Reproduction, growth and circadian activity of the snail Bradybaena fruticum (O. F. Müller, 1774) (Gastropoda: Pulmonata: Bradybaenidae) in the laboratory

Selected life cycle parameters of the snail Bradybaena fruticum were studied in the laboratory. The initial material for the laboratory culture was taken from a population in South Western Poland; the snails were kept in Petri dishes and plastic containers. The temperature, humidity and lighting conditions were maintained at a constant level (day 18°C, night 12°C, rh 80%, light:dark 12:12). Circadian activity observations were conducted outside the climatic chamber. Eggs — calcified, slightly oval, of mean dimensions 2.67x2.56 mm — were laid singly or in batches of 6–62, as a result of both biparental and uniparental reproduction. Incubation took 27–76 days and hatching was asynchronous. Hatching success was lower among eggs produced by single parents compared to eggs produced by two parents (c.a. 56 and c.a. 88%, respectively). Growth included fast (2.25 to 5 whorls) and slow (1.9–2.25 and >5 whorls) phases as well as lip formation, and took 261 to 420 days. The first eggs/batches were laid c.a. one year later, and for uniparentally reproducing snails the period was even longer. The growth of snails kept singly was faster than in those kept in groups. Juvenile snails were much more active than adults in the spring, summer and autumn but the adults were more mobile in the winter. In all seasons, juveniles were more active at night than adults.     

The effect of artificial photoperiod on growth and reproduction in the land snail Cepaea nemoralis

Summary

Specimens of Cepaea nemoralis were raised from egg to adult in the laboratory for 15.5 months in two artificial photoperiods: short-day (LD 8:16) and long-day (LD 16:8). Over 20% of the snails in each photoperiod were functional adults by the end of the experiment and had fully developed male and female reproductive systems as determined both by dissection and by oviposition. A total of 925 eggs were laid by animals reared in a long-day photoperiod, whereas animals in a short-day photoperiod laid 677 eggs. Animals reared in a long-day photoperiod grew slightly faster (2.04 mg/day compared to 1.73 mg/day), began laying eggs about 18 days sooner, and suffered higher mortality (19% compared to 11%) than animals reared in a short-day photoperiod. These results clearly establish for C. nemoralis that gametogenesis and the development of a functional hermaphroditic reproductive system are neither prevented nor significantly retarded by exposing the animals to a short-day photoperiod for their entire pre-reproductive life.     

Changes in the reproductive biology of Biomphalara glabrata infected with different doses of Echinostoma paraensei miracidia

The egg-laying rate, number of egg masses, number of eggs/mass, number of eggs hatched/snail and egg viability of Biomphalaria glabrata exposed to different doses (5 and 50) of Echinostoma paraensei miracidia were analyzed as indicators of reproductive activity. Polystyrene plates were placed in aquariums containing the snails and every other day for four weeks after infection the plates were removed to count the number of egg masses and eggs laid. After this, the plates were numbered individually and placed in new aquariums free of snails and the egg masses were observed daily to determine the hatching rate. On average there was an increase in the parameters evaluated in the infected snails in relation to the controls (uninfected snails), except for egg viability, which was significantly lower in the groups infected with 50 miracidia. These findings indicate that when infected, this host snail is able to increase its reproductive activity, suggesting an ecological strategy to maintain the species.     

Field and laboratory studies on the life-cycle, growth and feeding preference in the hairy snail Trochulus hispidus (L., 1758) (Gastropoda: Pulmonata: Hygromiidae)

For the first time the life cycle of the common land snail Trochulus hispidus was completely described in Central Europe (Poland). This is a semelparous species predominantly with an annual life cycle and the reproductive period lasting from April till October. The first young snails hatch in spring, grow rapidly in summer and reach ca. 4 whorls until winter. In spring of the next year they mature and reproduce. After that they die. There is hardly any growth from late autumn till early spring. The average proportional growth rate is ca. 0.3 whorl/month in the wild. The fastest growth is present in the youngest snails and then gradually decreases over the course of their age. Laboratory and field observations allowed for establishing the following life cycle parameters: eggs calcified, almost spherical, ca. 1.5 mm, laid in spring and summer in batches of between 1 and 47. Time to hatching is 6–24 days, hatching is asynchronous; newly-hatched snails have approximately 1.5 whorls. Analysis of food preferences revealed, that T. hispidus tends to restrict its diet during the life. Generally the youngest snails equally consumed leaves of all four tree species offered (Fraxinus excelsior, Acer pseudoplatanus, Tilia cordata and A. platanoides) whereas adults preferred F. excelsior over A. pseudoplatanus and A. platanoides.     

