Host location by larvae of a parasitic barnacle: larval chemotaxis and plume tracking in flow

Numerous studies describe stimulation and/or enhancement oflarval settlement by distance chemoreception in response tochemical factors emitted by conspecific adults, host and preyspecies and microbial films. However, active upstream trackingof odor plumes, needed in order to locate specific, spatiallylimited settlement sites, has thus far received little scientificattention. This study examines host location in flow and stillwater by larvae of the parasitic barnacle Heterosaccus dollfusi,which inhabits the brachyuran crab Charybdis longicollis. Experimentsincluded analysis of larval motion patterns under four conditions:still water, in flow, in still water with waterborne host metabolitesand in flow with host metabolites. Our results show that H.dollfusi larvae are capable of actively and effectively locatingtheir host in still water and in flow, using chemotaxis andrheotaxis and modifying their swimming pattern, direction, velocity,determination and turning rate to accommodate efficient navigationin changing environmental conditions.     

Host location by larvae of the reptile tick Amblyomma vikirri (Acari: Ixodidae)

The newly described tick Amblyomma vikirri has a narrow host range, being found mainly on the Australian lizard, Egernia stokesii and rarely on another lizard, Tiliqua rugosa. Both hosts are in the family Scincidae. Larvae of A. vikirri were as successful in locating E. stokesii as T. rugosa from a range of release distances between 20 and 120 mm from the host. Over this range the proportion of ticks which successfully located hosts declined and the time taken by successful ticks to locate hosts increased with increasing release distance. From 60 mm, larvae of A. vikirri located four other lizard species from the families Scincidae and Agamidae and two non-living targets as successfully as they did E. stokesii. The only evidence that there was any host specificity in the searching behaviour of larvae of A. vikirri was that A. vikirri larvae spent less time paused and questing when they were searching for E. stokesii than when they were searching for T. rugosa. Aponomma hydrosauri, a tick which commonly infests T. rugosa but not E. stokesii, spent less time paused and questing when it was searching for T. rugosa than when it was searching for E. stokesii. However, the results overall suggest that the narrow host range of A. vikirri cannot be explained by any ability of the larvae of that species to discriminate between their natural host and other reptile species.     

Zebrafish larvae exhibit rheotaxis and can escape a continuous suction source using their lateral line

Zebrafish larvae show a robust behavior called rheotaxis, whereby they use their lateral line system to orient upstream in the presence of a steady current. At 5 days post fertilization, rheotactic larvae can detect and initiate a swimming burst away from a continuous point-source of suction. Burst distance and velocity increase when fish initiate bursts closer to the suction source where flow velocity is higher. We suggest that either the magnitude of the burst reflects the initial flow stimulus, or fish may continually sense flow during the burst to determine where to stop. By removing specific neuromasts of the posterior lateral line along the body, we show how the location and number of flow sensors play a role in detecting a continuous suction source. We show that the burst response critically depends on the presence of neuromasts on the tail. Flow information relayed by neuromasts appears to be involved in the selection of appropriate behavioral responses. We hypothesize that caudally located neuromasts may be preferentially connected to fast swimming spinal motor networks while rostrally located neuromasts are connected to slow swimming motor networks at an early age.     

Host location and suitability of the armyworm larvae of Mythimna unipuncta for the tachinid parasitoid Exorista larvarum

This work evaluates the efficiency of Exorista larvarum (L.) (Diptera: Tachinidae) in localizing and parasitizing the larvae of the noctuid moth Mythimna unipuncta (Haworth) (Lepidoptera: Noctuidae) in laboratory conditions, in a wind tunnel and in PVC cages. The most important cue in host localization by E. larvarum females was host-induced plant volatiles. Visual cues, natural maize volatiles and artificially damaged plants were less efficient for host localization. Mortality in M. unipuncta larvae on which E. larvarum females laid eggs was high. This finding indicates that E. larvarum could effectively contribute to lowering the population size of M. unipuncta, even if only few parasitoids successfully complete their development in the host. Further studies with other possible hosts must be done to apply E. larvarum successfully against M. unipuncta larvae in maize fields.     

Behavior of red king crab larvae: Phototaxis,geotaxis and rheotaxis

Zoeae of Paralithodes camtschatica were positively phototactic to white light intensities above 1 × 10¹³ q cm^?2 s^?1. Negative phototaxis occurred at low (1 × 10¹² q cm^?2 s^?1), but not high intensities (2.2 × 10¹⁶q cm^?2 s^?1). Phototactic response was directly related to light intensity. Zoeae also responded to red, green and blue light. Zoeae were negatively geotactic, but geotaxis was dominated by phototaxis. Horizontal swimming speed of stage 1 zoeae <4 d old was 2.4 ± 0.1 (SE) cms^?1 and decreased to 1.7 ± 0.1 cm s^?1 in older zoeae (P <0.01). Horizontal swimming speed of stage 2 zoeae was not significantly different from ≥4 d old stage 1 zoeae. Vertical swimming speed, 1.6 ± 0.1 cm s^?1, and sinking rate, 0.7 ± 0.1 cm s^?1, did not change with ontogeny. King crab zoeae were positively rheotactic and maintained position in horizontal currents less than 1.4 cm s^?1. Starvation reduced swimming and sinking rates and phototactic response.     

