Effects of herbivory and mistletoe infection by <Emphasis Type="Italic">Psittacanthus calyculatus</Emphasis> on nutritional quality and chemical defense of <Emphasis Type="Italic">Quercus deserticola</Emphasis> along Mexican forest fragments

Mistletoes are parasitic plants that show effects that can parallel or contrast with those caused by herbivores to their host plants, particularly on aspects such as host biomass, resource allocation patterns, and interspecific interactions at the community level. In this study, we evaluated the potential synergistic effects of herbivory and infection by the mistletoe Psittacanthus calyculatus on nutritional quality and chemical defense of the white oak Quercus deserticola along forest fragments in Mexico. For this, we sampled leaves of parasitized oaks, unparasitized oaks and mistletoes at four forest fragments in the Cuitzeo basin, Michoacán state, Mexico, and measured herbivory levels and foliar water content, total nonstructural carbohydrates, phenols, flavonoids, and hydrolyzable tannins in each sample. Higher levels of infection by P. calyculatus were found in the smaller forest fragments, while foliar damage by herbivores was higher in larger forest fragments. At all sites, levels of herbivory were lower in the mistletoe than in both parasitized and unparasitized oaks. However, there was a positive relationship between herbivory levels in parasitized oaks and their mistletoes. Also, foliar water content and total phenol concentration were positively correlated between the oaks and the mistletoes. The results suggest that herbivory levels in parasitized hosts and mistletoes depend on the close physiological interaction between the nutritional quality and the chemical defense of the two plants involved. This is one of the few studies analyzing the chemical ecology of the interaction between plant hosts and plant parasites.     

Timing of invasive pollen deposition influences pollen tube growth and seed set in a native plant

Invasive plants may threaten the reproductive success of native sympatric plants by modifying the pollination process. One potential mechanism takes place through the deposition of invasive pollen onto native stigmas when pollinators are shared among species. We explore how pollen from the invasive plant Brassica nigra influences pre- and post-fertilization stages in the native plant Phacelia parryi, through a series of hand pollination experiments. These two species share pollinators to a high degree. P. parryi flowers were hand-pollinated with either pure conspecific pollen (the control) or with B. nigra pollen applied prior to, simultaneously with, or following conspecific pollen. Application of B. nigra pollen lowered seed set, with the simultaneous application resulting in the highest reduction. Pollen tube growth was also influenced by the presence of invasive pollen, with fewer conspecific pollen tubes reaching the base of P. parryi styles in treatments where B. nigra pollen was applied prior to or simultaneously with conspecific pollen. The deleterious effects of invasive pollen on native seed set in this study are likely not due to loss of stigmatic receptivity since seed set was less affected when heterospecific pollen was applied prior to conspecific pollen, but may instead involve interactions between interspecific pollen grains on the stigma or within the style. Our study highlights the importance of timing of foreign pollen deposition on native stigmas and suggests that interspecific pollen transfer between native and exotic plants may be an important mechanism of competition for pollination in invaded plant communities.     

Invasive South American floating plants are a successful substrate for native Central African pleuston

Eichhornia crassipes, commonly known as water hyacinth, is a free-floating perennial aquatic plant native to South America, which has been widely introduced on different continents, including Africa. E. crassipes is abundant in both the Congo (Africa) and Amazon (South America) River catchments. We performed a comparative analysis of the ostracod communities (Crustacea, Ostracoda) in the E. crassipes pleuston in the Amazon (South America) and Congo (Africa) River catchments. We also compared the ostracod communities from the invasive E. crassipes with those associated with stands of the native African macrophyte Vossia cuspidata. We recorded 25 species of ostracods associated with E. crassipes in the Amazon and 40 in the Congo River catchments, distributed over 31 ostracod species in E. crassipes and 27 in V. cuspidata. No South American invasive ostracod species were found in the Congolese pleuston. Diversity and richness of Congolese ostracod communities was higher in the invasive (Eichhornia) than in a native plant (Vossia). The highest diversity and abundance of ostracod communities were recorded in the Congo River. The result of principal coordinates analysis, used to evaluate the (dis)similarity between different catchments, showed significant differences in species composition of the communities. However, a dispersion homogeneity test (PERMDISP) showed no significant differences in the variability of the composition of species of ostracods (beta diversity) within Congo and Amazon River catchments. It appears that local ostracod faunas have adapted to exploit the opportunities presented by the floating invasive Eichhornia, which did not act as “Noah’s Ark” by introducing South American ostracods in the Congo River.     

