Response of the predatorRhizophagus grandis to host plant derived chemicals inDendroctonus micans larval frass in wind tunnel experiments (Coleoptera: Rhizophagidae,Scolytidae)

Summary Adults of the predatory beetleRhizophagus grandis are strongly attracted to both adult and larval frass of its specific prey,Dendroctonus micans, in walking bioassays. Spruce bark and resin are relatively unattractive. Solvent extracts of larval frass that were attractive toR. grandis adults in a flight wind tunnel contained a mixture of monoterpenes of host plant origin. A synthetic mixture of these monoterpenes, (+)—-pinene, (–)—-pinene, -phellandrene,dl limonene and 3-carene, was responsible for 70–80% of the activity of the most attractive extract. We suggest that a blend of monoterpenes in frass acts as a kairomone forR. grandis but that attraction to monoterpenes is only the first of a sequence of behavioural responses that ensures successful host location and identification.     

Threat-sensitive generalization of predator recognition by larval amphibians

Despite the importance of acquired predator recognition in mediating predator–prey interactions, we know little about the specific characteristics that prey use to distinguish predators from non-predators. Recent experiments with mammals and fish indicate that some prey lacking innate predator recognition have the ability to display anti-predator responses upon their first encounter with those predators if they are similar to predators that the prey has recently learned to recognize. This phenomenon is referred to as generalization of predator recognition. In this experiment, we documented for the first time that larval amphibians (woodfrog, Rana sylvatica) have the ability to generalize the recognition of known predators to closely related novel predators. Moreover, we demonstrated that this ability is dependent on the level of risk associated with the known predator. When red-bellied newt, Cynops pyrrhogaster (known predator), was paired with simulated low risk, tadpoles displayed fright responses to newts and novel tiger salamanders, Ambystoma tigrinum, but not to novel African clawed frogs, Xenopus laevis. However, when the newt was paired with simulated high risk, tadpoles generalized their responses to both tiger salamanders and African clawed frogs. Larval anurans seem to have a wider generalization frame than other animals.     

Temporal variability in zooplankton prey capture rate of the passive suspension feeder<Emphasis Type="Italic"> Leptogorgia sarmentosa</Emphasis> (Cnidaria: Octocorallia), a case study

There is increasing evidence that suspension feeders play a significant role in plankton–benthos coupling. However, to date, active suspension feeders have been the main focus of research, while passive suspension feeders have received less attention. To increase our understanding of energy fluxes in temperate marine ecosystems, we have examined the temporal variability in zooplankton prey capture of the ubiquitous Mediterranean gorgonian Leptogorgia sarmentosa. Prey capture was assessed on the basis of gut content from colonies collected every 2 weeks over a year. The digestion time of zooplankton prey was examined over the temperature range of the species at the study site. The main prey items captured were small (80–200 µm), low-motile zooplankton (i.e. eggs and invertebrate larvae). The digestion time of zooplankton prey increased when temperature decreased (about 150% from 21°C to 13°C; 15 h at 13°C, 9 h at 17°C, and 6 h at 21°C), a pattern which has not previously been documented in anthozoans. Zooplankton capture rate (prey polyp^–1 h^–1) varied among seasons, with the greatest rates observed in spring (0.16±0.02 prey polyp^–1 h^–1). Ingestion rate in terms of biomass (g C polyp^–1 h^–1) showed a similar trend, but the differences among the seasons were attenuated by seasonal differences in prey size. Therefore, ingestion rate did not significantly vary over the annual cycle and averaged 0.019±0.002 g C polyp^–1 h^–1. At the estimated ingestion rates, the population of L. sarmentosa removed between 2.3 and 16.8 mg C m^–2 day^–1 from the adjacent water column. This observation indicates that predation by macroinvertebrates on seston should be considered in energy transfer processes in littoral areas, since even species with a low abundance may have a detectable impact.Communicated by S.A. Poulet, Roscoff     

Localized defecation by pike: a response to labelling by cyprinid alarm pheromone?

