An analysis of diapause and resistance in the egg stage of Floronia bucculenta (Araneida: Linyphiidae)

Summary Floronia bucculenta hibernates in the egg stage; the egg sacs are deposited on the leaves of grass tussocks without any shelter. The morphogenesis of the eggs was divided into 10 arbitrarily chosen stages, in order to test the dependence of embryonic development on temperature in the laboratory. The eggs developed slowly at 23°C, 16°, 12.5°; embryogenesis stopped after 70–45 days, when prosomal appendage rudiments began to form. At 10°, 7.5°, 5°, 0° complete embryogenesis was possible until the emergence of the first complete stage. The eggs developed most rapidly at 5° (mean developmental time 203 days). The egg development was normal at 5° and 0°, when compared with the timetable of the embryogenesis of the linyphiid Bathyphantes gracilis, a species which has no egg diapause. At 7.5° and 10° the embryogenesis was strongly delayed during the median phases of development (elongation of the germ band, formation of prosomal appendages); after reversion the development was accelerated (postdiapause phase). After long exposure to low temperatures (-10° to +10°) the diapause was terminated. A temperature of 0° was optimal (minimal time of exposure 8–9 weeks). The time required for embryonic development of postdiapause eggs decreased hyperbolically with increasing temperature. In the field the median phases of embryogenesis were retarded by low ambient temperatures; diapause was terminated from late December to mid-January. The spread of hatching in spring was 7–15 days.During the diapause phase the O₂-consumption of the eggs at 25° was depressed. It rose from 1.55 (in late diapause) to 4.21 ml/100 eggs·h at the onset of postdiapause, whereas O₂-utilization did not change significantly at 5° (from 0.54 to 0.61 ml/100 eggs·h just after the termination of diapause).The diapause phase was not characterized by higher resistance to cold, drought, or flooding. As compared with single eggs removed from the cocoon, the silken wall of the intact egg sac did not affect the survival of postdiapause eggs exposed to-15° (LD₅₀=28 days); it raised, however, the survival time of eggs exposed to a R.H. of 32% (at 5°) or flooding by distilled water (at 5°): from LD₅₀=37 to 68 days at drought, from LD₅₀=30 to 92 days at flooding.Diapause is important for synchronizing the life-cycle of F. bucculenta with the seasonal fluctuations of environment. The egg stage is highly tolerant to the extreme factors of the winter. Some implications of the relation of the studied spider to its habitat are discussed.     

Effects of compound eye-removal on the photoperiodic response of the band-legged ground cricket, Pteronemobius nigrofasciatus

The band-legged ground cricket Pteronemobius nigrofasciatus shows a clear photoperiodic response at 25°C with respect to the control of the induction of embryonic diapause. When crickets were reared under a short-day (LD 12 12) photoperiod and then transferred to a long-day (LD 16 8) photoperiod upon adult emergence, the adults mainly laid nondiapause eggs. However, adults maintained continuously under short-day conditions laid dispause eggs. When compound eyes were bilaterally removed after adult emergence, the crickets mainly laid nondiapause eggs, irrespective of the photoperiod. Thus, the adults completely lost their sensitivity to photoperiod after bilateral removal of their compound eyes. Unilateral removal of the compound eye also affected the crickets under a short-day photoperiod, and the incidence of diapause eggs was intermediate between that laid by intact adults and that laid by adults after the bilateral removal of compound eyes. The incidence of diapause eggs in sham-operated crickets was not significantly different from that in intact crickets under both sets of photoperiodic conditions. These results show that P. nigrofasciatus perceives the photoperiod through its compound eyes.     

Effect of hydration,photoperiod and temperature on diapause termination in eggs ofPetrobia (Tetranychina) harti (Acari: Tetranychidae)

