Colonization of eucalypts in New Zealand by Australian insects

Since the 1860s, Australian insects have steadily colonized eucalypts in New Zealand. The rate of colonization has increased markedly over the last two decades. This increase may be related to increasing trade between the two countries. Currently there are 26 specialist eucalypt insect species and approximately 31 polyphagous insect species that can feed on Eucalyptus in New Zealand. The specialist eucalypt insects endemic to Australia have generally caused more damage than polyphagous or native insects. Eucalypt‐specific insects are dominated by sap sucking bugs, particularly psyllids, and defoliating Coleoptera and Lepidoptera. In some cases the major insect pest species have been those that are only occasional pests in Australia, for example Gonipterus scutellatus, Ctenarytaina eucalypti, Eriococcus coriaceus and Phylacteophaga froggatti. Some important insect pests have been rare, or even not described from Australia, prior to their appearance as a pest in New Zealand, for example Paropsis charybdis and Ophelimus eucalypti. Invading eucalypt insects are more likely to establish in the Auckland region than anywhere else in New Zealand.     

The role of blackbirds (

The naturalised European blackbird (Turdus merula) is the most widely distributed avian seed disperser in New Zealand. Together with the native silvereye (Zosterops lateralis) they are the major seed dispersers over large areas of New Zealand. I review the international literature on aspects of the ecology and behaviour of blackbirds relevant to their potential for dispersing weeds in New Zealand. Blackbirds eat a wide range of native and exotic fruit including many naturalised species. Their habitat preferences and behaviour result in germinable seeds being deposited in a range of sites, particularly in shrubby habitats, where seedling establishment is likely. Most seeds will be deposited within 50 m but some may be carried a kilometre or more to develop new invasive loci. Blackbirds therefore probably make a major contribution to the development of novel plant communities of naturalised woody weeds. These communities provide fruit more suited to non- endemic native birds and naturalised birds, than to endemic birds. The relative contribution of blackbirds and silvereyes to seed dispersal of native and exotic species requires investigation. The outcome may suggest potential for managing blackbirds as a vector of weed invasions.     

Heterogeneity in vertebrate and invertebrate herbivory and its consequences for New Zealand mistletoes

Vertebrate herbivores generally have greater effects than invertebrates on plants. However, few studies have investigated the effects of both invertebrate and vertebrate herbivores on a single plant species. In New Zealand, nationwide declines in mistletoe populations have often been attributed to possum herbivory, but never to insect herbivory. The main goal of the present study was to document levels of vertebrate and invertebrate herbivory on endemic New Zealand mistletoe plants to suggest whether herbivory is leading to mistletoe decline. In the present study, the annual amount of leaf loss from herbivory by the brushtail possum (Trichosurus vulpecula), insect herbivory and leaf abscission were measured in two populations each of three mistletoe species (Alepis flavida, Peraxilla colensoi, and Peraxilla tetrapetala, Loranthaceae). In two populations of each species from February 1997 to February 1998, abscission accounted for the most leaf loss (range 10–84% of total mean leaf area, mean 33%), whereas insects and possums usually removed small and similar amounts (less than 3%). Possum browse caused large amounts of abscission in only one population (A. flavida at Eglinton). Observed possum browse was more heterogeneous than insect browse among branches within a plant (possum coefficient of variation = 2.63, insect CV = 1.98, P < 0.001), among plants in a population (possum CV = 2.15, insect CV = 0.69, P < 0.001), and between populations (possum CV = 1.36, insect CV = 1.09). Moreover, insects damaged 100% of the study plants but never removed more than 16% of leaf area on a single plant, whereas possums only browsed 32% of the study plants but severely defoliated some plants. Thus, while the mean amount of biomass removed across a population may have important consequences for mistletoe survival, the effect of possums on mistletoe populations may also depend on the heterogeneity of browse among individuals in the population.     