Fathead minnows (Pimephales promelas) that have never encountered a predatory pike (Esox lucius), are able to detect conspecific alarm pheromone in a pike's diet if the pike has recently consumed minnows. It remains unclear how this minnow alarm pheromone is secreted by pike and if a pike is able to avoid being labelled as a potential predator by localizing these cues away from its foraging range. The first experiment determined that minnow alarm pheromone is present in pike feces when pike are fed minnows. Individual fathead minnows exhibited a fright response to a stimulus of pike feces if the pike had been fed minnows, but not if the pike had been fed swordtails, which lack alarm pheromone. Individual minnows also exhibited a fright reaction to alarm pheromone in the water (which contained no feces) housing pike which had been fed minnows, suggesting that alarm pheromone is also released in urine, mucous secretions and/or via respiration. The second experiment determined that test pike spent a significantly greater proportion of time in the home area of the test tanks (i.e. where they were fed) but the majority of feces were deposited in the opposite end of the test tank. By localizing their defecation away from the home or foraging area, pike may be able to counter the effects of being labelled as a predator by the alarm pheromone of the prey species.     

Uptake of dissolved organic matter by larval stage of the crown-of-thorns starfish Acanthaster planci

The life-history of the crown-of thorns starfish (Acanthaster planci) includes a planktotrophic larva that is capable of feeding on particulate food. It has been proposed, however, that particulate food (e.g. microalgae) is scarce in tropical water columns relative to the nutritional requirements of the larvae of A. planci, and that periodic shortages of food play an important role in the biology of this species. It has also been proposed that non-particulate sources of nutrition (e.g. dissolved organic matter, DOM) may fuel part of the nutritional requirements of the larval development of A. planci as well. The present study addresses the ability of A. planci larvae to take up several DOM species and compares rates of DOM uptake to the energy requirements of the larvae. Substrates transported in this study have been previously reported to be transported by larval asteroids from temperate and antarctic waters. Transport rates (per larval A. planci) increased steadily during larval development and some substrates had among the highest mass-specific transport rates ever reported for invertebrate larvae. Maximum transport rates (J _max ⁱⁿ) for alanine increased from 15.5 pmol larva^–1 h^–1 (13.2 pmol g^–1 h^–1) for gastrulas (J _max ⁱⁿ=38.7 pmol larva^–1 h^–1 or 47.4 pmol g^–1 h^–1) to 35.0 pmol larva^–1 h^–1 (13.1 pmol g^–1 h^–1) for early brachiolaria (J _max ⁱⁿ just prior to settlement=350.0 pmol larva^–1 h^–1 or 161.1 pmol g^–1 h^–1) at 1 M substrate concentrations. The instantaneous metabolic demand for substrates by gastrula, bipinnaria and brachiolaria stage larvae could be completely satisfied by alanine concentrations of 11, 1.6 and 0.8 M, respectively. Similar rates were measured in this study for the essential amino acid leucine, with rates increasing from 11.0 pmol larva^–1 h^–1 (or 9.4 pmol g^–1 h^–1) for gastrulas (J _max ⁱⁿ=110.5 pmol larva^–1 h^–1 or 94.4 pmol g^–1 h^–1) to 34.0 pmol larva^–1 h^–1 (or 13.0 pmol g^–1 h^–1) for late brachiolaria (J _max ⁱⁿ=288.9 pmol larva^–1 h^–1 or 110.3 pmol g^–1 h^–1) at 1 M substrate concentrations. The essential amino acid histidine was transported at lower rates (1.6 pmol g^–1 h^–1 at 1 M for late brachiolaria). Calculation of the energy contribution of the transported species revealed that larvae of A. planci can potentially satisfy 0.6, 18.7, 29.9 and 3.3% of their total energy requirements (instantaneous energy demand plus energy added to larvae as biomass) during embryonic and larval development from external concentrations of 1 M of glucose, alanine, leucine and histidine, respectively. These data demonstrate that a relatively minor component of the DOM pool in seawater (dissolved free amino acids, DFAA) can potentially provide significant amounts of energy for the growth and development of A. planci during larval development.     

