Prey discrimination by a generalist coccinellid predator: effect of prey age or parasitism?

1. Patterns of prey discrimination by the generalist predatory coccinellid Coleomegilla maculata lengi Timb. (Coleoptera: Coccinellidae) were studied in relation to prey quality, under laboratory conditions. 2. Choice experiments were performed in which second‐ and fourth‐instar coccinellids had the choice between Trichoplusia ni (Lepidoptera: Noctuidae) eggs that were young or old, unparasitised or parasitised by Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae). 3. Coleomegilla maculata larvae did not exhibit any preference for parasitised or unparasitised eggs at a similar stage of development but always preferred younger eggs, regardless of whether or not they were parasitised. Furthermore, the percentage of rejection was higher and handling time longer on the less preferred egg type. Pre‐imaginal development time, food intake to reach adulthood, and survival of coccinellid immatures were altered when coccinellid larvae were fed with parasitised and old unparasitised eggs. 4. These results indicate that C. maculata larvae select eggs based on their stage of development regardless of parasitism, and that prey quality of aged prey is lower. 5. Fourth‐instar coccinellid larvae spent less time in patches containing solely parasitised old eggs, and their level of exploitation was greatly reduced, compared with homogeneous patches containing unparasitised young eggs. This suggests that C. maculata larvae respond to variable patch quality by using flexible decision rules that reflect the payoff of the patch.     

Can Developmental and Behavioral Characteristics of the Multicolored Asian Lady Beetle Harmonia Axyridis Explain its Invasive Success?

Major impacts of biological invasions are widely recognized and underscore the need to understand the relation between life-history traits of invasive species and the invasion process. Growth of juveniles and adult survival of invasive species are key factors in invasion process. Life-history traits that increase juvenile fitness including increased rates of development and behavioral characteristics that facilitate competitive success such as increased predator efficiency and foraging ability may explain invasiveness of a species. Invasion of Harmonia axyridis Pallas (Coleoptera: Coccinellidae) in North America provides an opportunity to investigate life-history traits of juveniles of an invasive species. Here, we evaluate both developmental and behavioral traits that may explain the success of H. axyridis by comparing it to an ecologically similar indigenous species Coleomegilla maculata lengi Timberlake (Coleoptera: Coccinellidae). Three points may contribute to the invasiveness of H. axyridis. First, development of H. axyridis was faster during the 2nd larval instar than C. maculata, a characteristic that may reduce vulnerability at young instars. Second, H. axyridis reached the 4th instar more rapidly than C. maculata. The 4th instar of H. axyridis was also characterized by higher predation efficiency with increased voracity, lethal contact and search efficiency of pea aphids Acyrthosiphon pisum. Finally, surprisingly, a 5th larval instar occured in 33% of the individuals of H. axyridis and was characterized by the same developmental time, but with increased voracity and weight gain compared to 4th larval instars, suggesting an increased fitness of these individuals. These developmental characteristics coupled with increased predation efficiency and behavioral characteristics enhanced the juvenile growth and predatory abilities of this species and may contribute to the invasive ability of H. axyridis.     

The influence of prey behaviour on prey selection of the carnivorous plant Utricularia vulgaris

The mechanisms underlying differential prey selection of two microcrustaceans by the common bladderwort (Utricularia vulgaris) were studied in the laboratory. Functional response experiments with single prey showed that Utricularia had a higher attack rate coefficient and a longer handling time coefficient with the cladoceran Polyphemus pediculus than with the cyclopoid copepod Eucyclops serrulatus. Observation of predation rate, defined as number of prey eaten per unit time, from direct behavioural observation on single prey species, showed a higher predation rate with Polyphemus than on Eucyclops, at low prey densities. The opposite pattern was found at high prey density. When the two prey were presented simultaneously to the predator, Eucyclops was preferred over Polyphemus. Results from the situation with two prey and some of the results from the direct behavioural observations support field data on the diet of Utricularia, which shows that cyclopoid copepods are selected more frequently than Polyphemus.     

