Temperature tolerance of the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae) in tropical and temperate regions of Asia

Temperature tolerance was investigated in nine populations of Plutella xylostella Linnaeus from tropical and temperate regions of Asia. At all rearing temperatures between 15 and 35 degrees C, no clear differences were observed in female egg production or larval development between tropical and temperate populations. Thus, tropical populations did not show a high-temperature tolerance superior to that of the temperate populations. In all populations, the net reproductive rate (number of new females born per female) largely depended on the number of eggs laid per female, and egg production significantly decreased with increasing temperature (P < 0.001). Larval developmental rate also showed a significant positive correlation with temperature (P < 0.001). Per cent hatch of eggs and larval survival did not show a significant correlation with temperature: hatching was constant between 15 and 32.5 degrees C, but considerably lower at 35 degrees C. Larval survival was similar between 15 and 30 degrees C, appreciably lower at 32.5 degrees C and declined to 0% at 35 degrees C. Based on these results, environmental conditions under which P. xylostella can maintain a high population density throughout the year in tropical and subtropical regions are discussed.     

Variation in the hatching behaviour of Nematodirus battus: Polymorphic bet hedging?

Previous work on the transmission dynamics of Nematodirus battus, an important nematode parasite of farmed ruminants in temperate regions, suggests that it operates a bet-hedging strategy. Hatching of cold-sensitised eggs is concentrated in spring, while alternative hatching of non-cold-sensitised eggs in autumn mitigates the risk of poor conditions for hatching in spring or host absence during peak larval availability. Isolates from Scotland showed much less propensity to hatch without chilling than the previously characterised isolate from southern England. Nematodirus battus eggs from a hill farm in Scotland showed intermediate proportions of non-chilled hatching, perhaps related to unpredictability of climate at higher altitudes. Geographic polymorphism in larval behaviour appears to be present in the form of differing chilling requirements for egg hatching. Since bet-hedging through trait diversification is a plausible and demonstrated strategy for coping with environmental unpredictability, it is a likely target for adaptation to climate change. Predictions of disease epidemiology in a changing climate should incorporate parasite adaptation, but further theoretical and empirical characterisations of likely evolutionary responses are needed before this is possible for the most economically important systems.     

The influence of water and humidity on the hatching of Nematodirus battus eggs

This paper examines the influence of water on the ecology of the eggs of Nematodirus battus, with a view to estimating the importance of including rainfall in mathematical models of parasite abundance. The literature suggests that, under pasture conditions, the availability of moisture is unlikely to be limiting for egg development, while eggs and infective larvae are highly resistant to desiccation. In the presented experiment, eggs that had been kept in salt sludges at 95% and 70% RH and were subsequently put at 15°C produced only a mildly accelerated, but not a mass, hatch, in the first few days after return to water. Eggs kept at higher osmotic pressures died. Mass hatching of infective larvae, described at pasture when spells of rain follow periods of drought, is unlikely to occur as the result of a sudden water influx into eggs. Since water is not necessary for migration of infective larvae from the soil on to grass, such peaks in larval abundance are more likely to arise from the effects of temperature on hatching of eggs.     

Effects of temperature during chilling and pre-chilling periods on diapause and post-diapause development in a katydid, Eobiana engelhardti subtropica

In Eobiana engelhardti subtropica, early laid eggs reach the diapause stage in early autumn. For long periods before winter, the eggs are exposed to temperatures higher than their theoretical lower threshold for development. In contrast, late-laid eggs cannot reach their diapause stage before winter. Our study showed that E. e. subtropica copes with these difficulties via the thermal response involving embryonic diapause. In this katydid, the almost fully developed embryo undergoes an obligatory diapause. When diapause eggs were maintained at a temperature of 20 degrees C or higher, diapause persisted for a long time. Diapause was effectively terminated by temperatures ranging from 1 to 11 degrees C, and hatching occurred successfully at temperatures from 11 to 15 degrees C. In addition to the chilling temperature, pre-chilling temperature modified diapause intensity and hatching time. Diapause eggs hatched earlier after chilling when the pre-chilling temperature was lower, within a range of 14.5-25 degrees C. Thus, the low-temperature requirement for diapause termination prevents early laid eggs from untimely hatching in autumn, and low temperatures before and during winter decrease diapause intensity and shorten the hatching time in the following spring. When eggs were chilled before diapause, they tolerated chilling and averted diapause. Thus, even if eggs encounter low temperatures before diapause, they can hatch in the following spring.     