Petrobia harti (Ewing) displays a facultative summer diapause in the egg stage. An adult female will lay only either diapause or non-diapause eggs throughout her life. In the laboratory, diapause eggs are laid by females which develop on detachedOxalis articulata leaves under long-day photoperiods and a relatively low temperature of 19±1°C.Diapause occurs in a stage of advanced embryonic development, in which the embryo appears U-shaped when observed from the egg's ventral side. Embryonic development ceased at this stage, and no further growth occurred when the eggs were kept under a relative humidity of about 70% in various photoperiod and temperature conditions. However, when the eggs were hydrated by placing them on wet cotton wool, development in some embryos (apparently in those which had completed their diapause development) proceeded beyond the U-stage at a rate similar to that in non-diapause embryos and the eggs hatched.Under LD 168 and 19±1°C or 26±1°C, the later from oviposition the period of egg hydration started, the higher the percentage of diapause termination. Under LD 168 and 26±1°C, diapause termination occurred mostly during the first week of hydration, while at 19±1°C mostly during the second and third week.At 26±1°C, in eggs hydrated 15 days but not 30 days from oviposition, the percentage of diapause termination was higher under a long-day than under a short-day photoperiod.Under LD 168, when the eggs were hydrated continuously from oviposition or starting 15, 30 and 45 days from it, the percentage of diapause termination was higher at 26±1°C than at 19±1°C.The percentage of diapause-laying adult females and the intensity of egg diapause were higher when the pre-imaginal mites grew at LD 1212 and 19±1°C, than when they grew at LD 168 and 26±1°C. This maternal effect on egg diapause intensity was expressed when the eggs were maintained at LD 1212 and 19±1°C but not at LD 168 and 26±1°C.     

Influences of daylength and temperature on the period of diapause and its ending process in dormant larvae of burnet moths (Lepidoptera,Zygaenidae)

The onset of larval diapause in the burnet moth Zygaena trifolii is clearly characterized by the larva molting into a specialized dormant morph. In a potentially bivoltine Mediterranean population (Marseille) two types of diapause can occur within 1 year: firstly, a facultative summer diapause of 3–10 weeks, and secondly, an obligate winter diapause, which can be lengthened by a period of thermal quiescence to several months in temperatures of 5°C. For the first time, three successive physiological periods have been experimentally distinguished within an insect dormancy (between onset of diapause and molting to the next non-diapause stage), using chilling periods of 30–180 days at 5°C, and varying conditions of photoperiod and temperature. These stages are: (1) a continuous Diapause-ending process (DEP); (2) thermal quiescence (Q); and finally, (3) a period of postdiapause development (PDD) before molting to the next larval instar. The result of transferring dormant larvae from chilling at 5°C to 20°C depended on the length of the chilling period. After chilling for 120–180 days, molting to the next instar occurred after 6–10 days, independent of daylength. This period corresponds with the duration of PDD. After shorter chilling periods (90, 60, 30 days and the control, 0 days) the period to eclosion increased exponentially, and included both the latter part of the previous diapause process and the 6–10 day period of PDD. However, photoperiod also influences the time to eclosion after chilling. Short daylength (8 h light / 16 h dark: LD 8/16) lengthened the diapause in comparison to long daylength (16 h light / 8 h dark: LD 16/8). Short daylength had a similar effect during chilling at 5°C, as measured by the longer time to eclosion after transfer. The shorter time to eclosion resulting from longer chilling periods (30–90 days) demonstrates that the state of diapause is continuously shortened at 5°C, and corresponds to the neuroendocrine controlled DEP. Presumably the DEP has already started after the onset of diapause. When chilling was continued after the end of the DEP, which ranged between 90 and 120 days, thermal quiescence (Q) followed (observed maximum 395 days). Different photoperiodic conditions during the pre-diapause inductive period modified diapause intensity (measured as the duration of diapause), in that a photoperiodic signal just below the critical photoperiod for diapause induction (LD 15/9) intensified diapause. Experiments simulating the summer diapause showed that PDD occurred in the range of 10–25°C. Higher temperatures (15 and 20°C) shortened the DEP at LD 16/8, so that at 20°C many individuals had already terminated diapause after 10–40 days and had molted after the 6–10 days of PDD. A temperature of 25°C unexpectedly lengthened the DEP to 110 days in several individuals. The ecological consequences and the adaptive significance of variation in the duration of the diapause are discussed in relation to the persistence of local populations predictably variable and rare climatic extremes throughout the year.     

