Egg hatching of two locusts,Schistocerca gregaria and Locusta migratoria,in response to light and temperature cycles

The present study showed that the eggs of the desert locust, Schistocerca gregaria, and the migratory locust, Locusta migratoria, responded to photoperiod by hatching when placed on sand in the laboratory. S. gregaria mainly hatched during the dark phase and L. migratoria during the light phase. The importance of light as a hatching cue depended on the magnitude of the temperature change during the thermoperiod; photoperiod played a more important role in the control of hatching time in both species when the magnitude of the temperature change was small. In addition, the eggs of the two species that were covered with sand did not respond to photoperiod and hatched during both the light and dark phases, indicating that light did not penetrate through the sand. Because locust eggs are normally laid as egg pods and a foam plug is deposited between the egg mass and the ground surface, we tested a possibility that naturally deposited eggs perceived light through the foam plug. The eggs that were deposited and left undisturbed in the sand hatched during the light and dark phases at similar frequencies. These results suggest that the eggs of both locust species responded to light and controlled their hatching timing accordingly but would not use light as a hatching cue in the field. The evolutionary significance of the ability of eggs to respond to light in these locusts was discussed.     

A calibration method to generate seasonal hatching profiles for the fiddler crabs Uca pugnax (Smith, 1870) and Uca minax (LeConte, 1855) (Decapoda : Brachyura)

A statistical method for generating seasonal egg hatching profiles is applied to the brachyuran crabs Uca pugnax (Smith) and U. minax (LeConte) in New Jersey. Calibration experiments quantified the time course of egg development, using serial egg sampling at 1- to 2- day intervals from marked ovigerous females maintained in cages in the field. Egg stage was ranked from 1 to 10, based on morphological changes during development. Equations for predicting the number of days remaining until hatching from egg developmental stage were obtained from the calibration experiments, using stepwise polynomial regression. To cover the reproductive season, three consecutive calibration experiments using 15 or more females were run for U. pugnax; two for U. minax. Significant seasonal differences in the time course of egg development were detected. Weekly collections of females for each species were made; the date of larval release for each ovigerous female was predicted from the proximate calibration equation, yielding weekly hatching profiles. Weekly hatching profiles were summed to obtain seasonal hatching profiles. The average number of broods produced per female over the reproductive season was 1.9 for U. pugnax and 1.6 for U. minax. Hatching peaks for both species were associated with spring tides. The merits of this and other methods used to estimate daily variation in egg hatching of crabs are discussed.     

Ecophysiological attributes of adult overwintering in insects: insights from a field study of the nut weevil,Curculio nucum

Abstract Diapausing insect species have evolved a great diversity of life cycles, although overwintering occurs at a single development stage within most species. Understanding why diapause has evolved towards a given life stage requires investigation of both the ecological and physiological attributes. Notably, it is suggested that adult overwintering is more energy‐demanding than larval overwintering but it brings fitness gains by allowing adults to be synchronized with their seasonal requisites through an early spring emergence. This hypothesis is tested in field conditions in the nut weevil Curculio nucum, whose life cycle comprises an obligate 2‐year, nonfeeding underground phase, including a larval, followed by an adult, overwintering. In this species, adult wintering leads to an early spring emergence; at first glance, however, this does not enhance synchronization between weevils and their host because adults emerge more than 1 month before starting to breed. It is suggested that adult overwintering ultimately evolved in response to the phenology of the host, by allowing females to oviposit in nuts before their full sclerotinization. Adult overwintering appears to be costly because adults postpone reproduction for 1 year, incur a significant weight loss and require feeding before egg laying. Surprisingly, lipids are unaffected during diapause, lipogenesis even being likely in the summer metamorphosis. These results suggest that the lipids involved in egg production may entirely come from the larval stages, whereas the other nutrients are acquired through adult feeding but this remains to be tested.     

