Laid Egg Masses Research Articles

Upper thermal tolerance in anuran embryos and tadpoles at constant and variable peak temperatures

Anuran survival is strongly affected by exposure to high environmental temperatures. However, their upper thermal tolerances vary between species and within developmental stages. The aims of this research were to measure the median lethal temperature (LT50) of three anuran developmental stages (Gosner stages 10, 20, and 25) at a constant thermal regime, and of developing embryos (stage 10) until they became tadpoles (stage 25) exposed to daily peaks of temperatures between 1000 and 1600. Four Colombian species (Emerald-eyed Treefrog, Hypsiboas crepitans (Wied-Neuwied, 1824); Tungara Frog, Engystomops pustulosus (Cope, 1864); Rivero’s Toad, Rhinella humboldti (Gallardo, 1965); Emerald Glassfrog, Espadarana prosoblepon (Boettger, 1892)) were used in these experiments. An ontogenetic increase was observed in the upper thermal tolerance from embryos to tadpoles for all species studied. In addition, developing embryos exposed to peak temperatures showed a LT50fairly close to the mean of the maximum habitat temperatures, particularly in H. crepitans and E. pustulosus that lay egg masses exposed directly to the sun. Environmental temperatures in the microhabitat of species studied showed values remarkably higher than their experimental LT50. Therefore, we postulate that rapid increases in environmental temperatures, as result of global or local changes, might be a critical factor for anuran survival, mainly during the embryonic stages when they are more sensitive to temperature.

Changes in the locomotory and reproductive behavior of Biomphalaria glabrata infected with Schistosoma mansoni

The infection and development of a parasite may cause physiological, morphological and behavioral changes in its host. Changes in the locomotory activity of a host induced by their parasites may also influence the life-cycles of both host and parasite in the environment. The aim of the present work was to evaluate the locomotory activities of Biomphalaria glabrata before and after an experimental infection with Schistosoma mansoni relating to the shedding of cercaria. In addition, the reproductive parameters of infected B. glabrata were analyzed during the prepatent and patent periods of the infection. The locomotory activity was recorded using an image analysis biomonitoring system based on a Videomex V®. Five parameters were analyzed: ‘Distance traveled’, ‘Ambulatory time’, ‘Stereotypic time’, ‘Resting time’ and ‘Average speed’. The number of shed cercariae was counted twice at 45 and 52 days post-infection. The reproductive parameters of infected B. glabrata analyzed were the numbers of egg masses, eggs and hatched snails. All statistical analyses were performed using the R program. Of the 69 snails infected with S. mansoni, 33 (47.8%) shed cercariae (‘positive’) and 36 (52.2%) (‘exposed’) failed to exhibit any cercarial shedding prior to the end of the experiment. The locomotory activity of the all snails increased significantly after infection with S. mansoni. However, when the ‘positive’ and ‘exposed’ snails were compared, the former, shedding cercariae, were less motile. With regard to reproduction, 84.8% (28/33) of the ‘positive’ and 27.7% (10/36) of the ‘exposed’ snails failed to lay egg masses during patent period. The number of cercariae individually shed by each ‘positive’ snail presented a positive relation with ‘Stereotypic time’ and a negative relation with egg laying. Our findingshighlight the way in which infection with S. mansoni affects the locomotory and the reproductive behavior of B. glabrata. The number of cercariae shed is directly associated with the reduction/interruption in egg-laying and with an increase in random movement.

Flatworms (Schmidtea nova) prey upon embryos of the common frog (Rana temporaria) and induce minor developmental acceleration

Amphibians vary in the degree of pre-metamorphic developmental plasticity in response to risk of predation. Changes in hatching time and development rate can increase egg or tadpole survival respectively by shortening the duration of the more vulnerable stages. The intensity of predator induced developmental response and its direction, i.e. delayed, accelerated, or none, varies considerably between amphibian and predator species. We surveyed freshly deposited clutches of the European common frog Rana temporaria in a population in Braunschweig, Germany and found that 62% (N = 20) of the clutches contained planarians (Schmidtea nova), with an average of 3.94 ± 0.79 and a maximum of 13 planarians per clutch. A laboratory predation experiment confirmed that this planaria preys on R. temporaria eggs and early embryos. We further exposed freshly laid egg masses to either free, caged, or no planarians treatments using floating containers within a breeding pond where the two species co-occur. After 10 days exposure, embryos showed developmental stages 14-25 along the Gosner scale with statistically significant positive effects of both predator treatments. The observed effect was rather slight as predator-exposed individuals showed an increase by a single Gosner stage relative to those raised without planarians. The detected trend suggests that direct and indirect cues from flatworms, rarely considered as anuran predators, might induce a developmental response in R. temporaria early developmental stages.