Aggregation pheromone ofCarpophilus freemani (Coleoptera: Nitidulidae): A blend of conjugated triene and tetraene hydrocarbons

Summary Males ofCarpophilus freemani Dobson (Coleoptera: Nitidulidae) produce an aggregation pheromone to which both sexes fly in a wind-tunnel bioassay. The major pheromone component (ca. 30 ng per male per day in volatile collections) was identified as (2E,4E,6E)-5-ethyl-3-methyl-2,4,6-nonatriene. A minor component, (2E,4E,6E,8E)-7-ethyl-3,5-dimethyl-2,4,6,8-undecatetraene, was 3–10% as abundant as the major triene and was 5–20% as active when compared at relative doses ranging from natural proportions to 1:1. These compounds act synergistically: a mixture of major and minor components in natural proportions attracted more than twice as many beetles as the major component alone, and the mixture fully accounted for the activity of male-derived volatile collections. Six other male-derived conjugated hydrocarbons, ranging from 2% down to 0.04% as abundant as the major component, were also identified. These are (in order of decreasing bioassay activity when compared on an equal-weight basis): (3E,5E,7E)-6-ethyl-4-methyl-3,5,7-decatriene, (2E,4E,6E)-5-ethyl-3-me-thyl-2,4,6-octatriene, (3E,5E,7E,9E)-8-ethyl-4,6-dimethyl-3, 5,7,9-dodecatetraene, (2E,4E,6E,8E)-3,5,7-trimethyl-2,4,6, 8-undecatetraene, (3E,5E,7E)-5-ethyl-7-methyl-3,5,7-undecatriene, and (2E,4E,6E)-3,5-dimethyl-2,4,6-nonatriene. All structure identifications were confirmed by synthesis. In the wind tunnel, the pheromone acted synergistically with host-type volatiles such as propyl acetate, valeric acid, and ethanol. This concept was verified by fields tests in California, in which there was dramatic synergism between the pheromone and fermenting host materials. Pheromone biosynthesis is discussed.     

Do mountain log skinks (<Emphasis Type="Italic">Pseudemoia entrecasteauxii</Emphasis>) modify their behaviour in the presence of two predators?

Prey often adopt antipredator strategies to reduce the likelihood of predation. In the presence of predators, prey may use antipredator strategies that are effective against a single predator (specific) or that are effective against several predators (nonspecific). Most studies have been confined to single predator environments although prey are often faced with multiple predators. When more than one predator is present, specific antipredator behaviours can conflict and avoidance of one predator may increase vulnerability to another. To test how prey cope with this dilemma, I recorded the behaviours of lizards responding to the nonlethal cues of a bird and snake presented singly and simultaneously. Lizards use specific and conflicting antipredator tactics when confronted with each predator, as evidenced by refuge use. However, when both predators were present, lizards refuge use was the same as in the predator-free environment, indicating that they abandoned refuge use as a primary mechanism for predator avoidance. In the presence of both predators, they reduced their overall movement and time spent thermoregulating. This shift in behaviour may represent a compromise to minimize overall risk, following a change in predator exposure. This provides evidence of plasticity in lizard antipredator behaviour and shows that prey responses to two predators cannot be accurately predicted from what is observed when only one predator is present.Communicated by W. Cooper     

