Diapause‐inducing signals prolong nymphal development in the two‐spotted spider mite Tetranychus urticae

Female two‐spotted spider mite Tetranychus urticae are grown under different photoperiods and the photoperiodic regulation of diapause is examined. The photoperiodic response curve for diapause induction was of the long day–short day type, with critical day lengths (CDLs) of 2 and 12.5 h; diapause was induced between these CDLs. The preimaginal period is significantly longer in diapausing females than in non‐diapausing females; moreover, a significant positive correlation is detected between diapause incidence and deutonymphal period. Diapause incidence is high when long‐night photoperiods are applied against a background of continuous darkness in the stages including the deutonymph; this stage appears to be the most sensitive to photoperiod. These observations suggest that diapause‐inducing conditions inhibit nymphal development, particularly in the deutonymphal stage when photoperiodic time measurement for determination of reproduction or diapause is carried out.     

Maternal influence on diapause induction in Trichogramma (Hymenoptera: Trichogrammatidae): the dynamics of photosensitivity

It is known that the prepupal diapause in Trichogramma is dependent on temperature conditions of embryonic and larval development and on the photoperiodic conditions of preimaginal development of maternal females. However, the relative photosensitivity of different preimaginal stages has been never investigated. We studied the position of the photosensitive period over the preimaginal development of maternal females in T. embryophagum Htg. and T. principium Sug. et Sor. by transferring preimaginal stages between diapause‐averting ‘long’ day (L : D = 20 : 4) and diapause‐inducing ‘short’ day (L : D = 12 : 12). Results showed that the influence of maternal photoperiod on progeny diapause was determined during the late pupal stage (last days of preimaginal development at 20°C). During this time, the critical duration of the photoperiodic induction was extremely small: one short or long day caused almost the same effect as the permanent development under these conditions. As a whole, photoperiodic response in Trichogramma was found to be unusually rapid, labile and easily reversible which is probably explained by extremely small size and fast development of these egg parasitoids. The results of this study could be used for elaboration of optimal methods for Trichogramma mass rearing and storage and for prediction of its seasonal cycles under natural conditions.     

Effects of temperature and photoperiod on the termination of larval diapause in Lucilia sericata (Diptera: Calliphoridae)

Larvae of the blow fly, Lucilia sericata (Meigen), enter diapause in the third instar after cessation of feeding. The effects of temperature and photoperiod on the termination of diapause were examined. The diapause terminated spontaneously under the diapause-inducing condition of 20 degrees C and LD 12:12, although pupariation was not synchronous. Diapause development proceeded under a low temperature of 7.5 degrees C. Transfer to long-day conditions of LD 16:8 or to a high temperature of 25 degrees C induced prompt and synchronous pupariation. Low temperatures in winter probably play a predominant role in the termination of diapause under natural conditions.     

Summer and winter diapause in pupae of the cabbage butterfly,Pieris melete Ménétriés

The cabbage butterfly, Pieris melete is multivoltine with a pupal summer and winter diapause. Summer and winter diapause are induced principally by relatively long and short daylengths, respectively. The intermediate to relatively short daylengths of autumn permitted some pupae to develop without diapause in the field. A short daylength had a stronger diapause inducing effect than a relatively long one under higher temperatures. The principal sensitive phase for photoperiodic response occurred before the late 3rd larval instar. The critical daylength for wild autumnal populations was between 12h 30min and 12h 40min at an average temperature of 20.5 degrees C. A night interruption by 2h of light averted diapause most effectively when it was placed 10 to 12h after lights-off. High temperatures and long days during summer inhibited the incidence of diapause, suggesting that the occurrence of summer diapause is due to the specific climatic conditions occurring in April and early May, rather than to the high temperatures in summer. This indicates that the butterfly has a cryptic ability to reproduce in summer. High temperatures delayed diapause development, whereas low temperatures enhanced it, indicating that the optimum temperature of diapause development is lower. The diapause regulating mechanisms thus ensure that the species synchronises its development and reproduction with the growth seasons of the host plants and provide the species with a high degree of flexibility in its life cycle.     