Identification of the Key Weather Factors Affecting Overwintering Success of Apolygus lucorum Eggs in Dead Host Tree Branches

Understanding the effects of weather on insect population dynamics is crucial to simulate and forecast pest outbreaks, which is becoming increasingly important with the effects of climate change. The mirid bug Apolygus lucorum is an important pest on cotton, fruit trees and other crops in China, and primarily lays its eggs on dead parts of tree branches in the fall for subsequent overwintering. As such, the eggs that hatch the following spring are most strongly affected by ambient weather factors, rather than by host plant biology. In this study, we investigated the effects of three major weather factors: temperature, relative humidity and rainfall, on the hatching rate of A. lucorum eggs overwintering on dead branches of Chinese date tree (Ziziphus jujuba). Under laboratory conditions, rainfall (simulated via soaking) was necessary for the hatching of overwintering A. lucorum eggs. In the absence of rainfall (unsoaked branches), very few nymphs successfully emerged under any of the tested combinations of temperature and relative humidity. In contrast, following simulated rainfall, the hatching rate of the overwintering eggs increased dramatically. Hatching rate and developmental rate were positively correlated with relative humidity and temperature, respectively. Under field conditions, the abundance of nymphs derived from overwintering eggs was positively correlated with rainfall amount during the spring seasons of 2009–2013, while the same was not true for temperature and relative humidity. Overall, our findings indicate that rainfall is the most important factor affecting the hatching rate of overwintering A. lucorum eggs on dead plant parts and nymph population levels during the spring season. It provides the basic information for precisely forecasting the emergence of A. lucorum and subsequently timely managing its population in spring, which will make it possible to regional control of this insect pest widely occurring in multiple crops in summer.     

Costs and benefits of maternal behaviour in the green lynx spider (Oxyopidae,Peucetia viridans)

I examined the adaptiveness of maternal behaviour in the green lynx spider Peucetia viridans (Hentz), by measuring the costs and benefits to the female of egg-sac tending. P. viridans guards her egg sac for 6–8 weeks until the young have emerged and dispersed. I removed females from egg sacs in the field either immediately after oviposition or after they had guarded the egg sacs for 2 weeks, and compared the fate of these sacs with that of control sacs which had females present throughout. Survival rates of egg sacs were significantly improved by the presence of a female. The major sources of mortality were ant predation and sac dislodgement, both of which were significantly reduced by a guarding female, and mantispid brood parasitism, which was not affected by the female. To measure the spiders' lifetime reproductive output, I allowed caged females to construct egg sacs. Half had their first egg sac removed shortly after oviposition, while half were allowed to guard. Significantly more non-guarding than guarding females produced second egg sacs. Thus for the green lynx spider, egg sac guarding decreases lifetime egg production, but increases offspring survival. Under north Florida conditions, the benefits of guarding outweight the costs, and the females have a higher lifetime reproductive success than if they did not guard.     

Aspects of the ecology and energetics of the egg sac parasites of the wolf spider Pardosa lugubris (Walckenaer)

Summary The egg sacs of the wolf spider Pardosa lugubris are parasitised by two ichneumonid wasps, namely Gelis micrurus and Hidryta sordidus. The parasites are bivoltine, the first generation parasitising the summer egg sac of P. lugubris and the second generation parasitising, and overwintering in, the autumn egg sac. Parasitised egg sacs have a characteristic appearance.The degree of egg sac parasitism was 9.8% and 6.9% for the two egg sac batches in 1965 and 2.9% and 34.8% for those of 1966. The degree of parasitism varies from area to area as does the percentage parasitism attributable to the two species.The gross growth efficiency for Hidryta from the first egg sac is 31.2% and from the second 16.2%. 3.0% in 1965 and 4.3% in 1966, of the annual yield from P. lugubris to predators and parasites, goes to the egg sac parasites. This represents reductions in recruitment of 9.1% in 1965 and 10.9% in 1966.     

The effect of an alternating electromagnetic field upon early development in roach (<Emphasis Type="Italic">Rutilus rutilus</Emphasis>: Cyprinidae,cypriniformes)

The effect of an alternating electromagnetic field (EMF) upon three stages of roach’s (Rutilus rutilus) early development was studied. The studies covered the periods before gastrulation; from gastrulation until hatching; and from hatching until yolk sac resorption. It has been shown that the EMF effect is as stronger as earlier in the embryogenesis the roach was subjected to an impact. The following responses to EMF were registered: earlier hatching of prelarvae, increase in the morphological diversity of juvenile fish, decrease in body lengths and weights, and changes in the number of vertebrae in yearlings.     