Diapause Induction and Termination in Eggs of the Fruit Tree Red Spider Mite Panonychus Ulmi in Northern Greece

In apple orchards in northern Greece, females of Panonychus ulmi Koch were found to lay diapause eggs from late August to the beginning of October. The course of diapause termination in the field was determined by transferring diapause eggs during winter and early spring from apple orchards with the varieties Starkinson and Firiki to short days (LD 8:16) (1992–1996), and long days (LD 16:8) (1994–1995), both at 20 °C. Percentages of diapause termination were very low to zero from October to the beginning of January, then progressively increased throughout January and February. Diapause termination in 50% of the eggs occurred in the first half of February in lowland mite populations irrespective of the year and location from which the eggs originated, and about one month earlier in a population originating from an altitude of 300 m. For each sampling date throughout the winter, the mean number of days required for 50% egg hatch at 20 °C (T_50%) was similar under either a long (LD 16:8) or a short (LD 8:16) photoperiod. Diapause eggs collected in October 1995 from two orchards and maintained at 0, 5, 10 and 15 °C for various periods were subsequently transferred to 20 °C and LD 8:16, where TP_50% was determined. It was shown that temperature, duration of maintenance at the different temperatures and the orchard from which the eggs originated had a significant effect on T_50% and therefore on diapause development. Additionally, in our strains diapause intensity was much weaker than in strains from more northern latitudes and was terminated even without any cold exposure. The variation in diapause intensity in different strains of P. ulmi may have an adaptive significance for this widespread species.     

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.     

Biology of <Emphasis Type="Italic">Dermacentor silvarum</Emphasis> (Acari: Ixodidae) under laboratory conditions

The minimum life cycle of Dermacentor silvarum Olenev had a mean duration of 87.5 days (range 74–102 days) under laboratory conditions [(27±1 °C), 70% RH, 6 L: 18 D]. The mean time in (days) for the different stages of its cycle was as follows: incubation period of eggs was 15.3 days; prefeeding, feeding and premoulting periods of larvae and nymphs averaged 5.5, 4.0 and 7.3 days, and 5.2, 5.0 and 14.6 days, respectively; prefeeding, feeding, preoviposition and oviposition periods of female adults lasted for 7.8, 4.5, 4.3 and 14.0 days, respectively. There existed a highly significant correlation between engorged body weight of females and egg masses laid (r = 0.9877, p<0.001). The reproductive efficiency index (REI) and reproductive fitness index (RFI) in females were 11.09 and 9.58, respectively. No relationship between nymphal engorged body weight and resultant sexes was observed. Delayed feeding and non-oviposition (in June and July) existed in females, and low temperature (−10 °C) treatment for 45 days could terminate oviposition diapause. However, the egg masses laid by post-diapause females were significantly smaller than those laid by females engorged in March, April and May.     

Effects of temperature on the rates of oxygen consumption during morphogenesis and diapause in the egg stage of Letopterna dolobrata (Heteroptera,Miridae)

Summary Oxygen consumption at 25°C was measured continously throughout the egg stage of Leptopterna dolobrata (more than 9 months).The rate of O₂-uptake (l O₂/100 eggs · 1 h) is low in freshly laid eggs. Maintaining the eggs at a constant temperature of 16°C, respiration rises abruptly from the first day after oviposition and continues rising steadily for 3 days, reaching an average value of 1.4 l. Oxygen consumption persists at or near this high level during the developmental phase of prediapause, which lasts about 15 days. After some days of oscillating high and low values, respiration decreases, and from the 24th day a low level (0.3–0.4 l) is reached. If the eggs are incubated at 16°C continuously, this low diapause-level is maintained until the end of the experiments (42 weeks) and diapause is terminated in a few eggs only.A significant increase in the success of hatching is obtained by exposing the eggs to a sufficient period of chilling.24 groups of diapausing eggs were chilled at 5°C for certain periods (10, 18, 22, 26, 31, and 34 weeks) and afterwards transferred to 16°C and re-incubated. The changes of their O₂-uptake at 25°C were traced throughout their chilling and successive re-incubating periods.Oxygen consumption is greatly accelerated during the cold treatment of the eggs. The low values of the diapause-level are raised progressively during the first 6 weeks of chilling. After this primary rapid increase, respiration remains at a level 5-times as high as the diapause values over a period up to the 25th week at 5°C. This is almost exactly the duration of mesodiapause (6 months).The rates of O₂-uptake during the subsequent re-incubation at 16°C depend on the extent of chilling. The ability of diapause-breaking is correlated to the rates of O₂-uptake, measured after setting of re-incubation. If respiration never decreases by the onset of re-incubation, diapause is terminated in most of the eggs, and the rates of O₂-uptake increase as re-incubation goes on towards the emergence of the larvae (postdiapause period).A preliminary interpretation of the cold-stimulated O₂-uptake in diapausing Leptopterna-eggs is given.Dedicated to Prof. Dr. H. Precht (Kiel) on the occasion of his 65th birthday     