Intraguild interactions between two egg parasitoids of a true bug in semi-field and field conditions.

Research on interspecific competitive interactions among insect parasitoids has often been characterized by laboratory studies in which host insects are exposed to female parasitoids of different species in various sequences and combinations. In the last years, an increasing number of studies have investigated interspecific interactions under field and semi-field conditions although just a few number of works focused on egg parasitoids. In this work, we undertook a two-year study to investigate interspecific interactions between Trissolcus basalis (Wollaston) (Hymenoptera: Platygastridae) and Ooencyrtus telenomicida (Vassiliev) (Hymenoptera: Encyrtidae), two egg parasitoids of the pest Nezara viridula (L.) (Heteroptera: Pentatomidae) that co-occur in cultivated crops. Under semi-field (in out-door mesh cages) and field conditions, we investigated: 1) the seasonal occurrence of competing parasitoid species on sentinel egg masses; 2) the impact achieved by competing species on the shared host on naturally laid egg masses; 3) the outcome of intraguild interactions under controlled conditions. Results from sentinel egg masses showed that T. basalis occurs in May and successfully parasitizes hosts until the end of September/beginning of October, whereas O. telenomicida is mainly occurring in July-August. In both years, it was found that T. basalis is predominant. From naturally laid egg masses, results indicated that T. basalis achieves higher impact on the hosts, even in those egg masses which are parasitized by more than one female of different species ( = multiparasitism). Results from manipulating intraguild interactions showed that T. basalis achieves higher impact on N. viridula when released alone, but it suffers from competition with O. telenomicida. The ecological factors that play a role in intraguild interactions in the context of biological control perspective are discussed.

A test of the preference–performance hypothesis with stream insects: selective oviposition affects the hatching success of caddisfly eggs

Summary Under the preference–performance hypothesis (PPH), oviparous females select oviposition sites that optimise the fitness of their offspring (eggs or larvae). The resulting distribution and fitness of offspring may have knock‐on effects for population distribution patterns and dynamics during larval and adult stages. We tested the PPH for Australian caddisflies from two genera (family: Hydrobiosidae) that oviposit in different flow conditions. Apsilochorema spp. oviposit in slow flowing water, whereas Ulmerochorema sp. favour fast flows. We expected hatching success to be higher in velocities favoured by ovipositing females. In a field experiment, newly laid egg masses of each species were exposed to experimental ‘fast’ and ‘slow’ flow treatments throughout development and monitored until they hatched or died. In a second field experiment, we placed egg masses in a range of velocities (0.0–1.5 ms−1) to determine the threshold beyond which eggs were damaged by shear forces. The results supported the PPH for one species. Apsilochorema egg masses were sheared from the substratum in fast flows, but hatched with 100% success in favoured slow flows. The threshold velocity for Apsilochorema was 0.6–0.7 ms−1, well beyond the natural oviposition range of up to 0.3 ms−1. Ulmerochorema eggs hatched in all flows, suggesting that flow‐related mortality of the egg stage is unimportant for this species. Oviposition in fast flows might enhance the fitness of Ulmerochorema larvae or ovipositing females instead. Vulnerability to shear forces appears to explain why Apsilochorema lay eggs exclusively in slow flows. Shear may be a common cause of mortality for lotic insect eggs, and unseasonal spates or regulated flows may significantly affect recruitment of larvae. Selective oviposition affects the spatial distribution and survival of eggs and thus affects larval supply, and these supply dynamics are under‐studied in stream ecology.