A predator’s preference for egg-carrying prey: a novel cost of parental care

Using a subsocial spitting spider (Scytodes pallida) as the prey and a spider-eating jumping spider (Portia labiata) as the predator, the cost of parental care is investigated. Our findings suggest that being singled out as preferred prey by P. labiata is, for egg-carrying females of S. pallida, an important cost of parental care. In survival tests, during which P. labiata was given access to egg-carrying and eggless S. pallida females, egg-carrying females were preyed on more often than eggless females. In preference tests, motionless lures instead of living S. pallida were used. The lures were made by mounting dead egg-carrying and dead eggless S. pallida females in lifelike posture in webs. In these tests, P. labiata detected and identified, by vision alone, both kinds of prey (egg-carrying and eggless), and singled out egg-carrying females as preferred prey.Communicated by M.A. Elgar     

Defensive secretions from the larvae ofApatania fimbriata (Pictet) (Trichoptera: Limnephilidae)

Summary When the larvae of the caddis flyApatania fimbriata (Pictet) are threatened, drops of fluid appear on their head capsules. The secretions are produced in a gland in the dorsal part of the prothorax. The neck region contains an eversible sac with numerous single setae, groups of 3 setae, or rows of setae on the surface. The secretion is released through two paris of orifices on the lateral sides of the sac. For the most part the secretion is composed of some 30 fatty acids, with the major components having 12–14 carbon atoms and up to 4 double bonds (approx. 1–2 µg secretion per specimen). Biotests with synthetic saturated acids (C₆–C₁₂) in a stream and in the laboratory demonstrated a paralysing effect on small invertebrate predators (Rhyacophila sp.,Plectrocnemia conspersa, Hydropsyche sp., larvae, all Trichoptera). In choice experiments,Rhyacophila sp. larvae preferred larvae ofAgapetus fuscipes andDrusus annulatus (Trichoptera) as food as compared withApatania fimbriata larvae. Larger predators, such asDinocras cephalotes (Insecta, Plecoptera) and the fishCottus gobio, did not discriminate betweenApatania fimbriata and other prey species. The use of fatty acids in defensive secretions is interpreted as an adaptation to the running water environment. They are effective repellents againstRhyacophila sp. larvae, the most important predator in the natural environment ofApatania larvae.     

Effect of low dissolved oxygen concentrations on behavior and predation rates on red sea bream Pagrus major larvae by the jellyfish Aurelia aurita and by juvenile Spanish mackerel Scomberomorus niphonius

A shift in outcomes of predator-prey interactions in plankton community may occur at sublethal dissolved oxygen concentrations that commonly occur in coastal waters. Laboratory experiments were conducted to investigate how a decline in dissolved oxygen concentration alters the predation rate on fish larvae by two estuarine predators. Behavior and consumption of larval fish by moon jellyfish Aurelia aurita (103.1±12.4 mm in bell diameter) and by a juvenile piscivore, Spanish mackerel Scomberomorus niphonius (30.1±2.1 mm in standard length: SL), were observed under four oxygen concentration treatments (1, 2 and 4 mg l^–1 and air-saturated: 5.8 mg l^–1). Larvae of a coastal marine fish species, red sea bream Pagrus major (7.21±0.52 mm SL), were used as prey for the experiment. Bell contraction rate of the jellyfish did not vary among the oxygen concentrations tested, indicating a tolerance to low oxygen concentration. Gill ventilation rate of the Spanish mackerel increased and swimming speed decreased as the oxygen concentration decreased, indicating that oxygen concentrations 4 mg l^–1 are physiologically stressful for this species. The number of larvae consumed in 15 min. by jellyfish increased whereas those consumed by Spanish mackerel decreased with the decrease in oxygen concentration. Low oxygen concentrations that are commonly observed in coastal waters of Japan during summer have the potential to increase the relative importance of jellyfish as predator of fish larvae and to change the importance of alternative trophic pathways in estuarine ecosystems.Communicated by T. Ikeda, Hakodate     

Threat-sensitive learning of predators by larval mosquitoes <Emphasis Type="Italic">Culex restuans</Emphasis>