The relative importance of birds and insects as pollinators of the New Zealand flora

Native birds may have been underestimated as pollinators of the New Zealand flora due to their early decline in abundance and diversity on the mainland. This paper reconsiders the relative importance of birds and insects as pollinators to eight native flowering plants, representing a range of pollination syndromes, on two offshore island refuges. Experimental manipulations were made on five of these plant species to assess the relative effectiveness of bird and insect visitors as pollinators. In addition, foraging behaviour and the respective morphologies of flowers and visitors were measured at all eight plants to identify the main pollinators. The experimental measures showed that percentage fruit set was significantly higher in flowers exposed to birds than flowers from which birds were excluded in all manipulated plants. The observational measures revealed that for six of the flowering species (Sophora microphylla, Vitex lucens, Pittosporum crassifolium, Pittosporum umbellatum, Pseudopanax arboreus and Dysoxylum spectabile) the endemic honeyeaters were most likely to meet the conditions necessary for successful pollination. For the remaining two species (Metrosideros excelsa and Geniostoma ligus trifolium) the contribution by honeyeaters and insects to pollination was equivalent. The results suggest that the role of the endemic honeyeaters in pollination of the New Zealand flora, and the subsequent regeneration of native forest ecosystems, should be important considerations in ecosystem management.     

Plant hosts and parasitoid associations of leaf mining flies (Diptera: Agromyzidae) in the Canberra region of Australia

Abstract  Many leaf mining flies (Diptera: Agromyzidae) are important economic pests of agricultural crops and ornamental plants, and species-rich hymenopteran parasitoid complexes are important in their control. Australian agromyzids are poorly studied, and little is known about their host plants, ecology or natural enemies. We surveyed native and naturalised species of leaf mining flies in Tallaganda National Park, New South Wales and the Australian Capital Territory. Malaise and emergence trapping in Tallaganda yielded 70 agromyzid specimens from six species in four genera: Cerodontha Rondani, Liriomyza Mik, Phytoliriomyza Hendel and Phytomyza Fallen. Of the six species collected, three are Australasian species, two are naturalised species introduced from Europe and one could not be determined to species. The Australian Cerodontha ( Cerodontha ) milleri Spencer represented most of the individuals caught in both Malaise and emergence traps. A total of 163 agromyzid and 98 parasitic wasp specimens were reared from plant samples with agromyzid mines in the Canberra region. Most agromyzids and parasitoids were reared from the weed Sonchus oleraceus L. (Asteraceae). All the agromyzids reared belonged to two introduced species of the genera Phytomyza and Chromatomyia Hardy. The biodiversity of parasitic wasps reared was high with 14 species from seven genera and three families. Hemiptarsenus varicornis (Girault) (Eulophidae), a widespread Old World agromyzid parasitoid, was the most numerous parasitoid reared in our survey.     

Establishment and impact of insect agents deployed for the biological control of invasive Asteraceae: prospects for the control of <Emphasis Type="Italic">Senecio madagascariensis</Emphasis>

Several invasive Asteraceae have been targeted for biological control worldwide, with variable success. Senecio madagascariensis Poiret, which invades agricultural lands in Australia and Hawaii, is a recent target. Since several potential insect agents were recorded in the plant’s native range in South Africa, we assessed biocontrol efforts against asteraceous weeds to determine those most likely to deliver success. Some 108 insect species, from five orders and 23 families, were deployed against 38 weed taxa, mostly in the mainland USA, Canada, Australia and New Zealand. Coleoptera (mainly Curculionidae and Chrysomelidae), Diptera (Tephritidae) and Lepidoptera (Tortricidae) featured the most. Despite high establishment success (73% of releases across countries), only 37% of successful releases achieved meaningful impact. Although root-feeding and stem-feeding insects appeared to be the best candidates, neither insect family nor feeding guild significantly influenced the probability of success. This synthesis of the global contribution of different guilds of specialist herbivores to the management of invasive Asteraceae is guiding the selection of candidate agents for the biocontrol of S. madagascariensis in Australia.     