Soybean Aphid Predators in Québec and the Suitability of Aphis glycines as Prey for Three Coccinellidae

Since its invasion of North America in 2000, the soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae) has notably changed the arthropod community of the soybean agroecosystem. The objectives of this study were to characterize the foliar predatory fauna associated with A. glycines in commercial soybean fields in Québec, Canada, and to evaluate the suitability of A. glycines as prey for three coccinellid species: Harmonia axyridis Pallas, Propylea quatuordecimpunctata L. and Coleomegilla maculata lengi Timberlake (Coleoptera: Coccinellidae). Field surveys showed that several predators responded rapidly to expanding and increasing populations of the soybean aphid. Coccinellidae were the most important aphidophagous predators observed in 2002 (58.6%) and 2003 (44.8%), with mainly four native and naturalized species co-occurring with the soybean aphid throughout the growing season. Measurement of fitness parameters under laboratory conditions (survival, development time, longevity, fecundity) indicated that A. glycines is an excellent prey for the development and reproduction of all three of the coccinellid species studied. The intrinsic rate of natural increase (r_m) was highest for H. axyridis (0.238 d⁻¹), intermediate for P. quatuordecimpunctata (0.215 d⁻¹) and lowest for C. maculata (0.134 d⁻¹).     

Predation pressure on an imperfect Batesian micicry complex in the presence of alternative prey

Summary Differential predation pressure and the probability of predation on a Batesian mimicry complex and on alternative prey were estimatedin a field experiment. The mimicry complex was composed of a noxious model (Eleodes obscura (Say)) and a palatable mimic (Stenomorpha marginata (LeConte)). House crickets (Acheta domesticus) (Linn.) were used as alternative prey. The experiment was conducted for 23 nights in August and September to approximate the peak seasonal activity time period during which both models and mimics normally are exposed to predation while foraging and depositing eggs. Each night thirty prey in ratios of 16 models: 7 mimics: 7 crickets were exposed for 2.5 h to a suite of predators consisting of pallid bats (Antrozous pallidus), striped skunks (Mephitis mephitis) and ringtails (Bassariscus astutus) that had free access to the prey. The model-mimic ratio was similar to that found in nature. Predators obtained prey on 11 of the 23 nights and preferred the alternative prey (crickets) in proportions higher than was expected from a predation rate that was equal on all species of prey. Mimics were taken by predators at a rate proportional to their abundance, while models were taken at a rate considerably lower than their relative abundance. This suggests that at least some of the predators could distinguish between models and mimics and were willing to eat the mimics at higher frequencies than they were willing to eat the models. However, although the mimicry is not perfect with respect to the entire predator suite, the mimics still gain an advantage by resembling the models, compared to the predation levels on the alternate prey.     

Prey‐mediated changes in the selectivity of the predator Macrolophus pygmaeus (Heteroptera: Miridae)

When foraging in communities with mixed prey, generalist predators may be confronted with prey species that differ in quality, size and mobility and interact with one another. To examine prey selection, predation by Macrolophus pygmaeus (Heteroptera: Miridae) was recorded by providing a diet of either one or two prey species of Myzus persicae (third‐instar nymphs), Aphis gossypii (fourth‐instar nymphs), Trialeurodes vaporariorum (third‐instar nymphs) and Ephestia kuehniella (eggs). In the experiments, prey mobility, prey quality and prey biomass were considered. The biomass consumed by the predator was dependent on the combination of prey species and the quantity of biomass offered. In choice experiments with diets mixed of two prey species at equal densities, the predation to A. gossypii was significantly reduced in the presence of E. kuehniella but the rate of consumption of M. persicae, T. vaporariorum and E.kuehniella was not significantly affected by the coexistence of any other species in the mixed prey diet. When equal amounts of biomass from two prey species were provided in combination, the total consumed biomass was significantly reduced in the mixed prey diets composed of E. kuehniella eggs and aphid nymphs. Thus, under the mixed‐prey situation, prey selection by predators may be affected by interactions among prey species differing in traits such as quality, mobility and size.     