Bi- and trivoltine complex life cycles in a Kanto (Japan) population of a wild bruchid Kytorhinus sharpianus

The partial trivoltinism and overwintering of Kytorhinus sharpianus Bridwell (Coleoptera: Bruchidae) was studied in the Kanto district, Japan. The later in the summer eggs were laid by the first-generation adults, the higher was the incidence of larval diapause in the second generation. The incidence of diapause also fluctuated between years, influencing the abundance of third-generation larvae. A relatively large proportion of third-generation larvae did not attain the diapause stage by the beginning of winter. The diapause development of larvae in diapause was completed by mid-January. Immature larvae of the third generation also overwintered and emerged as adults in the spring.     

Antifeedant tests with larvae of Pseudaletia unipuncta: variability of behavioral response

The egg development of the African bushcricket Ruspolia differens is shown to be direct, without any delay, and to be highly synchronised. It is also strongly temperature dependent and closely fits the thermal summation equation Days=(T°C–14.8)/252, even if incubation temperatures (T) are changed during the course of development. In contrast egg development in the closely related Southern European Ruspolia nitidula is subject to a form of diapause after anatrepsis but its other developmental characteristics are very similar to R. differens. Diapause in R. nitidula may disappear in time without change of temperature and is thus unlike any diapause reported for other Tettigoniidae. Chilling diapausing eggs progressively synchronises and advances hatching, the full effect being achieved in 8 weeks at 8°C. Development in post-diapause eggs is independent of diapause treatment.The effect of partial cooling is clearly shown by the bimodality of hatching curves and a method of analysing and comparing these is discussed.The diapause syndrome acquired by R. nitidula is seen as a method by which this one species of a primarily tropical genus has been able to move into temperate zones. The role of this type of diapause in the phenology of R. nitidula is discussed.

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Zusammenfassung Die Eientwicklung der afrikanischen Laubheuschrecke Ruspolia differens (Orthoptera, Tettigoniidae) verläuft direkt, ohne Verzögerung, und ist sehr gut sychronisiert. Sie ist streng abhängig von der Temperatur und entspricht gut der Wärmesummenregel Tage=(T°C–14,8)/252 und zwar sogar dann, wenn die Zuchttemperatur (T) während der Entwicklung verändert wird. Im Gegensatz dazu durchläuft die Eientwicklung der nah verwandten südeuropäischen Ruspolia nitidula eine Art Diapause nach der Anatrepsis. Die übrigen Entwicklungsschritte sind sehr ähnlich mit R. differens. Die Diapause kann bei R. nitidula rechtzeitig ohne Temperaturwechsel verschwinden. Damit unterscheidet sie sich von den übrigen bei Tettigoniiden beschriebenen Diapauseformem. Durch Abkühlen wird das Schlüpfen diapausierender Eier synchronisiert und beschleunigt und zwar wird der volle Effekt nach 8 Wochen bei 8^o erreicht. Die Etwicklung der Nachdiapauseeier ist unabhängig von der Diapauseent-wicklung.Der Effekt partieller Kühlung wird klar ersichtlich aus der Bimodalität der Schlüpfkurven. Eine Methode zur Analyse und zum Vergleich der Kurven wird diskutiert. Das Diapauseverhalten, das sich R. nitidula erworben hat, kann als Methode betrachtet werden, mit der eine vorwiegend tropische Art in gemässigte Zonen vordringen konnte.

     

The influence of environmental factors on dormancy and duration of egg development in Metrioptera roeseli (Orthoptera: Tettigoniidae)

Summary Developing eggs of Metrioptera roeseli HGB. have an obligate embryonic diapause in stage 23 and a facultative initial diapause in stage 4. Initial diapause is lacking when the ovipositing females are kept at long day photoperiod (LD 16/8), but is induced at LD 14/10 and LD 8/16. When natural light conditions are given in the laboratory, the females mostly lay diapausing eggs from the end of August onwards. In eggs without initial diapause, a larger number of embryos reach a stage, in which the embryonic diapause can be broken by chilling, only at favorable temperature (4 weeks at 24°C or 8 at 18°C) and in contact with water before the first winter. Thus, some individuals of a given population of M. roeseli have an annual, others a biennial life cycle. The variability in the duration of egg development is due to a photoperiodically induced, facultative initial diapause and to a possible quiescence caused by insufficient temperature and/or moisture.     

