Development of the brine shrimp Artemia is accelerated during spaceflight

Developmentally arrested brine shrimp cysts have been reactivated during orbital spaceflight on two different Space Shuttle missions (STS-50 and STS-54), and their subsequent development has been compared with that of simultaneously reactivated ground controls. Flight and control brine shrimp do not significantly differ with respect to hatching rates or larval morphology at the scanning and transmission EM levels. A small percentage of the flight larvae had defective nauplier eye development, but the observation was not statistically significant. However, in three different experiments on two different flights, involving a total of 232 larvae that developed in space, a highly significant difference in degree of flight to control development was found. By as early as 2.25 days after reactivation of development, spaceflight brine shrimp were accelerated, by a full instar, over ground control brine shrimp. Although developing more rapidly, flight shrimp grew as long as control shrimp at each developmental instar or stage.     

Effect of food abundance on larval lake whitefish, Coregonus clupeaformis Mitchill, growth and survival

The effect of food ration on larval lake whitefish, Coregonus clupeaformis , growth and survival was determined in the laboratory using brine shrimp as the test prey. In replicate experiments, larval whitefish were fed one of seven different rations of brine shrimp over a 25 day period. Statistically significant differences were found between larval growth and survival at each feeding level. Larvae fed to excess were 1.33 times as long and 2.80 times as heavy as those on the 1.8 zooplankton/fish (z/f) ration. No mortality was recorded until after day 15 of the experiment by which time all larvae had resorbed their yolk sac. Total mortality followed within 1 week for all feeding densities with the exception of the three highest (18 z/f, 32 z/f and excess rations) where total mortality equalled 90%, 12% and 0%, respectively.     

Laboratory culture of the Nudibranch Tritonia diomedea bergh (Tritoniidae: Opisthobranchia) and some aspects of its behavioral development

Tritonia diomedea Bergh was reared from oviposition, through metamorphosis to reproductive maturity in the laboratory. The larvae of T. diomedea are planktotrophic and undergo considerable shell growth (from 144.6–329 μ average maximum shell length). Metamorphosis does not require induction, but there may be a preference to metamorphose in the presence of the probable adult prey, a small Virgularia sp. Larvae in cultures fed no food, Dunaliella tertiolecta Butcher Isochrysis galbana Parke, or Monochrysis lutheri Droop did not achieve metamorphic competence at near ambient sea-water temperatures (11.9±1.3 and 13.0±0.8°C). Larvae from cultures fed Monochrysis at room temperature (20.8±1.5°C) or fed a 1 : 1 mixture of Isochrysis and Monochrysis at near ambient sea-water temperatures did metamorphose. Even so, only those larvae fed the 1 : 1 mixture survived more than a few days following metamorphosis. Adult behavioral patterns developed gradually, feeding being first observed at 5 days, swimming in response to NaCl crystals at about 60 days, copulation at about 272 days, and oviposition at about 277 days after metamorphosis. Growth rates were determined for field collected Tritonia diomedea; smaller animals gained and lost weight relatively faster than larger animals.     

Morphological variation in a larval salamander: dietary induction of plasticity in head shape

