Phototactic and geotactic responses inAllothrombium pulvinum larvae (Acari: Trombidiidae)

Phototactic and geotactic responses of larvae ofAllothrombium pulvinum Ewing were examined in the laboratory.Allothrombium pulvinum larvae showed positive phototaxis and negative geotaxis. Positive phototaxis and negative geotaxis in larvalA. pulvinum and other trombidioids are adaptive, because these mechanisms help mites that hatch in dark soil to find hosts on plants above ground in the light.     

The role of light and gravity in the experimental transmission of Echinostoma caproni (Digenea: Echinostomatidae) cercariae to the second intermediate host, Biomphalaria glabrata (Gastropoda: Pulmonata)

Trematode cercariae inhabit predictable environments and respond to trigger cues with genetically fixed releaser responses when foraging for the upstream host. The effect of light and gravity on the transmission of Echinostoma caproni cercariae to Biomphalaria glabrata was investigated experimentally. Transmission chambers were constructed of clear polyvinyl chloride pipe. Snails were constrained within the chamber to prevent movement, while permitting the cercariae to swim freely. A trial consisted of 2 infected B. glabrata shedding E. caproni cercariae placed at the center of the chamber, with 5 uninfected B. glabrata placed 10 cm on either side (or above and below) of the shedding snails as sentinels. There was no significant difference in the prevalence of infection sentinel snails in either experiment (light vs. dark or top vs. bottom); however, mean intensity was significantly higher in sentinel snails in the dark portion of the chamber (42.5 vs. 10.4; P = 0.001) and the top of the transmission chamber (66.1 vs. 38.0; P = 0.0003). There was a high correlation between the number of metacercariae collected from sentinel snails and the total number of infective units (metacercariae + unsuccessful cercariae): r = 0.992 (light vs. dark) and r = 0.957 (top vs. bottom), respectively, at cercariae densities estimated from 22 to 3,304/L. The results suggest that cercariae of E. caproni exhibit negative photo- and geotaxis in searching for a second intermediate host. Stereotypical releaser responses to environmental trigger cues (light and gravity) allow E. caproni cercariae to exploit flexible strategies for completing the life cycle consistent with the broad range second intermediate and definitive hosts used by E. caproni cercariae and adults, respectively.     

Where to from here? The mechanisms enabling the movement of first instar caterpillars on whole plants using Helicoverpa armigera (Hübner)

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is an economically-important, polyphagous herbivore in Old World countries. The distribution of larvae within various host plants has been described, but few studies have tried to determine the behavioural mechanisms by which the given distributions arose. Our aim was to determine the mechanisms which enable larval movement on pea plants, starting with first instars. Observations and bioassays determined larval movement in response to light and angled surfaces, as well as the effect of feeding and plant volatiles on these responses. The majority (68–72%) of 1st instars were positively phototactic towards blue, green and white light and 42% towards UV light. In the dark, larvae showed negative geotaxis. The angle of their substrate also had a kinetic effect on larvae; the steeper the angle from horizontal the more larvae moved under all conditions. Phenylacetaldehyde (a flower volatile) suppressed larval movement except at 90°. (Z)-3-Hexenyl acetate (a green leaf volatile) reversed the direction of movement at the flattest angle. Feeding lessened the probability of moving. We suggest that phototaxis and geotaxis are behaviours common to larval lepidopterans (caterpillars), and that these basic behaviours are modulated by environmental, larval, and plant factors to give observed distributions. Using a multinomial model approach, we created a flow chart to qualitatively and quantitatively represent the decision-making process of first instar H. armigera in response to the factors influencing movement.     

The effect of light and darkness on the production of cercariae of Schistosoma haematobium from Bulinus globosus

The cercariae of Schistosoma haematobium showed a diurnal periodicity of emergence from Bulinus globosus in a twelve hour light/dark cycle. Peak emission occurred at 11.00 hrs with a smaller peak at 20.00 hrs, following the start of the period of darkness. In continuous illumination this second peak was not seen, indicating that only the morning peak is circadian in origin. The evening peak occurs in response to dark treatment and can be produced by periods of darkness ranging from eight seconds to one hour. The longer the period of dark treatment the longer the rise in output is maintained on return to light conditions. Subjection of snails to periods of dark treatment during the normal light period caused a reduction in the evening peak with the largest effect seen following the longest period of darkness. An increased output of cercariae was seen following fifteen minutes exposure to a range of light intensities, the largest increase occurring at 10,000 and 7000 lux and complete darkness. The rapidity of this reaction to variations in light intensity suggests that the cercariae of S. haematobium are showing emergence in response to shadows.     