Mycorrhizal detection of native and non-native truffles in a historic arboretum and the discovery of a new North American species, <Emphasis Type="Italic">Tuber arnoldianum</Emphasis> sp. nov.

During a study comparing the ectomycorrhizal root communities in a native forest with those at the Arnold Arboretum in Massachusetts (USA), the European species Tuber borchii was detected on the roots of a native red oak in the arboretum over two successive years. Since T. borchii is an economically important edible truffle native to Europe, we conducted a search of other roots in the arboretum to determine the extent of colonization. We also wanted to determine whether other non-native Tuber species had been inadvertently introduced into this 140-year-old Arboretum because many trees were imported into the site with intact soil and roots prior to the 1921 USDA ban on these horticultural practices in the USA. While T. borchii was not found on other trees, seven other native and exotic Tuber species were detected. Among the North American Tuber species detected from ectomycorrhizae, we also collected ascomata of a previously unknown species described here as Tuber arnoldianum. This new species was found colonizing both native and non-native tree roots. Other ectomycorrhizal taxa that were detected included basidiomycetes in the genera Amanita, Russula, Tomentella, and ascomycetes belonging to Pachyphlodes, Helvella, Genea, and Trichophaea. We clarify the phylogenetic relationships of each of the Tuber species detected in this study, and we discuss their distribution on both native and non-native host trees.     

Pollinator-mediated impacts of alien invasive plants on the pollination of native plants: the role of spatial scale and distinct behaviour among pollinator guilds

Alien invasive plant species can affect pollination, reproductive success and population dynamics of co-flowering native species via shared pollinators. Consequences may range from reproductive competition to facilitation, but the ecological drivers determining the type and magnitude of such indirect interactions remain poorly understood. Here, we examine the role of the spatial scale of invader presence and spatially contingent behavioural responses of different pollinator groups as potential key drivers, using the invasive Oxalis pes-caprae and the self-incompatible native annual Diplotaxis erucoides as a model system. Three treatments were assigned to native focal plants: (1) invader present at the landscape scale (hectares) but experimentally removed at the floral neighbourhood scale (pa); (2) invader present at both scales (pp); (3) invader absent at both scales (aa). Interestingly, we found pronounced spatially contingent differences in the responses of pollinators: honeybees and bumblebees were strongly attracted into invaded sites at the landscape scale, translating into native plant visitation facilitation through honeybees, while bumblebees almost exclusively visited Oxalis. Non-corbiculate wild bees, in contrast, showed less pronounced responses in foraging behavior, primarily at the floral neighborhood scale. Average heterospecific (Oxalis) pollen deposition onto stigmas of Diplotaxis was low (<1 %), but higher in the pp than in the pa treatment. Hand-pollination of Diplotaxis with Oxalis and conspecific pollen, however, reduced seed set by more than half when compared to hand-pollination with only conspecific pollen. Seed set of Diplotaxis, finally, was increased by 14 % (reproductive facilitation) in the pp treatment, while it was reduced by 27 % (reproductive competition) in the pa treatment compared to uninvaded populations. Our study highlights the crucial role of spatial scale and pollinator guild driving indirect effects of invasive on co-flowering native plant species.     