We examined diet-dependent plasticity in head shape in larvae of the eastern long-toed salamander, Ambystoma macrodactylum columbianum. Larvae in some populations of this species exhibit trophic polymorphism, with some individuals possessing exaggerated trophic features characteristic of a cannibalistic morphology in larval Ambystoma; e.g. a disproportionately broad head and hypertrophied vomerine teeth. We hypothesized that 1) head shape variation results from feeding upon different types of prey and that 2) cannibal morphs are induced by consumption of conspecifics. To induce variation, we fed three groups of larvae different diets: 1) brine shrimp nauplii only; 2) nauplii plus anuran tadpoles; 3) nauplii, tadpoles and conspecific larval salamanders. Comparisons of size (mass)-adjusted means revealed that this manipulation of diet induced significant variation in six measures of head shape, but not in the area of the vomerine tooth patch. For five of the six head traits, larvae that ate tadpoles and brine shrimp nauplii developed significantly broader, longer and deeper heads than did larvae that only ate brine shrimp nauplii. The ingestion of conspecifics, in addition to nauplii and tadpoles, significantly altered two head traits (interocular-width and head depth), compared to larvae only fed nauplii and tadpoles. Canonical discriminant function analysis detected two statistically reliable canonical variables: head depth was most highly associated with the first canonical variable, whereas three measures of head width (at the jaws, gills and eyes) and interocular width were most highly associated with the second canonical variable. Despite this diet-enhanced morphological variation, there was no indication that any of the three types of diet (including conspecific prey) induced the exaggerated trophic features of the cannibal morph in this species. These results illustrate that ingestion of different types of prey contributes to plasticity in head shape, but that some other proximate cue(s), either alone or in combination with diet variation, is essential to induce the extremes of trophic polymorphism in this species.     

Epizootiology of Eustrongylides ignotus in Florida: transmission and development of larvae in intermediate hosts

Under laboratory conditions, 2 modes of transmission of Eustrongylides ignotus (Nematoda: Dioctophymatoidea) to fish were identified. Eastern mosquitofish (Gambusia holbrooki) became infected after ingestion of either eggs of E. ignotus containing first-stage larvae or aquatic oligochaetes (Limnodrilus hoffmeisteri) containing third-stage larvae of E. ignotus. After removal from the uterus of gravid E. ignotus females and incubation for 17-28 days, depending on temperature, it was found that parasite eggs contained first-stage larvae that were infective to fish and oligochaetes. Larvae developed to the third stage in oligochaetes and were infective to fish 35-77 days postinfection (PI) and when fed to fish, developed to the fourth stage between 127 and 184 days PI. Eggs containing first-stage larvae fed directly to fish developed to the fourth stage between 84 and 105 days PI. The amount of time for development from the undifferentiated egg to the fourth-stage larva was 78-156 days shorter when fish ingested eggs containing first-stage larvae than when fish ingested oligochaetes containing third-stage larvae. Three species of large piscivorous fish, including black crappie (Pomoxis nigromaculatus), largemouth bass (Micropterus salmoides), and warmouth (Lepomis gulosus), were fed mosquitofish containing fourth-stage larvae. At necropsy, live E. ignotus larvae were recovered from all 3 species. Several fish had multiple infections after ingesting > 1 larva, indicating that bioaccumulation of the parasite in the food chain may occur.     

Manipulation of dietary lipids, fatty acids and vitamins in zooplankton cultures

1. A wide range of species that are cultivated in commercial mariculture are planktonic during at least part of their life cycle; for example, the larval stages of shellfish (shrimp and molluscs) and the live feeds (rotifers, brine shrimp, copepods) used in the larviculture of marine fish and shellfish. Over the last decades various techniques have been developed to deliver nutrients to these zooplanktonic organisms either through artificial diets or by manipulating the composition of the live prey fed to the carnivorous stages. This paper reviews the methodology that has allowed aquaculturists to gain knowledge of nutritional requirements and may offer interesting opportunities for ecologists to verify the importance of key nutrients in the natural food chain of marine as well as freshwater ecosystems.
2. Live micro-algae can be replaced partially or completely in the diet of filter-feeders such as rotifers, Artemia , shrimp larvae and bivalves, by various types of preserved algae, micro-encapsulated diets and yeast-based diets, whereas lipid emulsions and liposomes may be utilized to supplement specific lipid-and water-soluble nutrients, respectively. Microbound and micro-encapsulated diets have been designed to supplement live feed in the culture of micro-predators such as fish and shrimp larvae.
3. Live prey organisms, in particular rotifers and Artemia , can be 'bio-encapsulated' with a variety of enrichment diets to manipulate their content in certain nutrients, including ω3 highly unsaturated fatty acids (FA) and the vitamins C, A and E. Nevertheless, the enrichment techniques are not applicable for all nutrients and prey organisms. Phospholipid composition is difficult to manipulate through the diet of live feed and the enrichment of the essential FA docosahexaenoic acid (DHA) is hampered in most Artemia species due to the catabolism of this FA following enrichment.     