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.     

Evolution of overwintering strategies in Eurasian species of the Drosophila obscura species group

The phylogenetic relationship of Eurasian species of the Drosophila obscura species group remains ambiguous in spite of intensive analyses based on morphology, allozymes and DNA sequences. The present analysis based on sequence data for cytochrome oxidase subunit I (COI) and a-glycerophosphate dehydrogenase (Gpdh) suggests that the phylogenetic position of D. alpina is also ambiguous. These ambiguities have been considered to be attributable to rapid phyletic radiation in this group at an early stage of its evolution. Overwintering strategies are diversified among these species: D. alpina and D. subsihestris pass the winter in pupal diapause, D. bifasciata and D. obscura in reproductive diapause, and D. subobscura and D. guanche without entering diapause. This diversity may also suggest rapid radiation at an early phase of adaptations to temperate climates. On the other hand, adult tolerance of cold was closely related to overwintering strategy and distribution: D. obscura and D. bifasciata with reproductive diapause were very tolerant; D. alpina and D. subsilvestris which pass the winter in pupal diapause were less tolerant; D. subobscura having no diapause was moderately tolerant and D. guanche occurring in the Canary Islands was rather susceptible. Tolerance of high temperature at the preimaginal stages seemed to be also associated with overwintering strategy; i.e. lower in the species with pupal diapause than in those with reproductive diapause or without diapause mechanism.     

PHOTOPERIODIC CONTROL OF ADULT DIAPAUSE IN CHRYSOPERLA SINICA (TJEDER) (NEUROPTERA: CHRYSOPIDAE— I. CRITICAL PHOTOPERIOD AND SENSITIVE STAGES OF ADULT DIAPAUSE INDUCTION

Abstract  Photoperiodic sensitivity for diapause induction of the green lacewing, Chrysoperla sinica (Tjeder) was examined at 22°C. The adult diapause of C. sinica was induced by short-day photoperiods, and the critical photoperiod for its induction was between 12.5L-11.5D and 13L-11D.
Adults developed without diapause under long-day conditions, and entered diapause under short-day conditions. The adult stage was the uppermost sensitive stage for adult diapause induction, adults could go into diapause only when the emerging adults were under diapause-inducing short-day photoperiods. The short-day photoperiodic experience by transferring between 15L: 9D and 9L: 15D at preimaginal stages did not result in adult diapause under 15L: 9D photo regime, although some treatments extended the pre-oviposition period in adult stage. The results showed that the 3rd instar larvae and pre-pupae were more sensitive to the photoperiodic change from 15L: 9D to 9L: 15D photo regime than the other preimaginal stages.     

Cold hardiness in summer and winter diapause and post-diapause pupae of the cabbage armyworm, Mamestra brassicae L. under temperature acclimation

Cold hardiness and biochemical changes were investigated in winter and summer pupae of the cabbage armyworm Mamestra brassicae at the diapause and post-diapause stages under temperature acclimation. Diapause pupae were successively acclimated to 25, 20 and then 10 degrees C (warm-acclimated group). Pupae at the diapause and post-diapause stages were successively acclimated to 5, 0, -5 and then -10 degrees C (cold-acclimated groups). Supercooling point values in winter and summer pupae remained constant regardless of the diapause stages and acclimated temperatures. Warm-acclimated pupae at the diapause stage did not survive the subzero temperature exposure, whereas, cold-acclimated pupae achieved cold hardiness to various degrees. Winter pupae were more cold hardy than summer pupae, and pupae at the post-diapause stage were more cold hardy than those at the diapause stage. Trehalose contents in winter pupae rose under cold acclimation. Summer pupae accumulated far lower trehalose contents than winter pupae, with the maximal level occurring in winter pupae at the post-diapause stage. Glycogen content remained at a high level in diapause pupae after warm acclimation, whereas it decreased after cold acclimation. Alanine, the main free amino acid in haemolymph after cold acclimation, increased at lower temperatures in both diapause and post-diapause pupae, but the increase was greater in the diapause pupae. These results suggest that cold hardiness is more fully developed in winter pupae than in summer pupae, and cold acclimation provides higher cold hardiness in winter pupae at the post-diapause stage than at the diapause stage.     