A prerequisite for prey to show adaptive behavioural responses to predators is that the prey has the ability to recognise predators as threats. While predator recognition can be innate in many situations, learning is often essential. For many aquatic species, one common way to learn about predators is through the pairing of a novel predator odour with alarm cues released from injured conspecifics. One study with fish demonstrated that this mode of learning not only allows the prey to recognise the predatory cues as a threat, but also mediates the level of threat associated with the predator cues (i.e. threat-sensitive learning). When the prey is exposed to the novel predator with a high concentration of alarm cues, they subsequently show a high intensity of antipredator response to the predator cues alone. When exposed to the predator with a low concentration of alarm cues, they subsequently show a low-intensity response to the predator cues. Here, we investigated whether larval mosquitoes Culex restuans have the ability to learn to recognise salamanders as a threat through a single pairing of alarm cues and salamander odour and also whether they would learn to respond to salamander cues in a threat-sensitive manner. We conditioned individual mosquitoes with water or a low, medium or high concentration of crushed conspecific cues (alarm cues) paired with salamander odour. Mosquitoes exposed to salamander odour paired with alarm cues and subsequently exposed to salamander odour alone responded to the salamander as a threat. Moreover, the intensity of antipredator response displayed during the conditioning phase matched the response intensity during the testing phase. This is the first demonstration of threat-sensitive learning in an aquatic invertebrate.     

The aggregation pheromone ofIps duplicatus and its role in competitive interactions withI. typographus (Coleoptera: Scolytidae)

Summary Ips duplicatus withI. typographus co-inhabiting Norway spruce (Picea abies (L.) Karst.) would benefit from a pheromone blend distinct from that of the larger competitorI. typographus. GC-MS analysis showed thatI. duplicatus males feeding in the host produced ipsdienol (Id),cis-verbenol (cV),trans-verbenol (tV), myrtenol (Mt), andE-myrcenol (EM) and traces of 2-methyl-3-buten-2-ol (MB).I. duplicatus produced Id in approximately racemic form (48.9-54.5% (+)-(S)-isomer). The amounts of Id and EM released over a 9 day period had a maximum of 250 and 5 ng/h/male, respectively, on day 2. Exposure ofI. duplicatus males to myrcene and -pinene resulted in the production of small amounts of Id, cV, tV, Mt, andtrans-pinocarveol, but not of EM. In laboratory bioassays with walking beetles, the pheromone component Id alone was weakly attractive while EM was inactive, but in binary combination with Id strongly synergized attraction. A combination of EM and Id at a release rate equivalent to 100–200 males was more attractive in the field than 70 unmated males in a spruce log. The addition of myrcene ( a suggested pheromone precursor of Id) to Id did not enhance trap caches, while addition of EM increased catches > 10-fold. Subtracting EM from a blend of Id, EM, cV and MB drastically reduced trap catches while subtraction of cV or MB or both had no significant effect. Addition of EM over a wide concentration range to the synthetic pheromone ofI. typographus did not reduce the attraction of females of this species in the laboratory. A two-species pheromone interaction field test releasingI. typographus pheromone components (MB + cV) at 10–1000 male equivalents (ME) andI. duplicatus pheromone (Id + EM) at 0, 10–1000 ME in all possible combinations showed both positive intraspecific dose-response effects and an interspecific inhibition. Higher release rates of EM appeared to inhibitI. typographus, especially males. In a tree colonization model, the response of the two competing species to their respective pheromones show a good separation during the mass-attack with a small initial cross-attraction. It remains to be shown whether either of the two pheromone systems have in fact evolved in the present sympatry, or if they are an incidental effect of ancestry of these phylogenetically distantIps.     

