Induction of adult diapause and of low and high reproductive states in a parasitoid wasp,Ooencyrtus nezarae, by photoperiod and temperature

Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) was reared on eggs ofRiptortus clavatus (Thunberg) (Heteroptera: Alydidae) at various temperatures under long-day (L16:D8) or short-day (L10:D14) conditions. There was no diapause during egg, larval or pupal stages under any set of conditions examined. However, at 15°C under short-day conditions, vitellogenesis was arrested in all adult females and they entered diapause. At 15°C under long-day conditions, or at 20°C under short-day conditions, some adult females entered diapause. Under the latter set of conditions, the adult females laid eggs but they laid fewer eggs than under long-day conditions, Even at 25°C, under short-day conditions, adult females laid fewer eggs than under long-day conditions, and this low rate of oviposition was attributed to the retarded development of ovaries. Diapause adults reared at 15°C were more resistant to low temperature than nondiapause adults reared at 25°C.     

Ecdysteroids and adult diapause in the Colorado potato beetle, Leptinotarsa decemlineata

ABSTRACT. The difference in ecdysteroid activity in short-day (10-h photo-phase) and long-day (16-h photophase) Leptinotarsa decemlineata Say adults was characterized by high performance liquid chromatography, which revealed that for short-day beetles ecdysterone and ecdysone are the major constituents of the free ecdysteroids, whereas in long-day beetles products co-migrating with 2-deoxyecdysone and 2-deoxyecdysterone are just as abundant. Ecdysteroids were detected (15 ng/ml) only in the haemolymph of females. Ligation experiments showed that the induction of the diapause syndrome by inactivation of the corpora allata or the brain not only resulted in the formation of the typical diapause proteins but also in an increase of the ecdysteroid activity. It is suggested that adult diapause in L.decemlineata is regulated by a multifactorial system.     

Photoperiodic responses during larval development and diapause of two geographic ecotypes of the rice stem maggot, Chlorops oryzae

Chlorops oryzae is bivoltine in northern Japan but trivoltine in the southern part of the country. In the bivoltine strain, both the egg and larval stages were found to be sensitive to photoperiod. When the egg stage was exposed to a long-day photoperiod (16L:8D), larval development showed a short-day type response, and mature third-instar larvae entered a summer diapause under a long-day photoperiod (15L:9D). When eggs experienced short days, the first-instar larvae entered a winter diapause under short-day conditions, and the critical photoperiod in the larval stage ranged from about 14L:10D to about 12L:12D as the photoperiod experienced by the eggs increased from 12L:12D to 14L:10D. However, the development of the larvae after overwintering was not influenced by the photoperiod. In the trivoltine strain, larval development was retarded under a 14L:10D photoperiod but not under either shorter or longer photoperiods, when larvae had spent the egg stage under a 16L:8D photoperiod. The critical photoperiod of the larval stage for the induction of a winter diapause in the first instar was about 12L:12D, though it varied to some extent with the photoperiod during the egg stage. Thus, Chlorops oryzae was able to adapt itself to the local climatic conditions by the development of variable and complicated photoperiodic responses.     

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.     

Effects of temperature of adults and eggs on the induction of embryonic diapause in the band-legged ground cricket, Dianemobius nigrofasciatus

Abstract.  Eggs laid by adult female Dianemobius nigrofasciatus , reared under long-day (LD 16 : 8 h, 25 °C) or short-day (LD 12 : 12 h, 25 °C) conditions from the nymphal stage, are kept at several constant temperatures. At 22.5–30.0 °C, eggs laid by long-day adults show lower incidences of diapause than those laid by short-day adults. In both eggs laid by adults under long-day conditions and those under short-day conditions, the higher the temperature at which the eggs are kept, the lower the incidence of diapause. When eggs of long-day adults are exposed to a low-temperature pulse (10 °C, 24 h) on the day of deposition (day 0), the incidence of diapause increases. The low-temperature pulse on day 1 does not increase the incidence of diapause. By contrast, when the eggs of short-day adults are exposed to a high-temperature pulse (35 °C, 24 h) on day 0 or day 1, the incidence of diapause decreases. The temperature pulses on day 0 are more effective at diapause prevention. Staining of diapause eggs by the Feulgen–Rossenbeck method shows that the eggs enter diapause at the blastoderm stage, which is on day 1 or day 2 at 25 °C. The exposure of adults to long days and higher temperatures prevents the eggs from entering diapause. In D. nigrofasciatus , embryonic diapause is controlled by maternal effects, adult photoperiod and temperature, and egg temperature before or at diapause.     

