Egg and larval load assessment and its influence on oviposition behaviour of the leaf beetle Galerucella nymphaeae

The oviposition behaviour of the water-lily beetle Galerucella nymphaeae was examined. This species is a specialist herbivore on the floating leaves of nymphaeids Nymphaeaceae and especially on the yellow water-lily, Nuphar lutea. Females lay their eggs in clutches on the leaves, and after hatching, the larvae feed on the leaves. The quality of the leaves decreases quickly after the larvae hatch, and eventually the leaves will sink below the water surface, whereupon the eggs, 1st-instar larvae and pupae are killed by drowning. The influence of conspecific eggs, larvae and feeding tracks on the oviposition preferences of the beetles was tested. Females were allowed to choose between fresh leaves and leaves with conspecific eggs and larvae as well as between leaves with larvae and leaves with feeding tracks but no larvae. An attempt was also made to determine whether eggs and larvae affect the oviposition rate of females when they are not given the opportunity to oviposit on untouched leaves. The results indicate that females tended to avoid leaves with conspecific larvae or to exhibit a decreased oviposition rate on such leaves. Females also avoided conspecific eggs, although the oviposition rate was not influenced by the presence of conspecific eggs. When females were allowed to choose between leaves with larvae and leaves with feeding tracks, possible discrimination against leaves with larvae just fails to reach the 5% level.     

Pollination by flies, bees, and beetles of Nuphar ozarkana and N. advena (Nymphaeaceae)

Nuphar comprises 13 species of aquatic perennials distributed in the temperate Northern Hemisphere. The European species N. lutea and N. pumila in Norway, the Netherlands, and Germany are pollinated by bees and flies, including apparent Nuphar specialists. This contrasts with reports of predominant beetle pollination in American N. advena and N. polysepala. We studied pollination in N. ozarkana in Missouri and N. advena in Texas to assess whether (1) there is evidence of pollinator shifts associated with floral-morphological differences between Old World and New World species as hypothesized by Padgett, Les, and Crow (American Journal of Botany 86: 1316-1324. 1999) and (2) whether beetle pollination characterizes American species of Nuphar. Ninety-seven and 67% of flower visits in the two species were by sweat bees, especially Lasioglossum (Evylaeus) nelumbonis. Syrphid fly species visiting both species were Paragus sp., Chalcosyrphus metallicus, and Toxomerus geminatus. The long-horned leaf beetle Donacia piscatrix was common on leaves and stems of N. ozarkana but rarely visited flowers. Fifteen percent of visits to N. advena flowers were by D. piscatrix and D. texana. The beetles' role as pollinators was investigated experimentally by placing floating mesh cages that excluded flies and bees over N. advena buds about to open and adding beetles. Beetles visited 40% of the flowers in cages, and flowers that received visits had 69% seed set, likely due to beetle-mediated geitonogamy of 1st-d flowers. Experimentally outcrossed 1st-d flowers had 62% seed set, and open-pollinated flowers 76%; 2nd-d selfed or outcrossed flowers had low seed sets (9 and 12%, respectively). Flowers are strongly protogynous and do not self spontaneously. Flowers shielded from pollinators set no seeds. A comparison of pollinator spectra in the two Old World and three New World Nuphar species studied so far suggests that the relative contribution of flies, bees, and beetles to pollen transfer in any one population depends more on these insects' relative abundances (and in the case of Donacia, presence) and alternative food sources than on stamen length differences between Old World and New World pond-lilies.     

Relationship between freshwater gastropods and plant communities reflecting various trophic levels

Plant communities were examined in ponds in Brittany (north-west France) and then classified into six types reflecting different trophic levels: oligotrophic, oligodystrophic, mesotrophic, meso-dystrophic, meso-eutrophic an eutrophic. In 45 of these ponds, aquatic snails were sampled in order to determine the relationship between the gastropod species richness and the water trophic levels as indicated by plant community types. The second aim of this study was to determine whether some gastropod species were characteristic of a particular trophic level. The number of plant communities in the ponds was also taken into consideration.A trophic gradient was found along the F1 axis on the principal plane of the correspondence analyses. The species richnesses low or zero and especially the lymneid, Lymnaea glabra were close to the oligo-dystrophic and oligotrophic communities. In contrast, the highest numbers of snail species (5 and above) were found in the most eutrophic ponds where Hippeutis complanatus, Planorbis planorbis, Lymnaea stagnalis and Planorbarius corneus were particularly common. The latter species inhabited the ponds including on average the greatest number of macrophyte communities but no significant differences were found between snail species. The ponds which contained the greatest numbers of plant communities included the richest gastropod communities (7 and more) but also the poorest ones (0 or 1 species). Relationships between freshwater snails, macrophytes and trophic levels are discussed.Laboratoire de Zoologie et d'Ecophysiologie     