Effects of Zinc Fertilization of Corn on Hatching of Heterodera glycines in Soil

Experiments were conducted to determine the effects of zinc fertilizers on hatching and soil population densities of Heterodera glycines. In vitro egg hatching in solutions of reagent-grade zinc sulfate and zinc chloride and fertilizer-grade zinc sulfate was significantly greater than hatching in deionized water, whereas zinc chelate fertilizer significantly inhibited egg hatching relative to deionized water. In greenhouse experiments, no differences in cumulative percentage egg hatch were detected in soil naturally infested with H. glycines amended with fertilizer-grade zinc sulfate and zinc chelate at rates equivalent to 0, 1.12, 11.2, and 112 kg Zn/ha and subsequently planted with corn (Zea mays L.). In a field experiment, no significant differences in H. glycines egg population densities and corn yields were detected among plots fertilized with 0, 11.2, and 22.4 kg Zn/ha rates of zinc chelate. Yields of H. glycines-susceptible soybean planted in plots 1 year after zinc fertilization of corn plots also were not significantly affected. Zinc compounds significandy affected H. glycines egg hatching in vitro, but had no effect on hatching in natural soils.     

Development of the bitterling,Tanakia tanago (cyprinidae), with a note on minute tubercles on the skin surface

The development of eggs and larvae and minute tubercles on the skin surface in larvae ofTanakia tanago were observed. The eggs began to hatch approximately 52 hours after insemination and the larvae reached free-swimming stage 19 days after hatching at water temperature of 22±1°C. The egg and larval development and minute tubercles on the skin surface in larvae of this species were similar to those ofAcheilognathus lanceolata andA. limbata. However,T. tanago was distinguishable in egg and larval development fromA. lanceolata andA. limbata by the following characters: the perivitelline space was narrower, embryonic and larval development was faster, and minute tubercles on the skin surface of the anteriormost parts of the yolk sac, and of the body and head were hemispheric in shape. From these characters,T. tanago is considered to be more specialized thanA. lanceolata andA. limbata.     

Effects of temperature, salinity, and air exposure on development of the estuarine pulmonate gastropod Amphibola crenata

The primitive pulmonate snail Amphibola crenata embeds embryos within a smooth mud collar on exposed estuarine mudflats in New Zealand. Development through hatching of free-swimming veliger larvae was monitored at 15 salinity and temperature combinations covering the range of 2-30 ppt salinity and 15-25 °C. The effect of exposure to air on developmental rate was also assessed. There were approximately 18,000 embryos in each egg collar. The total number of veligers released from standard-sized egg collar fragments varied with both temperature and salinity: embryonic survival was generally higher at 15 and 20 °C than at 25 °C; moreover, survival was generally highest at intermediate salinities, and greatly reduced at 2 ppt salinity regardless of temperature. Even at 2 ppt salinity, however, about one-third of embryos were able to develop successfully to hatching. Embryonic tolerance to low salinity was apparently a property of the embryos themselves, or of the surrounding egg capsules; there was no indication that the egg collars protected embryos from exposure to environmental stress. Mean hatching times ranged between 7 and 22 days, with reduced developmental rates both at lower temperature and lower salinity. At each salinity tested, developmental rate to hatching was similar at 20 and 25 °C. At 15 °C, time to hatching was approximately double that recorded at the two higher exposure temperatures. Exposing the egg collars to air for 6-9 h each day at 20 °C (20 ppt salinity) accelerated hatching by about 24 h, suggesting that developmental rate in this species is limited by the rates at which oxygen or wastes can diffuse into and from intact collars, respectively. Similarly, veligers from egg capsules that were artificially separated from egg collars at 20 °C developed faster than those within intact egg collars. The remarkable ability of embryos of A. crenata to hatch over such a wide range of temperatures and salinities, and to tolerate a considerable degree of exposure to air, explains the successful colonization of this species far up into New Zealand estuaries.     