Methodical aspects of rearing decapod larvae,Pagurus bernhardus (Paguridae) andCarcinus maenas (Portunidae)

Improved methods for experimental rearing ofPagurus bernhardus andCarcinus maenas larvae are presented. Isolated maintenance was found essential for reliable statistical evaluation of results obtained from stages older than zoea-1. Only by isolated rearing is it possible to calculate mean values ±95% confidence intervals of stage duration. Mean values (without confidence intervals) can only be given for group-reared larvae if mortality is zero. Compared to group rearing, isolated rearing led to better survival, shorter periods of development and stimulated growth. Due to different swimming behaviorP. bernhardus zoeae needed larger water volumes thanCarcinus maenas larvae.P. bernhardus zoeae were reared with best results when isolated in Petri dishes (ca. 50 ml). They fed on newly hatched brine shrimp nauplii (Artemia spp.).P. bernhardus megalopa did not require any gastropod shell or substratum; it developed best in glass vials without any food.C. maenas larvae could be reared most sucessfully in glass vials (ca 20 ml) under a simulated day-night regime (LD 16:8); constant darkness had a detrimental effect on development, leading to prolonged stage-duration times.C. maenas larvae were fed a mixture of newly hatched brine shrimp naupli and rotifers (Brachionus plicatilis).     

Biochemical composition during growth and starvation of early larval stages of cultured spiny lobster (Jasus edwardsii) phyllosoma

We examined biochemical changes accompanying feeding and starvation from hatch to Stage VI (day 74 after hatch) in spiny lobster, Jasus edwardsii, phyllosoma larvae. Larval dry weights (dw) increased 17-fold from hatch (80+/-1 microg) to Stage VI (1415+/-44 microg). Larvae starved for 6-11 days at Stages II, IV and VI were 14-40% lighter than their fed counterparts fed enriched Artemia. The increases and losses in total dry weight during feeding and starvation were associated with changes in the content of protein (constituting 31.4-41.7% of dw) and carbohydrate (constituting 2.6-5.3% of dw), while larger changes in lipid content indicated its greater importance as an energy substrate. Lipid content increased from 7.9% of dw at hatch to its highest of 12.5% at Stage IV, but declined by 50% or more during starvation. This suggests that protein, carbohydrate and lipid are all important energy stores, although lipids are catabolized at a greater rate during food deprivation. The principal lipid class was polar lipid (PL; 79-92% of total lipid), followed by sterol (ST; 6-20%), with triacylglycerol and other lipid classes at <2%. PL were catabolized and ST were conserved during starvation. Changes in the fatty acid (FA) profile had mostly occurred before the first moult at day 8 after hatch, with gradual changes thereafter to Stage VI, reflecting their abundance in the Artemia diet. There was some conservation of the major essential FAs, 20:4n-6, 20:5n-3, 22:6n-3, and the FA profile showed large gains in the C(18) polyunsaturated FA, 18:1n-9, 18:2n-6. Ascorbic acid content increased 10-fold from hatch to the end of Stage I (36 and 333 microgg(-1) dw, respectively), while the content at the end of Stage II was higher in fed than that in starved larvae (439 and 174 microgg(-1) dw, respectively). Our study will assist in the development of alternatives to nutritionally incomplete diets, such as live ongrown Artemia, to meet the requirements of phyllosoma in culture.     