Temperature-controlled under-water egg dormancy and postflood hatching in Isotoma viridis (Collembola) as forms of adaptation to annual long-term flooding

Summary Incubation experiments with eggs of a population of Isotoma viridis, which is exposed to annual long-term flooding from about April to July, as well as field observations show that temperature controls both, underwater egg dormancy and immediate postflood hatching. The population is located at the Eder Freshwater Reservoir in Germany.If constant experimental temperatures are above 14°C, almost all eggs are nondormant. Dormancy is established at temperatures below 15°C, but embryonic development is completed. Experiments indicate that of the environmental factors that change drastically at the end of submergence (light, turgor pressure, oxygen, a.o.), only temperature acts as a hatching trigger. Hatching of the previously dormant eggs occurs at a constant threshold temperature of 16°C, mainly within 2 to 20 days after temperature elevation, but most of these eggs need even higher temperatures to hatch. Remaining eggs were partly stimulated to hatch by recooling them at 7°C for some days and then rewarming them again.The threshold temperatures observed are unusually high for Collembola and seem to be the result of selection by the special floodplain conditions. During normal years, the surface temperatures of submerged soil usually do not exceed threshold limits before summer drainage. This allows both, protection from under-water hatching and an optimal timing of hatching at the very beginning of the main terrestrial period. The experiments show that above the threshold temperature (in warm summers), individuals can hatch under water and survive submerged for 10–15 days. They can survive even longer in the water habitat, if emergent structures enable them to climb onto the water surface. Furthermore, a considerable polymorphism observed in some hatching properties improves the chance to survive under the unpredictable floodplain conditions.     

Abiotic factors influencing embryonic development, egg hatching, and larval orientation in the reindeer warble fly, Hypoderma tarandi

Wild-caught, tethered females of the reindeer warble fly, Hypoderma tarandi (L.) (= Oedemagena tarandi (L.)), (Diptera, Oestridae) were stimulated to oviposit on hairs of a reindeer hide. Newly laid eggs incubated at constant temperatures and relative humidities hatched within 3 days to 2 weeks, depending on the experimental conditions. Over a range of 7-40 degrees C, hatching only occurred between 20 and 37 degrees C. Eggs held at 100% relative humidity had lower hatchability and longer time to hatch relative to eggs held at 77% relative humidity. The average number of degree-days for hatching was 50.35. Between 20 and 33 degrees C there was a temperature-dependent linear trend in developmental rate, and the proportion of eggs hatching was highest, and least variable, at the mid-temperature ranges. The temperature range found in the natural host micro-habitat where H. tarandi commonly affix their eggs (close to the skin at the base of a host hair) was consistent with the experimental temperature treatments that produced the highest hatching rate. Newly emerged larvae displayed positive thermotaxis, while showing no phototaxic or geotaxic behaviour. Results indicate that constraints of the host environment, coupled with temperature-dependent hatching success, may impose a selective pressure on oviposition behaviour.     

Laboratory studies of factors affecting egg hatch of triops longicaudatus (LeConte) (Notostraca : Triopsidae)

Egg hatch was greatest (78.33%) for eggs not previously desiccated. A reduction in numbers hatched occurred as the relative humidity at which they were dried decreased. Some eggs hatched (0.67–79.33%) at pH levels of 3.10–10.01 with the highest hatch at pH 5.60. Water temperature greatly affected egg hatch. No hatch occurred until temperatures were above 14°C. A constant 29°C significantly inhibited hatching. Egg hatch increased 13.00 to 43.42% as salinity decreased from 2200 to 9.24 micromhos/cm. As little as 13 mm of flooded soil covering the eggs prevented them from hatching for 14 days. Eighteen percent hatch resulted when soil and eggs were redistributed to a 1 mm soil layer. Egg samples from the same parent, even though treated similarly, often hatched at greatly varying rates and only rarely was hatching 100% within a replication.     