Juvenile hormone-induced break and termination of diapause in the Colorado potato beetle

Topical applications of Cecropia juvenile hormone I (JH) and several analogues, 1 day after the initiation of diapause, induce a break in diapause 8 to 10 days later, characterized by emergence from the soil, feeding, mating, and reproduction. Activation is only temporary when beetles are kept in short-day photoperiods. The percentage of beetles activated and the duration of activation depend on the nature of the JH and the dose applied. JH application during prediapause only postpones diapause, whereas beetles which have spent 2 months in diapause are activated rather easily. Diapause is completely terminated when JH application is accompanied by a transfer of the beetles to long-day conditions. Thirty μg JH applied to allatectomized females in long-day conditions allows them to reproduce for over 50 days.The extent to which the endocrine system is involved in activation has been investigated. Allatectomy does not change JH-induced activation at long or short daylengths. Volumetric measurements indicate that the corpora allata remain inactive as long as measurable amounts of JH circulate in the blood. An increase in corpus allatum activity after day 8 further stimulates long-day oviposition. Gomoripositive neurosecretory cells in the brain are activated by JH within 1 day. The hypothesis is advanced that a JH-induced break or termination of diapause is mediated through the neuroendocrine system.     

Photoperiodic control of adult diapause in the predacious mite, Amblyseius potentillae: repeated diapause induction and termination

ABSTRACT. Photoperiodic control of facultative reproductive diapause was examined in females of the phytoseiid mite, Amblyseius potentillae (Garman). Full diapause was induced by rearing the mites from egg to adult under short-day photoperiods. Egg-laying females, however, which had experienced a long-day photoperiodic regime during pre-imaginal development, could still be induced to enter diapause when they were transferred to a short-day regime. Diapause development proceeded slowly under a short-day photoperiod, but was accelerated under long days. During diapause development under short days the photoperiodic sensitivity of the females diminished gradually and ultimately disappeared completely. However, after completion of diapause, sensitivity to photo-period reappeared. A second diapause could be induced in post-diapause females under short-day photoperiods and completed again under long-day photoperiods. These results show that A. potentillae remains sensitive to diapause-inducing and diapause-averting daylengths during the adult stage and that a second diapause may be induced after completion of the first one.     

Photoperiodic and temperature control of diapause induction and colour change in the southern green stink bug Nezara viridula

Abstract. The effect of photoperiod and temperature on the duration of the nymphal period, diapause induction and colour change in adults of Nezara viridula (L.) (Heteroptera: Pentatomidae) from Japan was studied in the laboratory. At 20 °C, the developmental period for nymphs was significantly shorter under LD 10 : 14 h (short day) and LD 16 : 8 h (long day) than under intermediate photoperiods, whereas at 25 °C it was slightly shorter under intermediate than short- and long-day conditions. It is assumed that photoperiod-mediated acceleration of nymphal growth takes place in autumn when day-length is short and it is unlikely that nymphal development is affected by day-length under summer long-day and hot conditions. Nezara viridula has an adult diapause controlled by a long-day photoperiodic response. At 20 °C and 25 °C in both sexes, photoperiodic responses were similar and had thresholds close to 12.5 h, thus suggesting that the response is thermostable within this range of temperatures and day-length plays a leading role in diapause induction. Precopulation and preoviposition periods were significantly longer under near-critical regimes than under long-day ones. Short-day and near-critical photoperiods induced a gradual change of adult colour from green to brown/russet. The rate of colour change was significantly higher under LD 10 : 14 h than under LD 13 : 11 h, suggesting that the colour change is strongly associated with diapause induction. The incidences of diapause or dark colour did not vary among genetically determined colour morphs, indicating that these morphs have a similar tendency to enter diapause and change colour in response to short-day conditions.     