Effect of thermoperiod on diapause intensity in Pyrrhocoris apterus (Heteroptera Pyrrhocoridae)

The intensity of adult diapause in Pyrrhocoris apterus was measured in two series of experiments as the duration of pre-oviposition period at a constant temperature of 25 degrees C after transfer from short (12L:12D) to long day conditions (18L:6D). Higher diapause intensity was induced with a thermoperiod than at constant temperatures. After the induction throughout larval instars 3-5 and during 4 weeks of adult life at short days and a thermoperiod of 25/15 degrees C the pre-oviposition period was 30+/-4 and 26+/-3 days. After induction at constant 25 degrees C the pre-oviposition period was 22+/-3 and 23+/-4 days, while after induction at constant 20 degrees C it was 17+/-4 and 19+/-4 days. Induction at a lower constant temperature of 20 degrees C was thus followed by a less intense diapause than the induction at a higher constant temperature of 25 degrees C. These counterintuitive results are discussed. The oxygen consumption rate measured at experimental temperatures prior to transfer from short to long days was higher at thermoperiodic conditions than at constant temperatures and it was similar at constant 20 and 25 degrees C. Thus, the oxygen consumption rate measured prior to the transfer was highest (indication of the least intense diapause) in the insects that showed later, after the transfer to long days, the longest pre-oviposition period (indication of the most intense diapause). Within the first two days after transfer to constant 25 degrees C, oxygen consumption rate measured at 25 degrees C decreased in the thermoperiodic insects, while it transiently increased in insects from constant 20 degrees C. Two days and later after the transfer, oxygen consumption rate was similar in all groups. Cold hardiness was not correlated with diapause intensity. The low lethal temperature in diapausing insects was correlated with the night temperature during diapause induction.     

Effects of Environmental Conditions and Aging on Eupyrene Sperm Movement in Male Adults of Polygonia c-aureum (Lepidoptera: Nymphalidae)

The effects of temperature, photoperiod and aging on eupyrene sperm movement from the testis to the duplex in Polygonia c-aureum male adults were examined in relation to seasonal form and imaginal diapause. In males of both summer and autumn forms obtained under long-day and short-day conditions, respectively, the number of eupyrene sperm bundles in the duplex increased linearly with age during the early stage of adult life at 21 degrees C, and no marked difference was observed between the two seasonal forms. Photoperiod during the adult stage did not influence the rate of sperm movement in autumn forms with diapause. The lower the temperature, the smaller the number of sperm bundles moved from the testis to the duplex. Sperm movement did not appear to occur during a period of chilling at 5 degrees C. Males of the autumn form which were pre-incubated for 30 days and chilled for 60 days failed to resume rapid sperm movement at the final incubation temperature of 21 degrees C. Those which were pre-incubated only for 15 days at 21 degrees C had much fewer sperm bundles in the duplex after chilling than those pre-incubated for 45 days. These results suggest the possibilities that eupyrene sperm movement is suppressed strongly during and after overwintering in the field, and that the eupyrene sperm to be used for reproduction in spring are transferred from the testis to the duplex before overwintering.     

