Phylogenetic relationships of Ceratitis fruit flies inferred from nuclear CAD and tango/ARNT gene fragments: Testing monophyly of the subgenera Ceratitis (Ceratitis) and C. (Pterandrus)

Systematic studies of Ceratitis (Tephritidae) fruit flies using molecular (i.e., COI, ND6, and period genes) and morphological (plus host-use characters) data have recently challenged the monophyly of the subgenera Ceratitis (Ceratitis) and Ceratitis (Pterandrus). In this paper, we report on the phylogenetic utility of three single-copy nuclear gene regions (two non-overlapping fragments of the carbamoylphosphate synthetase, CPS, locus of CAD, and a fragment of tango) within these taxa and investigate evolutionary relationships based on a concatenated ca. 3.4 kb data set that includes the six protein encoding gene regions. Results indicate that the CAD and tango genes provide useful phylogenetic signal within the taxa and are compatible with the previously studied genes. The two subgenera, as currently classified, are not monophyletic. Our molecular phylogenetic analyses support a revised classification in which (1) the subgenus C. (Pterandrus) comprises two lineages called A and B, (2) the C. (Pterandrus) B species should be included in C. (Ceratitis), and (3) the newly defined subgenera C. (Pterandrus) (=Pterandrus section A) and C. (Ceratitis) [=C. (Ceratitis) + C. (Pterandrus) section B] are reciprocally monophyletic.     

Invasion Genetics of New World Medflies: Testing Alternative Colonization Scenarios

The Mediterranean fruit fly (Ceratitis capitata) is an invasive agricultural pest with a wide host range and a nearly global distribution. Efforts to forgo the medfly's spread into the United States are dependent on an understanding of population dynamics in newly established populations elsewhere. To explore the potential influence of demographic and historical parameters in six medfly populations distributed from Mexico to Peru, we created population genetic null models using Monte Carlo simulations. Null expectations for genetic differentiation (F _ST) were compared with actual sequence variation from four highly polymorphic nuclear loci. Four colonization scenarios that were modeled led to unique genetic signatures that could be used to interpret empirical data. Unless current gene flow across Latin America was assumed to be very high, we could reject colonizations consisting of multiple introductions, each of low genetic diversity. Further, if simulated populations were small (N _e = 5 × 10² individuals per population), small invasions from a single source consistently produced F _ST values comparable to those currently observed in Latin America. In contrast, only large invasions from diverse sources were compatible with the observed data for large populations (N _e 5 × 10³). This study demonstrates that alternative population genetic hypotheses can be tested empirically even when departures from equilibrium are extreme, and that population genetic theory can be used to explore the processes that underlie biological invasions.     

Evaluation of Diachasmimorpha longicaudata (Hymenoptera: Braconidae) as a mortality factor of Ceratitis capitata (Diptera: Tephritidae) infesting Citrus species under laboratory and field-cage conditions

Ceratitis capitata (or medfly) is one of the major pests currently affecting fruit crops in northwestern Argentinian Citrus-producing areas. Medfly populations are sustained in large exotic fruits, such as Citrus paradisi, Citrus aurantium and Citrus sinensis, which are known to hinder the activity of almost all native parasitoid species. Therefore, a feasible approach to controlling medfly involves the use of exotic parasitoids such as Diachasmimorpha longicaudata. In this study, the prediction that parasitoid females would be proficient at finding medfly larvae infesting the Citrus species mentioned earlier was tested. Particularly, the variation in fruit species preference by parasitoid females, the efficacy of the parasitoid to kill medfly and the effect of host density on parasitoid performance were determined. Parasitoids were allowed to forage for 8 h on grapefruits and oranges artificially infested with medfly larvae under controlled (laboratory) and uncontrolled (field cage) environmental conditions. Fruit choice and no-choice tests were performed. Results were assessed by comparing the number of female visits to and ovipositor insertions into the fruit, and parasitoid emergence, parasitism and additional host mortality percentages. Parasitoid preference for visiting larger fruits (sour orange and grapefruit) may be related to the increased fruit surface area. Ovipositional activity on fruit was influenced by the variation of the larval host density per unit of fruit surface. The higher parasitism rates recorded from sweet orange would be mainly a result of both increased host density and fruit physical features. Nevertheless, D. longicaudata showed the capacity to parasitise hosts in all Citrus species tested.     