Biotic resistance and the spatiotemporal distribution of an invading woodwasp, <Emphasis Type="Italic">Sirex noctilio</Emphasis>

Quantifying the strength of interactions among introduced and native species across space and time is critical in understanding biological invasions as they can attenuate or amplify the magnitude of impact. The European woodwasp, Sirex noctilio F., a global threat to pines, is a recent invader to North America. It attacks and kills primarily Pinus resinosa and Pinus sylvestris, and encounters a diverse assemblage of potential competitors for this resource. We quantified spatial colonization patterns of this woodwasp and resident competitors including scolytine bark beetles, woodboring cerambycid and buprestid beetles, and the fungal root rot diseases Armillaria and Heterobasidion across an 80 year old pine plantation over 4 years. All xylophages were spatially aggregated, but only on a localized scale of 15–20 m. Colonizers occurred non-randomly within trees, with S. noctilio negatively or neutrally associated with all other colonizing agents, whereas all other insect and root rot colonizers were mostly positively co-associated. An autologistic regression with spatially-weighted variables indicated the probability of a dead tree exhibiting symptoms of S. noctilio attack was positively associated with tree density, host species (P. sylvestris), and density of S. noctilio-attacked trees from the current and previous year. Interspecific stand patterns were weaker; probability of attack was negatively associated only with root rot pathogens. Across spatial scales, there were mixed (woodborers) and neutral (bark beetles) associations between S. noctilio and other co-colonizing insects. Our results suggest that competitive interactions with resident species may be contributing to the limited success of S. noctilio in North America, but are unlikely to be driving it by themselves.     

Acorns of invasive Northern Red Oak (<Emphasis Type="Italic">Quercus rubra</Emphasis>) in Europe are larval hosts for moths and beetles

In their first phase of expanding into new areas, invasive plants often take advantage of the inability of existing herbivores and pathogenic species to exploit them. However, in the longer term local enemies may adapt to using these invasive species as a food source. This study assesses the use of mature acorns of two oak species in Europe (the native Pedunculate Oak Quercus robur and the invasive Northern Red Oak Quercus rubra) by moths Cydia fagiglandana and Cydia splendana and beetles Curculio spp. We show that acorns of invasive oak species can be equally attractive to C. splendana but only partially so to C. fagiglandana where infestation rates where significantly lower (approximately half) compared to the native oak. The infestation by Curculio beetles of Northern Red Oak was marginal, less than 1% of the rate in the native oak species. The larval final weights did not differ significantly between host species, but emergence of C. splendana and Curculio spp. took significantly longer in acorns of Northern Red Oak. It is likely that C. fagiglandana and C. splendana have increased their niche breadths by exploiting invasive oak species and avoiding competition with the Curculio weevils. Furthermore, the occurrence of Northern Red Oak could stabilize food resources during years when native oak species have poor acorn crops.     

Ant pollination of <Emphasis Type="Italic">Syzygium occidentale</Emphasis>, an endemic tree species of tropical rain forests of the Western Ghats,India

Although mutualism between ants and flowering plants is wide spread, ant pollination has not evolved as a major pollination syndrome. So far ant pollination has been reported largely in herbaceous species, growing in warm and dry habitats. While studying pollination ecology of Syzygium species (Myrtaceae), growing in tropical forests of the Western Ghats, India, we observed one of the ant species, Technomyrmex albipes, to be the dominant floral visitor in S. occidentale (Bourd.) Chithra among a range of other insect (species of Xylocopa and Trigona, and Apis cerana) and bird visitors. We studied the role of ant species in pollination when compared to other floral visitors. The fruit set in flowers exclusively visited by T. albipes was significantly higher than those visited by any other visitor. The day and night exclusive pollination experiments allowing only T. albipes indicated diel pollination by T. albipes, which was the only active flower visitor during the night. The breeding system of the species was studied through controlled pollinations. The species is partially self-compatible and exhibits considerable autogamy.     