Effects of copper and cadmium on growth,swimming and predator avoidance in Eurytemora affinis (Copepoda)

In this study we demonstrate the sensitivity of swimming behavior and predator-escape responses of nauplii of the estuarine copepod Eurytemora affinis to sublethal doses of Cu and Cd. Behavior was generally altered at metal doses below those affecting growth rates or survival of the copepods. Swimming velocities of Cu-dosed nauplii were different from controls at all concentrations of Cu tested (10–50 g l^-1 total Cu) after 24- to 48-h exposure, whereas development rate of nauplii was significantly reduced only after 96 h at 25 g l^-1. The 96 h LC50 for Cu was approximately 30 g l^-1 Cu. Naupliar swimming velocity was also affected by Cd. Swimming speeds were reduced after 24 h at 130 g l^-1, and development was slowed after 48 h at 116 g Cd l^-1. The 96-h LC50 was >120 g l^-1. Little is known of the adaptive role of specific motile behaviors in the success of larval copepods. We investigated the relationship of swimming speed to predator — prey interactions of the nauplii using both real and simulated predators. Nauplii exposed to Cu for 24 h were observed to be generally hyperactive, a condition which could increase their encounter frequency with predators. Reduced numbers of escape responses of nauplii to a simulated predator, another indication of increased vulnerability to predation, were observed only after 48-h exposure to Cu. Nevertheless, feeding rates of non-dosed larval striped bass on dosed nauplii (24 h at 25 g Cu l^-1) were significantly higher than on control nauplii. Feeding rates of larval mysid shrimp, however, were not higher on similarly dosed nauplii; 24 h exposure of nauplii to >30 g Cu l^-1 did result in increased predation by mysids.Contribution No. 272 of the US EPA Environmental Research Laboratory, Narragansett, Rhode Island 02882, USA     

Effect of host and larval frass volatiles on behavioural response of the old house borer,Hylotrupes bajulus (L.) (Coleoptera: Cerambycidae), in a wind tunnel bioassay

Summary. In a wind tunnel bioassay the effect of three concentrations of natural extracts of (1) Scots pine wood, Pinus sylvestris, and (2) larval frass on the behavioural response of unmated females and males of the old house borer, Hylotrupes bajulus, was tested and compared to the behavioural effects of the male-produced sex pheromone (3R)-3-hydroxy-2-hexanone. The influence on the behaviour of both sexes was found to be equally significant for the two higher concentrated hexane extracts of wood and larval frass. Therefore several synthetic monoterpenes present in the extracts and ethanol were tested at the two higher concentrations (1:100, 1:1000 vol/vol). Among the higher concentrated monoterpenoid hydrocarbons [(+)-α-pinene, (+)-β-pinene, (+)-limonene], only α-pinene increased the activity, orientation towards scent source and interest towards conspecifics. The tests with higher concentrated ethanol and the oxygenated monoterpenes [(-)-verbenone, (-)-trans-pinocarveol, (+)-terpinen-4-ol, (+)-α-terpineol, (-)-myrtenol] revealed that verbenone is the most effective stimulant for the females, followed by trans-pinocarveol, terpinen-4-ol and α-terpineol. For males, terpinen-4-ol was the only mediator significantly inducing attraction and orientation towards the scent source combined with an interest in conspecifics apparent by fighting or courtship behaviour. Males did not respond to verbenone which is a main compound of larval frass. Myrtenol and ethanol were ineffective in both sexes. In fact behavioural observations suggest that the beetles were repelled by the high dose of myrtenol. Using the ten-fold lower dose of the synthetic monoterpenes (1:1000 vol/vol), all semiochemicals except myrtenol lost activity. Myrtenol, however, induced behavioural responses, like increased activity and orientation towards scent source, only at the low concentration. Based on the results, primary attraction of unmated old house borer is probably mediated by monoterpenes of coniferous wood, while secondary attraction to infested wood would occur in response to volatiles of larval frass. Received 5 May 1999; accepted 30 September 1999     

Electrophoretic survey of genetic variation in Pecten maximus,Chlamys opercularis,C. varia and C. distorta from the Irish Sea