Thermal limits for the establishment and growth of populations of the invasive apple snail <Emphasis Type="Italic">Pomacea canaliculata</Emphasis>

Pomacea canaliculata is a South American freshwater snail considered as one of the world’s worst invasive alien species. A temperature of around 25 °C has usually been considered to be optimal for rearing P. canaliculata. Nevertheless, snails have not been reared under a wide range of temperatures to reveal the optimum for performance in terms of population increase. We investigated the effect of temperature on growth, survival and reproduction, estimating demographic parameters for P. canaliculata in the wide range of temperatures at which these snails are active (15–35 °C). No reproductive activity was evidenced for the snails reared at 15 °C, probably explained by the small sizes attained at this temperature. Temperatures above 25 °C did not promote a significant acceleration in growth so higher temperatures will not result in a reduction in time to reach maturity. In fact, snails from 25 and 30 °C began reproduction at the same age. We report here for the first time a detrimental effect of high temperatures that provoked a significant decrease in the contribution of snails to the next generation: the viability of eggs from the snails reared at 30 °C was very low and the snails exposed to a constant water temperature of 35 °C were unable to produce eggs. Our findings reveal a new environmental constraint that could be a determinant of the range limits of this species in invaded regions, especially during the coming decades, anticipating the scenario predicted from global warming.     

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.     

An investigation into the reproductive characteristics ofMicroctonus hyperodae (Hym.: braconidae), a parasitoid ofListronotus bonariensis (Col.: Curculionidae)

The reproductive tract of the parasitoidMicroctonus hyperodae was found to comprise 6.1±0.2 ovarioles containing a total of 40–60 oöcytes. After oviposition into its hostListronotus bonariensis, the parasitoid's egg volume increased by 205 times prior to hatching. At 19.1°C ovipositingM. hyperodae survived for a mean 21±4 days and laid a mean of 48±8 eggs.M. hyperodae collected from Colonia, Uruguay laid a mean of 62±15 eggs which was significantly more than the other ecotypes. Under caging conditions with an ample supply of hosts,M. hyperodae laid 51% of its eggs in the first 72 hours and on average 41% of the species' life-span occurred after the exhaustion of its egg supply. Minimum temperature forM. hyperodae oviposition was found to be c. 5°C; beyond this the rate of increase in egg-laying was approximately linear until 30°C whereafter the rate fell abruptly. There was effectively no egg-laying at 39°C. The parasitoid showed no preference for one host sex or the other either in the laboratory or under field conditions. Compared to otherMicroctonus spp.,M. hyperodae appeared to show low fecundity and high longevity. The adaptive implications of this are discussed.     

Seasonal characteristics and tetrodotoxin-producing ability of bacteria in gastropod Oliva hirasei

Lycoteuthis lorigera is among the most abundant mesopelagic squid on the continental slope of the south Atlantic. It is the dominant prey in some commercially harvested groundfish. Despite its abundance and importance in the mesopelagic foodweb, its general biology is poorly known. In this study, the spawning pattern and fecundity of L. lorigera from southern African waters were investigated. Both histological examination and length frequency analysis of ovaries in various stages of development revealed that the ovulation pattern of L. lorigera is asynchronous, which indicates a spawning strategy where batches of eggs are spawned repeatedly over time. More specifically, ovulation is group synchronous, where distinct batches of 1,200–2,400 eggs ripen in the ovary and accumulate in the oviducts. The potential fecundity was estimated to be 20,000–50,000 in immature females (n = 6) and 8,000–25,000 in mature females (n = 21). The number of ripe eggs in the oviducts suggests that batches of spawned egg masses contain between 1,000 and 4,000 eggs. The reproductive strategy of L. lorigera is discussed and compared to the reproductive strategies of oceanic squid inhabiting the continental slope of southern Africa.     