Diapause in the egg parasitoid Trichogramma cordubensis: role of temperature

The role of temperature in the induction of diapause in Trichogramma cordubensis (Hymenoptera: Trichogrammatidae), under controlled laboratory conditions, was investigated using Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs as hosts. Results indicate that prestorage temperatures and the duration of exposure of the parasitoids to these temperatures affected the induction of diapause. It was possible to induce diapause in prepupae of T. cordubensis by exposing the preimaginal stages (prior to the prepupal stage) to 10°C for at least 30 days, but adults emerged without diapause when the duration of exposure was of only 10 or 20 days. Parasitoids failed to enter diapause when prestorage temperatures were 7 or 12°C, regardless of the duration of exposure. However, at these two temperatures, preimaginal development of T. cordubensis was delayed, allowing short-term storage (40 days at induction temperatures followed by 30 days at 3°C) by keeping parasitoids in quiescence without reducing the percentages of adult emergence. Good percentages of adult emergence after long-term low-temperature storage (30 or 40 days at 10°C followed by six months at 3°C) occurred only when T. cordubensis was in diapause. The long-term storage of parasitoids in diapause allows an enlargement in the mass rearing potentialities of this species for future biological control releases by allowing producers to stockpile the parasitoids for release in the field season.     

Effect of photoperiod experienced by parents on diapause induction in Trichogramma cacoeciae

In the genus Trichogramma, the prepupal stage can survive the cold season in diapause. However, optimal conditions for the induction of this cessation of development during the process of mass production of the parasitoid in a biological control program depend on the species. In Trichogramma cacoeciae Marchal (Hymenoptera: Trichogrammatidae), diapause is induced more easily if the parents are reared under short‐day conditions (L10:D14), and if the temperature is 10 °C rather than 13 °C. However, the effect of parental photoperiod on diapause induction is weaker at lower temperatures (10 °C). Following diapause induction, individuals can be stored at 3 °C for several months, up to 1 year. Non‐optimal conditions led to the establishment of a quiescent state in some or all individuals. In such cases, it was necessary to reduce the storage period to 1 or 2 months only, to prevent high mortality rates and low fecundity.     

Life expectancy of Ctenophthalmus wladimiri Is.-Gurv., 1948 (Siphonaptera, Ctenophthalmidae) under laboratory conditions]

Laboratory studies have shown that at 75% humidity fleas, Ct. wladimiri, are less viable than at 100% humidity. At 100% humidity at a temperature from 0 to 10 degrees and without feeding newly born imagos survived up to 363 days, at a higher temperature from 18 to 30 degrees-from 44 to 163 days. At a temperature from 7 to 10 degrees imagos, which fed one time, lived up to 355 days and at 0 to 2 degrees-up to 287 days. Maximum life duration (1133 days) for periodically feeding fleas was at 100% humidity at a temperature from 7 to 10 degrees. Under such conditions 50% of fleas survived up to 114 days. Hungry but previously "prepared" for winter fleas lived at a temperature from 0 to 2 degrees not more than 376 days.     

Notes on the life-history of the rabbit flea Caenopsylla laptevi ibera Beaucournu & Marquez, 1987 (Siphonaptera: Ceratophyllidae) in eastern Spain

The rabbit flea Caenopsylla laptevi ibera occurs in arid environments of central and eastern Spain. Although the fleas breed during the coolest, most humid part of the year, the larvae survive and grow in sand at only 50-60% relative humidity. At 22 degrees C and 80% relative humidity eggs hatch in six days and the cocoon stage is reached 10-11 days after hatching. Female fleas emerge from pupation at about 17 days after cocoon spinning; males emerge a little later at a mean of 20 days. Adult fleas are mainly found on the host Oryctolagus cuniculus. Measurements of burrow microclimate confirmed that in south-eastern Spain burrow humidity was adequate for the development of C. I. ibera larvae over most of the year. However, breeding may be restricted for at least part of the year, as the larvae of C. I. ibera apparently cannot complete development at 25 degrees C or above. In the laboratory, fleas can enter a prolonged quiescent period while in the cocoon. This is possibly a facultative, pre-pupal diapause and the likely mechanism that accounts for the disappearance of adult fleas from the field by spring and their reappearance each autumn.     