Preference and consumption of Macrolophus pygmaeus preying on mixed instar assemblages of Myzus persicae

This study examines the effects of changes in the prey frequency and abundance on prey selection among the four instars of Myzus persicae by the predator Macrolophus pygmaeus under laboratory conditions. The central hypothesis was that M. pygmaeus will become more selective as prey density increases. It was also observed that M. pygmaeus can occasionally abandon a prey item that had already been killed (non-consumptive prey mortality). It was assumed that the frequency of this behavior would increase with the prey size and prey density. For these purposes prey selection was evaluated by simultaneously presenting all instars of M. persicae to the predator in equal proportions and at increasing densities. M. pygmaeus showed a higher predation rate and a higher preference for smaller prey instars at all prey densities. However, if the predation rate by the predator is expressed in terms of biomass consumed, then biomass gain was higher when feeding on the larger instars of M. persicae. The prey selectivity was indicated by the total prey mortality (consumptive plus non-consumptive prey mortality) as well as by the non-consumptive prey mortality, was associated with relatively high prey densities, depending on the prey instar. Therefore, we argued that the predatory impact of M. pygmaeus on the various instars of the aphid depends not only on prey traits but also on their relative abundance in a patch. Observed decreases in biomass gain from larger prey were likely the result of high prey availability at densities before saturation, which might have caused confusion in the predator’s prey selection.     

Development of an immunological technique for identifying multiple predator–prey interactions in a complex arthropod assemblage

A simplified but highly effective approach for the post‐mortem evaluation of predation on several targeted members of an arthropod assemblage that does not require the development of pest‐specific enzyme‐linked immunosorbent assay (ELISA) (e.g. pest‐specific monoclonal antibodies) or PCR assays (DNA primers) is described. Laboratory feeding studies were conducted to determine if predation events could be detected from predators that consumed prey marked with foreign protein. I determined that large and small rabbit immunoglobulin G (IgG)‐marked prey can be detected by a rabbit‐IgG‐specific ELISA in the guts of chewing and piercing–sucking type predators. I then conducted multifaceted inclusion and exclusion field cage studies to qualify the degree of interguild and intraguild predation occurring among a complex arthropod assemblage during four separate light phase treatments. The field cages contained an arthropod assemblage consisting of 11 or 12 species of predaceous arthropods and three pest species. The three pests introduced into the cages included third instar Trichoplusia ni marked with rabbit IgG, third instar Lygus hesperus marked with chicken IgG and Pectinophora gossypiella sentinel egg masses. The inclusion cages allowed foraging fire ants, Solenopis xyloni, to freely enter the cages while the exclusion cages contained barriers that prevented ant entry. The results obtained using the conventional inclusion/exclusion field cage methodology revealed that there was substantial interguild and intraguild predation occurring on the majority of the arthropods in the assemblage, particularly in those cages that included ants. I then precisely identified which predators in the assemblage were feeding on the three targeted pests by conducting three post‐mortem gut content analyses on each individual predator (1503 individuals) in the assemblage. Specifically, P. gossypiella egg predation events were detected using an established P. gossypiella‐egg‐specific ELISA, and third instar T. ni and L. hesperus predation events were detected using rabbit‐IgG‐specific and chicken‐IgG‐specific ELISAs, respectively. Generally, the gut ELISAs revealed that Collops vittatus, Spanagonicus albofasciatus and Geocoris punctipes readily preyed on P. gossypiella eggs; Nabis alternatus, Zelus renardii and spiders (primarily Misumenops celer) readily preyed on marked L. hesperus nymphs, and spiders, S. albofasciatus and N. alternatus readily preyed on T. ni larvae. Furthermore, the cage methods and the post‐mortem predator gut ELISAs revealed very few distinctive patterns of predation with regard to the light cycle the assemblage was exposed to.     