Population regulation in the land snail Arianta arbustorum: density effects on adult size,clutch size and incidence of egg cannibalism

Summary The relationships between local population density and adult size, clutch size and spatial distribution of egg batches were investigated in 11 natural populations of the land snail Arianta arbustorum in a forest near Uppsala, Sweden. Shell size of adults decreased with increasing population density as did clutch size. Within populations, clutch size scaled allometrically with shell size indicating size-specific fecundity. It is hypothesized that food unpalatability caused by mucus deposition slows down juvenile growth rate in high density populations, resulting in small adults and thus reducing their fecundity in subsequent years. The influence of the distance between batches on the incidence of egg cannibalism by hatchlings was examined in a laboratory experiment. In this experiment the number of eggs cannibalized increased with decreasing distance to the batch of hatching snails. Thus, in the field, eggs of highly aggregated batches suffer a high risk of cannibalism. In the 3 populations with the highest snail density, 21–39% of all batches were deposited close to each other (nearest neighbour distance 5 cm, i.e. less than hatchlings more within 1 day). These findings indicate that egg cannibalism can act as a population regulating factor.     

Larval development of the gastropod <Emphasis Type="Italic">Epheria turrita</Emphasis> (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.     

A comparative study of the ultrastructure and mineralogy of calcified land snail eggs (Pulmonata: Stylommatophora)

This study indicates that eggs containing calcium carbonate crystals occur in at least 36 of the 65 known families of the land snails (class Gastropoda: order Stylommatophora). Eggs from 22 of these families were available for examination. The x-ray diffraction data, available for the first time for 21 of these families, shows that these egg shells are all made of calcite only, or of a combination of calcite with smaller amounts of aragonite. All of the snail (body) shells examined were made of aragonite only. This is the first ultrastructural investigation of these egg shells, and it indicates that the eggs exhibit enough structural diversity to allow identification of parental animals to genus, and often to species level solely on the basis of egg shell ultrastructure. All of the calcified eggs may be divided into two groups: (1) partly calcified, with discrete crystals of CaCo₃ dispersed in the jelly layer, and (2) heavily calcified, with a hard, brittle egg shell made of fused crystals of CaCO₃ much like an avian egg. Both types of calcified eggs occur in oviparous as well as in ovoviviparous snails. Because of the wide distribution of calcified eggs in the Stylommatophora, and because of the occurrence of heavily calcified eggs in ancient families such as Partulidae, Endodontidae, and Zonitidae, the calcified egg is viewed as a primitive land snail trait associated with terrestrial adaptation. The function of the calcified egg shell, in addition to mechanical support of egg contents, is to supply the developing embryo with enough calcium to form the embryonic shell by the time of hatching.     

Effect of Temperature on the Biology of Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae) Reared on a Factitious Host,Antheraea pernyi (Lepidoptera: Saturniidae) Egg

Laboratory studies were conducted to investigate the effect of selected temperatures on the development, mortality, sex ratio, and emergence rate of Trichogramma dendrolimi Matsumura reared from a factitious host, oak silkworm, Antheraea pernyi (Guérin-Méneville) eggs. The comparison tests were conducted to investigate the fecundity on Dendrolimus spectabilis (Butler) eggs of T. dendrolimi reared from natural and factitious hosts, and artificial hosts. Developmental periods from egg to adult of T. dendrolimi reared at 26, 28, 30, and 32°C were 10.9, 9.6, 9.0, 8.6 days, respectively. Emergence rates of T. dendrolimi decreased 78.0, 88.4, 60.7, and 50.1% as temperature increased. The progeny sex ratios (i.e., females per male) were 7.3, 8.4, 8.2 and 6.9 at the respective temperatures. When adult T. dendrolimi emerged from A. pernyi eggs were kept in dark conditions for storage at different temperatures for 34 days, their mortality increased as temperature increased: 0% at 0°C; 10% at 4°C; 40% at 6°C; 50% at 18°C and 100% at ≥26°C. The fecundity of T. dendrolimi reared from three different hosts was investigated on D. spectabilis eggs. During the first day, the adult T. dendrolimi reared on A. pernyi eggs laid most eggs (99.0±10.7), followed by those reared on artificial hosts (76.6±24.5) and D. spectabilis eggs (63.4±35.9). Over the entire lifespan, T. dendrolimi reared on D. spectabilis eggs produced the highest number of eggs (218.0±27.9), followed by A. pernyi eggs (104.0±44.7) and artificial host (98.2±37.1). These results suggest that the temperature and three hosts factors had an effect on rearing of the T. dendrolimi on the factitious host, A. pernyi eggs.     