Legacy of avian-dominated plant?herbivore systems in New Zealand

Avian herbivores dominated New Zealand?s pre-settlement terrestrial ecosystems to an unparalleled extent, in the absence of a terrestrial mammal fauna. Approximately 50% (88 taxa) of terrestrial bird species consumed plant foliage, shoots, buds and flowers to some degree, but fewer than half these species were major herbivores. Moa (Dinornithiformes) represent the greatest autochthonous radiation of avian herbivores in New Zealand. They were the largest browsers and grazers within both forest and scrubland ecosystems. Diverse waterfowl (Anatidae) and rail (Rallidae) faunas occupied forests, wetlands and grasslands. Parrots (Psittacidae) and wattlebirds (Callaeidae) occupied a range of woody vegetation types, feeding on fruits/seeds and foliage/ fruits/nectar, respectively. Other important herbivores were the kereru (Columbidae), stitchbird (Notiomystidae) and two honeyeaters (Meliphagidae). Cryptic colouration, nocturnal foraging and fossil evidence suggest that avian populations were strongly constrained by predation. With the absence of migratory avian herbivores, plant structural, constitutive defences prevailed, with the unusual ?wire syndrome? representing an adaptation to limit plant offtake by major terrestrial avian browsers. Inducible plant defences are rare, perhaps reflecting longstanding nutrient-limitations in New Zealand ecosystems. Evidence from coprolites suggests moa were important dispersers of now rare, annual, disturbance-tolerant herb species, and their grazing may have maintained diverse prostrate herbs in different vegetation types. The impact of moa on forest structure and composition remains speculative, but many broadleaved woody species would likely have experienced markedly reduced niches in pre-settlement time. Several distinctive avian-mediated vegetation types are proposed: dryland woodlands, diverse turf swards, coastal herb-rich low-forest-scrubland, and conifer-rich forests. Since human settlement (c. 750 yrs ago), c. 50% of endemic avian herbivore species or c. 40% overall have become extinct, including all moa, 60% of waterfowl and 33% of rail species. Numerically, avian herbivore introductions (c. 24 taxa) since European settlement have compensated for extinctions (c. 27 taxa), but the naturalised birds are mostly small, seed-eating species restricted to human-modified landscapes. Several naturalised species (e.g. Canada goose, Branta canadensis; brown quail, Coturnix ypsilophorus) may provide modes and levels of herbivory comparable with extinct species. The original avian and current introduced mammal herbivore regimes were separated by several centuries when New Zealand lacked megaherbivores. This ?herbivory hiatus? complicates comparisons between pre-settlement and current herbivore systems in New Zealand. However, predation, animal mobility, feeding mode, nutrient transfer patterns and soil impacts were different under an avian regime compared with current mammalian herbivore systems. Levels of ecological surrogacy between avifauna and introduced mammals are less evident. Ungulates generally appear to have impacts qualitatively different from those of the extinct moa. Because of New Zealand?s peculiar evolutionary history, avian herbivores will generally favour the persistence of indigenous vegetation, while mammalian herbivores continue to induce population declines of select plant species, change vegetation regeneration patterns, and generally favour the spread and consolidation of introduced plant species with which they share an evolutionary history.     

Suboptimal oviposition of tephritid flies supports parasitoid wasps

1. Female insects lay eggs on low‐quality plants, resulting in progeny with no or low reproductive potential; this is referred to as ‘suboptimal oviposition’ in this study. 2. Here, it is reported that suboptimal oviposition of a tephritid fly species (Tephritis femoralis) supports the populations of parasitoid wasp species in a Tibetan alpine meadow. 3. Suboptimal oviposition was confirmed because the adult flies emerging from Asteraceae species Anaphalis flavescens flowerheads did not survive cold winters. 4. DNA barcoding of puparia indicated that tephritid larvae developing from suboptimal oviposition hosted populations of at least five parasitoid wasp species. Consequently, suboptimal oviposition has significant effects on parasitoid population dynamics and species diversity.     