Density-dependent predation ofChaoborus flavicans onDaphnia longispina in a small lake: the effect of prey size

Functional response curves of fourth instar larvae ofChaoborus flavicans preying on two size classes ofDaphnia longispina were examined throughout three summer seasons in a small forest lake. Data for each size class were fitted to Holling's disc equation. The parametersa (attack rate) andTh (handling time) were calculated for each prey size from these curves. Attack rate was greater and handling time was shorter for small (0.77 mm) than for large (1.82 mm)Daphnia. In 1:1 mixture of these prey size classes the predation rates ofChaoborus on smallDaphnia at prey densities above 20 l^–1 were greater than predicted from the single size-class experiments. The observed predation rates on largeDaphnia were lower than predicted at all prey densities. Since both single size-class and two size-class experiments were run during the same period of time the difference in observed and predicted predation rates could not be attributed to seasonal changes in prey preference ofChaoborus larvae. In experiments with a concentrated mixture of lake zooplankton (dominated byD. longispina)Chaoborus preference forDaphnia decreased as prey body size increased. There was no obvious correlation between selectivity coefficients and size-frequency distributions ofDaphnia. When medium-sizedDaphnia were omitted from calculations the preference of small over large prey did not differ significantly from the predictions of the single size-class model.     

Learning affects prey selection in larvae of a generalist coccinellid predator

Under natural conditions, generalist predatory insects have to cope with a variety of potential prey species that are not all equally suitable. Under these circumstances, learning may be adaptive if it allows adjustment to variations in resource quality and availability. Under laboratory conditions, we examined the learning ability and memory in the prey selection process of larvae of the predatory coccinellid Coleomegilla maculata ssp. lengi Timberlake (Coleoptera: Coccinellidae). Using choice tests, we studied prey rejection behaviour of C. maculata fourth instars towards prey of different quality and we also tested the influence of hunger and prior experience with other food types on the prey rejection behaviour of coccinellid larvae. Coleomegilla maculata larvae gradually changed their behaviour and rejected low‐quality hosts more frequently, whereas high‐quality hosts were nearly always accepted. After 48 h, the learned behaviour appeared to be partially forgotten. Hunger and experience with other food types prior to the test had little effect on the gradual change of behaviour but the quality of the food ingested influenced the initial level of prey rejection. Our results demonstrate that (1) C. maculata larvae can adjust their prey selection behaviour with experience to reject progressively less suitable prey, and (2) previous experience with other prey types can influence their initial preference.     

First report of <Emphasis Type="Italic">Harmonia axyridis</Emphasis> Pallas being attacked by <Emphasis Type="Italic">Dinocampus coccinellae</Emphasis> Schrank in Canada

Field parasitism of two lady beetles, a recently introduced species, Harmonia axyridis Pallas, and an indigenous species, Coleomegilla maculata lengi Timberlake, by Dinocampus coccinellae Schrank (Hymenoptera: Braconidae) was investigated in southwestern Québec. Adult coccinellids were sampled from June to September 2001 in alfalfa and corn fields. Parasitism rates were recorded by dissection and rearing of coccinellids in controlled condition. The average proportions of coccinellids with a parasitoid larva were 4.6%for H. axyridis and 32%for C. maculata but 0%of the H. axyridis and 5.9%of theC. maculatawere successfully parasitized. In July, more C. maculata than H. axyridiswere found to be parasitized and among all individuals dissected, C. maculata were more frequently found superparasitized than H. axyridis. Our results suggest that D. coccinellae is not well adapted to H. axyridis in Quebec. This is the first mention of H. axyridis being attacked by D. coccinellae in Canada.     

