Seasonal and habitat variations in diet of the invasive driftwood catfish Trachelyopterus galeatus in a Neotropical river basin,Brazil

The characteristics of successful invaders often include generalist traits that enable adaptation to new environments through plastic responses, including their diet. The use of trophic resources of invasive driftwood catfish Trachelyopterus galeatus of the Upper Paraná River basin, Brazil, were studied with diet analysis and stable isotopic niche metrics based on δ¹⁵N and δ¹³C to test differences between a free-from-dam and damming population, and between wet and dry season. Stomach content analyses revealed significant differences between the populations. The diet of the riverine free-flowing river population was macroinvertebrate dominated, with Coleoptera and Lepidoptera prominent. In the damming population, diet was largely plant based, although Coleoptera was also prominent. Trophic niche breadth comparisons revealed a larger niche in the free-from-dam population versus the damming population that was independent of season. In both sites had dietary differences between the wet and dry season according to stomach contents analyses, although these were less prominent according to stable isotope metrics. Therefore, the diet of this invader is relatively general and plastic, enabling their exploitation of the varying availability of food resources between free-from-dam and damming river sections, and between wet and dry season.     

Life history and host specificity ofAltica cyanea [Coleoptera: Chrysomelidae], a potential biological control agent for water primrose,Ludwigia adscendens

The life history and host-specificity of the flea beetle,Altica cyanea (Weber) [Coleoptera: Chrysomelidae], were studied to determine its potential value as a biological control agent for water primrose,Ludwigia adscendens (Onagraceae). Females laid a mean of 146 yellowish eggs in masses on this weed and larvae passed through 3 instars. This multivoltine insect completed a generation in 80–84 days. In preliminary host-specificity trials, larvae and adults fed slightly on 2 varieties ofTrapanatans, but they caused considerable damage toLudwigia spp.; no feeding occurred on rice. In host plant choice tests, larvae and adults preferred to feed onL. adscendens andL. prostata toT. natans. In these same tests, onlyLudwigia spp. supported complete development, but it was fastest onL. adscendens. Adults that were reared onL. adscendens lived longer and laid more eggs than those reared onL. prostata, suggesting thatA. cyanea may be a promising biological control agent forL. adscendens growing in rice-paddies. AdultZicrona coerulea L. [Hemiptera: Pentatomidae] preyed upon 3rd instarA. cyanea larvae in the laboratory.      

Ecological host-range of Lilioceris cheni (Coleoptera: Chrysomelidae), a biological control agent of Dioscorea bulbifera

Open-field host-specificity testing assesses the host-range of a biological control agent in a setting that permits the agent to use its full complement of host-seeking behaviors. This form of testing, particularly when it includes a no-choice phase in which the target weed is killed, may provide the most accurate assessment of the ecological host-range of an agent. We conducted a two-phase field host-specificity test with experienced and naïve adults of Lilioceris cheni Gressitt and Kimoto (Coleoptera: Chrysomelidae), a biological control agent of Dioscorea bulbifera L. (Dioscoreales: Dioscoreaceae). We followed field tests with a no-choice laboratory consumption study with the congeneric plant species that received test feeding in the field, and an additional field evaluation of spillover risk. Both experienced and naïve adults strongly preferred D. bulbifera to non-targets in the field. Within 47 h post-release, 90% of the released beetles that remained in the plots were found on D. bulbifera. In the laboratory no-choice test, the beetles consumed significantly more D. bulbifera and survived longer on this plant than the non-targets. All naïve beetles in the Dioscorea sansibarensis and Dioscorea villosa treatments and 75% of naïve beetles on Dioscorea floridana died within 7 d. Potted plants of the native D. floridana experienced minor test feeding in the spillover experiment when surrounded by large populations of L. cheni in the field. At the end of this experiment, L. cheni eggs and/or larvae were present on 83% of D. bulbifera plants but none of the D. floridana plants. We conclude that L. cheni is host-specific to D. bulbifera and does not pose a spillover risk to the native D. floridana.     