Temperature‐mediated survival,development and hatching variation of Pacific cod Gadus macrocephalus eggs

Laboratory‐validated data on the survival, development and hatching responses of fertilized Pacific cod Gadus macrocephalus eggs from the northern Japan stock were determined through an incubation experiment. The optimum temperature for survival until hatching ranged from 4 to 8° C. No significant difference in development rates was found between the populations from Mutsu Bay, Japan, and western Canadian coastal waters even though the samples may belong to different G. macrocephalus stocks. Gadus macrocephalus larvae hatched asynchronously from egg batches despite incubation under the same environment during their development. Both incubation temperature and temperature‐mediated hatch rank affect size and yolk reserve. These data suggest that variations in water temperatures within an ecological range markedly influence the development rates, survival and hatching of the eggs, as well as the stage at hatch larvae of G. macrocephalus. Asynchronous hatching and the production of offspring with variable sizes and yolk reserves are considered evolutionary bet‐hedging strategies that enable the species to maximize their likelihood of survival in an environment with variable temperatures.     

不同温度对三叶虫萤卵孵化和初孵幼虫发育的影响

本文研究了三叶虫萤Emeia pseudosauteri在不同恒温设置和室内变温条件下卵孵化率和初孵幼虫存活率,并通过直接最优法和直线回归法计算出了三叶虫萤卵的发育起点温度和有效积温。结果表明:12~30℃恒温条件下,卵的孵化率随着温度升高显著下降(P<0.05),且均低于室内变温条件(P<0.05)下的孵化率;初孵幼虫在恒温15℃下的存活率最高,为73.13%;低于12℃和高于30℃恒温中初孵幼虫均无法存活;在恒温条件12~30℃下,卵的发育历期随温度升高而缩短,其中恒温12℃下最长,发育历期为42.96 d(n=3),恒温30℃下最短,发育历期仅12.75 d(n=3)。通过直接最优法计算出三叶虫萤卵的发育起点温度为3.52℃,有效积温分别为382.20 d·℃。上述结果为三叶虫萤的人工繁育提供了参考。     

THE EFFECT OF TEMPERATURE ON EGGS AND IMMATURE STAGES OF CULEX ANNULIROSTRIS SKUSE (DIPTERA: CULICIDAE)

Abstract
No immature stages of Culex annulirostris were found during field sampling in 1979–1980 when the average water temperature was < 17 °C; they reappeared when the average water temperature was 19 °C and reached the peak density (mean 107 immatures/cylinder) at 26.5 °C.
The effect of 6 temperatures (15–40°C) on egg hatching, development and survival of the immature stages of Cx annulirostris in the laboratory showed that at 15 and 40°C, eggs failed to hatch and larvae died in the first instars. The optimum temperatures for egg hatching and the survival of immature stages were 25 and 30°C. At these temperatures, 85 and 82% respectively of egg rafts hatched, the mean number of larvae per raft was 258 ± 9.8 and 260 ± 11.4 with immature survival of 83.5 and 79.0% respectively. Mean time to hatch at 20–35°C ranged from 1.2 d (35°C) to 2.9 d (20 °C). Developmental times from first instar to adult ranged from 7.1 d (35 °C) to 25.2 d (20 °C). The threshold for development of the immatures was 15.6 ± 2.5°C and the thermal constant was 142.9 ± 26.5 day—degrees (incubation temperatures 20–35°C). At less suitable temperatures of 20 and 35 °C, hatching (57.5 and 45%), number larvae per raft (mean 139.8 ± 9.8 and 102.6 ± 14.2) and survival were low.     