The importance of honeydew as food for larvae of Chrysoperla carnea in the presence of aphids

Larvae of the common green lacewing Chrysoperla carnea are predacious and feed on a wide range of small, soft‐bodied arthropods. In addition to their feeding on prey arthropods to cover their nutritional requirements for growth and development, the consumption of non‐prey foods such as honeydew has been reported. It is commonly believed that these food supplements are primarily exploited by the larvae when prey is scarce or of low nutritional quality. Here, we assess whether C. carnea larvae also use honeydew when high‐quality aphid prey are readily available. In a choice experiment, the feeding behaviour of C. carnea larvae was observed in the presence of both aphids and honeydew. The larvae were starved, aphid‐fed, or honeydew‐fed prior to the experiment. The time spent feeding on honeydew compared with feeding on aphids was highest for starved larvae and lowest for honeydew‐fed larvae. Among the three treatments, the aphid‐fed larvae spent the most time resting and the least time searching. In an additional experiment food intake was assessed in terms of weight change when larvae were provided with an ad libitum supply of either aphids or honeydew. Larvae yielded a significant lower relative weight increase on honeydew compared with aphids. The reduced weight increase on honeydew was compensated when larvae were subsequently provided with aphids, but not when honeydew was provided again. This study showed that (i) prior honeydew feeding reduces overall aphid consumption, and (ii) larvae do consume honeydew even after they have been given ad libitum access to aphids. The fact that larvae of C. carnea still use honeydew as a food source in the presence of suitable prey underlines the importance of carbohydrates as foods.     

PLASTICITY OF JAW AND SKULL MORPHOLOGY IN THE NEOTROPICAL CICHLIDS GEOPHAGUS BRASILIENSIS AND G. STEINDACHNERI

I examined plasticity of jaw and skull morphology induced by feeding different diets in two species of the neotropical cichlid genus Geophagus. The two species possess different modes of development, which affect the size at which young begin feeding. I hypothesized that the difference in size at first feeding could lead to a difference in the amount of change inducible in the two species. The young of the substrate-spawning species, G. brasiliensis, which begin feeding at a smaller size, were predicted to be more plastic than those of the mouthbrooding species, G. steindachneri. The two diets used to induce differences were brine shrimp nauplii and chironomid larvae. Numerous measures of the jaw and skull differed significantly between groups fed the two diets but the amount of plasticity induced was small and would not present a problem for taxonomists. Contrary to my prediction, both the magnitude and pattern of plasticity induced in the two species was similar. Thus, mode of parental care and the size at which young begin feeding do not affect the degree of plasticity. Fish fed brine shrimp nauplii were longer in oral jaw region, but were shorter and shallower in the area behind the oral jaws. An additional group of G. brasiliensis was fed flake food to compare the results of this study to other studies. The differences in measures between fish fed brine shrimp diets and flake food diets were greater than those between fish fed brine shrimp and chironomid larvae. A possible role of plasticity for enhancing rather than retarding morphological evolution is discussed.     

Effects of toxic Alexandrium species on the survival and feeding rates of brine shrimp, Artemia salina

Zooplankton is an important link between phytoplankton and higher consumers in the marine food chain. To investigate the harmful effects of the toxic dinoflagellate Alexandrium species on zooplankton, 4 strains of Alexandrium spp., isolated from the Chinese coast, were used to test the species' effects on the survival and feeding rates of the brine shrimp, Artemia salina. The experiment was designed to assess the response of A. salina in each stage of its life cycle: nauplii, metanauplii, and adult. Each experiment was conducted in a 500 ml treatment that was added. The toxic treatments consisted of single strains of A. minutum, A. catanella, and A. tamarense (Nanhai and Donghai strain), while non-toxic species (dinoflagellate Prorocentrum donghaiense and diatom Chaetoceros minutissimus) were used as control treatments. An additional phytoplankton treatment consisted of, a mixture of A. tamarense (Nanhai strain) and P. donghaiense. Alexandrium spp. species were found to have lethal effects on the brine shrimp at a density of 2000 cells/ml. All the brine shrimps died within 24-168 hours of inoculation with the 4 treatments each containing single toxic Alexandrium species. During the feeding experiment, toxic Alexandrium spp. caused a reduction in the feeding rates in all the three stages of the life cycle of A. salina, whereas this response was not obvious in the treatment involving the nontoxic species P. donghaiense. The body surface of the brine shrimp that were fed on Alexandrium species was consistently covered by a sticky floc. Mortality of A. salina was observed to increase with the occurrence of the floc. The toxicity of the paralytic shellfish poisons (PSP) produced by the Alexandrium species was not significantly correlated with the survival or the feeding rate of the brine shrimp. When A. tamarense was mixed with P. donghaiense, the lethal effect of A. tamarense decreased, as shown by an increase in the survival and the feeding rates of the brine shrimp. A. salina metanauplii were found at the life stage most sensitive to the toxic algae and hunger. In summary, toxic Alexandrium spp. were found to have lethal effects on A. salina and to restrain the brine shrimp's feeding rate. Nontoxic Prorocentrum mitigated the toxicity of Alexandrium to a certain extent. The results also imply that the sticky material on the surface of the body of the brine shrimp may have been an important lethal factor rather than the PSP toxins.     