Thermal biology of Typhlodromips montdorensis: implications for its introduction as a glasshouse biological control agent in the UK

The recent unexpected local establishment of a non‐native predatory mite, Neoseiulus californicus (McGregor) (Acari: Phytoseiidae), in the UK prompted us to undertake this study, which investigated the thermal biology of an alien species Typhlodromips montdorensis (Schicha) (Acari: Phytoseiidae). Laboratory and field experiments on its cold tolerance were used to assess its establishment potential outside of glasshouse environments in the UK. Currently, T. montdorensis is being tested as a glasshouse biological control agent against thrips and spider mites, but is not yet licensed for release in the UK. Typhlodromips montdorensis has a developmental threshold of between 10.3 and 10.7 °C, and a thermal budget of between 108.7 and 105.3 degree‐days when estimated by weighted and simple linear regression, respectively. Under outdoor conditions, T. montdorensis could theoretically complete up to six generations a year. The supercooling points of female and larval T. montdorensis were ?22 to ?24 °C with 100% pre‐freeze mortality apparent in both acute and chronic low temperature exposures. Typhlodromips montdorensis were unable to enter diapause under a selected laboratory regime. No reproduction occurred in the field from November to March, with 100% mortality within 7–14 days of release during this period. It is concluded that T. montdorensis would be a ‘safe candidate’ for introduction as a glasshouse biological control agent in the UK.     

The potential for using red claw crayfish and hybrid African catfish as biological control agents for Schistosoma host snails

The potential of red claw crayfish and hybrid African catfish (Clarias gariepinus and Clarias ngamensis) as predators for Schistosoma host snails was evaluated in 2014 by monitoring the consumption of snails by crayfish and catfish in experimental tanks over time under laboratory conditions. After 15 days, both crayfish and catfish had significantly reduced the populations of Bulinus globosus. Crayfish consumed 6.9 snails d^?1, whereas catfish consumed 5.9 snails d^?1. However, when supplied with an alternative prey, Melanoides tuberculata (100 individuals per tank), crayfish clearly preferred M. tuberculata (100% consumed over seven days) to B. globosus (100 individuals per tank) (54% consumed over the same period). Catfish, conversely, did not have a clear preference for either prey species, consuming 77% and 88% of M. tuberculata and B. globosus, respectively. It was also observed that young catfish were more efficient predators than older ones, because of ontogenetic shifts in their diet with age. Hybrid catfish retain the molluscivorous characteristics of their parent stock and red claw crayfish also preys on Schistosoma host snails. However, the effectiveness of both predators is affected by the presence of an alternative prey. Therefore, under suitable conditions, these species can be considered for biological control of schistosomiasis transmission.     

Weed biological control: applying science to solve seemingly intractable problems

Abstract   Exotic weeds pose a problem of considerable economic and environmental importance to Australia. As a consequence, Australia has developed into a leading centre of research on weed biological control, with over 60 weeds the targets of past and current projects. Using primarily entomological examples, this review highlights the contributions made by Australian scientists to the development of theory and the improvement of practice in weed biological control. It also shows how biological control practitioners have made use of, and contributed to, broader theory and knowledge of plant-herbivore relationships. Finally, it concludes with some reflections on the future direction of biological control in Australia.     

外来种对生物多样性的影响及其控制

外来种是那些借助自身力量或其它外界力量传播到其未曾分布过的地域 ,并且能进行繁殖传播的生物。外来种入侵已成为一种引人关注的现象。外来种通过竞争、捕食、牧食、改变生境和传播疾病等方式对本地生物产生威胁 ,影响本地生物多样性。外来种入侵成了生物多样性丧失的两个主要影响之一 (另一影响是生境的破坏 )。因此 ,探寻阻止或减少外来种入侵的方法很有必要。目前 ,人们运用机械法、化学法和生物控制法来控制外来种。在外来种入侵的初始阶段或外来种数量不多时 ,运用机械法较好。化学法有带来新环境污染的危险。生物控制法是应用天敌来防治或消灭有害生物。在外来种的控制上 ,生物控制法有一些成功的案例 ,但它并不是万能的。有些生物控制剂可能对非目标种产生影响 ,这要求在释放前对生物控制剂作更严格的检测。     