Haemoglobin producing cells in freshwater snails

Summary One of the cell types occurring in the connective tissue of gastropods and bivalves is thepore cell. Cells of this type have a characteristic morphology in that their plasmamembrane has many invaginations bridged by cytoplasmic tongues. In the well developed granular endoplasmic reticulum and in these invaginations fine granular material, sometimes arranged in crystalline patterns, is present. InLymnaea stagnalis this material has been identified as haemocyanin on a morphological basis. Histochemical and ultrastructural results on pore cells of 2 snail species(Biomphalaria glabrata, Planorbarius corneus) having haemoglobin in their blood indicate that the pore cells in these species synthesize haemoglobin. Possible other functions of pore cells are briefly discussed.     

The impairment of mobility and development in freshwater snails (Physa fontinalis and Lymnaea stagnalis) caused by herbicides

1. The pulmonate freshwater snails Physa and Lymnaea and the earthworms Eisenia and Lumbricus can take up and concentrate a carbamate herbicide (chlorpropham). 2. The mobility of freshwater snails was diminished in the presence of the herbicides chlorpropham (carbamate), cycloate (thiocarbamate), pentanochlor (amide) and chloroxurone (urea derivate). 3. The egg-assemblies of Lymnaea stagnalis turned out to be suitable objects for testing the influences of herbicides upon embryonic development. 4. In the presence of chlorpropham, chloroxurone, cycloate, propanil, simazine and terbutryne, all applied in concentrations lower than in practical use, the period of egg-maturing was delayed and the total number of dead embryos increased. 5. Developing snail eggs were very sensitive towards triazine herbicides (simazine, terbutryne) reflecting in an ED50-value lower than 10(-7) M. 6. Similar herbicidal-induced effects suggested that the developing stages of snail embryos may be suitable models for the ecologically more important but experimentally less accessible earthworms.     

Oviposition Behavior and Offspring Emergence Patterns in Succinea thaanumi, an Endemic Hawaiian Land Snail

In this field study, newly laid egg clutches of Succinea thaanumi, an endemic Hawaiian land snail, were labeled and observed weekly over a 12‐mo period. Snails usually laid their clutches under leaf tips and, moreover, this placement affected snail emergence by mitigating the effects of dehydration through the leaf‐drip phenomenon. During droughts, the gel surrounding egg clutches dehydrated, pasting the embryos to the backs of leaves. The hygroscopic gel rehydrated once rains resumed. The majority of newly laid clutches contained shell‐less embryos which required more time for emergence than embryos laid with visible shells. More shelled embryos were laid subsequent to a 3‐wk drought, indicating that snails retained their eggs during adverse environmental conditions and laid them when conditions improved. The snails’ abilities to retain eggs in adverse conditions, but to lay more unshelled embryos over their lifetimes, contributed to their overall reproductive success.     

Phyto-adaptogens protect against environmental stress-induced death of embryos from the freshwater snail Lymnaea stagnalis.

The main purpose of the studies presented in this paper is twofold: 1) to evaluate whether phyto-adaptogens (Acanthopanax senticosus and Rhodiola rosea) are able to exert a protective action against stress-induced death of embryos of the pond snail Lymnaea stagnalis; and 2) whether a possible protective action by phyto-adaptogens can be explained by the induction of heat shock proteins. Enhancement in resistance by phyto-adaptogens was studied by applying plant extracts for a period of 20 hours to 3-day old larvae of the pond snail Lymnaea stagnalis. Subsequently they were exposed to a high and toxic dose of different environmental stressors. The following stress conditions were selected: a physical stress condition (heat shock: 43 degrees C for 4 minutes), an oxidative stress condition (superoxide radicals induced by menadione (600 microM for 2 hours)) and heavy metal-induced stress (copper (150 microM for 1 hour) or cadmium (20 microM during 1 hour)). Both Acanthopanax and Rhodiola exert a strong protective action against a lethal heat shock. These adaptogens also significantly protect against the negative effect of superoxide radicals as induced by menadione. With respect to the protective action against exposure to heavy metals a small but significant protection was observed against intoxication with copper or cadmium by the phyto-adaptogens. In summary, there appears to be a difference in efficiency in enhancing resistance to the various stress conditions used (heat shock>menadione>copper>cadmium). Based on the results presented in this paper, we can conclude that phyto-adaptogens are able to enhance the resistance against the different stress conditions tested in developing individuals of Lymnaea. Although the degree to which resistance is enhanced appears to depend on the type of stressor applied, our results confirm the definition of phyto-adaptogens as being universal enhancers of non-specific resistance against different kinds of stress conditions. With respect to the mechanism of enhanced resistance, the question was asked whether this protective action is caused by an induction of heat shock proteins (hsps), which are known to be involved in tolerance and adaptation. The phyto-adaptogens did not induce the synthesis of any of the hsps, nor did they modulate the normal heat shock induced synthesis of these stress proteins. We conclude that it is unlikely that hsps play a major role in obtaining an enhanced state of resistance provided by phyto-adaptogens.     