Relationship between capitulum size and pre-dispersal seed predation by insect larvae in common Asteraceae

The evolution of a showy floral display as an advertisement to pollinators could simultaneously advertise the availability of resources to pre-dispersal seed-predators. The hypotheses tested here are that the incidence of seed predation by bud-infesting insect larvae in capitula of Asteraceae is positively related to (1) capitulum size among species, (2) capitulum size within species, (3) capitulum lifespan, and (4) the degree of flowering asynchrony on individual plants. Three populations of each of 20 common herbaceous species of Asteraceae from disturbed ground and grassland habitats were monitored for the presence of pre-dispersal, seed-eating insect larvae. Mean capitulum size (receptacle width) of each species was measured. In a sub-set of eight species, individual capitula were tagged to determine their flowering phenology and lifespan (from anthesis to seed shedding). From these data an index of flowering synchrony on individual plants was derived. Among species, the incidence of larval infestation increased with capitulum size. Small-flowered species such as Achillea millefolium were largely free of bud-infesting larvae, whilst large-flowered species such as Arctium minus were heavily infested. In three cases investigated in greater detail, bud infestation was found to increase with capitulum size within species, suggesting a potential for natural selection to favour smaller capitula. No relationship was found between infestation levels and either capitulum lifespan or degree of flowering synchrony, and there was no evidence that the relationship between capitulum size and infestation was confounded by correlations with these other features. The results support hypotheses 1 and 2, but not 3 and 4. It is suggested that the characteristic capitulum size of each species may represent a trade-off between the opposing selection pressures of pollinators and pre-dispersal seed predators.     

The lack of genetic bottleneck in invasive Tansy ragwort populations suggests multiple source populations.

Jacobaea vulgaris (Asteraceae) is a species of Eurasian origin that has become a serious non-indigenous weed in Australia, New Zealand, and North America. We used neutral molecular markers to (1) test for genetic bottlenecks in invasive populations and (2) to investigate the invasion pathways. It is for the first time that molecular markers were used to unravel the process of introduction in this species.The genetic variation of 15 native populations from Europe and 16 invasive populations from Australia, New Zealand and North America were compared using the amplified fragment length polymorphisms (AFLP's). An analysis of molecular variance showed that a significant part (10%) of the total genetic variations between all individuals could be explained by native or invasive origin.Significant among-population differentiation was detected only in the native range, whereas populations from the invasive areas did not significantly differ from each other; nor did the Australian, New Zealand and North American regions differ within the invasive range. The result that native populations differed significantly from each other and that the amount of genetic variation, measured as the number of polymorphic bands, did not differ between the native and invasive area, strongly suggests that introductions from multiple source populations have occurred. The lack of differentiation between invasive regions suggests that either introductions may have occurred from the same native sources in all invasive regions or subsequent introductions took place from one into another invasive region and the same mix of genotypes was subsequently introduced into all invasive regions.An assignment test showed that European populations from Ireland, the Netherlands and the United Kingdom most resembled the invasive populations.     

Impacts of exotic invertebrates on New Zealand?s indigenous species and ecosystems

Biological invasions have significantly affected New Zealand?s native species and ecosystems. Most prominent are the effects of exotic mammals and plants, whereas few invertebrate invasions are known to have major effects on native ecosystems. Exceptions are the well-known cases of Vespula wasps in Nothofagus forest ecosystems and Eriococcus scale insects in Leptospermum shrublands. This limited impact is surprising because over 2000 exotic invertebrates have become established in New Zealand, among them many pests of exotic crop plants. The low impact of exotic invertebrates that invaded forests and other native ecosystems in New Zealand is in contrast to the situation in other parts of the world where many invertebrates have become important pests. We provide an overview of known invasions by exotic invertebrates in New Zealand, and explore in more detail several examples of invasive species, including herbivores, predators, parasitoids, decomposers and other groups in forests, grasslands, and other terrestrial ecosystems. Several hypotheses have been proposed to explain the comparative scarcity of such invasions that affect New Zealand?s indigenous ecosystems. There is a common view that New Zealand?s native species and ecosystems are inherently resistant to exotic invertebrate invaders, and there is some evidence to support this view. As a result of the high level of endemism in New Zealand?s flora, many native plants are phylogenetically distant from the host plants of many plant-feeding invaders. This provides some protection. Less host-specific plant-feeding insects, generalist predators, parasitoids and decomposers are less affected by such constraints, and these groups are perhaps more represented among the successful invaders of natural ecosystems. However, the shortage of studies on invader impacts on native species and ecosystems, compared with studies on economically important crops and production ecosystems, means that an unbiased comparison is not possible at this time. Furthermore, many invaders go through extended lag phases where their impacts are not easily noticed until they become more abundant and create more damage. Likewise, indirect effects of invaders, through more complex interactions in food webs, as well as impacts on ecosystem functions such as decomposition and pollination, are more subtle and difficult to detect without careful study. There is clearly a need for more research to determine more accurately which exotic invertebrates are already present, what their direct and indirect impacts are, and what generalisations and predictions about threats to native species and ecosystems are possible.     