A high‐throughput detection method for invasive fruit fly (Diptera: Tephritidae) species based on microfluidic dynamic array

Invasive species can be detrimental to a nation's ecology, economy and human health. Rapid and accurate diagnostics are critical to limit the establishment and spread of exotic organisms. The increasing rate of biological invasions relative to the taxonomic expertise available generates a demand for high‐throughput, DNA‐based diagnostics methods for identification. We designed species‐specific qPCR primer and probe combinations for 27 economically important tephritidae species in six genera (Anastrepha, Bactrocera, Carpomya, Ceratitis, Dacus and Rhagoletis) based on 935 COI DNA barcode haplotypes from 181 fruit fly species publically available in BOLD, and then tested the specificity for each primer pair and probe through qPCR of 35 of those species. We then developed a standardization reaction system for detecting the 27 target species based on a microfluidic dynamic array and also applied the method to identify unknown immature samples from port interceptions and field monitoring. This method led to a specific and simultaneous detection for all 27 species in 7.5 h, using only 0.2 μL of reaction system in each reaction chamber. The approach successfully discriminated among species within complexes that had genetic similarities of up to 98.48%, while it also identified all immature samples consistent with the subsequent results of morphological examination of adults which were reared from larvae of cohorts from the same samples. We present an accurate, rapid and high‐throughput innovative approach for detecting fruit flies of quarantine concern. This is a new method which has broad potential to be one of international standards for plant quarantine and invasive species detection.     

Odour-mediated foraging by yellowjacket wasps (Hymenoptera: Vespidae): predation on leks of pheromone-calling Mediterranean fruit fly males (Diptera: Tephritidae)

Predation is probably the most important male mortality factor in insect species with courtship displays that render males performing them conspicuous targets of predators. Sexually active Mediterranean fruit fly males, Ceratitis capitata (Wied.), aggregate in leks, where they participate in agonistic encounters and engage in visual, acoustic and pheromone-calling displays to attract receptive females. The objective of this study was to assess: a) whether sexually displaying C. capitata males in leks inside host and non-host foliage are subject to predation by the most prominent predators yellow-jacket wasps, Vespula germanica (F.), and if so, b) whether olfactory, visual or auditive stimuli are used by foraging wasps in locating male C. capitata prey. Studies were carried out in a citrus orchard and surroundings on the island of Chios, Greece. Observations were conducted using perforated containers hung within mulberry, fig or citrus foliage. Living C. capitata flies of different sex and either mature or immature were placed inside. Our results show that the yellowjacket wasps have learned to associate the presence of sexually active medfly males aggregated in leks with their prey's pheromone (kairomone). Foraging wasps, flying through the crowns of host trees, responded to the odour source of C. capitata male pheromone by approaching from downwind. Even inside dense citrus tree foliage, wasps keyed in on aggregations of pheromone-calling males using olfactory stimuli. Stimuli of visual and acoustic male signalling were only used at close range, after having followed the pheromone plume close to its source. Visual cues played a greater role in directing wasp foraging under more open and exposed host foliage conditions. Odour-based foraging of wasps inside host foliage in the mid-morning hours, when medfly male lekking activities peak, shifted gradually to a more visual-based host fruit patrolling in the afternoons to capture ovipositing and feeding medfly females. On ripe fruit, particularly fig, V. germanica visual prey hunting also included the capture of feeding medfly males, other feeding Diptera, as well as medfly larvae extracted from wasp-made perforations in the fruit.     

Population-specific demography and invasion potential in medfly

Biological invasions are constantly gaining recognition as a significant component of global change. The Mediterranean fruit fly (medfly) constitutes an ideal model species for the study of biological invasions due to its (1) almost cosmopolitan geographic distribution, (2) huge economic importance, and (3) well-documented invasion history. Under a common garden experimental set up, we tested the hypothesis that medfly populations obtained from six global regions [Africa (Kenya), Pacific (Hawaii), Central America (Guatemala), South America (Brazil), Extra-Mediterranean (Portugal), and Mediterranean (Greece)] have diverged in important immature life-history traits such as preadult survival and developmental times. We also tested the hypothesis that medfly populations from the above regions exhibit different population growth rates. For this purpose, data on the life history of immatures were combined with adult survival and reproduction data derived from an earlier study in order to calculate population parameters for the above six populations. Our results clearly show that medfly populations worldwide exhibit significant differences in preadult survival, developmental rates of immatures and important population parameters such as the intrinsic rate of increase. Therefore, geographically isolated medfly populations may share different invasion potential, since population growth rates could influence basic population processes that operate mostly during the last two stages of an invasion event, such as establishment and spread. Our findings provide valuable information for designing population suppression measures and managing invasiveness of medfly populations worldwide.     