Spatial autocorrelation and dispersal in mistletoes: field and simulation results

The infections of two species of mistletoes in Baja California, Mexico were investigated for spatial patterns of abundance, and for an effect of the dispersal patterns of mistletoe seeds on these spatial patterns. Mistletoe distributions were mapped and the dispersal of mistletoe seeds was observed. Most mistletoes seeds were dispersed locally to the parent tree or to nearby trees. While mistletoe distributions were highly clumped at the level of the individual tree, no spatial pattern was found above the scale of the individual tree. Infected trees were no more clumped than the overall host population, and infected trees had no more mistletoes on nearby surrounding trees than did uninfected trees. Trees showed no spatial autocorrelation in the number of mistletoes they supported. Simulations using a spatially explicit simulation model with local dispersal and stochasticity in seed dispersal, host mortality, and mistletoe mortality were used to interpret the field results. Simulation results suggest that dispersal patterns affect the overall level of variance in the number of mistletoes per tree but do not lead to spatial patterns in abundance above the scale of the tree. Thus, both simulation and field systems give the surprising result that local dispersal does not lead to spatial autocorrelation in the numbers of mistletoes per tree.Abbreviations AI = Arroyo Inspiracion - VSR = Valle San Rafael     

Sprouting capacity of <Emphasis Type="Italic">Persea borbonia</Emphasis> and maritime forest community response to simulated laurel wilt disease

There are numerous examples of how exotic insect pests and pathogens have altered the dominance of native tree species. Changes to the structure of associated communities will depend on whether the affected species survives and if so, the degree to which it is diminished. In the southeastern USA, Persea borbonia, a common tree found in many coastal plain habitats, is the primary host of laurel wilt disease (LWD); infection rates and main-stem mortality are catastrophically high (>90%) in invaded populations. We simulated the effects of LWD prior to its arrival in coastal Mississippi by girdling and then removing the main stems of P. borbonia trees. Over a 2-year period, we monitored P. borbonia persistence via basal resprouts, understory light availability, and community structure. Removal of P. borbonia main stems resulted in a 50% increase in light transmission (measured at 1 m above ground level). All treated individuals produced basal resprouts, the size and number of which were positively related to initial tree girth. Post-treatment increases in basal area were greatest for the sub-canopy species, Ilex vomitoria, and were significantly higher in treatment versus control plots. Woody seedlings and herbaceous plants showed no significant trends in composition and abundance over time or between control and treatment plots. Our results suggest that removal of P. borbonia and subsequent resprouting causes shifts in P. borbonia size class frequencies and sub-canopy species dominance but has negligible impacts on understory plant community dynamics.     

Sleeping site ecology,but not sex,affect ecto- and hemoparasite risk,in sympatric,arboreal primates (<Emphasis Type="Italic">Avahi occidentalis</Emphasis> and <Emphasis Type="Italic">Lepilemur edwardsi</Emphasis>)

Background

A central question in evolutionary parasitology is to what extent ecology impacts patterns of parasitism in wild host populations. In this study, we aim to disentangle factors influencing the risk of parasite exposure by exploring the impact of sleeping site ecology on infection with ectoparasites and vector-borne hemoparasites in two sympatric primates endemic to Madagascar. Both species live in the same dry deciduous forest of northwestern Madagascar and cope with the same climatic constraints, they are arboreal, nocturnal, cat-sized and pair-living but differ prominently in sleeping site ecology. The Western woolly lemur (Avahi occidentalis) sleeps on open branches and frequently changes sleeping sites, whereas the Milne-Edward’s sportive lemur (Lepilemur edwardsi) uses tree holes, displaying strong sleeping site fidelity. Sleeping in tree holes should confer protection from mosquito-borne hemoparasites, but should enhance the risk for ectoparasite infestation with mites and nest-adapted ticks. Sex may affect parasite risk in both species comparably, with males bearing a higher risk than females due to an immunosuppressive effect of higher testosterone levels in males or to sex-specific behavior. To explore these hypotheses, ectoparasites and blood samples were collected from 22 individuals of A. occidentalis and 26 individuals of L. edwardsi during the dry and rainy season.