Development of an embryo toxicity test with the pond snail Lymnaea stagnalis using the model substance tributyltin and common solvents

The development of a chronic mollusc toxicity test is a current work item on the agenda of the OECD. The freshwater pond snail Lymnaea stagnalis is one of the candidate snail species for such a test. This paper presents a 21-day chronic toxicity test with L. stagnalis, focussing on embryonic development. Eggs were collected from freshly laid egg masses and exposed individually until hatching. The endpoints were hatching success and mean hatching time. Tributyltin (TBT), added as TBT-chloride, was chosen as model substance. The selected exposure concentrations ranged from 0.03 to 10μgTBT/L (all as nominal values) and induced the full range of responses. The embryos were sensitive to TBT (the NOEC for mean hatching time was 0.03μgTBT/L and the NOEC for hatching success was 0.1μgTBT/L). In addition, data on maximum limit concentrations of seven common solvents, recommended in OECD aquatic toxicity testing guidelines, are presented. Among the results, further findings as average embryonic growth and mean hatching time of control groups are provided. In conclusion, the test presented here could easily be standardised and is considered useful as a potential trigger to judge if further studies, e.g. a (partial) life‐cycle study with molluscs, should be conducted.

Deleterious Activity of Natural Products on Postures of Spodoptera frugiperda (Lepidoptera: Noctuidae) and Diatraea saccharalis (Lepidoptera: Pyralidae)

The control of Lepidoptera pests should be carried out before hatching of their caterpillars to avoid damage to the crops. The aim of this work was to assess the activity of neem (trade name: Natuneem, producer: Base Fértil, Chapadão do Sul, Brazil) and pyroligneous extracts (trade name: Biopirol 7M, producer: Biocarbo, Itabirito, Brazil) at 10 mL/L (1%) and 20 mL/L (2%) contents on egg masses of different ages of Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) and of Diatraea saccharalis F. (Lepidoptera: Pyralidae) at Embrapa Corn and Sorghum in Sete Lagoas, Minas Gerais State, Brazil. The tests took place in an unbiased casualized design with 12 treatments and four replications. The insecticides were diluted in water, and 0.04 mL of the solution was applied to recently laid and one- and two-day-old eggs of S. frugiperda and D. saccharalis. Caterpillars hatching from recently laid egg masses of S. frugiperda was lower with 2% pyroligneous extract [(0.02 +/- 0.00)%]. Recently laid eggs and one- or two-day-old eggs of D. saccharalis presented lower caterpillar hatching with 1% neem extract [(0.00 +/- 0.00)%, (0.00 +/- 0.00)%, and (1.00 +/- 0.01)%] and 2% neem extract [(0.00 +/- 0.00)%], compared to 1% pyroligneous extract [(27.30 +/- 3.22)%, (28.40 +/- 3.32)%, and (37.80 +/- 4.14)%] and 2% pyroligneous extract [(42.20 +/- 4.49)%, (48.70 +/- 4.97)%, and (56.60 +/- 5.52)%], respectively. Neem and pyroligneous extracts had impact on hatching of S. frugiperda and D. saccharalis caterpillars.

Stimuli associated with viburnum leaf beetle (Pyrrhalta viburni) aggregative oviposition behavior

Viburnum leaf beetle, Pyrrhalta viburni (Paykull) (Coleoptera: Chrysomelidae), oviposits in terminal twigs of Viburnum spp. shrubs (Caprifoliaceae). Twigs react to oviposition by producing neoplasm that overgrows the egg mass. Pyrrhalta viburni oviposition behavior is aggregative: females prefer to lay egg masses on twigs previously infested by other females and to position their egg masses adjacent to existing ones. Female oviposition preferences were studied in a series of choice tests under laboratory conditions. The three components of the egg mass (cavity, eggs, and egg cap) were not sufficient to elicit complete aggregation oviposition response when presented separately. Cavity and egg cap elicited positional preference, but not the artificial cavity, artificial egg cap, or frass, suggesting that stimulatory cues might be associated with insect saliva and egg cap secretion. Females preferred to lay eggs on twigs that had produced wound tissue in response to previous oviposition. We conclude that twig choice and positional preference for oviposition are likely to be dissociated, and that twig wound response might be used by P. viburni females to locate twigs already infested and possibly less defended against subsequent oviposition. Pyrrhalta viburni females preferred to lay egg masses on heavily infested twigs rather than on lightly infested twigs. Females did not show preference for twigs infested with their own egg masses, but laid more egg masses on twigs infested by multiple females than on twigs infested by single females. We conclude that both egg mass and conspecific density affect oviposition preferences of P. viburni and discuss the possible ecological implications of this behavior.