Species-specific detection and quantification of common barnacle larvae from the Japanese coast using quantitative real-time PCR

Species-specific detection and quantification methods for barnacle larvae using quantitative real-time polymerase chain reaction (qPCR) were developed. Species-specific primers for qPCR were designed for 13 barnacle species in the mitochondrial 12S ribosomal RNA gene region. Primer specificity was examined by PCR using template DNA extracted from each of the 13 barnacle species, other unidentified barnacle species, and field collected zooplankton samples. The resulting PCR products comprised single bands following agarose gel electrophoresis when the templates corresponded to primers. The amplifications were highly species-specific even for the field plankton samples. The field plankton samples were subjected to qPCR assay. The calculated DNA contents for each barnacle species were closely correlated with the number of larvae measured by microscopic examination. The method could be applied to quantify barnacle larvae in natural plankton samples.     

Host location by a parasitoid using leafminer vibrations: characterizing the vibrational signals produced by the leafmining host

Abstract. The aim of this study was to characterize the vibrations produced by the apple tentiform leafminer Phyllonorycter malella (Ger.) (Lepidoptera, Gracillariidae). Host location using vibrations by one of its parasitoids Sympiesis sericeicornis Nees (Hymenoptera, Eulophidae) was postulated by Casas (1989) on the basis of detailed quantitative behavioural observations and has also been suggested by other authors on similar systems. Both host and parasitoid send and may receive vibratory signals; consequently we first attempted to characterize and classify the signals, one of the first steps required in the design of an adequate vibrational biotest. In this respect, our approach differs fundamentally from the familiar setting of host location via semiochemicals and is best framed within the context of vibratory communication. Vibrational signals produced by a moving larva and pupa were measured on several spots on the leaf using a laser vibrometer. The emitted signals were characterized by their temporal patterns of change in amplitude and frequency spectra. The vibrational patterns released by a moving larva were different from those released by a wriggling larva and a wriggling pupa in the time as well as in the frequency domains. Wriggling larvae and wriggling pupae triggered vibrations that were similar in frequency, but differed in their temporal pattern. Frequencies up to 15 kHz could be identified. The amplitudes and frequencies of the signals both decreased significantly from the tip to the base of the leaf. A wriggling pupa and a wriggling larva produced stronger signals than a foraging larva. All calculated parameters (displacement, velocity, acceleration, and duration of the signal components) of the vibrational signals were found to be in a range comparable with others used for well-known arthropod communication systems. The vibrations produced by the host displayed distinct characteristics: they could usually be distinguished easily from background noise; could be perceived anywhere on the leaf; and were specific for a certain host stage and activity. Our findings support the hypothesis that vibration signals represent a reliable source of information to foraging parasitoids and, therefore, explain certain behavioural patterns observed in a population of S. sericeicornis females foraging in the field.     

Balanomorph barnacle larvae in the plankton at McMurdo Sound,Antarctica

Summary Ten larvae of a balanomorph barnacle were collected in plankton samples from under the sea-ice of McMurdo Sound in the austral spring 1985. This is the first record of planktonic barnacle larvae in the Antarctic Ocean. By deduction they are identified as Bathylasma corolliforme (Hoek) stage II nauplii and cyprids. They are described, the first of larvae of any species of the Bathylasmatidae. Their occurrence in McMurdo Sound is discussed in view of the apparent absence of adults in the Sound.     

The symbiotic relationship between the hydrocoral Millepora dichotoma and the barnacle Savignium milleporum

Translocation of radioactive ¹⁴C and ³²P between the pyrgomatine barnacle Savignium milleporum and the hydrocoral Millepora dichotoma in the Red Sea was investigated in order to discover any mutual nutritional benefits. Translocation of photosynthetic products from endosymbiotic zooxanthellae to the hydrocoral was demonstrated. There was no evidence that carbon was further translocated to the barnacle. However, hydrocorals bearing barnacles accumulated significantly more ¹⁴C and ³²P than those with no barnacles. The possibility that the hydrocorals recycle substances excreted by the barnacles is discussed in the context of the oligotrophic environment of the Red Sea.     