Increased prey vulnerability as a result of prey-prey interactions

This study examines indirect effects in a trophic system with three levels, consisting of two prey species, a top predator, and an intermediate predator. Qualitative data showed that the activity of both the top predator Aeshna juncea (Odonata) and the active prey Heterocope saliens, (Copepoda) caused bouts of swimming in the sedentary prey Sida crystallina (Cladocera). These swimming bouts caused encounters, reactions, attacks and captures of S. crystallina by the intermediate predator Coenagrion hastulatum (Odonata). Quantitative data showed that C. hastulatum had a higher encounter frequency and a higher attack frequency on the sedentary prey when the active prey was present. This result was an effect of encounters between the two prey which increased swimming activity of the sedentary S. crystallina. The results suggest that interactions between prey 1 and prey 2, and between prey and predators, could influence the structure of natural communities.     

Coevolution of a marine gastropod predator and its dangerous bivalve prey

The fossil record of the interaction between the predatory whelk Sinistrofulgur and its dangerous hard‐shelled bivalve prey Mercenaria in the Plio‐Pleistocene of Florida was examined to evaluate the hypothesis that coevolution was a major driving force shaping the species interaction. Whelks use their shell lip to chip open the shell of their prey, often resulting in breakage to their own shells, as well as to their prey. Mercenaria evolved a larger shell in response to an intensifying level of whelk predation. Reciprocally, an increase in attack success (ratio of successful to unsuccessful attacks) and degree of stereotypy of attack position by the predator suggest reciprocal adaptation by Sinistrofulgur to increase efficiency in exploiting hard‐shelled prey. A decrease in prey effectiveness (ratio of unsuccessful to total whelk predation attempts) and an increase in the minimum boundary of a size refuge from whelk predation for Mercenaria may indicate that predator adaptation has outpaced prey antipredatory adaptation. Evolutionary size increase in Sinistrofulgur most likely occurred in response to prey adaptation to decrease the likelihood of feeding‐induced shell breakage and unsuccessful predation when encounters with damage‐inducing prey occur, coupled with (or reinforced by) an evolutionary response to the whelk's own predators. Predator adaptation to Mercenaria best explains temporal changes in whelk behaviour to decrease performance loss (shell breakage) associated with feeding on hard‐shelled prey; this behavioural change limits attacks on prey to when the whelk's shell lip is thickest and most resistant to breakage. Despite evidence of reciprocal adaptation between predator and prey, the contribution of Mercenaria to Sinistrofulgur evolution is likely only a component of the predator's response to dangerous bivalve prey. This study highlights the importance of understanding the interactions among several species in order to provide the appropriate context to test evolutionary hypotheses about any specific pair of species. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80 , 409–436.     

Effect of habitat complexity on the predation of Buenoa fuscipennis (Heteroptera: Notonectidae) on mosquito immature stages and alternative prey

Notonectids are well‐known predators in aquatic habitats, where mosquito larvae, chironomids, and cladocerans constitute their main diet. Our purpose was to assess the effect of structural complexity on the predatory ability of Buenoa fuscipennis, a common predator in aquatic habitats of Buenos Aires city (Argentina). Buenoa fuscipennis showed type 2 functional responses in both the presence and absence of prey refuge and no differences in attack rate or handling time between refuge treatments. Regarding mosquito size classes, B. fuscipennis exhibited a significantly higher preference for 2^nd instar larvae and no predation on pupae. In the presence of mosquito larvae and alternative prey, B. fuscipennis preferred mosquitoes over chironomid larvae and adult cladocerans over mosquito larvae. No switching behavior was detected in our experiments. Habitat structure only slightly affected the predator´s consumption rates on mosquito larvae. Overall, preference for prey did not vary with the presence of refuge, except for the preference for mosquitoes over chironomid larvae, which was significantly decreased in the presence of refuge as a consequence of reduced predation on mosquito larvae. The results suggest that B. fuscipennis could efficiently control mosquitoes in structurally simple habitats where chironomids are the most abundant alternative prey but not in temporary pools where cladocerans are abundant.     