Laboratory Culture, Growth, and the Life Cycle of the Little CuttlefishSepiola atlantica(Cephalopoda: Sepiolidae)

Pairs of Sepiola atlantica maintained in aquaria at ∼17°C successfully mated in the “male parallel position” for between 21 min and 77 min. Over a period of several weeks after mating, female S. atlantica laid egg masses containing 8–161 eggs. At 14.4°C, embryonic development took 33 days and the hatching phase lasted for 23 days (mean hatching success, 32%). Hatchlings emerged from the eggs at a mean dorsal mantle length (DML) of 1.91 mm and entered a pelagic paralarval phase lasting 6 days. Ten to 20 days after hatching, the internal yolk sac became exhausted, whereupon hatchlings were fed ad libitum on wild-caught Zooplankton at a density of ∼90 organisms/L or with enriched adult Anemia (density, 50 organisms/L). Hatchlings maintained on the Artemia diet all died within 38 days, whereas ∼38% of those fed on Zooplankton survived to this point, and the remaining juveniles subsequently attained adulthood when reared on a diet of Crangon crangon. These laboratory-reared juveniles matured and successfully mated, but the females did not lay any eggs. Females subsequently died 230–250 days after hatching and 10–19 days after mating, at a DML of between 21.7 mm and 23.2 mm, whereas the smaller males died 265–293 days after hatching (DML, 17.4–21.4 mm). Growth (increase in DML) of S. atlantica had 2 phases. Growth during the first 120 days was relatively slow at 0.05 mm/day (0.043 mm/day in males and 0.055 mm/day in females), increasing slightly thereafter to day 210, after which growth leveled off. These data indicate that S. atlantica has a similar life cycle to other scpioids.

Environmental constraints on oviposition limit egg supply of a stream insect at multiple scales

Species with complex life cycles pose challenges for understanding what processes regulate population densities, especially if some life stages disperse. Most studies of such animals that are thought to be recruitment limited focus on the idea that juvenile mortality limits the density of recruits (and hence population density), fewer consider the possibility that egg supply may be important. For species that oviposit on specific substrata, environmental constraints on oviposition sites may limit egg supply. Female mayflies in the genus Baetis lay egg masses on the underside of stream rocks that emerge above the water's surface. We tested the hypothesis that egg mass densities are constrained by emergent rock densities within and between streams, by counting egg masses on emergent rocks. All emergent rocks were counted along 1-km lengths of four streams, revealing significant variation in emergent rock density within streams and a more than three-fold difference between streams. In each stream, egg mass density increased with the density of emergent rocks in 30-m stretches. We used regression equations describing these small-scale relationships, coupled with the large-scale spatial variation of emergent rocks, to estimate egg mass densities for each 1-km stream length, a scale relevant to population processes. Scaled estimates were positively associated with emergent rock density and provided better estimates than methods that ignored environmental variation. Egg mass crowding was inversely related to emergent rock density at the stream scale, a pattern consistent with the idea that oviposition substrata were in short supply in streams with few emergent rocks, but crowding did not compensate entirely for differences in emergent rock densities. The notion that egg supply, not larval mortality, may limit population density is an unusual perspective for stream insects. Environmental constraints on egg supply may be widespread among other species with specialised oviposition behaviours.

Larval size in Elysia stylifera is determined by extra-embryonic provisioning but not egg size

Marine invertebrates that lay egg masses provision their offspring in a variety of ways, and in some groups, egg size is not the sole determinant of offspring size at independence. Supple- mental, maternally derived resources, such as extra-embryonic nutrients, may increase offspring size without increasing egg size — options not available to broadcast spawners. Extra-embryonic nutri- ents, such as nurse eggs, can increase offspring size and performance, but little is known about other forms of larval nutrition. Larvae of the sea slug Elysia stylifera have access to intra- and extra-capsu- lar resources in the egg mass prior to an obligate planktonic feeding period. We investigated the effects of maternal body size on egg size, capsule size, extra-capsular yolk (ECY), and fecundity, and how variance in these traits affected larval size at hatching. Larger mothers produced larger and more eggs, but larval size was unrelated to maternal size, egg size, or fecundity. Larval size instead depended upon the size of the egg capsule and amount of ECY available to each developing embryo: when capsule size was small, increasing ECY per larva increased larval size, and conversely, when ECY per larva was small, increasing capsule size increased larval size. Under theoretical considera- tions, ECY appears to supplement egg provisioning. Intra-capsular fluid and ECY add to the already diverse set of known mechanisms of offspring provisioning in marine invertebrates, and may provide insight into the factors affecting life-history evolution in marine invertebrates.