Effects of toxic Alexandrium species on the survival and feeding rates of brine shrimp, Artemia salina

Zooplankton is an important link between phytoplankton and higher consumers in the marine food chain. To investigate the harmful effects of the toxic dinoflagellate Alexandrium species on zooplankton, 4 strains of Alexandrium spp., isolated from the Chinese coast, were used to test the species' effects on the survival and feeding rates of the brine shrimp, Artemia salina. The experiment was designed to assess the response of A. salina in each stage of its life cycle: nauplii, metanauplii, and adult. Each experiment was conducted in a 500 ml treatment that was added. The toxic treatments consisted of single strains of A. minutum, A. catanella, and A. tamarense (Nanhai and Donghai strain), while non-toxic species (dinoflagellate Prorocentrum donghaiense and diatom Chaetoceros minutissimus) were used as control treatments. An additional phytoplankton treatment consisted of, a mixture of A. tamarense (Nanhai strain) and P. donghaiense. Alexandrium spp. species were found to have lethal effects on the brine shrimp at a density of 2000 cells/ml. All the brine shrimps died within 24-168 hours of inoculation with the 4 treatments each containing single toxic Alexandrium species. During the feeding experiment, toxic Alexandrium spp. caused a reduction in the feeding rates in all the three stages of the life cycle of A. salina, whereas this response was not obvious in the treatment involving the nontoxic species P. donghaiense. The body surface of the brine shrimp that were fed on Alexandrium species was consistently covered by a sticky floc. Mortality of A. salina was observed to increase with the occurrence of the floc. The toxicity of the paralytic shellfish poisons (PSP) produced by the Alexandrium species was not significantly correlated with the survival or the feeding rate of the brine shrimp. When A. tamarense was mixed with P. donghaiense, the lethal effect of A. tamarense decreased, as shown by an increase in the survival and the feeding rates of the brine shrimp. A. salina metanauplii were found at the life stage most sensitive to the toxic algae and hunger. In summary, toxic Alexandrium spp. were found to have lethal effects on A. salina and to restrain the brine shrimp's feeding rate. Nontoxic Prorocentrum mitigated the toxicity of Alexandrium to a certain extent. The results also imply that the sticky material on the surface of the body of the brine shrimp may have been an important lethal factor rather than the PSP toxins.     