Freshwater snails of Oman,South Eastern Arabia

A systematic account is given of the extant freshwater snail fauna of Oman, based on recent collections made in Dhofar and in the northern mountainous areas. Also included are certain species found in brackish coastal localities. A total of 8 freshwater species is regarded as belonging to the fauna of normal freshwater; 7 have been found alive (Thiara scabra, Melanoides tuberculata, Lymnaea natalensis, Gyraulus piscinarum, Biomphalaria arabica, Bulinus wrighti and Indoplanorbis exustus) and one is known only as shells (Paludestrina glaucovirens). This report of G. piscinarum is the first for Oman and may be the first reliable identification for Arabia. Three taxa from brackish water, Gangetia miliacea, Iravadia quadrasi and Melanoides sp., are new for the fauna of Oman and of the whole Arabian peninsula. The finding of G. miliacea provides the first instance of any member of the Stenothyridae living west of the Gulf of Oman and identified from whole snails rather than empty shells. I. quadrasi is the first member of its genus to be found alive west of the Gulf of Oman.     

Host-plant affinities of two biotypes of Dactylopius opuntiae (Homoptera: Dactylopiidae): enhanced prospects for biological control of Opuntia stricta (Cactaceae) in South Africa

1. Until recently, neither the phycitid moth Cactoblastis cactorum nor the cochineal insect Dactylopius opuntiae have been satisfactory biological control agents of Opuntia stricta in South Africa.
2. In marked contrast, both of these agents have kept O. stricta under biological control for many decades in Australia.
3. In an attempt to improve the situation in South Africa, a stock of D. opuntiae was obtained from O. stricta in Australia during 1996.
4. Host-specificity tests confirmed that the newly imported D. opuntiae from Australia is a different biotype to the one already established in South Africa.
5. The Australian ('stricta') biotype thrives on O. stricta but is unable to develop satisfactorily on O. ficus-indica , while the converse is true for the South African ('ficus') biotype, which thrives on O. ficus-indica but fares poorly on O. stricta .
6. The integrity of the host-plant specificity of the two biotypes of D. opuntiae has important implications for biological control of Cactaceae in South Africa, and has greatly enhanced prospects that O. stricta can be brought under biological control successfully.     

Biological control and the species status of two host-associated populations of Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae).

Abstract Populations of the morphologically defined taxon Trissolcus basalis (Wollaston) from two major hosts (Nezara viridula [L.] and Agonoscelis rutila [F.]) were tested, using biological criteria, to determine whether they represented populations of one genetical species, or whether they represented populations of two host-associated sibling species. Individuals from both hosts exhibited no obvious courtship differences and they selected mates at random in mate-choice experiments. In addition, female wasps produced offspring of both sexes after mating with a male from either population. We conclude that the individuals of the two populations tested constitute a single genetical species.     

No Genetic Evidence for Hybridization Between Rio Grande Sucker, Catostomus Plebeius, and the Introduced White Sucker, Catostomus Commersoni, in the Rio Grande

Hybridization with the introduced white sucker, Catostomus commerson, has been blamed in part for the decline of the Rio Grande sucker, C. plebeius, in the upper Rio Grande basin of Colorado and New Mexico but without convincing evidence. Here we report results from a genetic study of hybridization between the two species across their sympatric range in New Mexico. We used two nuclear microsatellite markers and one mitochondrial DNA marker to identify hybrids. These genetic methods detected no F1 or backcross hybrids in larvae, young-of-the-year or adults from the upper Rio Grande basin. This indicates that hybridization between the two species occurs rarely, if ever.     

Aquatic snails of the Jonglei region,southern Sudan,and transmission of trematode parasites

An account is given of the aquatic gastropod molluscs obtained in a survey made to assess future ecological effects of the Jonglei Canal now under construction in the Sudd region of southern Sudan. A total of about 23 species of aquatic snail lives in this region, of which a number are utilised as intermediate hosts by trematode parasites infecting man, livestock and wild herbivores, causing the diseases schistosomiasis, fascioliasis and amphistomiasis. Public health and veterinary authorities should be alert to the possibility that the Jonglei Canal will increase snail populations and raise the prevalence of parasitic diseases.Jonglei Range Ecology Survey.     