Influence of temperature, photoperiod and humidity on oviposition and egg hatch of the root-feeding flea beetle Longitarsus bethae (Chrysomelidae: Alticinae), a natural enemy of the weed Lantana camara (Verbenaceae)

The root-feeding flea beetle Longitarsus bethae Savini & Escalona, was introduced into South Africa as a candidate biological control agent for the noxious and invasive weed, Lantana camara L. As part of the study to predict the beetles' survival in its new range, the influence of climatic conditions on its egg development and reproductive performance were investigated in the laboratory. The threshold temperature (T degrees) and degree-days (DD) required for egg hatch were determined after exposing the eggs to various constant temperatures (12, 17, 22, 27 and 32 degrees C) in separate growth chambers. The DD required for egg hatch was 178.6, and the temperature threshold required for egg hatch was 11.3 degrees C. Survival of eggs varied from 27 to 56% at 32 and 17 degrees C, respectively, and was optimum between 17 and 25 degrees C. Oviposition was examined under high and low relative humidity (RH) regimes while egg hatch was determined at six RH levels, each maintained in a separate controlled growth chamber set at a constant temperature (25 degrees C). Whilst RH had no influence on oviposition, eggs were highly susceptible to aridity, and continuous exposure to relative humidity below 63% for more than three days was wholly lethal at 25 degrees C. Optimum egg hatch occurred at RH between 85 and 95% for up to 12 days. The effect of day length on oviposition and subsequent egg hatch was investigated under two photoperiod regimes. Neither oviposition nor subsequent egg hatch was influenced by photoperiod. The knowledge obtained will be useful for mass rearing as well as field release programmes for L. bethae.     

Nematodirus battus: development of cold hardiness in dormant eggs

Thermistors and an amplified bridge were used to detect supercooling points of Nematodirus battus eggs weighing ca. 1 microgram wet weight. A cooling rate of about 1 C min-1 was achieved with a manually controlled cold stage using the Peltier effect. The supercooling point of eggs fell during chilling at 5 +/- 1 C for up to 8 weeks from -34.48 +/- 0.49 C to -37.17 +/- 0.76 C. Juveniles freed from these eggs were less cold hardy than intact eggs but chilling improved their supercooling to a greater extent from -19.33 +/- 1.38 C to -32.10 +/- 0.68 C. These results were obtained with eggs showing the characteristic hatching response for this species after transfer from chilling at 5 C to higher temperatures (5-37 +/- 1 C). The results indicate eggs of N. battus acclimate to chilling at a time when previous work had established an increase in their trehalose content.     

Embryonic developmental patterns and energy expenditure are affected by incubation temperature in wood ducks (Aix sponsa)

Recent research in birds has demonstrated that incubation temperature influences a suite of traits important for hatchling development and survival. We explored a possible mechanism for the effects on hatchling quality by determining whether incubation temperature influences embryonic energy expenditure of wood ducks (Aix sponsa). Because avian embryos are ectothermic, we hypothesized that eggs incubated at higher temperatures would have greater energy expenditure at any given day of incubation. However, because eggs incubated at lower temperatures take longer to hatch than embryos incubated at higher temperatures, we hypothesized that the former would expend more energy during incubation. We incubated eggs at three temperatures (35.0°, 35.9°, and 37.0°C) that fall within the range of temperatures of naturally incubated wood duck nests. We then measured the respiration of embryos every 3 d during incubation, immediately after ducks externally pipped, and immediately after hatching. As predicted, embryos incubated at the highest temperature had the highest metabolic rates on most days of incubation, and they exhibited faster rates of development. Yet, because of greater energy expended during the hatching process, embryos incubated at the lowest temperature expended 20%-37% more energy during incubation than did embryos incubated at the higher temperatures. Slower developmental rates and greater embryonic energy expenditure of embryos incubated at the lowest temperature could contribute to their poor physiological performance as ducklings compared with ducklings that hatch from eggs incubated at higher temperatures.     

Temperature effects on embryonic development and the life cycle of Diphyllobothrium dendriticum

Diphyllobothrium dendriticum eggs collected from hamster faeces were incubated at 10 or 20 degrees C, or maintained at 4 degrees C for 11-30 months. On day 65, 20-50% of eggs failed to hatch at 10 degrees C and 42-51% did not hatch by day 21 at 20 degrees C. Our study indicates that eggs begin to hatch in mid-August and persist until October in many lakes within the natural range of D. dendriticum. Our results demonstrate that eggs stored at 4 degrees C will hatch, suggesting they can persist in the environment for long periods and contribute to the D. dendriticum life cycle in high Arctic lakes by hatching months or years after release.     