Adaptive strategies of overwintering adults: Reproductive diapause and mating behavior in a grasshopper,Stenocatantops splendens (Orthoptera: Catantopidae)

Abstract To understand the adaptive strategies of the overwintering adults of Stenocatantops splendens, the mechanism of maintenance and termination of the reproductive diapause, the variation in mortality between overwintering females and males, and the mating strategy of the males were investigated. The results indicated that the adult reproductive diapause in natural conditions was mainly regulated by photoperiod in the fall – long photoperiods promoted reproductive development and short photoperiods maintained reproductive diapause, and the sensitivity of the overwintering adults to photoperiod was over before the end of the winter. When transferred from natural conditions to controlled laboratory conditions on dates from September through February, pre‐oviposition became increasingly shorter with increasingly deferred transfer dates regardless of photoperiod conditions. The adults treated with low temperature for 30 days in September through November had significantly shorter pre‐oviposition, suggesting that low temperatures in winter had an important role in the termination of reproductive diapause. The female had a significantly lower supercooling point than the male, which was related to their lower mortality after winter. In addition, observations of wild populations of the species indicated that mating behavior prior to winter and the duration of pre‐mating period were not affected by photoperiod; mating and sperm transfer were mostly completed by November. Compared with females only mating before winter, females mating in the spring had shorter life span, longer pre‐oviposition, lower hatching rate and laid fewer egg pods while showing no significant difference with regard to ovipositional interval, per pod number of eggs and nymph dry weight.     

洱海周边2种寄生蜂对拟环纹豹蛛和星豹蛛卵孵化的影响

为探讨Hidryta sp．和Idris sp．对云南洱海周边拟环纹豹蛛Pardosa pseudoannulata（Boes．＆Str．）和星豹蛛Pastvigera C．L．Koch卵孵化的影响,对具卵囊的拟环纹豹蛛和星豹蛛进行为期1年的野外采集和室内卵囊孵化观察,发现Hidryta sp．寄生蜘蛛卵囊后,每个卵囊内仅羽化出1只蜂,不再有幼蛛孵化出;而被Idris sp．寄生后每个卵囊羽化出一至数十只蜂,仍有幼蛛孵化出。比较未被寄生与被寄生蜘蛛卵囊的孵化量显示,拟环纹豹蛛未被寄生与被Idrissp．寄生后的孵化量间无显著差异（P〉0．05）;星豹蛛未被寄生与被Idris sp．寄生后的孵化量问存在显著差异（P〈0．01）。比较单位个体孵化量显示,Hidrytasp．对拟环纹豹蛛卵孵化的影响程度大于Idris sp．;而Hidrytasp．对星豹蛛卵孵化的影响程度小于Idris sp．。     

Moisture during Egg Incubation Adversely Affects Hatching of the West Indian Sweetpotato Weevil,Euscepes postfasciatus (Coleoptera: Curculionidae), When the Eggs are Incubated En Masse

We compared the egg-hatching of Euscepes postfasciatus (Fairmaire) with and without moisture treatment to test whether moisture is necessary during egg incubation when a large number of eggs are gathered into a mass. Moisture treatment exhibited significant undesirable effects on hatching (reduction of hatchability, delay of hatching, and increase of the variance of hatching date) compared to no moisture treatment. In addition, moisture treatment significantly increased the incidence of fungus on the egg surface, which can subsequently contaminate the larval artificial diet. Based on these results, we concluded that moisture is not necessary for incubating E. postfasciatus eggs. Two possible explanations for the undesirable effects of moisture on hatching were discussed: a direct effect by preventing respiration of the eggs and an indirect effect through fungal infection of the eggs.     

Physiological costs during the first maternal care in the wolf spider Pardosa saltans (Araneae,Lycosidae)

Many arachnids like other terrestrial arthropods, provide extensive maternal care. Few studies have quantified the underlying physiological costs of maternal care. We investigated how maternal care affects the free-moving wolf spider’s (Pardosa saltans) energy requirements. We described in detail their basic reproduction biology (i.e. carrying cocoon and young) and we evaluated the variation in the females’ energy reserves during maternal care. Our results show that mothers guard eggs until hatching and then guard their spiderlings for 27–30 more days. Laboratory observations indicated that spiderlings start leaving the maternal abdomen gradually 5–7 days after hatching. Females carry an egg sac (cocoon) that can weigh up to 77% of their post-reproduction weight and carry young that weigh 87–100% of their body mass. Females lost weight over time despite regular food intake, while carrying cocoon and young; but their weights increased gradually during the dispersal of young. The contributions of proteins, glucose and triglycerides to maintain females’ energy were calculated. Their energetic state varied during maternal care, in particular lipid levels declined, during the care of spiderlings when the females’ predatory behaviour was inhibited. Our results show that the maternal care provided by P. saltans females is particularly costly physiologically, during the 30 days following egg sac formation and development of spiderlings, even when food is available.     