A laboratory study on the short-term zonal oscillations of the trochid Monodonta turbinata (Born) (Mollusca: Gastropoda)

Zonal oscillations of Monodonta turbinata (Born) were monitored with an actographic device which precluded clustering behaviour. Unfed snails maintained their cyclic pattern of behaviour for up to 8 days under a light-dark cycle which simulated the natural one. Under constant conditions of light or dark, however, the snails ceased migration and occupied a zonal position typical of day and night, respectively. Experiments in diffuse light and with light from below the floor of the experimental tank showed that the downward migration of M. turbinata in the daytime depends on positive geotaxis combined with negative phototaxis whilst the upward migration at night depends on a negative geotaxis. This mechanism is similar to that described in other littoral molluscs. There was no evidence of an endogenous control of rhythmic zonal activity.     

思茅新木蛾幼虫取食行为的研究

本文对思茅新木蛾Neospastis simaona Wang幼虫的取食行为、取食偏好性以及明暗条件对其取食量的影响进行了观察研究,为该昆虫的防治提供了理论依据。研究结果表明:思茅新木蛾幼虫随着龄期的增加,取食次数增多,取食总时间增加,但一次取食时间无明显变化;思茅新木蛾幼虫对木荷(Schima superba)有强烈嗜食性,4龄幼虫喜食木荷幼叶,5、6龄幼虫对木荷幼叶、成熟叶无明显偏好性;明暗条件对思茅新木蛾4至6龄幼虫的取食量没有显著影响(P>0.05)。     

Sunscreen for Fish: Co-Option of UV Light Protection for Camouflage

Many animals change their body pigmentation according to illumination of their environment. In aquatic vertebrates, this reaction is mediated through aggregation or dispersion of melanin-filled vesicles (melanosomes) in dermal pigment cells (melanophores). The adaptive value of this behavior is usually seen in camouflage by allowing the animal to visually blend into the background. When exposed to visible light from below, however, dark-adapted zebrafish embryos at the age of 2 days post fertilization (dpf) surprisingly display dispersal instead of aggregation of melanosomes, i.e. their body coloration becomes dark on a bright background. Melanosomes of older embryos and early larvae (3–5 dpf) on the other hand aggregate as expected under these conditions. Here we provide an explanation to this puzzling finding: Melanosome dispersion in larvae 3 dpf and older is efficiently triggered by ultraviolet (UV) light, irrespective of the visual background, suggesting that the extent of pigmentation is a trade-off between threats from predation and UV irradiation. The UV light-induced dispersion of melanosomes thereby is dependent on input from retinal short wavelength-sensitive (SWS) cone photoreceptors. In young embryos still lacking a functional retina, protection from UV light predominates, and light triggers a dispersal of melanosomes via photoreceptors intrinsic to the melanophores, regardless of the actual UV content. In older embryos and early larvae with functional retinal photoreceptors in contrast, this light-induced dispersion is counteracted by a delayed aggregation in the absence of UV light. These data suggest that the primary function of melanosome dispersal has evolved as a protective adaption to prevent UV damage, which was only later co-opted for camouflage.     

Seasonal dynamics of diurnal production and rhythmic of diurnal production of the cercaria Diplostomum volvens Nordmann, 1832 in molluscs of the genus Lymnaea from lakes of the Karasuk water system

Infection rate of the cercariae Diplostomum volvens in molluscs of the genus Lymnaea in natural conditions (Western Siberia) was examined in 1990-1994. Experimental studies have shown that light and water temperatire are main factors regulating rhythmic of diurnal production of cercariae by molluscs.     

Effects of ultraviolet radiation on an intertidal trematode parasite: an assessment of damage and protection

Trematode parasites are integral components of intertidal ecosystems which experience high levels of ultraviolet radiation. Although these parasites mostly live within hosts, their life cycle involves free-living larval transmission stages such as cercariae which are directly exposed to ambient conditions. UV has previously been shown to considerably reduce the survival of cercariae. Here, we investigated potential mechanisms of protection and damage related to UV in the intertidal trematode Maritrema novaezealandensis. Firstly, the presence of sunscreen compounds (i.e. mycosporine-like amino acids) was quantified in the parasite tissue producing cercariae within a snail host, as well as in the free-swimming cercariae themselves. Secondly, levels of oxidative stress in cercariae after exposure to UV were investigated (i.e.protein carbonyls, catalase and superoxide dismutase). Thirdly, the DNA damage (i.e. cyclobutane–pyrimidine dimers) was compared between cercariae exposed and not exposed to UV. Lastly, functional aspects(survival and infectivity) of cercariae were assessed, comparing cercariae under light conditions versus dark after exposure to UV. We confirmed the presence of my cosporine-like amino acids in cercariae-producing tissue from within snail hosts, but were unable to do so in cercariae directly. Results further suggested that exposure to UV induced high levels of oxidative stress in cercariae which was accompanied by a reduction in the levels of protective antioxidant enzymes present. We also identified higher levels of DNA damage in cercariae exposed to UV, compared with those not exposed. Moreover, no clear effect of light condition was found on survival and infectivity of cercariae after exposure to UV. We concluded that cercariae are highly susceptible to UV damage and that they have very little scope for protection against or repair of UV-induced damage.     