Founding events in species invasions: genetic variation, adaptive evolution, and the role of multiple introductions

Invasive species are predicted to suffer from reductions in genetic diversity during founding events, reducing adaptive potential. Integrating evidence from two literature reviews and two case studies, we address the following questions: How much genetic diversity is lost in invasions? Do multiple introductions ameliorate this loss? Is there evidence for loss of diversity in quantitative traits? Do invaders that have experienced strong bottlenecks show adaptive evolution? How do multiple introductions influence adaptation on a landscape scale? We reviewed studies of 80 species of animals, plants, and fungi that quantified nuclear molecular diversity within introduced and source populations. Overall, there were significant losses of both allelic richness and heterozygosity in introduced populations, and large gains in diversity were rare. Evidence for multiple introductions was associated with increased diversity, and allelic variation appeared to increase over long timescales (~100 years), suggesting a role for gene flow in augmenting diversity over the long‐term. We then reviewed the literature on quantitative trait diversity and found that broad‐sense variation rarely declines in introductions, but direct comparisons of additive variance were lacking. Our studies of Hypericum canariense invasions illustrate how populations with diminished diversity may still evolve rapidly. Given the prevalence of genetic bottlenecks in successful invading populations and the potential for adaptive evolution in quantitative traits, we suggest that the disadvantages associated with founding events may have been overstated. However, our work on the successful invader Verbascum thapsus illustrates how multiple introductions may take time to commingle, instead persisting as a ‘mosaic of maladaptation’ where traits are not distributed in a pattern consistent with adaptation. We conclude that management limiting gene flow among introduced populations may reduce adaptive potential but is unlikely to prevent expansion or the evolution of novel invasive behaviour.     

Influence of settlement time, human population, park shape and age, visitation and roads on the number of alien plant species in protected areas in the USA

Abstract. I examined a data set of 77 protected areas in the USA (including national and state parks) to determine which of the following variables most strongly influence alien plant species richness: park area, climate (temperature and precipitation), native species richness, visitation rate, local human population size, total road length, park shape and duration of European settlement. Many of these predictor variables are intercorrelated, so I used multiple regression to help separate their effects. In support of previous studies, native species richness was the best single predictor of alien species richness, probably because it was a good estimator of both park area and habitat diversity available for establishment of alien species. Other significant predictors of alien species richness were years of occupation of the area by European settlers and the human population size of adjacent counties. Climate, visitation rate, road length and park shape did not influence alien species richness. The proportion of alien species (alien richness/native richness) is inversely related to park area, in agreement with a previous study. By identifying which variables are most important in determining alien species richness, such findings suggest ways to reduce alien species establishment.     

Complex interactions among fish, snails and macrophytes: implications for biological control of an invasive snail

The golden apple snail (Pomacea canaliculata), a native of freshwater wetlands of South America, has invaded many Asian countries and grazed heavily in agricultural and wild areas. Common carp (Cyprinus carpio) has been proposed as a biological control agent against this snail, but little is known about its impact on non-target aquatic plants and animals. In a 8-week enclosure experiment, we quantified the impact of common carp on three species of aquatic macrophytes and nine species of snails, including the apple snail, in a shallow pond. The results showed that the apple snail or carp alone significantly reduced the plant biomass, although the apple snail had a stronger overall herbivorous effect than the carp. The carp completely removed juvenile apple snails, but had only a weak predatory effect on larger apple snails and no effect on the adults’ oviposition frequency. Furthermore, the carp significantly reduced the populations of most species of other snails that occurred naturally in the pond. Our results thus indicate that common carp can be an effective biological control agent against the invasive apple snail, but caution should be taken about its potential to reduce wetland floral and faunal diversity.     

