Pupal diapause of Helicoverpa armigera (Lepidoptera: Noctuidae): sensitive stage for thermal induction in the Okayama (western Japan) population

Helicoverpa armigera (Hübner) exhibits a facultative pupal diapause, which depends on temperature and photoperiod. Pupal diapause is induced at 20 degrees C by short photoperiods and inhibited by long photoperiods during the larval stage. However, in some pupae (35% of males and 57% of females) of a non-selected field population from Okayama Prefecture (34.6 degrees N), diapause is not induced by short photoperiods. In the present experiment, the importance of temperature for diapause induction was studied in the non-diapausing strain, which was selected from such individuals reared at 20 degrees C under a short photoperiod of 10L:14D. Furthermore, the sensitive stage for thermal determination of pupal diapause was determined by transferring larvae of various instars and pupae between 20 degrees C and 15 degrees C. Diapause was induced by 15 degrees C without respect to photoperiod. When larvae or pupae reared from eggs at 20 degrees C under a short or a long photoperiod were transferred to 15 degrees C in the periods of the middle fifth instar to the first three days after pupation, the diapause induction rate was significantly reduced in both males and females, especially in females. In contrast, when larvae or pupae reared at 15 degrees C were transferred to 20 degrees C in the same periods, diapause was induced in males, but not in females. However, the diapause induction rate of pupae transferred to 20 degrees C on the fourth day after pupation was significantly increased in females. The results show that temperature is the major diapause cue in the photoperiod-insensitive strain and the periods of middle fifth larval instar to early pupal stage are the thermal sensitive stages for pupal diapause induction with some different responses to temperatures between males and females in H. armigera.     

Host plant urease in the hemolymph of the silkworm, Bombyx mori

Urease activity was detected in the hemolymph of the silkworm, Bombyx mori from the beginning of spinning to the pharate adult stage if the larvae were reared on mulberry leaves throughout the 5th-instar (the last larval instar). In contrast, no urease activity was detected in the hemolymph of insects fed artificial diets, resulting in accumulation of urea during the spinning stage. To identify the hemolymph urease, the enzyme was highly purified from the hemolymph of the spinning larvae that had been reared on mulberry leaves and the properties of the purified enzyme were compared with those of the mulberry leaf urease. Four out of six monoclonal antibodies raised against jack bean seed urease cross-reacted equally with the silkworm hemolymph urease and the mulberry leaf urease. Under reducing conditions, the hemolymph urease and the mulberry leaf urease migrated at 90.5 kDa on SDS-PAGE gels. The first 20 N-terminal sequence of the hemolymph urease revealed complete identity with that of the leaf urease. The optimum pH for activity and Km value for urea were almost the same for the two enzymes. In conclusion, these two ureases are very likely identical, strongly suggesting that the mulberry leaf urease passes through the larval gut wall into the hemolymph without being digested. In addition, oral administration of mulberry leaf urease just before spinning induced considerable urease activity in the hemolymph of the larvae, but the same treatment did not induce enzyme activity in the hemolymph of the larvae three days before the onset of spinning. These results suggest that the silkworm larvae acquire the host plant urease specifically at the end of the feeding stage in order to degrade urea accumulated in the hemolymph.     

Geographic and parental influences on diapause by a polyphagous insect herbivore

1 Facultative diapause permits insects to initiate an additional generation when conditions are favourable, or to enter diapause when they are not. Although the principle environmental cues for diapause induction are often temperature and photoperiod, we demonstrated recently that the quality of host plant consumed by the larvae of Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae) influences the proportion of larvae that enter diapause and therefore voltinism. 2 Previous work has also suggested that non‐Mendelian parental effects influence diapause by C. rosaceana larvae, but the mechanism was not established. Here, we report further evidence for parental effects on diapause and examine whether parental diet influences diapause induction. 3 We collected larvae of C. rosaceana from six sites at three latitudes in the Province of Québec. There was an increase in the proportion of larvae entering diapause with increasing latitude. Rearing larvae under identical conditions on artificial diet for two generations significantly reduced variation in diapause among populations within a given latitude, and supported the existence of parental effects that influence offspring diapause. 4 Experiments with different host plants and high‐ vs. low‐quality artificial diets provided no evidence that the parental effects on offspring diapause were based on the quality of food consumed by parents. Diapause in C. rosaceana appears influenced by a hierarchy of cues, including temperature, photoperiod, current larval diet and parental environment.     