Effect of nematode Panagrellus redivivus density on growth, survival, feed consumption and carcass composition of bighead carp Aristichthys nobilis (Richardson) larvae

The study aimed to determine the optimum density of free‐living nematodes in feeding bighead carp, Aristichthys nobilis, larvae. In the first experiment, carp stocked at 25 larvae L^?1 were fed varying levels of nematodes (50, 75, 100, 125 and 150 per ml) twice a day for 21 days from the start of exogenous feeding. Final body weight was significantly higher (P < 0.05) in larvae fed 125 and 150 nematodes per ml than in those fed 50 and 75 per ml, but survival was low (61.8 and 63.6%, respectively). Survival rate was highest in larvae fed 100 nematodes ml^?1 (81.3%). Carcass analysis showed that larvae fed 125 and 150 nematodes ml^?1 had significantly lower body protein and higher body lipid than those fed other nematode densities. Carcass ash was similar for larvae fed 50–100 nematodes ml^?1 but it decreased significantly at the higher nematode densities. Carp larvae in a subsequent experiment were given 50, 75 and 100 nematodes ml^?1 per feeding. Newly hatched Artemia was the control feed. Nematode consumption and growth of the larvae were determined. Larvae were sampled at intervals of 2–4 days and the nematodes in the gut were counted and measured. At each nematode density, the number of nematodes present in the gut of the larvae increased significantly with time. At each sampling day, the number of nematodes in the gut did not differ significantly among treatments (P > 0.05) although it tended to increase with nematode density at day 2 and day 4 but decrease at day 7 onward. The carp larvae consumed significantly shorter nematodes on day 2 and day 4 than on the succeeding sampling days regardless of nematode density. However, the length of nematodes in the gut of the larvae did not differ significantly among the nematode densities. The final body weight of larvae increased with increasing nematode density. The body weight of larvae fed 100 nematodes ml^?1 did not differ significantly from that of larvae given Artemia nauplii. Results show that bighead carp larvae should be fed 100 free‐living nematodes per ml at each feeding time.     

Complementary Behaviors of Maternal and Offspring <Emphasis Type="Italic">Spodoptera littoralis</Emphasis>: Oviposition Site Selection and Larval Movement Together Maximize Performance

The selection of oviposition and feeding sites within cotton plants by Spodoptera littoralis was investigated in the field in 2 years, 2007 and 2008. The female moths exhibited significant oviposition preference for young leaves (YL), particularly the 3rd and 4th leaves from top. The larvae originating from egg batches deposited on YL fed mostly in situ for about 5 days, after which they gradually moved their feeding site toward fully expanded or mature leaves on the same individual plant or on neighboring plants. Larvae hatching from batches deposited on fully expanded leaves (FE) fed in situ only for about 2 days, after which they moved toward younger leaves, where they fed for about 3 more days. After the fifth day, however, larvae of the two groups dispersed mainly downward and outward from their hatching site until the end of a 12-day observation. Larvae hatching from eggs deposited on mature or pre-senescent leaves (MP) moved mainly horizontally to other plants after a slight upward shift. The YL and FE larvae grew significantly faster than MP larvae, both in the field and in a laboratory experiment. In the laboratory experiment, the larval period was shorter and the pupal weight was higher when the animals were offered young leaves or young and fully expanded leaves, than when the animals were offered mature and pre-senescent leaves during the first 5 days after hatching. Possible causes and advantages of the exhibited oviposition preference, as well as the apparent ability of larvae to correct for small egg misplacements made by the females, are discussed.     

Influence of whorl region from resistant and susceptible corn genotypes on fall armyworm (Lepidoptera: Noctuidae) growth and development

The effect of diets prepared from whorl tissue of resistant and susceptible corn genotypes, Zea mays L., on the larval growth, development, and physiology of fall armyworm, Spodoptera frugiperda (J. E. Smith), was analyzed. Larvae reared on an optimized artificial diet had a higher growth rate and developed faster than those reared on lyophilized whorl tissue from resistant and susceptible genotypes. Larvae reared on the resistant material were smaller and had a longer developmental period. Larvae reared on yellow-green and green whorl sections from resistant plants were significantly smaller than those reared on the same sections of susceptible plants. There was no significant difference in weight when larvae were reared on the yellow whorl regions from either resistant or susceptible lines. Physiological indices were determined for larvae fed resistant and susceptible lyophilized and fresh whorl material. Larvae fed resistant lyophilized material had significantly lower growth rate (GW) and efficiency of conversion of ingested food to body substance (ECI) than those reared on artificial diet or susceptible material. However, there were no significant differences in consumption index (CI), approximate digestibility (AD) and efficiency of conversion of digested food to body substance (ECD) between larvae reared on lyophilized tissue from resistant and susceptible genotypes. Larvae reared on fresh yellow-green whorl sections from resistant plants had significantly lower GW, ECI, and ECD than those reared on susceptible material. In contrast, no significant differences in any of the estimated food consumption and utilization indices were observed between larvae reared on fresh yellow whorl sections from resistant or susceptible plants. These results suggest that some components of whorls from resistant plants, especially the yellow-green region, inhibit food utilization in fall armyworm larvae.     