Cuticular hydrocarbons from six species of tephritid fruit flies

Cuticular alkanes obtained from larvae and adults of six species of tephritid fruit flies, Anastrepha ludens, A. suspensa, Ceratitis capitata, C. rosa, Dacus cucurbitae, and D. dorsalis were analyzed by gas chromatography. The same four major alkanes were shown to be present by capillary GC-mass spectra in all Anastrepha and Ceratitis larvae. Profiles were obtained from individual larvae and adult specimens that showed statistical differences between species, whereas profiles of conspecific life forms including pupae of A. suspensa from different locations showed some similarities. Sexual dimorphism was not observed in alkanes extracted from adults. A novel series of alkadienes was found in all Anastrepha and Ceratitis but not in Dacus.     

Consumption of introduced prey by native predators: Argentine ants and pit-building ant lions

When populations of native predators are subsidized by numerically dominant introduced species, the structure of food webs can be greatly altered. Surprisingly little is known, however, about the general factors that influence whether or not native predators consume introduced species. To learn more about this issue, we examined how native pit-building ant lions (Myrmeleon) are affected by Argentine ant (Linepithema humile) invasions in coastal southern California. Compared to areas without L. humile, invaded areas contained few native ant species and were deficient in medium-sized and large bodied native ants. Based on these differences, we predicted that Argentine ants would negatively affect ant lion larvae. Contrary to this expectation, observational surveys and laboratory growth rate experiments revealed that Myrmeleon were heavier, had longer mandibles, and grew more quickly when their main ant prey were Argentine ants rather than native ants. Moreover, a field transplant experiment indicated that growth rates and pupal weights were not statistically different for larval ant lions reared in invaded areas compared to those reared in uninvaded areas. Argentine ants were also highly susceptible to capture by larval Myrmeleon. The species-level traits that presumably make Argentine ant workers susceptible to capture by larval ant lions—small size and high activity levels—appear to be the same characteristics that make them unsuitable prey for vertebrate predators, such as horned lizards. These results underscore the difficulties in predicting whether or not numerically dominant introduced species serve as prey for native predators.     

Fruit tree genetics at a turning point: the almond example

 The large size and the long generation time of fruit trees generally reduce the possibilities of obtaining genetic information on the transmission and heritability of useful agronomic traits in these species. However, from breeding work carried out with fruit trees, an important amount of data is now available, although large differences are apparent among the different species. There is not much information known about almond compared to what is available on other Prunus fruit species, but more data have been accumulated on it than on most of the other nut trees, thus making almond special among all the temperate fruit and nut species. Only five qualitative traits have been described in almond, with an additional two also possibly qualitative. Heritabilities have been estimated for an important number of quantitative traits, mainly phenological times and fruit characters. Important information is available on molecular markers, including enzymes, RFLPs, RAPDs and other recently developed markers. Linkages, however, have only been established among molecular markers, allowing accurate genetic maps to be built but not yet enabling agronomical characters to be located in these maps, probably because the latter have not been sufficiently studied. The effectiveness of the application of genetic maps in plant breeding will depend on the accuracy of the study of different agronomic traits and their expression, implying more field work and recognition of this work. Ultimately, any new fruit cultivar has to be grown in the field and has to allow the grower to make a profit. Received: 1 June 1997 / Accepted: 1 September 1997     

基于表型性状和SSR标记的57份辣椒种质遗传多样性分析

为了解辣椒(Capsicum annuum)种质资源的遗传多样性,以57份辣椒种质资源为材料,对34个表型性状进行变异度、多样性及主成分分析,分别基于表型性状和SSR分子标记进行聚类分析。结果表明,种质间的34个表型性状存在差异,平均变异系数为40.67%,平均Shannon-Weiner多样性指数为1.20;提取的10个主成分可以代表辣椒种质表型性状75.972%的遗传信息,其中第1主成分占比22.317%,主要由果实横径、单果重、果肩形状和果顶性状所组成;19对SSR引物的平均Nei’s基因多样性指数及香农信息指数分别为0.48和0.80;基于表型性状和SSR标记均将57份辣椒分为4类,但2种聚类结果间的相关性不显著(r=-0.175 9)。这为辣椒育种的亲本选配及种质资源评价提供理论依据。     