Food selection by young larvae of the gulf menhaden (Brevoortia patronus) was studied in the laboratory at Beaufort, North Carolina (USA) in 1982 and 1983; this species is especially interesting, since the larvae began feeding on phytoplankton as well as microzooplankton. When dinoflagellates (Prorocentrum micans), tintinnids (Favella sp.), and N1 nauplii of a copepod (Acartia tonsa) were presented to laboratory-reared, larval menhaden (3.9 to 4.2 mm notochord length), the fish larvae ate dinoflagellates and tintinnids, but not copepod nauplii. Larvae showed significant (P<0.001) selection for the tintinnids. Given the same mixture of food items, larger larvae (6.4 mm notochord length) ate copepod nauplii as well as the other food organisms. These feeding responses are consistent with larval feeding in the northern Gulf of Mexico, where gulf menhaden larvae between 3 and 5 mm in notochord length frequently ate large numbers of dinoflagellates (mostly P. micans and P. compressum) and tintinnids (mostly Favella sp.), but did not eat copepod nauplii. As larvae grew, copepod nauplii and other food organisms became important, while dinoflagellates and tintinnids became relatively less important in the diet. Since the tintinnids and nauplii used in the laboratory feeding experiments were similar in size as well as carbon and nitrogen contents, the feeding selectivity and dietary ontogeny that we observed were likely due to a combination of prey capturability and larval fish maturation and learning.Contribution No. 5575 of the Woods Hole Oceanographic Institution     

The poison gland of the antMyrmicaria eumenoides and its role in recruitment communication

Summary The antMyrmicaria eumenoides is a significant arthropod predator. For rapid attraction of large numbers of nestmates to newly discovered food sources the ants use an efficient recruitment communication system based on the poison gland secretion. Workers exhibit age-based division of labour. Young workers perform brood-care; their poison gland reservoir develops and reaches its final size of 0.5 µl at an age of 6 weeks, when they become foragers. The secretion deposited during combat with enemies or prey is composed of equal amounts of both a high volatile and a low volatile fraction. Within the high volatile fraction (+)—limonene is the main component (97%) and is the only olfactory trigger to alert ants in the vicinity and to recruit them to places of combat, where they assemble. Ants respond to synthetic (+)—limonene in exactly the same way as to the poison gland secretion when applied at the same airborne concentrations. Further components of the high volatile fraction are four additional monoterpene hydrocarbons and hexanoic nitrile. The high volatile and the low volatile fraction of the poison gland secretion each have dual functions: The low volatiles, of which the main component is an alkaloid, serve as a fixative and extend the effective period of the limonene signal by modifying its evaporation kinetics. On the other hand the high volatile recruitment signal (+)—limonene is also the solvent for the alkaloid and enhances its spreading on the surface of the cuticle of arthropod enemies or prey.     

Aggressive mimicry,prey-specific predatory behaviour and predator-recognition in the predator-prey interactions of Portia fimbriata and Euryattus sp., jumping spiders from Queensland

Summary Adults and large juveniles of Queensland Portia fimbriata, a salticid spider known to prey on other spiders (including other salticids), are shown to use prey-specific predatory behaviour against Euryattus sp., one of the salticids on which it feeds. Euryattus females are unusual because they nest inside suspended rolled-up leaves. P. fimbriata used vibratory displays to lure Euryattus females from their nests. These displays seem to mimic the courtship displays of Euryattus males. Other species of Portia and other populations of P. fimbriata, in habitats in which Euryattus is not known to occur, did not practise this prey-specific behaviour. In the laboratory, Euryattus — but not Jacksonoides queenslandica, another salticid on which P. fimbriata is known to feed — readily recognized approaching Portia as a potential predator. A possible evolutionary arms race between Portia and Euryattus is discussed. Offrint request to: R.R. Jackson     

Prey-capture benefits in a mixed-species group of Amazonian tamarins,Saguinus fuscicollis and S. mystax