Post-translationally modified tubulins in Artemia: prelarval development in the absence of detyrosinated tubulin

The synthesis of post-translationally modified tubulins was examined during Artemia development. Tubulin, either purified to homogeneity or in cell-free extracts, was blotted to nitrocellulose and probed with a panel of antibodies. When purified tubulin was examined, tyrosinated tubulin underwent a large decrease as development progressed and this was accompanied by the appearance of detyrosinated tubulin in samples from organisms developed 24 hr. The inclusion of carboxypeptidase inhibitors had a small effect on the relative amounts of tyrosinated and detyrosinated tubulins in 24-hr preparations. The amount of alpha- and beta-tubulin in cell-free extracts of Artemia either remained relatively constant during development or increased slightly. The same result was obtained for acetylated and tyrosinated tubulin. Detyrosinated tubulin first appeared in 24-hr cell-free extracts and was only post-translationally modified tubulin to increase, relative to the total amount of tubulin, as the brine shrimp developed. As revealed by immunofluorescence staining, detyrosinated tubulin occurred in many cell types of developing nauplii and was prominently displayed in mitotic figures. Artemia, a complex metazoan animal, is thus able to grow for an extended period of time in the absence of detyrosinated tubulin. This isoform is however, synthesized in early larvae and may be required for the development of elongated cells including those which encircle the gut. Detyrosination remains as the only developmentally related change observed for brine shrimp tubulin.     

Choristoneura fumiferana entomopoxvirus prevents metamorphosis and modulates juvenile hormone and ecdysteroid titers

Larvae of the spruce budworm, Choristoneura fumiferana, infected with C. fumiferana entomopoxvirus (CfEPV) continue to feed and grow without undergoing metamorphosis and die as moribund larvae. The lethal dose (LD(50)) and lethal time (LT(50)) values for fourth instar larvae are 2.4 spheroids and 25.2 days, respectively. One hundred percent of the control fourth instar larvae, which were fed water instead of virus, pupated by 18 days post feeding (PF). Only 30% of the larvae that were fed the LD(50) dose and none of the larvae that were fed the LD(95) dose pupated by 18 days PF. Of the control larvae, 95% became adults by 24 days PF, whereas in the treated group only 2% of larvae that were fed the LD(50) dose and none of the larvae that were fed the LD(95) dose became adults by 24 days PF. Some of the virus-treated larvae died as either larval/pupal or pupal/adult intermediates. These phenotypic effects were similar to the larval/pupal and pupal/adult intermediates, resulting from treating larvae with juvenile hormone (JH) or its analogs, which suggests that EPV may cause such abnormalities by modulating JH and/or ecdysteroid titers. In untreated sixth instar larvae the JH titer decreased to low levels by 24 h after ecdysis and remained low throughout larval life. EPV-fed sixth instar larvae had 2112 pg/ml on day 0, 477 pg/ml on day 1 and 875 pg/ml on day 8 of the sixth instar. Control larvae contained 860 ng of ecdysteroids per ml hemolymph on day 8 of the sixth instar, whereas EPV-treated larvae of the same age (30 days PF) had only 107 ng of ecdysteroids per ml of hemolymph. Thus, EPV infection results in increased JH titer and decreased ecdysteroid titer. Northern hybridization analysis was performed using RNA isolated from control and EPV-fed larvae and cDNA probes for (i) juvenile hormone esterase (JHE), which is JH inducible, (ii) Choristoneura hormone receptor 3 (CHR3), which is ecdysteroid inducible, and (iii) larval specific diapause associated protein 1 (DAP1), whose expression is larval specific. EPV-treated larvae showed higher levels of JHE and DAP1 mRNA and lower levels of CHR3 mRNA, indicating that they had higher levels of JH and lower levels of ecdysteroids. Thus, our data show that EPV prevents metamorphosis by modulating ecdysteroid and JH levels.     