Antifouling activity of simple synthetic isocyanides against larvae of the barnacle Balanus amphitrite

Twelve simple linear isocyanides were synthesized and examined for antifouling activity and toxicity against cyprid larvae of the barnacle, Balanus amphitrite. Larval settlement was inhibited, with EC50 values of 0.046-1.90 microg ml(-1), and they were much less toxic (LD50 values ranging over 21.28 microg ml(-1)) than CuSO4 (EC50 0.30 microg ml(-1) and LD50 2.95 microg ml(-1)). The data indicate that simple linear isocyanides are promising non-toxic antifouling agents.     

Host location by Coccygomimus turionellae (Hymenoptera: Ichneumonidae)

Host location by the pupal parasitoid, Coccygomimus turionellae, was cued by both olfaction and contact chemoreception with host odor serving as a directional cue. The hosts' cocoons, silk, and pupae were all effective in evoking a response in the wasps. Preimaginal conditioning was not apparent but host species influenced the intensity of the wasp's response. Although efficiency was reduced, experienced wasps were able to locate hosts without air movement. The wasps responded to visual contrast and to three-dimensional effects, but not to specific shapes. In the absence of odor or tactile cues, visual attraction resulted in antennal palpation of the area, but very little ovipositor probing. Olfactory stimulation prior to visual or tactile tests significantly increased general activity and increased response to the cue itself. The most important cue to tactile or visual responses was contrast with the surroudings. Overall response was greater to tactile cues than to visual cues, and ovipositor probing occurred more often.

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Resume La découverte de l'hôte par le parasite de chrysalides, Coccygomimus turionellae est due à la fois à l'olfaction et à une perception chimique de contact, l'odeur de l'hôte servant de facteur orientateur. Les cocons des hôtes, la soie et la chrysalide provoquent tous une réponse de l'Ichneumonide. Le conditionnement préimaginal n'est pas apparent, mais les espèces hôtes influent sur l'intensité de la réponse. Les adultes répondent aux contrastes entre les objets et le fond, aux dimensions des objets dans les trois plans mais non à leur forme. La stimulation olfactive avant les tests visuels ou tactiles augmente significativement l'activité générale et la réponse elle-même. Le facteur le plus important pour les réponses visuelles et olfactives est le contraste avec le fond. La réponse globale aux facteurs tactiles est supérieure à celle aux facteurs visuels, les sondages par la tarière étant plus fréquents.

     

Seasonal species composition and distribution of barnacle larvae in Avacha Inlet (Kamchatka)

The annual dynamics of the numbers and distribution of barnaclelarvae in Avacha Inlet were studied. Planktonic cirripede larvaewere found in the area studied from late March at a temperatureof –1–0°C until October. The highest densityof 18 000 m^–3 was observed in mid-April. Balanus crenatusand Semibalanus cariosus were the dominant species, Chthamalusdalli and Balanus balanus larvae being less abundant. Naupliardensity was maximal at 0–5 m and decreased with depth.Maximum densities of B.crenatus larvae were observed in RakovayaBay, where there are many ships and a seawater-cooled powerstation. Most nauplii of the intertidal barnacle S.cariosus,which prefers wave-exposed open coast, were taken in the AvachaInlet narrows Settling on artificial substrata was most intensivefrom late May to early June     

Sex determination in the larvae of the parasitic barnacle Heterosaccus lunatus: an experimental approach

Heterosaccus lunatus parasitizes the portunid crab, Charybdis callianassa, in Moreton bay, Queensland, Australia. With the host crabs maintained at 25 °C this sacculinid rhizocephalan released larval broods every 5-6 days. This study examines the effect of photoperiod on the sex proportions of successive larval broods of individual parasites. Parasitized host crabs were maintained individually in circulating 25 °C seawater within two light-tight boxes, each with a controlled light-dark cycle operating. Box A had an LD 16:8 cycle (summer) and Box B an LD 8:16 cycle (winter). Both boxes had five host crabs and when parasites released their larval broods the larvae were flushed out and retained in a filter. Each captured brood then had its larvae sized to determine the proportions of the two sexes present. H. lunatus is ideal for such study because the sex(es) of all the larval stages (four naupliar stages and the cyprid) can be unequivocally identified by size (length). The experiment was run over a 6-week period during March and April 2004 when a total of 86 larval broods were released and their sex proportion(s) determined. It is concluded that larval sex determination is effected by photoperiod, with females becoming dominant under the winter condition (LD 8:16) and males dominant under the summer condition (LD 16:8). All initial broods were male dominated, so for Box A broods the male preponderance was maintained, whilst for Box B broods there was the progressive changeover to female preponderance. Such environmental sex determination is unusual because it is oogenesis which is being controlled, whereby two ovum sizes can be produced, either singly or together, the larger being the male egg. Further work is now necessary to verify the likely hormonal control processes involved.     