The Effect of Age on the Phytochrome-Mediated Chlorophyll Formation in Dark-grown Bean Leaves

The effect of red and far-red treatment on chlorophyll synthesis in dark-grown bean leaves was studied at various ages. Although the effect was pronounced in the old leaves, no effect was observed in the young ones (4 days old). In the 5-day old leaves a measurable effect of red light pretreatment can be observed, whereas the far-red reversal effect was not observed. — The length of the dark period between the red pretreatment and the continuous illumination is also age dependent. Leaves older than 6 days show a maximum at about six hours, while in the young leaves the red light effect increases with the time of dark incubation up to the 24 hours tested. — The reversal effect of far-red light on protochlorophyllide regeneration was also examined. The far-red light has no reversal effect on leaves younger than 6 days old, while on the old leaves it has such an effect.     

Toxicity of zinc to schistosoma Mansoni Cercariae in a Chemically Defined Water Medium

Time-until-death studies were run on cercariae of Schistosoma mansoni in 15 concentrations of zinc (from zinc sulfate) ranging from 57.6 ppm to 1 ppb. A chemically defined water medium was used for the dilution and control medium, and a partially enclosed slide chamber was perfected for the detailed observation of test cercariae. In concentrations of less than 57.6 ppm, zinc was found to have little lethal effect on cercariae during that period in which these larvae were most likely to be infective (0–6 hours) after emergence. Zinc concentration of 1 ppb killed all test cercariae within 46 hours at 21–22°C.At the highest concentration tested, 57.6 ppm zinc immobilized all test organisms within 6 hours at 21–2°C. The average time for 100 percent mortality for the control was 49 hours. The cercaricidal effects of zinc were shown to be insignificant in concentrations that would not be detrimental to other aquatic organisms.     

环境因子对两种海洋双壳类幼体趋性行为中的调节作用

本文研究了温度、盐度和重金属等几种因子对缢蛏和长牡蛎幼体趋地性和趋光性行为的影响。结果表明:1)降低温度能增强缢蛏幼体的正趋地性,而长牡蛎幼体却由正趋地性转变为负趋地性,同时两种幼体的正趋光性受到抑制作用;升高温度对缢蛏幼体趋光性的影响不明显,但能加强牡蛎幼体的正趋光性。2)盐度提高时缢蛏幼体的正趋光性趋于增强,正趋地性趋于减弱。3)重金属Cu和Zn在各自的亚致死浓度下具有提高缢蛏幼体正趋地性和降低正趋光性的作用,而牡蛎幼体的正趋地性却趋于减弱,正趋光性趋于增强。本文据上述幼体的行为变化,还讨论了这几种因子对幼体垂直分布的调节作用。     

Patterns and processes of larval emergence in an estuarine parasite system

Trematode parasites in intertidal estuaries experience constantly varying conditions, with the presence or absence of water potentially limiting larval transport between hosts. Given the short life spans (< or =24 h) of cercariae, emergence timing should be optimized to enhance the probability of successful transmission. In the present study, field measurements and laboratory experiments identified processes that regulate the emergence of cercariae from their first intermediate snail hosts in an intertidal marsh. Larvae emerged over species-specific temperature ranges, exclusively during daylight hours, and only when snails were submerged. The three factors operate over different temporal scales: temperature monthly, light diurnally (24-h period), and water depth tidally (12-h period). Each stimulus creates a necessary condition for the next, forming a hierarchy of environmental cues. Emergence as the tide floods would favor transport within the estuary, and light may trigger direct (downward or upward) swimming toward host habitats. Abbreviated dispersal would retain asexually reproduced cercariae within the marsh, and local mixing would diversify the gene pool of larvae encysting on subsequent hosts. In contrast to the timing of cercarial release, emergence duration was under endogenous control. Duration of emergence decreased from sunrise to sunset, perhaps in response to the diminishing lighted interval as the day progresses. Circadian rhythms that control cercarial emergence of freshwater species (including schistosomes) are often set by the activity patterns of subsequent hosts. In this estuary, however, the synchronizing agent is the tides. Together, exogenous and endogenous factors control emergence of trematode cercariae, mitigating the vagaries of an intertidal environment.     