Survival of Coregonus albula (L.) (Teleostei) embryos incubated at different thermal conditions

Eggs of Coregonus albula were incubated at constant temperatures: 1.1, 2.0, 2.9, 4.9, 6.6, 8.4, and 9.9 °C, and the percentage of normal hatch was 20.6, 11.8, 30.4, 61.0, 51.7, 32.6, and 14.6%, respectively. The lower and upper median tolerance limit (TL 50) defined as the interpolated temperature at which embryos survival to hatch was 50% of the highest response (61% at 4.9 °C) were 2.9 and 8.5 °C, respectively. The optimum temperature range delimited by lower and upper TL 75 was encompassed by 4.0 and 7.2 °C.Eggs of C. albula incubated at variable temperature in a commercial hatchery showed a very high survival (up to 76%). Similarly low survival observed during hatching of embryos at constant temperatures of 1.1 and 2.0 °C could be hightened (to about 90%) by raising the temperature in the beginning of hatching period. This phenomenon was utilized in the technique of delaying C. albula embryos' mass hatching for the purpose of synchronization in time of stocking the lakes with the time of appearence of good thermal and food conditions for C. albula larvae.The conception of the optimal thermal conditions for Coregoninae embryogenesis was developed as the course of incubation temperature, securing the highest survival rate during embryogenesis and also during the larval period.     

The life cycle of Paraquimperia tenerrima: a parasite of the European eel Anguilla anguilla

Previous studies on the life history of the nematode eel specialist Paraquimperia tenerrima (Nematoda: Quimperiidae) have failed to determine whether an intermediate host is required in the life cycle. In the laboratory, eggs failed to hatch below 10 degrees C, hatching occurring only at temperatures between 11 and 30 degrees C. Survival of the free-living second stage larvae (L2) was also temperature dependent, with maximal survival between 10 and 20 degrees C. Total survival of the free-living stages (eggs and L2) is unlikely to exceed a month at normal summer water temperatures, confirming that parasite could not survive the 6 month gap between shedding of eggs in spring and infection of eels in early winter outside of a host. Eels could not be infected directly with L2, nor could a range of common freshwater invertebrate species. Third stage larvae (L3) resembling P. tenerrima were found frequently and abundantly in the swimbladder of minnows Phoxinus phoxinus from several localities throughout the year and were able to survive in this host in the laboratory for at least 6 months. Third stage larvae identical to these larvae were recovered from minnows experimentally fed L2 of P. tenerrima, and eels infected experimentally with naturally and experimentally infected minnows were found to harbour fourth stage larvae (L4) and juvenile P. tenerrima in their intestines. Finally, the whole life cycle from eggs to adult was completed in the laboratory, confirming that minnows are an obligate intermediate host for P. tenerrima.     

Long-term storage and viability of Ochlerotatus albifasciatus (Diptera: Culicidae)

The viability of Ochlerotatus albifasciatus (Macquart) eggs stored at room temperature and at 5 degrees C was studied over 31 months. After 12, 18 and 31 months of storage, eggs were acclimatized at 22 degrees C for ten days, and then inundated twice every seven days. The effect of the storage period on the percentage of hatching was analyzed by one way ANOVA. Differences on the hatching response between the first and second flooding were analyzed by paired t-test. Differences on the hatching response between the two storage conditions were analyzed by Mann-Whitney rank test. Results showed that (1) Oc. albifasciatus eggs were able to survive and hatch over 31 months; (2) the percent hatching of eggs stored at 5 degrees C was higher than that of eggs stored at room temperature; and (3) low temperatures and long periods without water favor installment hatching.     