Maternal impact on egg development in Lymnaea stagnalis: a growth factor is produced by the albumen gland in the reproductive tract

Summary

In the freshwater snail Lymnaea stagnalis, perivitellin fluid is the main source of nutrition for developing embryos; it contains predominantly galactogen and proteins. The fluid is produced by the albumen gland, a large exocrine organ in the female reproductive tract. To further define the protein products of this gland and provide more information about the maternal contribution to egg development, albumen glands were extracted and the extracts purified by reversed-phase HPLC. One major HPLC peak fraction exhibited neurotrophic activity when bioassayed on identified Lymnaea neurons in vitro; it has been partially sequenced and has the highest degree of sequence identity with epidermal growth factor (EGF). These results demonstrate that a growth factor with neurotrophic activity is produced by the albumen gland, and is packaged along with the eggs to serve a growth-promoting function in the embryo.     

Oviposition site selection by herbivorous beetles: a comparison of two thistle feeders, Cassida rubiginosa and Henosepilachna niponica

In insects that feed on plants in both adult and larval stages, it is often difficult to distinguish oviposition preference from adult feeding preference, because oviposition can occur at or in proximity to feeding sites. In the present study, characteristics of oviposition site selection of two beetle species, Cassida rubiginosa Müller (Coleoptera: Chrysomelidae) and Henosepilachna niponica (Lewis) (Coleoptera: Coccinellidae), were investigated in the field and laboratory, with particular attention to relationships with adult feeding sites. In the field, distances between adult feeding scars and egg masses differed for C . rubiginosa and H . niponica , with the former being very small and the latter averaging 24.6 cm. The same tendencies for the distances between adult feeding scars and egg masses of the two beetle species were confirmed in cages in which only female beetles were released. Cassida rubiginosa restricted egg laying to host plants in the field and to leaves in laboratory assays. On the other hand, H . niponica placed 8% of egg masses on plants adjacent to host plants in the field and often placed eggs on artificial substrates rather than leaf discs in laboratory assays. These results suggest that oviposition and female feeding sites are virtually inseparable in the case of C . rubiginosa , while H . niponica females do not necessarily keep to host plant leaves as oviposition substrates and they tend to oviposit at some distance from their feeding sites. Results are discussed in relation to proximate and ultimate causes of host selection behavior.     

Interpopulation differences in hemocyte DNA-comet parameters of snail Lymnaea stagnalis from regions with different environmental loads

Research on hemocytes of snail Lymnaea stagnalis from regions with different environmental loads has been carried out by comet assay. Significant interpopulation differences in hemocyte DNA-comet parameters and sensitivity of hemocyte genetic material to external damaging factors (heavy-metal Sr, in particular) have been revealed by means of software analysis of hemocyte DNA-comet images. Two snail populations are characterized by high genetic identity; therefore, the different proliferative activity in the hemocytes of snail Lymnaea stagnalis from different ecological zones revealed by comet assay may be considered as an indicator of the intensity of damaging effects and environmental quality.     

Up to what point are cercariogenesis and sporocystogenesis reversible in schistosomes?

A study of larval development of Schistosoma haematobium in the snail Planorbarius metidjensis infected by transplanted sporocysts showed that some embryos in daughter sporocysts have characters intermediate between cercariae and sporocysts. These embryos are interpreted to be nearly mature cercariae that have partially reverted to be secondary sporocysts. If this explanation is correct, it would mean that the embryos which develop within trematode daughter sporocysts can differentiate either into cercariae or into a new generation of sporocysts, but originate from a single type of germinal cell.     

Immuno-localization of ferritin polypeptides in oocytes and somatic tissue of the freshwater snails Lymnaea stagnalis L. and Planorbarius corneus L.