Experimental investigations on the behaviour of the cercariae of an ectoparasitic digenean Transversotrema patialense: general activity patterns

The activity patterns of the cercariae of Transversotrema patialense have been examined by monitoring the behaviour of individual larvae. Records of three different behavioural modes, namely active, tail-first swimming, passive dropping and resting periods were made separately. The age- and temperature-dependence of the activity patterns during the spontaneously active life of the cercariae were examined and estimates made of the absolute speeds of swimming and dropping. Through the temperature range 25--32 degrees C, the spontaneously active life of cercariae declined from about 18 h to about 6 h. Within this interval, after an initial period of high activity rates, a gradual decline in activity followed. The decline was a result of a decreasing frequency of swimming events rather than any change in the durations of such events. The neural control and energetic significance of the cercarial activity patterns are discussed.     

Role of eosinophils in the destruction of schistosomula of Schistosoma mansoni in vivo (preliminary report)

Schistosoma mansoni cercariae mechanically transformed into schistosomula were injected, either dead or alive, into the tail vein (2.000 larvae/0,15 ml) of Balb/c mice which were either previously infected with S. mansoni (10 weeks/50 cercariae) or non-infected. Histological examination of the lungs 24, 48, 72 and 96 hours after injection revealed that inflammatory reaction around schistosomula occurred only in the groups injected with dead schistosomula (killed by freezing and thawing). In non-infected animals the reaction was predominantly macrophagic while in those infected many eosinophils appeared around the dead larvae. These results are at variance with those obtained in vitro and suggest that in vivo the participation of eosinophils in the schistosomulum induced reaction in sensitized animals is secondary to the death of the larvae.     

The ontogeny of physiological response to light intensity in early stage spiny lobster (Jasus edwardsii) larvae

Early stage phyllosoma larvae of the spiny rock lobster Jasus edwardsii were examined for swimming speed, feeding, oxygen consumption and nitrogen excretion as instantaneous performance indicators when exposed to different irradiance levels. Swimming speed was measured in recently hatched Stage I larvae while all other parameters were measured in larvae from hatch to mid-Stage V. The swimming speed of recently hatched Stage I phyllosoma increased logarithmically between light intensities of 2.9 x 10(14) and 1.8 x 10(16) quanta s(-1) cm(-2) indicating that, within this range, swimming activity was only suppressed at the lowest irradiance level. Larvae examined under dark (no light) conditions showed lower feed intake, oxygen consumption and nitrogen excretion than larvae under low (7.7 x 10(12) q s(-1) cm(-2)) and high (3.9 x 10(14) q s(-1) cm(-2)) light intensities, and this was a consistent pattern observed throughout development from hatch to Stage V. There was no difference in feeding, oxygen consumption and nitrogen excretion between larvae exposed to low and high light intensities. However, from mid-Stage I to mid-Stage V, the metabolic feeding efficiency (feed intake:oxygen consumption ratio) was consistently higher in larvae exposed to low light intensity than in phyllosoma assessed in the dark and under high irradiance. A light intensity of about 7.7 x 10(12) quanta s(-1) cm(-2) and no higher than 3.9 x 10(14) quanta s(-1) cm(-2) is recommended to stimulate feeding and optimise metabolic feeding efficiency in early larval stages of J. edwardsii.     

The influence of anhydrobiosis on the infestation of Biomphalaria glabrata by Schistosoma mansoni miracidium

410 Biomphalaria glabrata (Caribbean strain of Guadeloupe) have been infected with one miracidium of Schistosoma mansoni, 110 snails, used as controls have been kept into water; the survival rate was 96.4% after 4 weeks and 25.4% produced cercariae. 300 snails were kept on wet soil, and submitted for 6 weeks to progressive desiccation. The survival rate was 23.4% but only 9 of them produced cercariae. Periodic variations of the production of male and female larvae have been shown by the weekly test of the cercariae productions. In previously desiccated snails, the production of male and female cercariae is similar while in controls the production of female larvae is more important. In experimental snails, the larval development seems to be stopped during anhydrobiosis. The production of cercariae is just delayed for the length of the dry keeping.     

Strain dependent response of circadian rhythms during exposure to continuous illumination

Enzymes activities were measured, at three hours intervals, during 30 hours, in various tissues of C57BL/6J and A/J male mice. The measurements, were carried out on mice which were exposed for two, five and twenty one days to continuous illumination. Identical measurements were performed also on mice which were kept in alternating 14 hours light: 10 hours dark. Activity patterns of each group were analysed to test the presence, or absence, of rhythm characteristics. The results of the experiments with C57BL/6J have been previously reported. The comparison of the results, which were obtained from the two strains revealed that under exposure to alternating light: dark conditions all activity patterns exhibited a significant circadian rhythm. Except for one enzyme (thymus GAPD), the times of peak activity (acrophase) were identical for all other examined enzymes, in both strains. On the other hand when the two strains were exposed to continuous illumination they differed in their response to the effect of continuous light. The activity of the same enzyme exhibited different periodicity and/or different acrophase in each of the two strains. This variability reflects the existence of genetic differences, between the strains in the free running behavior of these enzymes' activity rhythms.