A Theoretical Model of the Winter Survival Dynamics of Meloidogyne spp. Eggs and Juveniles

A theoretical model of the winter survival dynamics of Meloidagyne spp. was developed by considering the roles of egg hatching and juvenile mortality and the initial populations of eggs and juveniles at the onset of winter. Two distinct patterns of juvenile dynamics appear which depend upon the numerical values of the model parameters. The model predicts whether eggs or juveniles are the major component of overwintering nematode populations at any time prior to planting. The model could be elaborated to include egg viability and differential mortality of eggs but at some cost in ease of mathematical analysis. A general procedure for fitting the proposed model to experimental or observational data is outlined.     

Development and the influence of nurse egg allotment on hatching size in Searlesia dira (Reeve, 1846) (Prosobranchia : Buccinidae)

The reproductive biology of the intertidal prosobranch Searlesia dira (Reeve, 1846) was examined with special attention given to variability in the nurse egg to embryo ratio among capsules, among clutches and among geographically isolated populations. Embryos and nurse eggs were distributed among the capsules in a manner consistent with the hypothesis that nurse eggs were genetically predetermined, that each female had a genetically defined nurse egg to embryo ratio, and that each capsule represented a random sample of that ratio. The binomial distribution of embryos and nurse eggs among the capsules resulted in some capsules receiving many more embryos per nurse egg than others. The number of nurse eggs an embryo succeeded in eating was proportional to the number of capsule-mates sharing a capsule. Embryos eating more nurse eggs hatched out at a larger size. Differences in the nurse egg to embryo ratios among capsules in the same clutch were much larger than that of the mean ratios among clutches. Among-site differences in the mean nurse egg to embryo ratios suggest that selection pressure for different mean hatching sizes may have acted on the mean nurse egg to embryo ratios.In contrast to the predictions of optimal hatching size theory, hatching size varied widely within clutches as a consequence of differences in nurse egg to embryo ratios among capsules. This variance may be adaptive for species that lay their eggs months before juveniles emerge into an unpredictable environment, or simply be a consequence of an imperfect mechanism for increasing hatching size.     

Comparison of cold tolerance in eggs of two cicadas, Cryptotympana facialis and Graptopsaltria nigrofuscata, in relation to climate warming

The population of the cicada Cryptotympana facialis began to increase in Osaka, Japan, during the late 20th century. Climate warming is considered a major cause, although the relationship between temperature and the cicada population increase remains unclear. By examining cold tolerance in overwintering eggs of C. facialis in relation to another cicada, Graptopsaltria nigrofuscata , whose population has recently decreased in Osaka, we tested the hypothesis that warming has caused the population increase of C. facialis by decreasing egg mortality due to winter temperatures. A short-term (24 h) cold exposure experiment demonstrated that the half-lethal temperatures (LT50) of C. facialis and G. nigrofuscata were −23.3°C and −28.9°C, respectively, although these extreme low temperatures never occurred in Osaka during the 20th century. Prolonged exposure to −5°C for up to 30 days had no harmful effects on the hatching rate in either species. Overwintering mortality was also assessed under naturally fluctuating conditions by transferring eggs to cooler elevated sites that mimicked the environment prior to the current warming. Eggs of C. facialis that overwintered at the cooler site exhibited similar hatching rates to those maintained at the original site. The results of these experiments consistently indicated that overwintering eggs of C. facialis possess adequate tolerance to the low temperatures of the 20th century. Therefore, we rejected our initial hypothesis that recent increases in the C. facialis population have been caused by warming-related reductions in overwintering egg mortality.     