Neural control of the corpus allatum in the Colorado potato beetle, Leptinotarsa decemlineata: An electron microscope study utilizing the in vitro tannic acid Ringer incubation method

The release of material from neurosecretory synapses in the corpora allata of the Colorado potato beetle, Leptinotarsa decemlineata was visualised by an electron microscope procedure which involved tissue incubation in tannic acid. Using morphometry, the frequency of exocytosis phenomena was quantified in beetles kept under two different photoregimes. The number of exocytosis phenomena in the neurosecretory synapses in the corpora allata of beetles kept under short days was significantly higher than that of beetles reared under long-day conditions. In addition, the corpus allatum gland cells appeared to be more richly innervated by neurosecretory synapses under short-day than under long-day conditions. Previous studies using the in vitro radiochemical assay showed that the corpus allatum activity of short-day beetles is at least partly restrained by neurally mediated factors. The present morphological data strongly imply that this corpus allatum inhibitory substance is released from the neurosecretory synapses.     

Changes in mechanical properties of the cuticle and lipid accumulation in relation to adult diapause in the bean bug,Riptortus clavatus

Photoperiodically controlled adult diapause in the bean bug, Riptortus clavatus (Thunberg) (Heteroptera: Alydidae) was due to suppression of corpus allatum activity under short-day conditions. The mechanical extensibility of the cuticle of the pronotum was significantly higher in nondiapause adults reared under long-day conditions than in diapause adults reared under short-day conditions. Furthermore, diapause adults accumulated significantly larger amount of lipids than nondiapause ones. It was then examined whether these two characteristics of adult diapause also depend on activity of the corpus allatum, by removal of the corpus allatum and transection of the nervi corporis allati. Even after these two kinds of surgery, adults responded to photoperiod and showed similar differences both in mechanical properties of the cuticle and in lipid content between long-day and short-day conditions. Therefore, inactivity of the corpus allatum is not responsible for the stiffer cuticle or higher lipid accumulation in diapause adults.     

Alternative life cycles controlled by temperature and photoperiod in the oligophagous bug, Dybowskyia reticulata

Abstract. Effects of temperature and photoperiod on the induction and re-induction of adult diapause were examined in Dybowskyia reticulata (Dallas) (Heteroptera: Pentatomidae). Adults collected from the field after overwintering in early summer continued oviposition under long-day conditions of LD 16:8 h at 20 or 25°C, while they re-entered diapause under short-day conditions of LD 12:12 h at 25, 27.5 or 30°C. By contrast, adults reared in the laboratory from eggs at 20 or 25°C entered diapause under both long-day and short-day conditions, whereas those reared at 27.5 and 30°C entered diapause only under short-day conditions. Under quasi-natural conditions in 1993, when summer temperature was low, most adults of the first generation entered diapause in late July. However, in the warmer summer of 1996, oviposition was recorded in many females that ecdysed into adults from July to early August. Even though the seeds of the host plants occur in a restricted period from early summer to early autumn, in warmer years D. reticulata may produce a second generation. The response to temperature with a threshold between 25 and 27.5°C in D. reticulata brings about a switch between the univoltine and bivoltine life cycles.     

Hormonal control of seasonal morphs by the timing of ecdysteroid release in Araschnia levana L. (Nymphalidae: Lepidoptera)