Food selection by freshwater snails in the Gezira irrigation canals,Sudan

Stomach content analysis was carried out on samples of the freshwater snail species Biomphalaria pfeifferi, Bulinus truncatus, Bulinus forskalii (Pulmonata, Planorbidae), Lymnaea natalensis (Pulmonata, Lymnaeidae), Melanoides tuberculata, Cleopatra bulimoides (Prosobranchia, Thiaridae) and Lanistes carinatus (Prosobranchia, Ampullariidae) from different irrigation canals in Sudan. In order to evaluate overlap in diet selection among these species, sites with two or more of the above-mentioned species present were selected. For some species food choice was examined in relation to size groupings. In addition, samples of Marisa cornuarietis (Prosobranchia, Ampullariidae) from small ponds in Sudan, samples of Biomphalaria pfeifferi and Helisoma duryi (Pulmonata, Planorbidae) from drainage canals in an irrigation scheme in northern Tanzania, and samples of H. duryi from fish ponds in the coastal area of Kenya were also analysed. The results indicate a great similarity in the food choice of these species, especially among the pulmonate species. All species feed on fine detritus, epiphytic algae and decaying macrophytes. No fresh fragments of aquatic macrophytes were found and animal remains were found only on a few occasions. However, the stomach contents of the ampullarid species were characterized by large fragments of dead macrophyte tissue, while the composition of the finer particles showed a great resemblance to that of the pulmonate species. The diet of the thiarid species is essentially the same as that of the pulmonate species, although in one site Cleopatra bulimoides showed a greater preference for green algae. Apart from the avoidance of blue-green algae, there was little evidence of selection of certain algal components of the Aufwuchs for the pulmonate species. Detritus constitutes the major component of the stomach content of all these snail species.     

Hydroperiod,predators and the distribution of physid snails across the freshwater habitat gradient

1. Studies of species distributions across environmental gradients further our understanding of mechanisms regulating species diversity at the landscape scale. For some freshwater taxa the habitat gradient from small, shallow and temporary ponds to large, deep and permanent lakes has been shown to be an important environmental axis. Freshwater snails are key players in freshwater ecosystems, but there are no comprehensive studies of their distributions across the entire freshwater habitat gradient. Here we test the hypothesis that snail species in the family Physidae are distributed in a non‐random manner across the habitat gradient. We sampled the snails, their predators and the abiotic environment of 61 ponds and lakes, spanning a wide range in depth and hydroperiod. 2. Temporary habitats had the lowest biomass of predators. Shallow permanent ponds had the highest biomass of invertebrate predators but an intermediate fish biomass. Deep ponds and lakes had the highest fish biomass and intermediate invertebrate biomass. Five species of physids occurred in the regional species pool and 60 of the 61 ponds and lakes surveyed contained physid snails. Each pond and lake contained an average of just 1.2 physid species, illustrating limited membership in local communities and substantial among‐site heterogeneity in species composition. 3. Physids showed strong sorting along the habitat gradient, with Physa vernalis found in the shortest hydroperiod ponds and Aplexa elongata, P. gyrina, P. acuta and P. ancillaria found in habitats of successively greater permanence. When organised into a site‐by‐species incidence matrix with sites ordered according to their hydroperiods, we found the pattern of incidence to be highly coherent, showing that much of the heterogeneity in species composition from one pond to another is explained by hydroperiod. We also found that the number of species replacements along this gradient was higher than random, showing that replacement is more important than nesting in describing species composition in ponds of different hydroperiod. 4. Discriminant analysis showed that pond depth, invertebrate biomass and fish biomass were the best predictors of species composition. Analysis of these niche dimensions showed that P. vernalis and A. elongata were most successful in shallow, temporary ponds with few predators. P. gyrina and P. acuta were typically found in ponds of intermediate depth and high predator abundance. P. ancillaria was found in the deepest lakes, which had abundant fish predators but few invertebrate predators. Of the five species considered, P. ancillaria, P. vernalis and A. elongata were relatively specialised with regard to key habitat characteristics, P. gyrina was moderately generalised and P. acuta was remarkably generalised, since it alone occurred across the entire freshwater habitat gradient. The exceptional habitat breadth of P. acuta stands in contrast to distributional studies of other freshwater taxa and deserves further attention.