Few immigrant phytophagous insects on woody plants in Europe: legacy of the European crucible?

Exotic phytophagous insects are invading forest ecosystems worldwide. So far, 109 invasive insects on woody plants, 57 from North American (NA), and 52 from Asia (A) have established populations in European forests. Four orders account for about 84% of the immigrants: Homoptera 39%, Lepidoptera 13%, Coleoptera 19%, and Hymenoptera 13%. The majority of these invasive species (63% of NA and 77% of A) live on deciduous trees, of which 36% have been introduced from NA and Asia. The remaining insect species (37% NA and 25% A) live on various conifers, of which 53% have also been introduced. Most (57%) of the NA insects feeding on coniferous plants live upon their introduced, native host plants. These data suggest that many NA immigrant phytophagous species in Europe have been successful in establishing permanent populations because their native hosts preceded or accompanied them into Europe and/or were asexually reproducing species. We propose that fewer invasive phytophagous insects have become established in European compared to North American woodlands because of the unique legacy of the European Pleistocene/Holocene crucible (i.e. endless cycles of populations contracting into highly disparate, dispersed metapopulation refugia and eventually expanding out of them) on European species and ecosystems that caused highly diminished heterogeneity. This translates to fewer and less penetrable tri-trophic niches in Europe due to fewer and less available host plants, but greater zootic resistance per niche derived from more competition-hardened competitors and possibly natural enemies. Moreover, many European species are probably superior invasion specialists because the crucible favored traits that are conducive to success in highly subdivided, and extinction-prone metapopulations: asexual reproduction, polyploidy, and other traits especially conducive to persistence under stress, and explosive growth/spread under amelioration.     

The spatial population dynamics of insects exploiting a patchy food resource

The population dynamics of ten species of phytophagous insects and seven parasitoids inhabiting the flowerheads of two herbaceous plants, Centaurea nigra and Arctium minus, were studied, and three main aspects of their ecology were examined, namely, rates of population extinction, density dependence in population changes from one generation to the next, and movements between populations. The study was based on monitoring the insect populations on more than 50 patches of each plant, scattered over 5 km² of arable farmland and the results were used to test the relative importance of immigration and population regulation to the persistence of these populations. This paper describes the study of movements between patches of food plant. Experimentally planted new patches of plants were rapidly colonised by all species and this appeared to be unaffected by distance from a source population, up to the maximum distance of 800 m considered in the experiment. Large patches tended to be colonised more readily than small ones. Movements between plant patches were studied with the use of chemical markers (Rb, Sr, Dy and Cs) which were applied as chloride salts to individual patches, and which were translocated to the flowerheads and so to insects feeding on the seed, and to their parasitoids. Initial experiments in the laboratory showed that these elements could be readily detected by ICP (Inductively Coupled Plasma) mass spectrometry in the bodies of all species reared on potted plants sprayed with solutions containing them. Background levels of strontium were patchily high on the study area, but the other elements were naturally either absent or in very low concentrations. Four patches of each plant were marked with a different element in 1991. In 1992, samples of four species of tephritid fly and two parasitoids were collected from all patches, and analysed for the four elements. These analyses showed that individual of all species moved considerable distances, with movements of up to 2 km being commonly recorded. Estimates of rates of immigration to patches showed that movement plays an important role in the population dynamics of these insects. There was some evidence that immigration was density-dependent: it was highest when the resident populations (numbers per flowerhead) were low.     