δ18O‐derived incubation temperatures of oviraptorosaur eggs

In order to determine the incubation temperature of eggs laid by non‐avian dinosaurs, we analysed the oxygen isotope compositions of both eggshell carbonate (δ¹⁸O_c) and embryo bone phosphate (δ¹⁸O_p) from seven oviraptorosaur eggs with preserved in ovo embryo bones. These eggs come from the Upper Cretaceous Nanxiong Formation of Jiangxi Province, China. Oviraptorosaur theropods were selected because of their known brooding behaviour as evidenced by preserved adult specimens fossilized in brooding posture on their clutch. Incubation temperature of these embryos was estimated based on the following considerations: eggshell δ¹⁸O_c value reflects the oxygen isotope composition of egg water fluid; embryo bones precipitate from the same egg fluid; and oxygen isotope fractionation between phosphate and water is controlled by the egg temperature. A time‐dependent model predicting the δ¹⁸O_p evolution of the embryo skeleton during incubation as a function of egg temperature was built, and measured δ¹⁸O_c and δ¹⁸O_p values used as boundary conditions. According to the model outputs, oviraptorosaurs incubated their eggs within a 35–40°C range, similar to extant birds and compatible with the known active brooding behaviour of these theropod dinosaurs. Provided that both eggshell and embryo bones preserved their original oxygen isotope compositions, this method could be extended to investigate some reproductive traits of other extinct groups of oviparous amniotes.     

Impacts of declining water levels on the quantity of fish habitat in coastal wetlands of eastern Georgian Bay,Lake Huron

The aim of this study was to examine whether the presence of non-toxic filamentous cyanobacteria can cause egg abortion in Daphnia. To test this hypothesis, we fed females of Daphnia pulicaria with the green alga Scenedesmus obliquus from birth until eggs were laid in the brood chamber. Gravid Daphnia females were then exposed to media containing either S. obliquus or filaments of a non-toxic strain of the cyanobacterium Cylindrospermopsis raciborskii. The females were then observed throughout the whole period of egg development and all events of egg abortion were recorded. Experiments were conducted at three temperatures: 16, 20, and 24°C. In the presence of cyanobacteria, the proportion of aborted eggs ranged from 2.6 to 12.9%, compared with 0–1.8% in the green algae treatment. The number of aborted eggs, but not the number of egg-aborting females, tended to increase at higher temperature. Our data indicate that interference by non-toxic cyanobacterial filaments may affect the reproductive success of Daphnia, not only through suppression of their fecundity, but also via an increase in the number of aborted eggs. Therefore, the reproductive rate of Daphnia based on the fecundity of females may be overestimated in situations where filamentous cyanobacteria are present.     