Contrasting levels of genotype by environment interaction for life history and morphological traits in invasive populations of Zaprionus indianus (Diptera: Drosophilidae)

It has been demonstrated that phenotypic plasticity and genotype by environment interaction are important for coping with new and heterogeneous environments during invasions. Zaprionus indianus Gupta (Diptera: Drosophilidae) is an Afrotropical invasive fly species introduced to the South American continent in 1999. This species is generalist and polyphagous, since it develops and feeds in several different fruit species. These characteristics of Z. indianus suggest that phenotypic plasticity and genotype by environment interaction may be important in this species invasion process. In this sense, our aim was to investigate the role of genetic variation for phenotypic plasticity (genotype by environment interaction) in Z. indianus invasion of the South American continent. Specifically, we quantified quantitative genetic variation and genotype by environment interactions of morphological and life history traits in different developmental environments, that is, host fruits. This was done in different populations in the invasive range of Z. indianus in Argentina. Results showed that Z. indianus populations have considerable amounts of quantitative genetic variation. Also, genotype by environment interactions was detected for the different traits analyzed in response to the different developmental environments. Interestingly, the amounts and patterns of these parameters differed between populations. We interpreted these results as the existence of differences in evolutionary potential between populations that have an important role in the short‐ and long‐term success of the Z. indianus invasion process.     

火龙果种质资源果实特性的遗传多样性分析

为筛选火龙果(Hylocereus undatus)优良种质资源,对22份种质资源果实的表型性状、农艺性状、品质性状进行遗传多样性分析。结果表明,火龙果种质资源果实的表型性状、农艺性状和品质性状具有丰富的遗传多样性和较高的变异性,表型性状的多样性指数(H′)为0～1.04,品质性状为0.40～2.01;农艺性状的变异系数(CV)为0.06～0.38,品质性状为0.01～0.62。聚类分析表明,在遗传距离为15时,火龙果22份种质资源可分为5类,说明不同资源间亲缘关系较远。这为发掘火龙果的育种潜力,筛选优异基因资源,改良种质奠定了基础。     

我国口岸小条实蝇属截获情况分析

[目的] 小条实蝇属害虫原产非洲,在我国无分布且具有一定的入侵风险。分析该虫在我国口岸的截获情况,能更好地利用已知实蝇截获数据防范实蝇人为传播。[方法] 经动植物检验检疫信息资源共享服务平台查询,统计小条实蝇属的有害生物类别、截获途径及截获地区等。[结果] 全国口岸共截获8种共计524批次的小条实蝇属害虫;地中海实蝇的截获批次数最多,为415批次,为小条实蝇属截获率的79.2%;截获的种类最多的国家来自尼日利亚,5种;截获批次最多的国家为南非,71批次;截获方式最多的为旅客携带物,占总批次的68.3%;在我国口岸中,广东口岸截获批次最多,占总数的57.4%。[结论] 从今后防控的重点种类、加大查验力度、推广新技术在鉴定上的应用、应急预案等几个方面,加强针对该类有害生物的检验检疫措施。     

Population structure and cryptic genetic variation in the mango fruit fly,Ceratitis cosyra (Diptera,Tephritidae)

The fruit fly Ceratitis cosyra is an important agricultural pest negatively affecting the mango crop production throughout Africa and also feeding on a variety of other wild and cultivated hosts. The occurrence of deeply divergent haplotypes, as well as extensive morphological variability, previously suggested possible cryptic speciation within Ceratitis cosyra. Here we provide the first large-scale characterisation of the population structure of Ceratitis cosyra with the main objective of verifying cryptic genetic variation. A total of 348 specimens from 13 populations were genotyped at 16 polymorphic microsatellite loci. Hardy-Weinberg equilibrium (HWE) deviations were observed in 40.4% of locus-population combinations and suggested the occurrence of genetic substructuring within populations. Discriminant Analysis of Principal Components (DAPC) showed genetic divergence between the vast majority of vouchers from Burundi and Tanzania (plus a few outliers from other African countries) and all other specimens sampled. Individual Bayesian assignments confirmed the existence of two main genotypic groups also occurring in sympatry. These data provided further support to the hypothesis that Ceratitis cosyra might include cryptic species. However, additional integrative taxonomy, possibly combining morphological, ecological and physiological approaches, is required to provide the necessary experimental support to this model.     