Life history of a dipteran predator (Scathophagidae: Acanthocnema) of insect egg masses in a northern California stream

Summary1. Little is known about the predators of insect eggs in fresh waters. This study describes aspects of the life history of a scathophagid fly (Acanthocnema sp.), whose larvae are predators of aquatic insect eggs.2. Because the Acanthocnema predator oviposits its eggs on the surface of aquatic insect egg masses, all insect egg masses were collected regularly within a 200‐m reach of Redwood Creek (California, U.S.A.) between September 2003 and June 2007. Acanthocnema predators were found predominantly within egg masses of the caddifly Neophylax rickeri (Trichoptera: Uenoidae).3. There was a mean of 0.25 Acanthocnema individuals per N. rickeri egg mass (n = 2367 egg masses). In general, N. rickeri egg masses were more commonly found clustered in aggregations (93.7%) than singly (6.3%), and Acanthonema were found more often within the aggregations of N. rickeri (98.7%) compared to singly laid egg masses (1.3%).4. The duration of the Acanthocnema predator life stages was: egg 2.9 ± 0.8 (mean ± SD) days, larva 15.6 ± 10.2 days, pupa 80.3 ± 24.9 days and adult 7.2 ± 4.8 days. The short duration of the Acanthocnema egg stage (1–7 days) compared to that of its prey N. rickeri (2–4 weeks) raises the probability that the undeveloped eggs of N. rickeri would be available to the young predators upon hatching. Egg consumption of N. rickeri eggs by Acanthocnema averaged 262.6 eggs per larval period.5. Acanthocnema had a bivoltine life cycle in which the first generation fed exclusively on N. rickeri egg masses in the winter and the second generation fed on the egg masses of several species, including other Trichoptera (Brachycentridae) and Diptera (Ceratopogonidae, Chironomidae) in the spring. These findings suggest differing feeding strategies by the first and second generations of Acanthocnema in response to the seasonal availability of prey species. This type of autecological information is important for understanding mechanisms of community interactions.

Larval development of the gastropod Epheria turrita (Gastropoda: Littorinidae)

The larval development and microsculpture of the shell of the prosobranch gastropod Epheria turrita were studied in laboratory conditions. The mollusk laid egg masses on the thalli of macrophytes. An egg mass looked like a flattened ring or a spiral, from 1 up to 6 mm in diameter. The number of eggs in egg masses depended on their size and varied from several hundreds up to several thousands. The free-swimming larvae were released from the egg masses 7–8 days after the beginning of cleavage at a water temperature of 10 ° C. The larval protoconch was translucent, the mouth was wide, S-shaped and curved. The protoconch microsculpture was presented by fine granules merging into thin radial costae at lateral surfaces.

Oceanobacillus chironomi sp. nov., a halotolerant and facultatively alkaliphilic species isolated from a chironomid egg mass

Chironomids (Diptera; Chironomidae) are the most abundant insects in freshwater aquatic habitats. Females of the genus Chironomus lay egg masses containing hundreds of eggs embedded in a gelatinous matrix. A bacterial strain, designated T3944D(T), was isolated from a chironomid egg mass sampled from a waste-stabilization pond in northern Israel and was found to be Gram-positive, motile by peritrichous flagella, endospore-forming, halotolerant and facultatively alkaliphilic. Comparative 16S rRNA gene sequence analysis showed that strain T3944D(T) belonged to the genus Oceanobacillus, exhibiting the highest levels of similarity with the sequences of Oceanobacillus oncorhynchi subsp. incaldanensis DSM 16557(T) (94.9 %), Oceanobacillus oncorhynchi subsp. oncorhynchi JCM 12661(T) (94.8 %), Oceanobacillus iheyensis JCM 11309(T) (94.7 %) and Oceanobacillus picturae LMG 19416 (94.5 %). Strain T3944D(T) grew optimally at 1-3 % NaCl, pH 8.5 and 37 degrees C. The major cellular fatty acids were anteiso-C(15 : 0) (60.0 %) and anteiso-C(17 : 0) (12.9 %) and the DNA G+C content was 38.1 mol%. On the basis of its phenotypic properties and phylogenetic distinctiveness, strain T3944D(T) represents a novel species in the genus Oceanobacillus, for which the name Oceanobacillus chironomi sp. nov. is proposed. The type strain is T3944D(T) (=LMG 23627(T)=DSM 18262(T)).