Araschnia levana L. occurs in two seasonal morphs. Larvae reared under short-day conditions become diapause pupae and emerge as red spring-morph butterflies. Long-day larvae become non-diapause pupae, which emerge as black and white summer morphs. Pupae reared under these different conditions were joined in parabiosis. Both underwent adult development without diapause and the long-day animals developed into the summer morph as normal. The morph of short-day animals depended on the time of parabiosis. When they were joined to fresh long-day pupae 1 day after their own pupation, summer morphs resulted. When parabiosis began 4 days after pupation or later, spring morphs resulted. Extirpation of the brain-corpora cardiaca-allata complex from long-day pupae affected neither non-diapause development nor the summer morph. Adult development could be prevented by removal of head and prothorax. When adult development was initiated in the remaining bodies by 20-hydroxyecdysone 14 days after pupation, the spring morph resulted.—Injection of 20-dydroxyecdysone into 3-day-old short-day pupae initiated adult development and led to the summer morph. Injections into 10-day-old short-day pupae led to the spring morph. The same was true in diapause pupae deprived of their brain-corpora cardiaca-allata complex. These results indicate that seasonal diphenism in A. levana is controlled only by the timing of ecdysteroid release, which initiates adult development. There is no direct influence of the brain on wing coloration.     

Juvenile hormone changes associated with diapause induction, maintenance, and termination in the beet webworm, Loxostege sticticalis (Lepidoptera: Pyralidae)

At 22°C and under a long-day photoperiod of L:D 16:8, all the last fifth instar Loxostege sticticalis larvae undergo prepupal stage and pupate without diapause. Under a short-day photoperiod of L:D 12:12, in contrast, they all enter diapause with approximately 36 days diapause maintenance and then terminate diapause spontaneously, although only 44% of the larvae terminated diapause successfully. Changes in hemolymph juvenile hormone (JH I) titers of diapause-destined larvae across diapause induction, maintenance and termination were examined using HPLC, and were compared with those of non-diapause-destined larvae from the fifth instar through pupation. JH I titer of the earliest fifth instar diapause-destined larvae remained at a high level with a peak of 220.4 ng/ml, though it decreased continuously to a minimum of 69.0 ng/ml on day 5 in the fifth instar when the larvae stopped feeding to enter diapause. During the diapause maintenance, JH I titer of the mature larvae increased significantly and maintained a high level until day 31 in prepupae. JH I titer declined and fluctuated at low level from 5 days before pupation. In contrast, JH I titer of both the fifth instar non-diapause-destined larvae and prepupae remained and fluctuated at low level consistently, as well as decreased before pupation. These results indicate that diapause induction and maintenance in this species might be a consequence of high JH, whereas diapause termination can be attributed to low JH titer, which was in agreement with the hormonal regulation observed in many other larval-diapausing insects.     

Effects of temperature and photoperiod on termination of pseudopupal diapause in the bean blister beetle, Epicauta gorhami

Larvae of the bean blister beetle, Epicauta gorhami (Coleoptera: Meloidae), feed on grasshopper eggs in soil and undergo hypermetamorphosis. This beetle undergoes larval diapause in the fifth instar as a pseudopupa, a form characteristic of hypermetamorphosis in meloid beetles. This pseudopupal diapause is maintained for a long period if the larvae are kept under continuous diapause-inducing short-day conditions. In the present study, the effects of temperature and photoperiod on termination of pseudopupal diapause in E. gorhami were examined using pseudopupae obtained under 12L-12D at 25°C. Diapause was terminated by exposure to low or high temperature, but not by transfer to long-day conditions. The pseudopupal stage comprises diapause and post-diapause phases despite its unchanging appearance. The optimum low temperature for diapause termination was 10-15°C, and a higher or lower temperature was less effective. There was an individual variation in the low temperature requirement for diapause termination and post-diapause development may not occur until this requirement is satisfied. Although under natural conditions pseudopupae may encounter low temperatures that are effective for diapause termination at different ages, our results show that pseudopupae at various ages respond similarly to low temperature exposure. This response may ensure that resumption of development synchronizes in a population.     