Stiffness and checking of <Emphasis Type="Italic">Eucalyptus nitens</Emphasis> sawn boards: genetic variation and potential for genetic improvement

A trial was undertaken to assess the extent to which variation in sawn-board quality traits of plantation-grown Eucalyptus nitens is under genetic control and amenable to genetic improvement. Five hundred and sixty trees from 129 families and three central Victorian races were sampled from an open-pollinated progeny trial in Tasmania, Australia. Acoustic wave velocity (AWV) was assessed on standing trees and sawlogs. Wedges from disks extracted from sawlogs were assessed for basic density and checking. Processed boards from 496 of the trees were assessed for board stiffness (static modulus of elasticity, MOE), and internal and surface checking. Genetic differences among races were significant for AWV and MOE traits. The Southern race had the highest mean values for these traits. Significant additive genetic variation within races was observed in all traits, demonstrating that the quality of plantation-grown E. nitens boards could be improved through breeding. Estimated narrow-sense heritabilities were 0.85 for standing-tree AWV, 0.71 for log AWV, 0.37 for board MOE, and ranged from 0.20 to 0.52 for checking traits. A strongly positive genetic correlation (r _g = 1.05) was observed between standing-tree AWV and board MOE, indicating that AWV could be used as a selection trait to improve E. nitens board stiffness. The genetic correlation between basic density and board MOE was also positive (r _g = 0.62). However, a significant and adverse genetic correlation (r _g = 0.61) was identified between basic density and surface check length. Wood stiffness and checking traits were more-or-less genetically independent, and genetic correlations between surface and internal checking were positive but only moderate (r _g = 0.48–0.52).     

High levels of genetic divergence and inbreeding in populations of cupuassu (Theobroma grandiflorum)

Theobroma grandiflorum (cupuassu) is an important fruit tree native to the Brazilian Amazon. Establishing the genetic diversity and structure of populations is critical to define long-term strategies for cupuassu conservation presently threatened by rapid deforestation. Three natural populations collected at the putative center of diversity, three groups of accessions established at a germplasm collection, and one derived from commercial plantings were analyzed. The genetic diversity was assessed using 21 polymorphic microsatellite loci originally developed for Theobroma cacao, disclosing a total of 113 alleles. The estimated genetic diversity parameters averaged over cupuassu populations (A = 3.53 alleles per locus; H _e = 0.426; H _o = 0.346) were lower than the values reported for other Neotropical tree species. The three natural populations presented a positive and significant fixation index (f), ranging from 0.133 to 0.234. Cupuassu apparently adhered to a general pattern of genetic diversity structure of some Neotropical tree species occurring at low densities, with a low intrapopulation genetic diversity and important levels of endogamy, possibly due to biparental inbreeding derived from the presence of spatial genetic structure in the populations. A high level of genetic divergence was detected among the natural populations (θ _p = 0.301), a strong differentiation caused by limited gene flow, and suggesting that human interference in spreading and/or stimulating plantings might have had a smaller effect than expected. The approximate location of the T. grandiflorum center of diversity could not be confirmed by analyzing natural populations from the putative region.     

Assessing the invasive potential of the Mediterranean fruit fly in California and Italy