Influence of temperature and photoperiod on embryonic development in the dragonfly Sympetrum striolatum (Odonata: Libellulidae)

Temperature and photoperiod play major roles in insect ecology. Many insect species have fixed degree‐days for embryogenesis, with minimum and maximum temperature thresholds for egg and larval development and hatching. Often, photoperiodic changes trigger the transfer into the next life‐cycle stadium. However, it is not known whether this distinct pattern also exist in a species with a high level of phenotypic plasticity in life‐history traits. In the present study, eggs of the dragonfly Sympetrum striolatum Charpentier (Odonata: Libellulidae) are reared under different constant and fluctuating temperatures and photoperiodic conditions in several laboratory and field experiments. In general, and as expected, higher temperatures cause faster egg development. However, no general temperature or light‐days for eyespot development and hatching are found. The minimum temperature thresholds are distinguished for survival (2 °C), embryogenesis (6 °C) and larval hatching (above 6 °C). Low winter temperatures synchronize hatching. Above 36 °C, no eyespots are visible and no larvae hatch. In laboratory experiments, light is neither necessary for eyespot development, nor for hatching. By contrast to the laboratory experiments, the field experiment show that naturally changing temperature and photoperiod play a significant role in the seasonal regulation of embryonic development. The post‐eyespot development is more variable and influenced by temperature and photoperiod than the pre‐eyespot development. This developmental plasticity at the end of the embryogenesis might be a general pattern in the Libellulidae, helping them to cope with variation in environmental conditions.     

Developmental and reproductive biology of Scirtothrips perseae (Thysanoptera: Thripidae): a new avocado pest in California

The developmental and reproductive biology of a new avocado pest, Scirtothrips perseae Nakahara, was determined in the laboratory at five constant temperatures, 15, 20, 25, 27.5 and 30 degrees C. At 20 degrees C, S. perseae exhibited greatest larval to adult survivorship (41%), and mated females produced a greater proportion of female offspring at this temperature when compared to 15, 25, 27.5 and 30 degrees C. Average lifetime fecundity and preoviposition period was greatest at 15 degrees C at 39.6 eggs per female and 17.6 days, respectively. Jackknifed estimates of net reproduction (Ro), capacity for increase (rc), intrinsic rate of increase (rm), and finite rate of increase (lambda) were all significantly greater at 20 degrees C than corresponding values at 15, 25 and 27.5 degrees C. Population doubling time (Td) was significantly lower at 20 degrees C, indicating S. perseae populations can double 33-71% faster at this temperature in comparison to 15, 25 and 27.5 degrees C. Mean adult longevity decreased with increasing temperature, from a maximum of 52.4 days at 15 degrees C to a minimum of 2.4 days at 30 degrees C. Developmental rates increased linearly with increasing temperatures for eggs and rates were non-linear for development of first and second instar larvae, propupae, pupae, and for egg to adult development. Linear regression and fitting of the modified Logan model to developmental rate data for egg to adult development estimated that 344.8 day degrees were required above a minimum threshold of 6.9 degrees C to complete development. An upper developmental threshold was estimated at 37.6 degrees C with an optimal temperature of 30.5 degrees C for egg to adult development. Unmated females produced only male offspring confirming arrhenotoky in S. perseae.     

Thermal requirements for the development and reproduction of Nysius huttoni White (Heteroptera: Lygaeidae)

Nysius huttoni White is an economically important pest of wheat and brassica crops in New Zealand. Because of its frequent presence in export fruit packages, it is also considered an important quarantine pest to countries that trade with New Zealand. To provide critical information for the pest risk analysis, forecast and management of N. huttoni, we investigated the effect of five consistent temperatures (10, 15, 20, 25, and 30 degrees C) on its development, survival and reproduction. At 10 degrees C both eggs and nymphs did not develop but the latter grew. Nymphs could survive 10 degrees C for >1.5 mo, with the fifth instar nymphs surviving for up to 145 d. Adults could live for at least 100 d at this temperature. This species could not complete its lifecycle at or below 15 degrees C. Between 15 and 30 degrees C, fifth instar stage was significantly longer than other nymphal stages. Egg hatch rate and total survival rate for all stages were significantly higher at 20 degrees C than at other test temperatures. The developmental rate of different life stages increased linearly with the increase of temperatures from 15 to 30 degrees C. The estimated low temperature threshold for the completion of lifecycle was 11.9 degrees C, and that for mating and oviposition was 12.3 and 16.8 degrees C, respectively. The thermal requirement for completing a life cycle of N. huttoni was 625 DD. The time needed for completing a life cycle was similar for both sexes. Temperature had little effect on adult body weight and sex ratio. Implications of the above findings are discussed.