Male body size and brooding success under natural conditions in the freshwater Japanese goby, Rhinogobius sp. OR (orange type)

Males of the Japanese goby Rhinogobius sp. OR (orange type) establish nests under stones in streams. They provide care to egg masses until hatching. We carried out field observations and a field experiment in a natural stream to examine the effect of male body size on brooding success. An experiment excluding guarding males indicated that their presence has a positive effect on nest defense. Field data showed that male body size was positively correlated with the size of the egg mass that was initially found at the nest. Furthermore, a sequential increase in egg mass size seen in the nests of larger males indicated that multiple females spawned during a single breeding cycle of larger males. To examine male brooding success, two dependent variables, egg mass persistence (days from initial egg mass to disappearance or hatching) and hatching success were analyzed. The results indicated that the variation found in both dependent variables was significantly explained by two independent variables, namely, initial egg-mass size and the number of matings. It is also suggested that male body size indirectly influenced brooding success through positive correlations with these independent variables.     

The importance of hatching from resting eggs for population dynamics and genetic composition of Daphnia in a deep reservoir

1. Cyclical parthenogens, organisms switching between sexual and asexual mode of reproduction, are common in aquatic habitats. In permanent waterbodies with year‐round persistence of populations, the relevance of sexually produced resting eggs for population dynamics and structure is still largely unexplored. 2. The aim of this study was to investigate the importance of recruitment from resting eggs to Daphnia spp. in a deep dimictic reservoir with overwintering populations (Saidenbach Reservoir, Germany). We linked field studies on Daphnia population dynamics, hatching rates and diapausing egg abundances in the sediment with allozyme analysis of the genetic variability of both the pelagic population and hatchlings from resting eggs. 3. We found higher hatching rates at intermediate depths (10–18 m), although highest diapausing egg abundances were found in the deeper parts of the reservoir. From the extensive field data, we calculated a population budget for the main basin of the reservoir, which showed that hatched daphnids accounted for <1% of the total abundance and explained only a tiny fraction of population growth. 4. The genetic composition (MultiLocus Genotypes, MLG) of the pelagic population was relatively stable throughout the stratified period with up to five among 39 detected MLGs attaining frequencies >5% per date. From 11 MLGs differentiated among hatched daphnids, three were recovered in the pelagic population in perceptible, albeit low frequencies (1–4%). 5. We conclude that the contribution of hatched animals to the spring population dynamics is negligible in situations with an overwintering population present and will only become relevant if densities are extremely low. In this type of system, the significance of the resting egg bank is presumably mainly related to the maintenance of genetic diversity.     

Embryonic stage of obligatory diapause and effects of abiotic conditions on egg hatching in the balsam twig aphid,Mindarus abietinus

Diapause‐mediated dormancy in overwintering insect eggs has rarely been studied with regard to the ecological factors controlling postdiapause development. In insects of temperate latitudes, water availability at the end of winter, in interaction with temperature, could control the resumption of development for insect stages in postdiapause quiescence. The balsam twig aphid, Mindarus abietinus Koch (Hemiptera: Aphididae), overwinters as eggs in southern Québec, Canada, on balsam fir, Abies balsamea (L.) Miller (Pinaceae), in Christmas tree plantations, where it is known as a pest. Previous work has shown that eggs of this aphid maintain low water content during winter, presumably to survive sub‐zero temperatures. Conversely, in late winter and early spring, they passively or actively absorb surrounding moisture, which is accompanied by notable changes in size, shape, and fresh mass. The primary objective here was to determine the embryonic stage at which winter diapause starts and is maintained in M. abietinus, a relatively primitive aphid. Secondly, we tested the hypothesis that free water availability to postdiapause eggs, in combination with temperatures above developmental threshold, is essential for embryonic development and hatching, by experimentally soaking field‐collected eggs in water at controlled frequencies. We observed that embryogenesis starts at the time of egg laying and stops after a few days, before the anatrepsis stage of blastokinesis is complete, when the germ band has not yet entirely immersed itself into the yolk. We also found that water surrounding overwintered eggs on fir shoots, in interaction with temperature regime, significantly increases M. abietinus egg hatching rates. Potential impacts of environmental factors such as precipitation are discussed in relation to M. abietinus egg hatching rates and potential for population growth in spring.