and of phenolic extracts from unwounded (fresh) and wounded phloem of Scots pine were measured against Leptographium wingfieldii, a fungus associated with Tomicus piniperda. Bioassays were performed in micro-wells in a standard medium in the absence and presence of Scots pine phloem. In both media, methanol extracts from the unwounded and wounded phloem, PS, PSM and PC inhibited fungal growth. Tax and Cat had no effect or stimulated fungal growth. The presence of Scots pine phloem in the liquid medium reduced the inhibitory effect of phenolic compounds. At low concentrations (10−4–10−5 M), the fungus seemed to be able to degrade PS, PSM and PC while, whatever the Cat and Tax concentrations, it did not seem to degrade them. These results suggest that three phenolic compounds have a potential fungitoxicity in vitro and that, in vivo, these phenols could play a role in the efficiency of the induced reaction to stop fungal growth.

Defence reactions of Norway spruce (Picea abies Karst.) to artificial insertion of Dendroctonus micans Kug. (Col., Scolytidae)

Swarming Dendroctonus micans were artificially inserted into Norway spruce on several occasions from 1987 to 1989. Resin flow was measured 2 cm below the beetle hole, either immediately below or 10 and 20 mm away on the same side as gallery extension. Four to six weeks later, the bark was removed and the status of the beetle recorded (alive, dead, successful or failed attacks, etc.), as were size and characteristics of the maternal gallery. The induced reaction was also characterized, by size and quantity of induced resin it contained (concentration and total quantity). Beetles and galleries were collected to test for the presence of fungi. In 1990, scarifications were performed on other spruces, and beetles were inserted into various holes located in relation to these slits; the same parameters as before were measured.

Wound reactions of Scots pine (Pinus sylvestris L) to attacks by Tomicus piniperda L. and Ips sexdentatus Boern. (Col., Scolytidae)

Bark beetles Tomicus piniperda and Ips sexdentatus were artificially inserted in Scots pines. Attacks were also provoked in other trees by attractants. Resin flow corresponding to each introduction was measured in the case of artificial insertions. In all cases, gallery length, reaction zone length and the total quantity of induced resin contained in the whole reaction were measured 5–6 weeks after insertions or attacks. The attempt of gallery construction (beginning of gallery boring) and the beginning of oviposition were also noted in each case, as well as the presence of associated fungi.