GROWTH AND DEVELOPMENT OF VEINED RAPA WHELK RAPANA VENOSA VELIGERS

Planktonic larvae of benthic fauna that can grow quickly in the plankton and reduce their larval period duration lessen their exposure to pelagic predators and reduce the potential for advection away from suitable habitats. Veined rapa whelks (Rapana venosa, Muricidae) lay egg masses that release planktonic veliger larvae from May through August in Chesapeake Bay, USA. Two groups of veliger larvae hatched from egg masses during June and August 2000 were cultured in the laboratory. Egg mass incubation time (time from deposition to hatch) ranged from 18–26 d at water temperatures between 22°C and 27°C. Four stages of rapa whelk veliger development along a time series from hatch to settlement were described using external morphological features. Rapa whelk veligers were measured at three-day intervals from hatching through the onset of spontaneous settlement. A four-parameter Gompertz growth model was used with length at age data from cultures of rapa whelk veligers to estimate maximum growth rates for June and August hatched groups. Larval rapa whelks settled at shell lengths of 1.18–1.24 mm after planktonic larval periods ranging from 24–42 d. Maximum larval growth rates observed in August (0.03 mm d−1) are 50% lower than maximum larval growth rates observed for June hatched rapa whelk veligers (0.071 mm d−1). Daily larval growth rates from hatch to first spontaneous settlement for rapa whelk veligers ranged from 0.002–0.099 mm d−1 with maximum growth rates occurring between 12–18 d post hatch in June. Larval period duration, or the time from hatch to first spontaneous settlement, was 12 days shorter for June hatched larvae than for August hatched larvae. Water temperature was not significantly correlated with larval growth rates (mm d−1) in either June or August. Plasticity in larval period duration may enhance survival and dispersal opportunities for planktonic rapa whelk veligers.

UV-Induced Mortality in Encapsulated Intertidal Embryos: Are Mycosporine-Like Amino Acids an Effective Sunscreen?

Mycosporine-like amino acids (MAAs) are believed to protect a variety of marine organisms against the negative effects of ultraviolet radiation (UVR). However, their role in protecting developing intertidal encapsulated embryos remains untested. In the present study, we focused on the UV protective role of natural concentrations of MAAs for two intertidal gastropod species, Bembicium nanum and Siphonaria denticulata, which lay egg masses in habitats exposed to direct sunlight. We predicted that in both species, a higher concentration of MAAs within the egg mass would increase the likelihood of embryonic survivorship in the presence of UVR. Egg masses from both species were collected along the rocky shores of southeastern New South Wales, and a portion from each was subjected to one of three separate spectral treatments: full spectrum, UV-B block, and UV block. Proportions of surviving embryos were recorded following 72 hr exposure to spectral treatment. In addition, MAAs in each egg mass were quantified. Levels of variation in MAA concentration were striking, with S. denticulata egg masses showing more intraspecific variation than those of B. nanum. Surprisingly, survivorship under all spectral treatments was extremely high for both species, irrespective of MAA concentration. Under full spectrum treatments, B. nanum survivorship and total MAA concentration were significantly and positively correlated; however, MAA accounted for just 23.6% (R = 0.486) of the variation in survivorship. In contrast, survivorship in S. denticulata was not correlated with MAA concentration under full spectrum light. We conclude that the dependence on MAAs as photoprotection may be species-specific; however, it is likely that both species possess alternative mechanisms that minimize the negative effects of UVR.