Impact of whitefish on an enclosure ecosystem in a shallow eutrophic lake: selective feeding of fish and predation effects on the zooplankton communities

Bag-type enclosures (75 m³) with bottom sheets and tube-type enclosures (105 m³) open to the bottom sediment were stocked with exotic whitefish (Coregonus lavaretus maraena) to study their predation effects on the plankton community. The fish fed mainly on adult chironomids during the period of their emergence (earlier part of the experimental period). Thereafter, the food preference was shifted to larvae of chironomids and crustacean zooplankters. The predation effects on the plankton community were not evident in the bag-type enclosures where zooplankton densities were consistently low. The fish reduced the crustacean populations composed ofBosmina fatalis, B. longirostris andCyclops vicinus in the tube-type enclosures where the prey density was high (above ca. 50 individuals 1⁻¹). The results suggested that the intensity of predation depended on the prey density. Rotifers increased in the fish enclosure, probably becauseCoregonus reduced the predation pressure byCyclops vicinus on rotifers and allowed the latter to increase. In the fish enclosures, no marked changes in species composition were observed. Zooplankton predated by the fish seemed to be distributed near the walls of the enclosures. Problems of enclosure experiments for examining the effects of fish predation on pelagic zooplankton communities are discussed.     

The feeding behaviour of larvae, nymphs and adults of Rhipicephalus appendiculatus.

The pre-feeding and feeding periods of larvae, nymphs and adults of Rhipicephalus appendiculatus on rabbits (Oryctolagus cuniculus) were investigated. Larvae and nymphs required at least 8-9 days after hatching and moulting respectively before they could attach and start feeding, while adults required at least 6-9 days. But longer periods of starvation improved the proportion of ticks that successfully fed. After attachment, there was always an initial period of slow feeding, which was followed by a phase of very rapid feeding before the engorged ticks detached from the host. Larvae detached 4-5 days after attachment, nymphs detached after 5-6 days and adults detached 7-9 days after attachment.     

Are crustaceans linked to the ciguatera food chain?

Synopsis Adult brine shrimp, Artemia spp., were used as an experimental organism to elucidate the role that crustacea may play in the transference of ciguatera toxins. Some ciguatera-implicated dinoflagellates were highly toxic to brine shrimp that had consumed them. Four clones of Gambierdiscus toxicus were fed in four trials at rates ranging from 2 to 480 cells per adult brine shrimp; the 24 h LD₅₀ for the four clones were 2.8, 33.4, 41.1, and 104.5 cells per brine shrimp. Dinoflagellates Prorocentrum concavum and P. lima were also fed to adult brine shrimp, but minimal mortalities occurred at cell concentrations ranging up to 1000 cells per test animal. Tilapine cichlid (Oreochromis niloticus ×O. mossambicus) young fed brine shrimp containing G. toxicus cells displayed behavioral abnormalities ranging from spiral swimming to loss of equilibrium. The present data suggest that toxins accumulated by dinoflagellate-consuming crustaceans could produce toxicity in zooplanktivorous fish species, or to detritivores in cases where dinoflagellate consumption resulted in crustacean mortalities. Field studies of the ciguatera food chain should be expanded to include examination of crustacean diets to more fully define their role in toxin transfer.