Summary Antibodies were raised in rabbits against the 19000 Mr and 24000 Mr polypeptides of snail ferritin from Lymnaea stagnalis L. Anti-24000 Mr polypeptide antibodies were purified by an affinity-purification step and were made monospecific for their antigen by preabsorption with the 19000 Mr antigen. These purified antibodies were then used for in situ detection of their respective antigens by the indirect immunofluorescence method. The 19000 Mr polypeptide was found widely distributed in tissues of both pulmonate snails investigated (Lymnaea stagnalis L. and Planorbarius corneus L.) with the most intense antigen-directed fluorescence in certain connective tissue cells, secretory cells of the midgut gland and Sertoli cells and epithelia of the gonadal acini. In contrast, the 24000 Mr polypeptide could be detected only in yolk platelets of vitellogenic oocytes. The results indicate that yolk and somatic cell ferritins differ in immunoreactivity and structure and, accordingly may differ in function.This investigation was supported by the Deutsche Forschungsgemeinschaft. I greatly appreciate the advice given to me by Drs. U. Mays and V. Riedel, Münster.     

Predation and the distribution and abundance of a pulmonate pond snail

Summary The abundances of a freshwater pulmonate snail, Lymnaea elodes were studied in a temporary pond and a permanent, more productive pond in northeastern Indiana, USA. When snails from both populations were reared in each of the ponds in containers excluding predators, snails grew to be 1.3 to 2 times as large in the more productive pond, and laid 9 times as many eggs. However, field sampling data showed adults to be more abundant in the temporary pond. The only obvious difference between the two ponds was the presence of the molluscivorous central mudminnow (Umbra limi) in the permanent pond. These fish fed upon L. elodes when eggs and juvenile snails were abundant. In an experiment in the temporary pond, addition of mudminnows lowered egg and juvenile snail survival in pens where snail abundances had been increased. We suggest that vertebrate predators like the mudminnow can be significant sources of mortality for thin shelled species like L. elodes, possibly excluding them from habitats like lakes and rivers.Address for offprint requests     

Small effective population sizes in a widespread selfing species, Lymnaea truncatula (Gastropoda: Pulmonata)

We present here a spatial and temporal population genetic survey of a common freshwater snail, also a predominantly selfing species, Lymnaea truncatula. The rate of genetic diversity loss was quantified by estimating the effective size (Ne) of the snail populations, using two different methods. A temporal survey allowed estimation of a variance effective size of the populations, and a spatial survey allowed the estimation of an inbreeding effective size, from two-locus identity disequilibria estimates. Both methods were consistent and provided low Ne values. Drift due to (i) high amounts of selfing and (ii) fluctuations in population sizes because of temporary habitats, and also selection coupled to genome-wide linkage disequilibria, could explain such reductions in Ne. The loss of genetic diversity appears to be counterbalanced only very partially by low apparent rates of gene flow.     

Structure, localization and potential role of a novel molluscan trypsin inhibitor in Lymnaea.

Eggs and egg masses of the freshwater gastropod mollusc Lymnaea provide a microenvironment for developing embryos. Secretions of the exocrine albumen gland of Lymnaea are packaged in the eggs of an egg mass before the eggs are laid externally. The perivitelline fluid that directly surrounds individual oocytes is the main source of nutrition for developing embryos. During early stages of development, the perivitelline fluid is initially internalized by pinocytosis and degraded by lysosomes; in later stages, the embryo ingests the fluid. We previously found that the albumen gland produces large amounts of Lymnaea epidermal growth factor. The albumen gland also appears to produce significant amounts of a novel Lymnaea trypsin inhibitor (LTI), a second peptide that was purified and characterized from Lymnaea albumen gland extracts. The primary structure was determined by microsequence analysis, mass spectrometry, and C-terminal sequence analysis, and showed that LTI is a 57-residue glycosylated peptide. Comparison of the LTI sequence with other known serine protease inhibitors indicates that LTI is a member of the bovine pancreatic trypsin inhibitor family. Reverse phase-high performance liquid chromatography, microsequence analysis, mass spectrometry, and immunocytochemistry demonstrated that abundant amounts of intact LTI are packaged in egg masses. The presence of a trypsin inhibitor in the perivitelline fluid compartment of the egg mass may minimize digestion of peptides and proteins in the perivitelline fluid that are important for the development of the embryo, for example, Lymnaea epidermal growth factor.     