Reproduction of the calanoid copepod Calanus propinquus in the southern Weddell Sea,Antarctica: observations in laboratory

Reproduction of the dominant Antarctic copepod Calanus propinquus was studied in February–April, 1989 aboard the R.V Dmitry Mendeleev during cruise N° 43 to the Weddell Sea. Single females were kept at 0 °C in the laboratory for 56 days with abundant food concentration (above 300 µg C l^–1 of Platymonas viridis). Females released clutches at night at 2–3 day intervals. Most clutches contained from 10 to 40 eggs, mean 37.3 eggs female^–1. Average carbon content of an egg was 0.37 ± 0.05 µg C. The maximum daily egg production rate of 30–50 eggs female^–1 d^–1 was observed for the first 3 days of the laboratory incubation, corresponding to 3.7–6.2% body C. The state of gonadal development of females showed the decline of the reproductive season in late February. The data suggest that egg laying in the region under study starts in December and lasts until March. The state of ovarian maturation, changes in vertical distribution and biochemical body composition of females suggest the possibility of two-year life cycle in C. propinquus in the southern Weddell Sea.     

Daily egg production ofTemora longicornis (Copepoda,Calanoida) during winter and early spring in the Marsdiep (Southern North Sea)

Mature females of the copepodTemora longicornis from the Marsdiep tidal inlet were incubated at ambient water temperature during the winter of 1989/1990 to estimate their egg production during 24 hours. Throughout winter this production remained at a level of 0 to 10 eggs per female. In March a steep rise to 60 to 80 eggs coincided with an equally steep rise in chlorophyll-a from 4 to 20 g.l^–1. Excess food given during incubation tended to increase the observed production rate only in October at relatively high temperature. Additive effects of rising food level and temperature on daily egg production were found in spring. In March and April 1988 and 1990 the observed maximum daily egg production per female increased from about 20 at 5°C and 5 g.l^–1 chlorophyll to 70 at almost 10°C and 20 g.l^–1. The egg production in winter gives a prebloom potential to maintain a stock of premature stages ready to utilize the algal spring bloom. Early spawning before April can also contribute to the development of the abundance peak of adults in May–June. Due to growth rates increasing with temperature in the months March and April, most of the adults at their peak density may have hatched from eggs before the period of maximum egg production rate at the end of April. The exceptionally high production rate observed at the end of March may be related to a developingPhaeocystis bloom.     

Impact of increasing temperatures and exposure duration on egg hatch in the hemlock looper,Lambdina fiscellaria

As the growing season is expected to begin earlier under climate change, insects should initiate reproduction several days or weeks earlier than they used to. In eastern Canada, hemlock looper (HL) Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae) females generally oviposit in September, with eggs entering an obligatory diapause quickly after their deposition. We therefore simulated an early start of the HL reproduction cycle of 2, 4, 6, or 8 weeks to examine the extent to which freshly laid eggs from two populations (island and mainland) can withstand exposure to four temperature conditions (15, 20, 25 °C, or fluctuating temperature in an outdoor insectary), with all treatments ending on 1 September 2007. On this date, half the eggs from each population were immediately incubated at 15 °C, while the rest were stored in an outdoor insectary until their incubation at 15 °C the following spring. In a separate experiment, the effect of temperature on pre‐diapause duration was determined from the number of days required for eggs to change colour after oviposition. The pre‐diapause phase was completed faster as temperature increased. Regardless of incubation date and population, percent hatch decreased significantly after 6‐8 weeks of exposure to 25 °C or in the outdoor insectary. Under most treatments, the odds of dying as pharate larvae increased with exposure duration. When eggs were incubated at 15 °C immediately after treatment, time to hatch and diapause duration remained constant over treatments, except at 25 °C when they both decreased. After 8 weeks of exposure to 15 or 20 °C, eggs transferred outdoors were more likely to hatch precociously than those exposed to 25 °C or insectary conditions. Globally, mortality seemed greater among eggs stored outdoors than among those kept indoors. Most eggs that survived the winter hatched synchronously after incubation in spring. Overall, larger eggs from the island population survived better than smaller eggs from the mainland population.     