Results

L. edwardsi, but not A. occidentalis, harbored ectoparasites, namely ticks (Haemaphysalis lemuris [Ixodidae], Ornithodoros sp. [Argasidae]) and mites (Aetholaelaps trilyssa, [Laelapidae]), suggesting that sleeping in tree holes promotes infestation with ectoparasites. Interestingly, ectoparasites were found solely in the hot, rainy season with a prevalence of 75% (N = 16 animals). Blood smears were screened for the presence and infection intensity of hemoparasites. Microfilariae were detected in both species. Morphological characteristics suggested that each lemur species harbored two different filarial species. Prevalence of microfilarial infection was significantly lower in L. edwardsi than in A. occidentalis. No significant difference in infection intensity between the two host species, and no effect of season, daytime of sampling or sex on prevalence or infection intensity was found. In neither host species, parasite infection showed an influence on body weight as an indicator for body condition.

Conclusions

Our findings support that sleeping site ecology affects ectoparasite infestation in nocturnal, arboreal mammalian hosts in the tropics, whereas there is no significant effect of host sex. The influence of sleeping site ecology to vector-borne hemoparasite risk is less pronounced. The observed parasite infections did not affect body condition and thus may be of minor importance for shaping reproductive fitness. Findings provide first evidence for the specific relevance of sleeping site ecology on parasitism in arboreal and social mammals. Further, our results increase the sparse knowledge on ecological drivers of primate host-parasite interactions and transmission pathways in natural tropical environments.

     

Truffle diversity (<Emphasis Type="Italic">Tuber</Emphasis>, Tuberaceae) in British Columbia

To improve baseline data for the developing truffle industry in British Columbia, we compiled existing Tuber species sequences from published and unpublished studies and generated new ITS sequences for truffles belonging to Tuber collected in the province. In doing so, we obtained evidence that 13 species of Tuber occur in the province, including six introduced and seven native species, two of which are putative undescribed species. Of the native species, the Tuber anniae species complex is widely distributed in the province while Tuber beyerlei appears to be much more restricted in distribution. Four of the introduced species have commercial value (Tuber melanosporum, Tuber aestivum, Tuber brumale, and Tuber borchii) as do two of the native species (Tuber gibbosum and Tuber oregonense). Focused sampling on likely tree hosts, both hardwood and Pinaceae species, as well as in currently unexplored parts of the province seems likely to expand our knowledge of the diversity and distribution of Tuber species in British Columbia.     

A morel improved growth and suppressed <Emphasis Type="Italic">Fusarium</Emphasis> infection in sweet corn

A post-fire morel collected from Populus simonii stands in Mt. Qingling was identified as Morchella crassipes Mes-20 by using nuclear ribosomal DNA internal transcribed spacer phylogeny. It was inoculated into sweet corn to observe colonized roots in purified culture and in greenhouse experiments. The elongation and maturation zones of sweet corn were remarkably colonized at the cortex intercellular and intracellular cells, vessel cells, and around the Casparian strip, forming ectendomycorrhiza-like structures. Colonization was also observed in the zone of cell division proximal to the root cap. Greenhouse assays with sweet corn showed that this morel stimulated the development of the root system and significantly increased the dry root biomass. M. crassipes also significantly reduced the incidence of Fusarium verticillioides in the kernels of mature ears when inoculated into young ears before Fusarium inoculation and prevented Fusarium infection in corn ears compared with that of the control in the greenhouse. When grown under axenic conditions, M. crassipes produced the phytohormones abscisic acid, indole-3-acetic acid, and salicylic acid. The benefits to plants elicited by M. crassipes may result from these phytohormones which may improve the drought resistance, biomass growth and resistance to Fusarium.     