Physiology of diapause and cold hardiness in the overwintering pupae of the fall webworm Hyphantria cunea (Lepidoptera: Arctiidae) in Japan

The fall webworm Hyphantria cunea Drury, which was accidentally introduced to Japan in 1945, overwinters on the ground in pupal diapause. Diapause termination, as indicated by the respiration rate and the period required for adult emergence, began in March and ended in April. Cold hardiness (the ability to survive exposure to -15 degrees C) decreased linearly with diapause development from November to the following April under field conditions. Cold hardiness of diapause pupae (DP) decreased as the acclimation temperature decreased from 15 to -10 degrees C, whereas cold hardiness of non-diapause pupae (NDP) remained high as the acclimation temperature decreased from 5 to -5 degrees C. However, H. cunea in Japan can survive exposure to -5 degrees C for two weeks, whether it is in a diapause or non-diapause state. Trehalose was the main sugar detected in the body, but its level was less than 0.8%. Trehalose levels increased in field-collected pupae from January to March. DP accumulated less trehalose than NDP, as the acclimation temperature was decreased from 5 to -5 degrees C. The alanine content in field-collected pupae increased from November to February. Both diapause and low temperature caused an accumulation of alanine. These results suggest that under field conditions, overwintering pupae of H. cunea in Japan do not accumulate high levels of sugars and polyols and do not develop a high level of cold hardiness. Furthermore, DP do not accumulate high levels of sugars and polyols and their ability to survive exposure to -15 degrees C is not greater than that of NDP. The physiological and biochemical bases of diapause in H. cunea from Japan are discussed.     

Biphasic effect of low temperature on completion of winter diapause in the onion maggot,Delia antiqua

The effect of low temperature on completion of winter diapause was investigated in the onion maggot, Delia antiqua (Diptera: Anthomyiidae). Diapause was completed under constant diapause-inducing conditions of 15 degrees C and 12L-12D, without any exposure to lower temperature. The pupal period for 50% adult emergence was 117 days. None of the cold treatments at 5.6 degrees C examined in the present study advanced adult emergence; on the contrary, they delayed it. Detailed analyses of the results revealed that diapause development in D. antiqua comprises two phases which differ in sensitivity to low temperature, with the phase shift occurring at around day 60 at 15 degrees C and 12L-12D. In the first phase of diapause development, low temperature (5.6 degrees C) had no effect on diapause development. In the latter phase, by contrast, diapause development was retarded in proportion to the duration of cold treatment.     

Development, survival, and reproduction of the predatory mite Kampimodromus aberrans (Acari: Phytoseiidae) at different constant temperatures

Development, survival, and reproduction of the predatory mite Kampimodromus aberrans Oudemans were studied at constant temperatures in the range from 15 to 35 degrees C under laboratory conditions. Larval developmental rate for both males and females increased gradually from 15 to 35 degrees C and decreased at higher temperatures. Lactin's nonlinear model described with adequate accuracy the relationship between developmental rate and temperature. The model predicted that lower and upper threshold temperatures for preimaginal development ranged from 9.8 to 11.8 degrees C and from 37.2 to 39.8 degrees C, respectively. The intrinsic rate of population increase (rm) at the different temperatures ranged from 0.0442 to 0.1575, with the highest value recorded at 25 degrees C. At 33 degrees C a negative rm value was estimated. The rm values determined at different temperatures were fitted to Lactin's nonlinear model, and the lower and upper threshold and the optimal temperatures for population increase were 10.5, 32.4, and 27.6 degrees C, respectively. These data indicate that K. aberrans may be better adapted to intermediate temperatures around 27 degrees C and, therefore, could be a useful biocontrol agent of spider mites during spring and early summer when such temperatures are prevalent in northern Greece. The results could also be useful in developing a population model for K. aberrans under field conditions.     