四种材料作为异色瓢虫产卵载体的适合性比较

比较了蚕豆苗叶片、甘蓝叶片、小油菜叶片和纸条作为人工扩繁异色瓢虫Harmoniaaxyridis(Pallas)时产卵载体的适合性。异色瓢虫对这 4种产卵载体有明显的选择性 ,多在蚕豆苗叶片和甘蓝叶片上产卵 ,纸条上次之 ,在小油菜叶片上产卵很少。在产卵载体对单雌产卵量影响方面 ,蚕豆苗叶片、甘蓝叶片和纸条 3者之间的差异不显著 ,且产于这 3种载体上的卵块在 ( 1 0± 1 )℃下冷藏的孵化率没有明显差异。由于纸条不会出现枯萎现象 ,易制成卵卡 ,所以可用作卵商品化时的产卵载体 ,而蚕豆苗叶片和甘蓝叶片可作为保留虫源或繁殖时的产卵载体。     

Molluscicidal effect of nicotinanilide and its intermediate compounds against a freshwater snail Lymnaea luteola, the vector of animal schistosomiasis

The molluscicidal effect of nicotinanilide was evaluated and compared with niclosamide (2',5-dichloro-4'-nitrosalicylanilide, ethanolamide salt) against different stages of the freshwater snail Lymnaea luteola i.e., eggs, immature, young mature, and adults. Calculated values of lethal concentrations (LC50 and LC90) showed that both nicotinanilide and niclosamide as toxic against eggs, immature, and adults. The young mature stage of the snails was comparatively more tolerant to both molluscicides than the other stages. The toxicity of the intermediate compounds of nicotinanilide against the young mature stage of the snails showed them as ineffective. The mortality pattern of the snails exposed to LC90 concentration of these molluscicides showed niclosamide to kill faster (within 8 to 9 h) than nicotinanilide (26 to 28 h). In view of the above studies it may be concluded that both molluscicides are toxic against all the stages of the L. luteola snails.     

Development of Fasciola hepatica in Lymnaea columella infected with miracidia derived from cattle and marmoset infections

The development of Fasciola hepatica from two species of definitive hosts, i.e. cattle (Bos taurus) and a marmoset (Callithrix penicillata) in the snail Lymnaea columella was determined based on the production of rediae and cercariae and snail survival rate. More rediae and cercariae at 60-74 days post-infection were produced by snails infected by cattle-derived miracidia (cattle group) than by those infected by marmoset-derived miracidia (marmoset group). Among the L. columella parasitized by the marmoset group, the survival rate and the percentage of positive snails were higher than among those parasitized by the cattle group. Eggs of F. hepatica released in cattle faeces were significantly bigger than those released in marmoset faeces. Miracidia originating from parasites that completed their development in cattle were more efficient in infecting the intermediate host. These results suggest that vertebrate-host origin influences the eggs produced by the parasite and the infection rates in the snail host L. columella.     

Individual growth of the great ramshorn snail <Emphasis Type="Italic">Planorbarius corneus</Emphasis> (Gastropoda,Planorbidae) embryos

Individual growth of the great ramshorn snail Planorbarius corneus has been studied by intravital video imaging. As has been observed, the types of growth change over the embryogenesis. The linear dimensions slightly but in a statistically significant manner decrease during the stages of cleavage to blastula. Starting from the stage of blastula to trochophore, the embryo diameter remains constant to commence increasing at the stage of middle trochophore. During the larval stages (trochophore and veliger), the growth is synchronous (in Dettlaffs, biological time units) for the embryos in both the same clutch and different clutches. The growth at that time is exponential but later desynchronizes in individual clutches. The embryos in eight clutches grew and developed slower and hatched later as compared with the remaining five egg clutches. An accelerated growth follows an asymptomatic pattern according to the von Bertalanffy equation. A retarded growth is describable with a linear equation. The observed differences are likely to be associated with the number of embryos in a clutch. All types of changes in the linear dimensions observed in the great ramshorn snail embryogenesis can be described with the same united equation.     

Storage and incubation of Echinostoma revolutum eggs recovered from wild Branta canadensis, and their infectivity to Lymnaea tomentosa snails

Echinostoma revolutum eggs recovered from naturally infected wild Canada geese (Branta canadensis) were cold stored (4-6 degrees C) for up to 72 weeks. Successful hatching followed incubation for from 6 to 8 days at an optimum temperature of between 25 and 30 degrees C. A partial life cycle from adult worm to metacercarial encystment in Lymnaea tomentosa snails was completed in the laboratory. Snails were infected both by free miracidia and by ingestment of unhatched embryonated eggs. Infection was equally successful in environmental temperature ranges from 10 to 25 degrees C, and at challenge levels of 2, 5 or 10 embryonated eggs per snail. Exposure to 10 eggs was lethal. Ingestion by snails of embryonated eggs with successful infection at 10 degrees C suggests that embryonated eggs may be used to infect wild snails when the environmental water temperature has reached 10 degrees C.