The screening of sponge extracts for antifouling activity using a bioassay with laboratory-reared cyprid larvae of the barnacle Balanus amphitrite

Antifouling coatings based on organotin compounds possess a world-wide threat to the environment and due to growing restrictions there is a need for environmentally safe antifouling systems. TNO is working on the development of novel antifouling systems based on secondary metabolites from sponges. Screening for natural antifoulants is conducted using a settlement assay with cyprid larvae of the barnacle Balanus amphitrite Darwin. Forty-four sponges (35 species) were collected from around the island of Curaçao in the Caribbean and settlement assays were performed with the ethyl-acetate extracts. Thirty-one extracts significantly inhibited cyprid settlement at 0.1 mg ml⁻¹, of which 22 significantly inhibited settlement at 0·01 mg ml⁻¹.     

Host location behaviour of Stomoxys calcitrans

Laboratory experiments on the host-finding behaviour of Stomoxys calcitrans conducted in a large slow-speed wind tunnel, showed that visual and olfactory stimuli and temperature and humidity are implicated. The flies landed preferentially on targets of low reflectance, but the effect of reflectance was influenced by the conspicuousness of the target against the background. The release of CO₂ and olfactory stimuli emanating (from a human arm), from the target enhanced flight activity. The results suggest that carbon dioxide induced imprecisely directed upwind flight, whereas human skin odour elicited precisely directed upwind orientation to its source. Skin odour may have an arrestant effect on flies landing on the target. Odours from mammalian blood and sweat had no effect. An increase in the temperature and humidity of the target airstream failed to influence the behaviour of the flies. However, the release of a target airstream which was both warm and moist, and contained CO₂ or skin odour increased the landing rate on the target. It is concluded that warmth and moisture induced settling by activated flies.

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Zusammenfassung Das Wirtslokalisations-Verhalten der blutsaugenden musciden Fliege Stomoxys calcitrans wurde in einem Windkanal untersucht, der in einer 3,24 m³ großen Flugkammer einen nahezu laminaren Luftstrom von 0,2–0,25 m/sec erzeugte. Ziele, von welchen bei kontrollierter Temperatur und Luftfeuchtigkeit dem Windkanal-Luftfluß zwei Luftströme zugeführt werden konnten, wurden in den Apparat gebracht. Diese Ziel-Luftströme konnten mit olfaktorischen Reizen versetzt werden und die Reflexion der Zieloberfläche konnte variiert werden. Die Wirkung ausgewählter olfaktorischer und visueller Reize sowie der Temperatur und Luftfeuchtigkeit auf die Reaktion von 24 Std gehungerten Fliegen beiderlei Geschlechts wurden untersucht. Die Anzahl der Landungen auf einer Kontrolle und auf einem Testziel, die sich nur hinsichtlich des zu untersuchenden Reizes unterschieden, wurde als Kriterium der Wirksamkeit dieser Reize benutzt.Die Fliegen landeten bevorzugt auf Zielen mit geringer Reflexion, doch wurde die Wirkung der Reflexion durch die Erkennbarkeit des Zieles gegen den Hintergrund beeinflußt. Wenn CO₂ und olfaktorische Reize vom Arm einer menschlichen Versuchsperson vom Testziel freigelassen wurden, wurde ein Anstieg der Flugaktivität und der Landeraten an beiden Zielen beobachtet. Die Ergebnisse lassen vermuten, daß CO₂ einen ungenau gerichteten Flug gegen die Luftströmung auslöst, während menschlicher Hautduft eine genau windaufwärts gerichtete Orientierung zu seiner Quelle hervorruft. Die Beobachtungen geben weiterhin Veranlassung zu der Annahme, daß der Hautgeruch einen Verweileffekt auf die Fliegen ausübt, die auf dem Ziel gelandet sind. Düfte von Blut und Hautsekreten von Säugetieren hatten keine Wirkung.Ein Anstieg der Temperatur und Luftfeuchtigkeit des Ziel-Luftstroms hatte keinen Einfluß auf die Reaktion gegenüber dem Ziel, es sei denn, die Fliegen waren zugleich durch CO₂ oder Hautgeruch aktiviert. Sogar nach einer solchen Aktivierung blieb die Wirkung aus, wenn der LLuftstrom nicht sowohl warm (35°) als auch feucht (100% rel. LF) war. Die Ergebnisse führen zu der Vermutung, daß Wärme und Feuchtigkeit, die nur in der näheren Umgebung des Wirtes wahrnehmbar sind, die aktivierten Fliegen zur Landung veranlassen.Die Befunde lassen beträchtliche Ähnlichkeiten im Wirtsfinde-Verhalten zwischen Stomoxys calcitrans und Mücken erkennen, sowohl hinsichtlich der mitwirkenden Reize als auch der Reaktionen, die sie hervorruten.