Reproductive bionomics of the soft tick, Ornithodoros turicata (Acari: Argasidae)

The effects of different temperatures and relative humidities (RHs) were tested on various reproductive parameters of Ornithodoros turicata, an argasid tick that inhabits gopher tortoise burrows in Florida, USA. The pre-oviposition, oviposition and incubation periods of the ticks decreased as temperature increased. These periods were also affected by the RH. The number of eggs oviposited was affected significantly by the combined effect of temperature and RH. Fewer eggs were laid by ticks in the 24°C regimes and the 27°C/95%RH regime compared to those in the other temperature/RH groups. There was an inverse relationship between the number of eggs oviposited and the percentage of hatched larvae that was correlated with the temperature and RH. Ticks reared at 27°C/90%RH and 30°C/90%RH laid more eggs than those reared in the other combinations of temperature and humidity but fewer larvae hatched from these eggs. The reproductive fitness index (RFI) values were highest in females held in the 24°C groups and the 30°C/95%RH group, although significantly more larvae hatched at the lower temperatures. The optimum reproductive conditions for O. turicata under laboratory conditions appear to be 24°C and 90–95%RH. While mating occurred at all temperatures, none of the females laid eggs at 22°C. The ticks may move preferentially to low temperatures when not feeding to remain above the critical equilibrium humidity and/or below the critical metabolic level necessary for prolonged survival. However, most female ticks oviposited after 45 days when moved to 27°C/95%RH. Ornithodoros turicata females may have a limited capability to delay oviposition until an optimal microenvironment for egg deposition can be located in the burrow.     

Effects of temperature on the life-history traits of Sancassania (Caloglyphus) berlesei (Acari: Astigmatina: Acaridae) feeding on root-knot nematodes,Meloidogyne spp. (Nematoda: Meloidogynidae)

Sancassania (Caloglyphus) berlesei (Michael) is a cosmopolitan and free-living mite that inhabits soil as well as laboratory colonies of insects and fungi and may have a role as a biocontrol agent of nematodes. In this study, we investigated the effects of temperature on the development, reproduction, and food consumption of S. berlesei fed egg masses of root-knot nematodes, Meloidogyne spp., an important group of agricultural pests. Mites were reared at 20, 25 or 30 °C in the dark. The mites could feed on the nematode egg masses, and their developmental time decreased at higher temperatures. Time from the egg to adult was similar in females and males reared at the same temperature. Adult females lived longer than males at 25 °C, but not at 20 or 30 °C. Generally, females showed a higher rate of food consumption than males. Females laid the largest number of eggs at 20 and 25 °C (199.7 and 189.8 eggs/female, respectively), but the intrinsic rate of natural increase was highest at 30 °C (r _m = 0.29). In comparing our data with previous reports, we noted that S. berlesei that fed on egg masses of root-knot nematodes showed a longer developmental time and a lower reproductive rate than Sancassania mites that fed on other diets. Nonetheless, the relatively high value of r _m (e.g., at 25 and 30 °C) suggests that this mite may have certain advantages as a biocontrol agent of root-knot nematodes.     

Field and laboratory studies on the effects of temperature on the development of the carrot fly (Psila rosae F.)

The thermal requirements for the pre-oviposition period, egg, larval, pupal and adult stages of the carrot fly were measured under field conditions and at a range of constant temperatures in the laboratory. In the laboratory, the pre-oviposition period lasted from 4 days at 24^oC to 28 days at 9^oC. In general, female carrot flies laid about 20–40 eggs in each batch. Once the first eggs had been laid, subsequent batches were laid after an average of 3 days at 24^oC to 7 days at 11.5^oC. The numbers of days required for egg, larval and pupal development ranged from 5, 31 and 24 days respectively at 21.5^oC to 25, 145 and 84 days respectively at 9^oC. Under laboratory conditions, complete development from egg to adult required from 60 days at 21.5^oC to 254 days at 9^oC. Newly-formed carrot fly pupae were exposed to temperatures of 22–30^oC for various 5–10 day periods during pupal development. Exposure to temperatures of 24^oC and 26^oC caused some, and exposure to 28^oC and 30^oC caused all, of the pupae to delay development. Pupae were sensitive to high temperatures only for approximately 4–10 days after pupation. Under field conditions between mid-May and early September, full carrot fly development (egg-adult) took 84–100 days. The numbers of day-degrees required (base temperatures of 2^oC and 4^oC) for carrot fly development in the laboratory and in the field were similar for egg hatching but not for the pre-oviposition period or for egg-adult development. The thermal requirement for fly development in the field varied between inoculation dates, fewest day-degrees being required when development was rapid.     