Short-day and low-temperature conditions promote reproductive maturation in the terrestrial slug, Lehmannia valentiana

Terrestrial slugs (Lehmannia valentiana) collected from a field in Osaka, southwestern Japan, were reared under long-day (16-h light and 8-h darkness, LD 16:8) or short-day conditions (LD 12:12) at 15, 20, or 25 degrees C for 60 days. Slugs reared under short-day conditions were heavier than those reared under long-day conditions; however, slugs reared at 15 degrees C gained more weight regardless of the photoperiodic condition. Gonads were significantly heavier under short-day conditions than under long-day conditions, and oogenesis and spermatogenesis were also induced under short-day conditions. Under short-day conditions, reproductive maturation was suppressed at 25 degrees C as compared with 15 and 20 degrees C, whereas under long-day conditions, lower temperatures induced reproductive maturation. In contrast, slugs reared under short-day conditions at 20 degrees C from the time of hatching gained more weight than those reared under long-day conditions at the same temperature. Moreover, short-day conditions induced reproductive maturation, similar to that observed in the field-collected slugs. In conclusion, short-day and low-temperature conditions promoted growth and reproductive maturation, whereas long-day and high-temperature conditions suppressed them in L. valentiana. Thus, L. valentiana reproduces from late autumn to spring in Osaka.     

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.     

Relationship between photoperiod and secretion of the diapause hormone during larval stages of the silkworm, Bombyx mori L., reared on an artificial diet

The suboesophageal ganglion of the silkworm, Bombyx mori synthesizes sufficient diapause hormone to produce diapause eggs, regardless of the photoperiodic conditions experienced during the larval stages. When larvae destined to produce non-diapause eggs are implanted with the brain-suboesophageal ganglion complex from larvae which have been reared under short-day conditions, the resulting adults lay diapause eggs. The larvae receiving the complex from larvae reared under long-day conditions gave rise to adults which did not produce any diapause eggs. The brains from pupae which have been reared under long-day conditions show an activity inhibiting the secretion of diapause hormone by the suboesophageal ganglion. The mechanism through which the brain controls the secretion of diapause hormone from the suboesophageal ganglion can be modified by photoperiodic conditions during the larval stages.     

Induction of reproductive diapause via perception of photoperiod through the compound eyes in the adult blow fly, Protophormia terraenovae

Covering and surgical removal of the compound eyes were performed to localize photoreceptors for photoperiodic responses in the blow fly Protophormia terraenovae (Diptera, Calliphoridae). Adult females showed a long-day photoperiodic response to control reproductive diapause. When the compound eyes were bilaterally covered with silver paint, diapause incidence increased under diapause-preventing conditions, i.e., a long-day photoperiod and constant light, as though flies were kept under constant darkness. Neither silver painting on a medial region of the head capsule nor control painting in which both compound eyes were painted in a clear solvent caused significant effects on diapause incidence. Unilateral painting of the compound eye caused an increment of diapause incidence under constant light but no effects under a long-day photoperiod. When the compound eyes were bilaterally removed, all the flies developed their ovaries both under a long-day and a short-day photoperiod. Unilateral removal of the compound eye also caused ovarian development under a short-day photoperiod, whereas removal of one antennal lobe or all ocelli caused no effects on diapause incidence. Since P. terraenovae completely lost responsiveness to photoperiod after blinding of the compound eyes, it is likely that this fly perceives photoperiod through its compound eyes. Accepted: 18 February 1997     

Interactions between dietary nitrogen and simulated autumn conditions on diet consumption and reproductive development in the boll weevil, Anthonomus grandis

ABSTRACT. Dietary nitrogen content and short-day, cool scotophase temperature were investigated for effects on diet consumption and reproductive development in the female boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae). Experimental weevils were maintained from the day of adult eclosion on cottonseed flour diets on a LD10:14 h, 27:15C cycle. Control weevils were maintained under long-day conditions (LD13:11) at a constant 27C.
Diets containing 4% and 1.7% N were labelled with a ¹⁴C-amino acid mixture and fed to individual females for 24 h to permit determinations of diet consumption rate, amino acid absorption, and reproductive allocation of the assimilated amino acids.
Females fed the 1.7% N diet under long-day, 27C laid 50% fewer eggs than females fed the 4% N diet under the same regimen. Egg production was depressed further by the 1.7% N diet when combined with short-day, and cool scotophase temperatures. These latter conditions delayed, but did not prevent, attainment of a high rate of egg production by females fed the 4% N diet.
The short-day, cool temperature regimen also stimulated diet consumption but reduced the allocation of absorbed ¹⁴C amino acids towards oogenesis.