The effect of abiotic factors on foraging and oviposition success of the aphid parasitoid,Aphidius rosae

Searching patterns and oviposition success of the aphid parasitoid Aphidius rosae were analysed in different abiotic conditions (simulated wind, simulated drizzling rain, simulated shower, high temperature, low humidity, standard conditions) in the laboratory. Residence times, time allocation and oviposition success did not differ significantly between females foraging on rose shoots during periods with high temperature (>33°C) and low humidity (35%–40% relative humidity) and females searching under standard laboratory conditions (20°C, 65%–70% relative humidity, no wind). A wind speed of 2 m/s reduced the oviposition numbers significantly, and females spent much more time resting than searching for hosts. Females did not leave a shoot during wind, but departed quickly after wind had ceased. Simulated drizzling rain or simulated showers had the strongest effects on A. rosae foraging. Both types of rain prevented all foraging activities including departure from the shoot, and females laid no eggs during rain. After rain had stopped, females were mainly engaged with cleaning themselves and laid relatively few eggs compared to standard conditions. The impact of unfavourable abiotic environmental factors like wind or rain may help to explain why many parasitoids lay only a small proportion of their available eggs when foraging in the field.     

The effect of cold temperature exposure and long-day photoperiod on the termination of the reproductive diapause of newly emerged female Pissodes strobi (Coleoptera: Curculionidae)

Abstract

• 1 There is confusion in the literature concerning a possible reproductive diapause in the adult white pine weevil Pissodes strobi.
• 2 We evaluated the effects of temperature, photoperiod, feeding substrate and mating status on the sexual maturation and oviposition of female white pine weevils.
• 3 Less than 30% of female P. strobi became sexually mature and laid eggs without experiencing dormancy under a temperature regime of 2 °C for 4 weeks.
• 4 Among the females that experienced a cold temperature treatment after emergence, 80% laid eggs after dormancy when exposed to a long‐day (LD 16 : 8 h) photoperiod and 17.6% laid eggs when exposed to a short‐day (LD 8 : 16 h) photoperiod.
• 5 Significantly more eggs were laid by all the females (with and without a cold treatment) when subjected to a long‐day photoperiod compared with a short‐day photoperiod.
• 6 A period of cold temperature followed by exposure to a long‐day photoperiod with warmer temperatures is required to break reproductive diapause and to obtain a good oviposition response in female P. strobi.
• 7 This study reveals the existence of much intraspecific variation in the response of the white pine weevil to temperature and photoperiod with respect to the induction and termination of reproductive diapause.

     

Biology of Dermacentor silvarum (Acari: Ixodidae) under laboratory conditions

The minimum life cycle of Dermacentor silvarum Olenev had a mean duration of 87.5 days (range 74–102 days) under laboratory conditions [(27±1 °C), 70% RH, 6 L: 18 D]. The mean time in (days) for the different stages of its cycle was as follows: incubation period of eggs was 15.3 days; prefeeding, feeding and premoulting periods of larvae and nymphs averaged 5.5, 4.0 and 7.3 days, and 5.2, 5.0 and 14.6 days, respectively; prefeeding, feeding, preoviposition and oviposition periods of female adults lasted for 7.8, 4.5, 4.3 and 14.0 days, respectively. There existed a highly significant correlation between engorged body weight of females and egg masses laid (r = 0.9877, p<0.001). the=" reproductive=" efficiency=" index=" (rei)=" and=" reproductive=" fitness=" index=" (rfi)=" in=" females=" were=" 11.09=" and=" 9.58,=" respectively.=" no=" relationship=" between=" nymphal=" engorged=" body=" weight=" and=" resultant=" sexes=" was=" observed.=" delayed=" feeding=" and=" non-oviposition=" (in=" june=" and=" july)=" existed=" in=" females,=" and=" low=" temperature=" (−10 °c)=" treatment=" for=" 45 days=" could=" terminate=" oviposition=" diapause.=" however,=" the=" egg=" masses=" laid=" by=" post-diapause=" females=" were=" significantly=" smaller=" than=" those=" laid=" by=" females=" engorged=" in=" march,=" april=" and=">     