An Experimental Test of Trade-Offs Associated with the Adaptation to Alternate Host Plants in the Introduced Herbivorous Beetle, <Emphasis Type="Italic">Ophraella communa</Emphasis>

The adaptation to alternate host plants of introduced herbivorous insects can be vital to agriculture due to the emergence of crop pests. Historically, it is assumed that there are trade-offs associated with the adaptation to new host plants; a generalist genotype that adapts to an alternate host is expected to have a relatively lower fitness on the ancestral host than a specialist genotype (physiological cost) or a relatively lower host-searching ability for the ancestral host plant (behavioral cost). In this study, we tested the costs of adaptation to a new host plant in the introduced herbivorous insect, Ophraella communa LeSage (Coleoptera: Chrysomelidae). In its native range (United States), O. communa feeds mostly on Ambrosia artemisiifolia L. (Asterales: Asteraceae) and cannot utilize the related species, Ambrosia trifida L. (Asterales: Asteraceae), as a host plant. On the other hand, the introduced O. communa population in Japan utilizes A. trifida extensively, and is adapting to it, both physiologically and behaviorally. We compared larval performance on the ancestral and alternate plants and adult host-searching ability between the native and introduced beetle populations. The introduced O. communa showed higher larval survival and adult feeding preference for the alternate host plant A. trifida than did the native O. communa, indicating that the introduced O. communa has rapidly adapted to the alternate host plant. However, there are no differences in either larval performance on the ancestral host A. artemisiifolia or host-searching accuracy between the native and introduced O. communa.     

External Reinfection of a Fungal Pathogen Does not Contribute to Pathogen Growth

Chytridiomycosis is an emerging infectious disease of amphibians caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), which has led to devastating declines in amphibian populations worldwide. Current theory predicts that Bd infections are maintained through both reproduction on the host’s skin and reinfection from sources outside of the host. To investigate the importance of external reinfection on pathogen burden, we infected captive-bred individuals of the highly susceptible Panamanian Golden Frog, Atelopus glyphus, and wild-caught glass frogs, Espadarana prosoblepon, with Bd. We housed the animals in one of three treatments: individually, in heterospecific pairs, and in conspecific pairs. For 8 weeks, we measured the Bd load and shedding rate of all frogs. We found that Atelopus had high rates of increase in both Bd load and shedding rate, but pathogen growth rates did not differ among treatments. The infection intensity of Espadarana co-housed with Atelopus was indistinguishable from those housed singly and those in conspecific pairs, despite being exposed to a large external source of Bd zoospores. Our results indicate that Bd load in both species is driven by pathogen replication within an individual, with reinfection from outside the host contributing little to the amplification of host fungal load.     

Effects of alien invasion by <Emphasis Type="Italic">Bombus terrestris</Emphasis> L. (Apidae) on the visitation patterns of native bumblebees in coastal plants in northern Japan

When alien pollinator species enter a native community of pollinators in which resource partitioning has been established, the pollination network between plants and pollinators may be modified through the interactions between the pollinators over the use of floral resources. We observed the floral-use patterns of native (Bombus hypocrita and B. deuteronymus) and alien (B. terrestris) bumblebee species in a coastal grassland in northern Japan. We analyzed the factors determining resource partitioning patterns. B. hypocrita tended to visit flowers with shallow or wide open corollas, such as Rosa rugosa, whereas B. deuteronymus visited flowers with complex or deeper corollas, such as Lathyrus japonicus. Given the wider floral preference of B. terrestris, floral use by the alien bumblebees consistently overlapped with that of native bumblebees. The visitation of B. terrestris to R. rugosa flowers was positively correlated with that of B. hypocrita. These bumblebee species frequently used similar floral resources, in part because of the large overlap in the seasonality of their foraging activity. The visitation frequency of B. deuteronymus to L. japonicus flowers was independent of the visitation frequency of other bumblebee species. The major visitation periods of the bumblebees to L. japonicus flowers reciprocally differed between B. deuteronymus and B. terrestris, suggesting phenological resource partitioning between these species. Our study suggests that phenological niche partitioning is more common in specialized flowers (L. japonicus) than in generalized flowers (R. rugosa).     