Oviposition strategies employed by the western spruce budworm: tests of predictions from the phylogenetic constraints hypothesis

Abstract1 Predictions from the Phylogenetic Constraints Hypothesis were tested for the first time in an eruptive forest Lepidopteran species, the western spruce budworm.2 In previous work, we established that western spruce budworm females exhibit oviposition preferences with regard to tree age, tree vigour and host species. However, there was no evidence to support a link between oviposition preference and larval performance, which supports the Phylogenetic Constraints Hypothesis.3 Our preference data led us to test whether female budworms use oviposition strategies to select the sites where they lay their egg masses. Our experiments were designed to make direct comparisons between latent and eruptive insect herbivores with respect to two oviposition behaviours: egg retention and avoidance of conspecifics. This type of research has not previously been conducted on any eruptive forest Lepidopteran.4 Female budworms retained eggs instead of laying them on less preferred hosts in two of three experiments, but the percentage of eggs they retained was significantly less compared to latent insect herbivores.5 In addition, female budworms actively avoided oviposition in areas with the highest density of conspecific egg masses, but they laid egg masses in all the other locations provided. This contrasts with the pattern seen in latent insect herbivores, which consistently avoid laying their eggs near any sites already used by conspecifics.6 Our research indicates that there are extreme differences between latent and eruptive insect herbivores with respect to egg retention and avoidance of conspecifics, thus supporting the Phylogenetic Constraints Hypothesis.

Influence of common carp on apple snail in a rice field evaluated by a predator - prey logistic model

The hypothesis that common carp can be used for the control of apple snails in rice fields was tested experimentally. In a rice field, 12 plots of 4 2 5 m were set and enclosed by plastic walls to prevent snail emigration and immigration. The experiment continued from June to September. Three replicated treatments were used for the plots: zero, four and 12 carp were released, giving carp densities of 0.0, 0.2 and 0.6 m−2, respectively. Snail densities were estimated by the Jolly-Seber mark-recapture method. Newly laid egg masses were counted and measured for size, and hatching was monitored. The numbers of eggs per egg mass (y) were estimated using a regression equation obtained from the product of the maximum length and width of the egg mass (x): y =0.10x1.24. Using these measures and the monthly mean hatching rate obtained from eggs laid in two outdoor aquaria from April to September, the number of hatched eggs was used to estimate the birth rate over a given time. A logistic model incorporating these estimates revealed that the snail population proliferated only in the zero-carp plot throughout the experiment. The study, together with other reports on snail longevity, predicts that a snail population would be eliminated in 2 years at a stocking density of 2000 carp hectare−1, if no immigration of the snail occurred.

Reproduction and larval development of the gastropodAlaba vladivostokensis in Vostok Bay, the Sea of Japan

The reproduction and development of the prosobranch gastropodAlaba vladivostokensis Bartsch were studied. In Vostok Bay,A. vladivostokensis reproduces in the warmest season at water temperatures of 19–23°C. The females lay egg masses in the shape of flat, coiled bands on eelgrass leaves and on sargosso thalluses. The total period of development from egg laying to larval settling takes 25–27 days. The reproduction and development patterns and larval morphology ofA. vladivostokensis are similar to that ofAustralaba picta (A. Adams), which inhabits the coast of Japan. It is suggested that the population ofA. vladivostokensis in Peter the Great Bay should considered as part of the wide geographical range ofA. picta.

Impact of Low-Level Radiation on Fertility and Fecundity of Nezara viridula(Hemiptera: Pentatomidae)

The southern green stink bug, Nezara viridula (L.), was exposed to ionizing radiation of <10 Gy in the 4th instar and rendered partially sterile. Females laid nonviable eggs in high proportions and had significantly lower fecundity than controls. Diet and inbreeding status affected fecundity, fertility, and the reproductive response after irradiation. One inbred group became sterile with the combined stress of radiation and diet. When irradiated (5 Gy) and nonirradiated wildtypes mated, the proportion of nonviable eggs laid was intermediate to that laid by pairs of irradiated wildtype bugs and pairs of nonirradiated bugs. Other mixed-treatment pairings and outcrosses gave variable results. Adult progeny from irradiated pairs showed an “all or none” form of recovery with regard to fitness. Fertile pairs laid egg masses with a majority of eggs hatching. However, almost half the pairs were infecund or laid only sterile eggs. Overall, fecundity was significantly less in progeny of irradiated inbred or irradiated wildtype bugs. At higher levels of radiation, nymphs either died before reaching the adult stage or became sterile. At 20 Gy, half survived to the adult stage. One female laid sterile eggs when mated to a nonirradiated male. Nonirradiated females produced no egg masses after mating with the irradiated males. At 40 and 60 Gy, mid-instar 4th-instar nymphs became emaciated. Most underwent a delayed molt and died in the 5th instar. At 80 Gy, most died in the 4th instar.