Cryptic local adaptation of the herbivorous ladybird beetle Henosepilachna pustulosa in the ability to use the thistle Cirsium boreale

Local adaptation to different host plants is important in the diversification of phytophagous insects. Thus far, much evidence of the local adaptation of insects with respect to host use at the physiological level has been gathered from systems involving less mobile insects and/or divergent hosts such as plants belonging to different families or genera. On the other hand, the prevalence of such local adaptation of insects with moderate or high dispersal ability to the intraspecific variation of herbaceous hosts is largely unknown. In the present study, we examined the occurrence and degree of local adaptation of the herbivorous ladybird beetle Henosepilachna pustulosa (Kôno) (Coleoptera: Coccinellidae) to its primary host, the thistle Cirsium boreale Kitam. (Asteraceae), through reciprocal laboratory experiments using beetles and thistles from three locations with a range of approximately 200 km. Concerning the larval developmental ability, obvious patterns of local adaptation to the thistles from respective natal locations were detected, at least in some combinations of beetle populations. Similar tendencies were detected concerning adult feeding acceptance, although the statistical support was somewhat obscure. Overall, our results indicate that the degree of local adaptation of insect species with moderate dispersal ability to conspecific herbaceous hosts is occasionally as strong as that involving less mobile insects and/or heterospecific hosts, indicating the potential of such cryptic local adaptation to promote ecological/genetic differentiation of phytophagous insect populations.     

Potential risk of accidental introduction of Asian gypsy moth (Lymantria dispar) to Australasia: effects of climatic conditions and suitability of native plants

1 The potential risk of the establishment of the Asian strain of the gypsy moth (AGM) (Lymantria dispar) in New Zealand and Australia (Australasia) was assessed from a study of the insect's host range and potential distribution. In New Zealand, viable eggs of AGM have been continuously intercepted on cargo from Asia, and therefore there is a high probability of accidental introductions of AGM to Australasia. 2 We predicted potential distribution ranges of AGM based on climatic conditions. Asian gypsy moth is predicted to be able to persist in N and SE New Zealand and SE and SW Australia. 3 Using three populations of AGM and 59 species (seven families) of plant (55 from Australasia and four from elsewhere), we also conducted laboratory trials to examine the ability of AGM larvae to complete development on native plants from Australasia. Asian gypsy moth was able to complete development on 26 out of the 55 native species tested. Furthermore, larval performance on at least five species of Australian native plant was as good as on AGM's preferred host species (Quercus pubescens and Q. robur). 4 Larval performance of AGM was poor on all but one species of New Zealand native tree species (Nothofagus solandri), and therefore the risk of establishment in the indigenous forests of New Zealand is considered to be low. 5 Given the suitability of some Australian plants and the climatic suitability for the establishment of AGM, this insect should be treated as a serious quarantine threat and managed accordingly, particularly in Australia.     

Non-native plants rarely provide suitable habitat for native gall-inducing species

For insect herbivores, a critical niche requirement—possibly the critical niche requirement—is the presence of suitable host plants. Current research suggests that non-native plants are not as suitable as native plants for native herbivores, resulting in decreases in insect abundance and richness on non-native plants. Like herbivores, gall-forming insects engage in complex, species-specific interactions with host plants. Galls are plant tissue tumors (including bulbous or spindle-shaped protrusions on leaves, stems and other plant organs) that are induced by insects through physical or chemical damage (prompting plants to grow a protective tissue shell around the insect eggs and larvae). As such, we hypothesized that gall-inducing insect species richness would be higher on native than non-native plants. We also predicted higher gall-inducing insect species richness on woody than herbaceous plants. We used an extensive literature review in which we compiled gall host plant species by genus, and we assigned native or non-native (or mixed) status to each genus. We found that native plants host far more gall-inducing insect species than non-native plants; woody plants host more gall-inducing species than herbaceous plants; and native woody plants host the most gall-inducing species of all. Gall-inducing species generally are a very cryptic group, even for experts, and hence do not elicit the conservation efforts of more charismatic insects such as plant pollinators. Our results suggest that non-native plants, particularly non-native woody species, diminish suitable habitat for gall-inducing species in parallel with similar results found for other herbivores, such as Lepidopterans. Hence, the landscape-level replacement of native with non-native species, particularly woody ones, degrades taxonomically diverse gall-inducing species (and their inquilines and parasitoids), removing multiple layers of diversity from forest ecosystems.