Summary Tamarins of the genus Saguinus feed on a wide range of arthropods and small vertebrates, which compose a critical component of their diet. This paper examines the foraging patterns and capture success of the Avila-Peres saddle-back (S. fuscicollis avilapiresi) and the red-capped moustached tamarin (S. mystax pileatus) in very stable mixed-species groups, and whether and how any foraging benefits for either species resulted from their association. Moustached tamarins actively searched for prey items which were mainly well exposed on the midstorey foliage. Saddle-back tamarins, on the other hand, foraged at lower heights, largely by manipulating a variety of microhabitats potentially concealing embedded prey. The foraging activity of the numerically dominant and larger-bodied moustached tamarins often resulted in prey items escaping to lower substrates, usually the forest leaf-litter. The beating effect of this species substantially facilitated captures of large, mobile prey items by saddle-backs, which were highly adept at locating and retrieving flushed prey. It is estimated that, while saddle-backs obtained 66–73% of their prey biomass from flushed items, this proportion was substantially lower (2–9%) for moustached tamarins. Commensal insectivory appears to involve a highly asymmetric benefit to saddle-backs, and a low cost to moustached tamarins, which partly explains the stability of mixed-species groups. Correspondence to the present address     

Is boldness affected by group composition in young-of-the-year perch (Perca fluviatilis)?

In young-of-the-year perch (Perca fluviatilis), individuals within groups differed in the degree of boldness, estimated by habitat utilisation and feeding activity in visual contact with a potential predator. We looked at changes in individual behaviour in connection with change of group composition. During the first period, perch were randomly assigned to groups, and time spent in open habitat versus in vegetation and number of prey attacks were registered. The perch were then categorised into personality types (shy, bold, intermediate) according to their behaviour. During the second period, fish were observed when sorted into new groups, each containing only one personality type. Shy individuals showed the largest changes in behaviour, and increased both the time spent in the open and the number of prey attacks when placed into the new groups. Feeding activity in shy fish during the second period was affected by group composition during the first period. After regrouping, bold individuals decreased their time in the open, whereas intermediate individuals did not change behaviour. Time in the open habitat was, to some extent, influenced by the behaviour of the other members of the group, but number of prey attacks was not. The behaviour of fish of the different personality types we have defined in this study seemed to be based on innate traits, but also modified by the influence of other group members and by habituation to the environment.Communicated by J.Krause     

Defence effectiveness of easy bleeding sawfly larvae towards invertebrate and avian predators

Summary. Easy bleeding is a phenomenon discovered in some tenthredinid insects which possess a particularly low mechanical resistance of the integument, leading under mechanical stress to haemolymph exudation. It has a defensive effect against ants and wasps through harmful plant compounds which are sequestered in the haemolymph. Here we describe etho-ecological and some chemical aspects of the defence of easy bleeders and specify the range of predators to which easy bleeding might be effective. Beside a high haemolymph deterrence associated with low integument resistance across sawfly species, we also detected toxicity of the haemolymph of some species to workers of the ant Myrmica rubra. The behaviour of easy bleeders is to move slowly and, once disturbed, to become motionless, thereby probably impeding the tendency of a predator to attack. This behaviour had no beneficial effect for easy bleeders when attacked by the predatory bug Podisus maculiventris. Bugs could successfully and without harm prey on sawfly larvae without evoking easy bleeding. For the easy bleeder Athalia rosae, host plants with different secondary metabolite profiles, and, consequently, changes in haemolymph chemistry only slightly affected the feeding behaviour of the bugs. To test the effectiveness of easy bleeding towards a vertebrate predator, easy bleeders were offered to birds, Sturnus vulgaris. The body colouration of the sawfly larvae was of prime importance in determining the predators response when testing birds in a group. It is likely that easy bleeding is a defence strategy directed primarily towards foraging insects with biting-chewing mandibles and that it is much less active towards predatory insects with piercing-sucking mandibles as well as birds. The involvement of chemical and/or physical cues in the strategy is discussed with respect to these types of predators.