Heterogeneity of twoBeauveria bassiana strains revealed by biochemical tests,protein profiles and bio-assays ofLeptinotarsa decemlineata (Col.: Chrysomelidae) andColeomegilla macultata lengi (Col.: Coccinellidae) larvae

Biochemical profiles on API Rapid CH^* strips and protein profiles on polyacrylamide gels in the presence of sodium dodecyl sulfate were used to distinguish two strains of the entomopathogenic fungusBeauveria bassiana (Balsamo) Vuillemin, ARSEF 2991 and ATCC 44860. Next, the toxicity of these two strains was determined at concentrations of 10², 10⁴, 10⁶ and 10⁸ blastospores/ml on larvae of the Colorado potato beetleLeptinotarsa decemlineata Say (Coleoptera: Chrysomelidae) and of its predator, the spotted ladybird beetle,Coleomegilla maculata lengi Timberlake (Coleoptera: Coccinellidae). Both strains were highly toxic toL. decemlineata larvae. However, the two strains exhibited different levels of toxicity forC. maculata larvae: ARSEF 2991 was toxic, whereas ATCC 44860 caused little coccinellid larval mortality.

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Résumé Les profils biochimiques sur galeries API Rapid CH^* et les profils protéiques sur gels de polyacrylamide ont été utilisés pour distinguer deux souches du champignon entomopathogèneBeauveria bassiana (Balsamo) Vuillemin. La toxicité de ces deux souches a été déterminée à des concentrations de 10², 10⁴, 10⁶ et 10⁸ blastospores/ml sur des larves du doryphore,Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae) et de la coccinelle maculéeColeomegilla maculata lengi Timberlake (Coleoptera: Coccinellidae). Les deux souches deB. bassiana se sont avérées actives à l'égard des larves deL. decemlineata. Toutefois la souche ARSEF 2991 s'est avérée pathogène pour les larves deC. maculata, alors que la souche ATCC 44860 a provoqué une faible mortalité des larves.

     

Prey DNA detection success following digestion by intraguild predators: influence of prey and predator species

Intraguild predation (IGP) has been increasingly recognized as an important interaction in ecological systems over the past two decades, and remarkable insights have been gained into its nature and prevalence. We have developed a technique using molecular gut-content analysis to compare the rate of IGP between closely related species of coccinellid beetles (lady beetles or ladybirds), which had been previously known to prey upon one another. We first developed PCR primers for each of four lady beetle species: Harmonia axyridis, Coccinella septempunctata, Coleomegilla maculata and Propylea quatuordecimpunctata. We next determined the prey DNA detection success over time (DS(50) ) for each combination of interacting species following a meal. We found that DS(50) values varied greatly between predator-prey combinations, ranging from 5.2 to 19.3 h. As a result, general patterns of detection times based upon predator or prey species alone are not discernable. We used the DS(50) values to correct field data to demonstrate the importance of compensation for detection times that are specific to particular predator-prey combinations.     

Predation of Colorado potato beetle eggs by a polyphagous ladybeetle in the presence of alternate prey: potential impact on resistance evolution

The influence of prey choice on the predation of a target prey item by a polyphagous insect predator was investigated in field plot studies. The target prey consisted of eggs of the Colorado potato beetle (CPB), Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), and the predator was the 12‐spotted ladybeetle, Coleomegilla maculata Lengi (Coleoptera: Coccinellidae). Eggs of the European corn borer (ECB), Ostrinia nubilalis Hübner (Lepidoptera: Pyralidae), and nymphs and adults of the green peach aphid, Myzus persicae Sulzer (Homoptera: Aphididae), comprised the alternative prey choices. The objectives of these studies were to: (1) examine predation in a multiprey scenario likely to occur in an agroecosystem, and (2) use the data to simulate the impact of predator‐induced mortality on the evolution of resistance to Bt‐transgenic plants in the target herbivore. Simulations of the rate of resistance evolution were carried out using a deterministic genetic model. Experiments were performed using potato field plots planted in a manner reflecting a 25% or 50% non‐transgenic refuge. CPB eggs were infested so as to mimic the densities of resistant and susceptible populations that might occur in commercial Bt‐transgenic plantings. Densities of predators and alternate prey species were chosen to represent those that might typically occur in potato crops in the eastern USA. Simulation results indicated that when ECB eggs were present, predation on CPB eggs either became inversely spatially density‐dependent, or increased significantly in a density‐dependent manner. When aphids were present, predation became positively density‐dependent. Model simulations predicted that ECB egg presence is beneficial, in that resistance was delayed by up to 40 pest generations (as compared to the scenario with CPB as the only prey), while aphid presence accelerated resistance evolution by 18 generations. Results suggest that resistance management strategies should take into account the composition of prey species available to generalist predators typically present, so as to best delay pest adaptation to Bt‐toxins.     