The polyphagous tropical Mediterranean fruit fly (Ceratitis capitata Weid. (medfly)) was detected in California in 1975, and a large-scale detection/eradication campaign was begun in the absence of sound knowledge of the fly’s potential invasiveness and geographic distribution. Persistent measurable populations of the fly have not been found in California, but a scientific explanation for this has not developed. A physiologically based demographic system model (CASAS) was developed to examine the effects of temperature on medfly’s potential distribution across the ecological zones of Arizona–California (AZ–CA), and in Italy where the fly is established. The system model simulates the daily age-mass structured dynamics of a tree host composed of sub-unit populations of leaves, stem, roots and fruit, as well as the age-structured dynamics of medfly life stages. Total pupae tree⁻¹ year⁻¹ was used as the metric of favorability for medfly at 151 locations in AZ–CA during 1995–2006, and at 84 locations in Italy during 1999–2005. The results were mapped using GRASS GIS. AZ and the southern desert areas of CA are unfavorable for medfly because of high summer temperatures, while much of CA, including many frost-free areas, is too cold. Only the area of south coastal CA (San Diego, Orange and Los Angeles Counties) is potentially favorable for medfly, but in the absence of measurable populations, we cannot say whether it is established there. The majority of medfly discoveries over the past 35 years have occurred in south coastal CA, but discoveries also occurred in Santa Clara County in northern CA, mostly during 1975 and 1980–1981. Santa Clara County, just south of San Francisco Bay, is generally marginal for medfly, but favorability increased approximately 10% during the period 1979–1981. Medfly has been established in Italy for decades, and our model predicts its wide distribution in the southern and western regions of the country. The fly is restricted in northern areas and at higher elevations of Italy by winter temperatures. Temperature is expected to increase in CA and the Mediterranean Basin. We used two scenarios consisting of increasing observed daily temperatures +2 and +3°C to examine the effects on the potential distribution of the fly in CA and Italy. Increasing temperatures expand the favorable range for medfly northward along the coast of CA, but decrease it in the southern reaches of current favorability. A similar but greater increase in geographic range is predicted for Italy. We examine critically some ongoing eradication programs in CA, and question the scientific basis for them. We also review some climate matching approaches used to assess the potential geographic distribution of invasive species.     

Understanding biological conservation strategies: a molecular-genetic approach to the case of myrtle (<Emphasis Type="Italic">Myrtus communis</Emphasis> L.) in two Italian regions: Sardinia and Calabria

Myrtle (Myrtus communis L.), a shrub widespread in the Mediterranean area, is the only species belonging to the Myrtaceae family growing in Europe. The pharmacological and aromatic properties of myrtle have caused a growing interest in this plant. The use of myrtle as an aromatic plant is traditionally established in the Italian regions of Sardinia and Calabria, where it is subjected to an ecological stress due to the large biomass removal for liquor production and environmental damage. The reduction in size and number of wild populations is often related to a loss of genetic variation and reproductive potential. In this study fluorescent amplified fragment length polymorphisms (fAFLPs) were employed to assess the genetic variation within and among natural populations of myrtle from Sardinia and Calabria to gain new insights into their fitness and survival potential. AMOVA analysis indicated that genetic variation was greater within populations (51.86%) than among populations (16.99%), as previously reported for outcrossing species. A significant amount of variation (31.15%) was attributed to variation between Sardinia and Calabria population groups, suggesting a genotypic differentiation between the myrtle populations of these two regions. Intra-population genetic variation, assessed by estimating expected unbiased heterozygosity (H _E), ranged from 0.0595 to 0.2595. These values resulted correlated with population extension (r = 0.918; P < 0.01) and with two reproductive parameters: seed germinability (r = 0.793; P < 0.01) and number of seeds per fruit (r = 0.631; P < 0.05). A moderate gene flow among Sardinia myrtle populations and Calabria populations (1.2719 and 1.0478, respectively) counteracts the low level of genetic variation observed in some␣populations and avoids their differentiation and isolation.     

A taxonomic,biogeographical and ecological overview of invasive woody plants

Abstract. Invasive plants are considered to be a major threat to the earth's biodiversity, but have not been sufficiently investigated. To address this problem a relational database on invasive woody plants has been set up. It is based on 2045 bibliographical references and contains records on 653 species representing 110 families. The families with the largest number of invasive species are: Rosaceae, Mimosaceae, Papilionaceae and Pinaceae. Out of 1060 recorded invasive events an equal number are reported from continents and oceanic islands. The highest number of invasive woody species are recorded from Europe, followed by the Pacific islands, North America, New Zealand, Australia, Indian Ocean islands and southern Africa. Included in these regions are areas which have fewer highly invasive species, e.g. islands on continental shelves, such as the British Isles. Although most invasions occur in disturbed habitats, most natural communities are susceptible to woody plant invasions. Data on species attributes are only available for a minority of species but indicate that invasive woody plant species may be either insect or wind-pollinated, have a wide array of fruit types, fruit and seed sizes, number of seeds per fruit and dispersal agents. The relative frequency of several attributes varies with the degree of invasiveness. Thus it is not yet possible to determine which set of attributes favours invasiveness and therefore it is difficult to make predictions.