The Insect Growth Regulator Pyriproxyfen Terminates Egg Diapause in the Asian Tiger Mosquito,Aedes albopictus

The Asian tiger mosquito, Aedes albopictus, is a highly invasive mosquito species that transmits chikungunya and dengue. This species overwinters as diapausing eggs in temperate climates. Early diapause termination may be a beneficial strategy for winter mosquito control; however, a mechanism to terminate the diapause process using chemicals is not known. We tested the hypothesis that a hormonal imbalance caused by the administration of juvenile hormone analog would terminate egg diapause in A. albopictus. We tested the insect growth regulator pyriproxyfen on all developmental stages to identify a susceptible stage for diapause termination. We found that pyriproxyfen treatment of mosquito eggs terminated embryonic diapause. The highest rates of diapause termination were recorded in newly deposited (78.9%) and fully embryonated (74.7%) eggs at 0.1 and 1 ppm, respectively. Hatching was completed earlier in newly deposited eggs (25–30 days) compared to fully embryonated eggs (71–80 days). The combined mortality from premature diapause termination and ovicidal activity was 98.2% in newly deposited and >98.9% in fully embryonated eggs at 1 ppm. The control diapause eggs did not hatch under diapausing conditions. Pyriproxyfen exposure to larvae, pupae and adults did not prevent the females from ovipositing diapausing eggs. There was no effect of pyriproxyfen on diapausing egg embryonic developmental time. We also observed mortality in diapausing eggs laid by females exposed to pyriproxyfen immediately after blood feeding. There was no mortality in eggs laid by females that survived larval and pupal exposures. In conclusion, diapausing eggs were the more susceptible to pyriproxyfen diapause termination compared to other life stages. This is the first report of diapause termination in A. albopictus with a juvenile hormone analog. We believe our findings will be useful in developing a new control strategy against overwintering mosquito populations.     

Resting eggs of the marine rotifer Brachionus plicatilis Müller: development,and effect of irradiation on hatching

Diapause and hatching of Brachionus plicatilis Müller resting eggs were examined through histological and optical approaches. Compound microscope observations on 1% toluidine blue-stained embryo sections suggests that the total number of nuclei in an embryo during the internal diapause period increased from 22 on Day 2 to 39 (each n = 1) on Day 6. The outer layer of embryo membrane gradually thickens from 1.2 (Day 0) to 4.0 µm (Day 8) (each n = 10).Resting eggs that have completed maturation and are in the external diapause period require light for hatching. The threshold of light (halogen lamp) intensity for hatching was estimated to be 4400 lux for 30 min. Hatching rate decreased with longer wavelength irradiation (mercury lamp). Irradiation at more than 350 nm caused 1–25% hatching, but it reached 50–60% at 250–310 nm light. The addition of hydrogen peroxide or prostaglandins (E ₁, E ₂ or F ₂) caused resting egg hatching even in darkness. The production of peroxide in seawater caused by light as well as the oxidation of fatty acid to prostaglandins inside the embryo is a possible mechanism of resting egg hatching.     

Effects of selected physical and chemical treatments of Colorado potato beetle eggs on host acceptance and development of the parasitic wasp, Edovum puttleri

Effects of various physical and chemical treatments of Colorado potato beetle [Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)] eggs on parasitization and development of the egg parasitoid Edovum puttleri (Hymenoptera: Eulophidae) were investigated. UV irradiation did not affect host acceptance but reduced host suitability for UV exposure times 90 min. Susceptibility of host eggs to UV irradiation varied with host age; eggs were most vulnerable to damage from irradiation at 12, 18, and 24 h post-oviposition. The rate of parasitization also was influenced by host age. Percent parasitization was greatest in freshly laid eggs and 24–30 h old eggs. Seventy-seven percent of host eggs frozen at –20 °C (5 min) were parasitized by E. puttleri, but extended exposure of eggs to –20 °C reduced both acceptance and suitability. Host eggs that had been washed with hexane (removal of kairomone and sticky layer) also were parasitized. After 5 min of washing, application of kairomone significantly increased the rate of parasitism (from 74.7% to 88.2%), but with longer periods of washing, kairomone application had no significant effect on percent parasitism. Thus, the sticky material(s) coating the egg did not appear to be essential for parasitization to occur. Our results provide effective methods and times for treating Colorado potato beetle eggs to maximize parasitization and development of E. puttleri.