Differential predation by Coleomegilla maculata on Colorado potato beetle strains that vary in growth on tomato

This study tests the hypothesis that the generalist predator Coleomegilla maculata DeGeer causes differential mortality of Colorado potato beetle, Leptinotarsa decemlineata (Say), larvae differing in their degree of genetic adaptation to tomato (Lycopersicon esculentum Mill.) as a host plant. Results of a series of laboratory experiments demonstrate that adult C. maculata can cause higher mortality to nonadapted than adapted Colorado potato beetle larvae. The extent of differential mortality caused by C. maculata depended on age of potato beetle larvae; presence of potato beetle eggs; whether or not the predator had a choice among prey items; and, in choice situations, the ratio of adapted to nonadapted potato beetle larvae. Although adult C. maculata have the potential to prey differentially on tomato-adapted and nonadapted Colorado potato beetle larvae in mixed populations, the magnitude of differential predation in a natural setting could be highly variable.     

The feeding behaviour of Leptodora kindti and its impact on the zooplankton community of Neusiedler See (Austria)

Leptodora kindti is a very efficient invertebrate predator. Its searching mode of preying is tactile. The setae of the first thoracic limb act as mechanoreceptors, the other thoracic limbs, thorax and head together form the shape of an open basket in which after encounter the prey is pushed in by the aid of the first thoracic limbs and the furca. In Neusiedler See, small individuals of Diaphanosoma brachyurum (0.6–0.9 mm) are the preferred prey, rarely copepods are taken. The predation rate is influenced by temperature, prey density and predator size and varies between less than one and 12 prey items per predator per day. At high predator densities, Leptodora will have a substantial effect on the Diaphanosoma population of Neusiedler See.     

Consumption rates and prey preference of the invasive gastropod Rapana venosa in the Northern Adriatic Sea

The alien Asian gastropod Rapana venosa (Valenciennes 1846) was first recorded in 1973 along the Italian coast of the Northern Adriatic Sea. Recently, this predator of bivalves has been spreading all around the world oceans, probably helped by ship traffic and aquaculture trade. A caging experiment in natural environment was performed during the summer of 2002 in Cesenatico (Emilia-Romagna, Italy) in order to estimate consumption rates and prey preference of R. venosa. The prey items chosen were the Mediterranean mussel Mytilus galloprovincialis (Lamarck 1819), the introduced carpet clam Tapes philippinarum (Adams and Reeve 1850), both supporting the local fisheries, and the Indo-Pacific invasive clam Anadara (Scapharca) inaequivalvis (Bruguière 1789). Results showed an average consumption of about 1 bivalve prey per day (or 1.2 g wet weight per day). Predation was species and size selective towards small specimens of A. inaequivalvis; consumption of the two commercial species was lower. These results might reduce the concern about the economical impact on the local bivalve fishery due to the presence of the predatory gastropod. On the other hand, selective predation might probably alter local community structure, influencing competition amongst filter feeder/suspension feeder bivalve species and causing long-term ecological impact. The large availability of food resource and the habitat characteristics of the Emilia-Romagna littoral makes this area an important breeding ground for R. venosa in the Mediterranean Sea, thus worthy of consideration in order to understand the bioinvasion ecology of this species and to control its likely further dispersal.