Development of immature stages and comparative demography of two cucurbit-attacking fruit flies in Reunion Island: Bactrocera cucurbitae and Dacus ciliatus (Diptera Tephritidae)

On Reunion Island, two species of Dacini, Bactrocera cucurbitae (Coquillett) and Dacus ciliatus Loew, infest 16 host plant species belonging to the family Cucurbitaceae from sea level to 1,600 m. These two species represent two primary pests of this plant family on the island. Melon fly, Bactrocera cucurbitae, and Ethiopian fruit fly, D. ciliatus, larval development was studied at four different constant temperatures (15, 20, 25, and 30 degrees C) with three host plants (cucumber, pumpkin, and squash). Adult life histories of these two species were studied at 25 degrees C with the three host plants. The results led to the conclusion that B. cucurbitae had a faster egg incubation time. Its preimaginal instars developed significantly faster than those of D. ciliatus independent of temperature. B. cucurbitae and D. ciliatus had similar mean preoviposition duration and egg hatching success. Fecundity was significantly higher for the melon fly on cucumber and pumpkin and lower on squash. Two distinctly different life- history patterns were evident: (1) later onset of reproduction, longer oviposition time, longer life span, and higher fecundity (B. cucurbitae) and (2) early reproduction, lower oviposition time, shorter life span, and lower fecundity (D. ciliatus). These results are useful for improving laboratory-rearing methods and for building simulation models to predict Dacini population dynamics.     

Cold-Hardiness and Supercooling Capacity in Diapausing and Nondiapausing Stages of the Cabbage Root Fly Delia radicum

Supercooling point (SCP) values and cold-hardiness were measured in individual ontogenetic stages of Delia radicum (Diptera:Anthomyiidae) in various physiological states (winter diapause, summer quiescence, and normal development). Winter diapause-destined mature third-instar larvae had a lower SCP (-9.9 degrees C) than their nondiapause counterparts (-5.2 degrees C), and more of them survived exposure to -10 degrees C for 5 h to pupariation and adult emergence. Values of SCPs were equal in both diapause and nondiapause states of prepupal and pupal stages. The lowest SCP (ca. -20 degrees C) was found in the stage of phanerocephalic pupa (PCP) regardless of the physiological state. The cold-hardiness of PCP corresponded with a low SCP value only in diapausing pupae stored for 80 days at 3 degrees C and in pupae which had terminated their diapause and whose further development was inhibited by storage at low temperatures (3 degrees C). Such pupae survived exposure to temperatures close to their SCP (14 days at -17 degrees C). However, this high cold-hardiness was only acquired after some time and/or exposure to 3 degrees C, as the PCP at the beginning of diapause showed significantly impaired cold-hardiness despite the fact that their SCP was low. The cold-hardiness of nondiapausing PCP did not correspond at all to that of low SCP, as no pupa survived the exposure to -17 degrees C for 1 day; survival rates at temperatures of -13.5 and -10 degrees C were also remarkably lower than those in diapausing pupae. Cold-hardiness in D. radicum was closely connected with the diapause syndrome but the changes in SCP value corresponded rather with the ontogeny of this insect. Copyright 1993, 1999 Academic Press.     

Temperature-dependent regulation of reproduction in the diving beetle Dytiscus sharpi (Coleoptera: Dytiscidae)

The effects of temperature on the mating behavior, gonad development, germ cell maturation, and egg spawning of the predaceous diving beetle Dytiscus sharpi (Coleoptera; Dytiscidae), were investigated. By field observations, we found that mating behavior started in October and occurred more frequently from November to December. Under our laboratory breeding conditions, we observed almost the same seasonal variation in mating behavior. We found that temperatures lower than 20 degrees C were required to trigger mating behavior. We also found the same temperature threshold triggered gonadogenesis as well as spermatogenesis. Furthermore, for females, exposure to lower temperatures (<8 degrees C) during the winter was required for egg maturation and spawning in spring; that is, there was a second threshold for successful female reproduction. We conclude that the termination of summer reproductive diapause of D. sharpi is regulated in a temperature-dependent manner, thus effecting the adaptation of D. sharpi to southern warm habitats.