Culture of naked quail (Coturnix coturnix japonica) ova in vitro for avian transgenesis: Culture from the single-cell stage to hatching with pH-adjusted chicken thick albumen

We first examined the pH change of the albumen of quail (Coturnix coturnix japonica) eggs before and after they were laid, as well as that of laid eggs. The pH rose rapidly after laying and continued to increase gradually in storage. Incubation at 37.5°C accelerated the increase in the pH of infertile eggs, while that of fertile eggs remained low during incubation. Referring to these results, we obtained a protocol for producing quail hatchlings by culture in vitro from naked ova. The naked ovum was filled with chicken (Gallus domesticus) thick albumen, the pH of which had been adjusted to 7.2–7.4. The ovum was cultured at 41.5°C in 20% CO₂ in air for the first 24 h. Then the embryo was moved to a surrogate quail egg shell that had been filled with non-pH-adjusted chicken thin albumen and cultured for a further 48 h in 100% air. The embryo was transferred again to a surrogate chicken egg shell and cultured under the same conditions until hatching. The culture yielded quail chicks with a hatchability of 19.4%. The method proposed here should be applicable to the production of transgenic birds.     

Summer dormancy ensures univoltinism in the predatory bug Picromerus bidens

The seasonal cycle of Picromerus bidens L. (Heteroptera: Pentatomidae) is usually considered to be univoltine with an obligatory winter egg diapause. Seasonal adaptations of the species were studied in the laboratory and in field experiments. When reared under short-day photoperiodic conditions (L12:D12 and L14:D10), all females began to lay eggs synchronously soon after their emergence. However, in the females reared under long-day conditions (L18:D6 and L20:D4) and outdoors in June–July, oviposition was significantly delayed. This delay in reproduction induced by photoperiodic conditions and then spontaneously terminated was considered to be aestivation. Egg batches laid by females in the laboratory and in the field were kept at 25 °C for two months. From 30.8 to 93.8% of batches contained eggs which hatched without cold treatment between day 14 and 60 after oviposition. The proportion of eggs hatched was 17.7 to 20.9% in the short-day regimes, while it was significantly less (5.7 to 6.0%) under long-day conditions. It is concluded that in some eggs diapause is of low intensity and that if under natural conditions the first batches had been laid at the end of June, nymphs would have hatched at least from some eggs during the same season even without cold treatment. Such untimely hatching would have resulted in the death of nymphs and adults unprepared for overwintering. A photoperiodic response which induces aestivation in the early emerging adults in June–August may prevent early oviposition and occurrence of a second generation and thus maintains univoltinism in P. bidens.     

Environmental control of the seasonal life cycle of a zoophytophagous mirid, <Emphasis Type="Italic">Adelphocoris triannulatus</Emphasis> (Hemiptera: Miridae)

Adelphocoris triannulatus (Stål) (Heteroptera: Miridae) is a zoophytophagous bug that inhabits grasslands and crop fields, and is widely distributed in eastern Asia. In this study, the seasonal occurrence and environmental factors controlling the seasonal life cycle of this bug were investigated in a local population in southern Kyushu, Japan. When insects were reared under different photoperiods at 20 and 25 °C, they produced diapause or nondiapause eggs depending on the photoperiod: when reared under short-day photoperiods (≤?13 h/day), females laid diapause eggs, whereas they laid nondiapause eggs when reared under long-day photoperiods (≥?14 h/day). Because the developmental duration of the pre-adult stages and maturation (minimum duration of one generation) is estimated to be approximately 30 days at summer temperatures, these results suggest that this bug has a multivoltine seasonal life cycle. In agreement with the laboratory results, only nondiapause eggs were produced until mid-August in the field, and an increasing proportion of diapause eggs were produced from early September. In addition to these findings, field sampling from spring to autumn in 2009 indicated that three or four generations were produced in one year. These results suggest that egg diapause plays a role in preventing nymphs of A. triannulatus from developing in winter, and thereby ensures the survival of the population in adverse seasons.