     

Community structure of insect herbivores on introduced and native Solidago plants in Japan

We compared community composition, density, and species richness of herbivorous insects on the introduced plant Solidago altissima L. (Asteraceae) and the related native species Solidago virgaurea L. in Japan. We found large differences in community composition on the two Solidago species. Five hemipteran sap feeders were found only on S. altissima. Two of them, the aphid Uroleucon nigrotuberculatum Olive (Hemiptera: Aphididae) and the scale insect Parasaissetia nigra Nietner (Hemiptera: Coccidae), were exotic species, accounting for 62% of the total individuals on S. altissima. These exotic sap feeders mostly determined the difference of community composition on the two plant species. In contrast, the herbivore community on S. virgaurea consisted predominately of five native insects: two lepidopteran leaf chewers and three dipteran leaf miners. Overall species richness did not differ between the plants because the increased species richness of sap feeders was offset by the decreased richness of leaf chewers and leaf miners on S. altissima. The overall density of herbivorous insects was higher on S. altissima than on S. virgaurea, because of the high density of the two exotic sap feeding species on S. altissima. We discuss the importance of analyzing community composition in terms of feeding guilds of insect herbivores for understanding how communities of insect herbivores are organized on introduced plants in novel habitats.     

Reduced seed predation after invasion supports enemy release in a broad biogeographical survey

The Enemy Release (ER) hypothesis predicts an increase in the plant invasive capacity after being released from their associated herbivores or pathogens in their area of origin. Despite the large number of studies on biological invasions addressing this hypothesis, tests evaluating changes in herbivory on native and introduced populations and their effects on plant reproductive potential at a biogeographical level are relatively rare. Here, we tested the ER hypothesis on the South African species Senecio pterophorus (Asteraceae), which is native to the Eastern Cape, has expanded into the Western Cape, and was introduced into Australia (>70–100 years ago) and Europe (>30 years ago). Insect seed predation was evaluated to determine whether plants in the introduced areas were released from herbivores compared to plants from the native range. In South Africa, 25 % of the seedheads of sampled plants were damaged. Plants from the introduced populations suffered lower seed predation compared to those from the native populations, as expected under the ER hypothesis, and this release was more pronounced in the region with the most recent introduction (Europe 0.2 % vs. Australia 15 %). The insect communities feeding on S. pterophorus in Australia and Europe differed from those found in South Africa, suggesting that the plants were released from their associated fauna after invasion and later established new associations with local herbivore communities in the novel habitats. Our study is the first to provide strong evidence of enemy release in a biogeographical survey across the entire known distribution of a species.     

HOST RACE RADIATION IN THE SOAPBERRY BUG: NATURAL HISTORY WITH THE HISTORY

Evolution by natural selection is remarkably well documented in the diversification of soapberry bug populations on their native and recently introduced host plants. In this century, populations of this native seed-eating insect have colonized three plant species introduced to North America. Each new host differs in fruit size from the native hosts, providing an unplanned experiment in natural selection of the insect's beak length. In each of three host shifts, beak length has increased or decreased in the direction predicted from fruit size. Furthermore, museum specimens show historical changes consistent with the host shift scenario inferred from beak length values in contemporary populations. The extent to which beak length evolution has been accompanied by evolution in other body size characters differs between the races, suggesting that the evolution has proceeded differently in each case. In all cases, significant evolution has occurred in as little as 20–50 years (40–150 generations), creating a species-level mosaic of response to simultaneous directional, diversifying, and normalizing selection.