Habitat fragmentation provides a competitive advantage to an invasive tree squirrel, <Emphasis Type="Italic">Sciurus carolinensis</Emphasis>

Changes in the composition of biological communities can be elicited by competitive exclusion, wherein a species is excluded from viable habitat by a superior competitor. Yet less is known about the role of environmental change in facilitating or mitigating exclusion in the context of invasive species. In these situations, decline in a native species can be due to the effects of habitat change, or due to direct effects from invasive species themselves. This is summarized by the “driver-passenger” concept of native species loss. We present a multi-year study of tree squirrels that tested the hypothesis that tree canopy fragmentation, often a result of human development, influenced the replacement of native western gray tree squirrels (Sciurus griseus) by non-native eastern gray tree squirrels (Sciurus carolinensis). We tested this hypothesis along a continuum of invasion across three study sites in central California. We found that within the developed areas of the University of California at Santa Cruz campus and city of Santa Cruz, S. carolinensis excluded S. griseus from viable habitat. The competitive advantage of S. carolinensis may be due to morphological and/or behavioral adaptation to terrestrial life in fragmented hardwood forests. We classify S. carolinensis as a “driver” of the decline of native S. griseus in areas with high tree canopy fragmentation. Future habitat fragmentation in western North America may result in similar invasion dynamics between these species. Our study warrants consideration of existing and predicted interactions between potentially invasive species that co-occur with native species where land use change is proposed.     

Differences in interactions of aboveground and belowground herbivores on the invasive plant <Emphasis Type="Italic">Alternanthera philoxeroides</Emphasis> and native host <Emphasis Type="Italic">A. sessilis</Emphasis>

Plant invasions may result in novel plant-herbivore interactions. However, we know little about whether and how invasive plants can mediate native above- and belowground herbivore interactions. In this study, we conducted greenhouse experiments to examine the interaction between a native defoliating beetle, Cassida piperata, and a native root-knot nematode, Meloidogyne incognita, on the invasive alligator weed, Alternanthera philoxeroides. We also included their native host A. sessilis in the experiments to examine whether the patterns of above- and belowground herbivore interaction vary with host plants (invasive vs. native). We analyzed total carbon and nitrogen in leaves and roots attacked by M. incognita and C. piperata. M. incognita slightly negatively affected feeding by C. piperata on A. philoxeroides, and the leaf area damaged decreased as the number of M. incognita increased. M. incognita had a negative impact on total leaf nitrogen, but had no impact on total leaf carbon. M. incognita egg production on A. philoxeroides roots decreased as the amount of damage caused by C. piperata increased. Herbivory by C. piperata did not affect total root carbon or nitrogen. M. incognita and C. piperata did not affect each other on the native plant A. sessilis. These results suggest that invasive plants can mediate native above- and belowground herbivore interactions. The knowledge of how invasive plants affect those interactions is crucial for better understanding the impacts of biological invasions on native above- and belowground organisms.     

Reproductive interference between two serious pests,oriental fruit flies <Emphasis Type="Italic">Bactrocera carambolae</Emphasis> and <Emphasis Type="Italic">B. dorsalis</Emphasis> (Diptera: Tephritidae), with very wide but partially overlapping host ranges

Bactrocera carambolae and B. dorsalis (Diptera: Tephritidae) are extremely destructive pests of fruits and vegetables in the Asia-Pacific region. Earlier reports have described that B. carambolae and B. dorsalis, respectively, use mainly star fruit and mango, suggesting a certain level of host partitioning which can be ascribed neither to differences in larval food qualities nor host-specific parasitoid mortality. This study specifically examined reproductive interference (antagonistic sexual interaction) between B. carambolae and B. dorsalis as a potential factor strongly affecting their host partitioning. We observed mating behaviors, especially interspecific courtships and mating, by cohabiting the conspecific and heterospecific pairs together. Consequently, we quantified their effects on the reproductive success of females. Males of both species frequently courted their own females, but they also courted females of other species. Courtship refusal by females was not selective in males of either species. This incomplete discrimination of both sexes led to frequent occurrences of interspecific sexual interactions in both species, but only B. carambolae females showed reduced reproductive success. These results suggest that B. dorsalis, superior in reproductive interference, can occupy high-quality mango, whereas B. carambolae, inferior in reproductive interference, must use low-quality star fruit.