Recycling of urea associated with the host plant urease in the silkworm larvae,Bombyx mori

Urea concentration and urease activity in the midgut content were compared between larvae of the silkworm, Bombyx mori fed an artificial diet and those fed fresh mulberry leaves. A considerable amount of urea was found in the midgut content of the both larvae, however it was significantly lower in the larvae fed fresh mulberry leaves than in the larvae fed the artificial diet; average urea concentrations in the midgut content of the larvae fed fresh mulberry leaves and the artificial diet were 2.9 and 4.6 &mgr;mol/g, respectively. Urea in the midgut content seems to be secreted from the insect itself since the amount of urea in both diets were negligibly small. Urease activity was detected only in the midgut content of the larvae fed fresh mulberry leaves but not in other tissues of the larvae. On the other hand, no urease activity was detected in the midgut content of the larvae fed the artificial diet. Subsequently, to elucidate the role of mulberry leaf urease in the midgut lumen, larvae that had been reared on the artificial diet were switched to fresh mulberry leaves. The diet switch caused a rapid decrease in urea concentration in the midgut content and an increase in ammonia concentration in the midgut content, suggesting that secreted urea could be hydrolyzed to ammonia by mulberry leaf urease in the midgut lumen. Furthermore, to investigate the physiological significance of mulberry leaf urease on urea metabolism of the silkworm, (15)N-urea was injected into the hemocoel, and after 12 h the larvae were dissected for (15)N analysis. A considerable amount of (15)N was found to be incorporated into the silk-protein of the larvae fed fresh mulberry leaves, but there was little incorporation of (15)N into the silk-protein of the larvae fed the artificial diet. These data indicate that urea is converted into ammonia by the action of mulberry leaf urease in the midgut lumen and used as a nitrogen source in larvae fed mulberry leaves.     

Pupal diapause of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) mediated by larval host plants: pupal weight is important

Facultative diapause, a strategy that allows insects to initiate additional generations when conditions are favorable or to enter diapause when they are not, has a profound effect on the ecology and evolution of species. Most previous studies have concentrated on the role of photoperiod and temperature in inducing facultative diapause in insects. In contrast, here we studied pupal diapause mediated by larval host plants in the cotton bollworm Helicoverpa armigera, and confirmed that pupal weight is a critical factor. Two groups of third instar H. armigera larvae, kept at 25 °C with L:D = 8:16 and 20 °C with photoperiod of L:D = 8:16, respectively, were fed on six host plants and on artificial diet (as a control) to determine how larval host plants affect diapause incidence and related traits (such as pupal weight and developmental duration). The data showed larval host plants affected diapause incidence significantly and the effects could be masked by low temperature. Further analysis showed that pupal size, not the length of the sensitive stage, affected the decision to enter diapause. In a further experiment, third-instar to final-stage larvae deprived of artificial diet for 2 days demonstrated a direct relationship between pupal weight and diapause incidence. These results suggest that larval host plants, by affecting pupal size, may influence diapause occurrence in H. armigera. This has important adaptive significance for both over-wintering survival and the possibility for completing an additional generation.     

Photoperiodic induction of the pupal diapause in the tobacco hornworm, Manduca sexta

A study was made of photoperiodic induction of the facultative pupal diapause in the tobacco hornworm, Manduca sexta, reared on artificial diet in the laboratory. The species entered a prolonged diapause when the egg and larval feeding stages were reared in daily photoperiods of 13·5 hr or less. Diapause was induced in all insects at photoperiods ranging from 1 to 13 hr, and part of the population entered diapause at only 15 to 30 min of light per day. Photoperiods of 14 hr or more and continous darkness prevented diapause. Duration of diapause varied with the inductive photoperiod in which the hornworms were reared during the sensitive period. Insects reared in longer diapause-inducing photoperiods within a range of 12 to 13·25 hr remained in diapause longer than those reared in shorter photoperiods. There was no difference in the rate of larval development of hornworms reared in diapause-inducing vs diapause-preventing photoperiods. Temperatures of 26 to 30°C were most favourable for the photoperiodic induction of diapause; at 21°C, the critical photoperiod and incidence of diapause were decreased. Diapause induction was suppressed by low (18°C) and higher (33°C) temperatures. The number of inductive 12L:12D (light = 12 hr; dark = 12 hr) cycles required to induce diapause ranged from as few as 5 for some insects to as many as 12 for others when the post-inductive régimen was continuous light, but with insects previously held in continuous dark, as few as 2 12L:12D cycles during the last 2 days of larval feeding induced diapause in 38 per cent of the population. Only 3 to 4 cycles of 15L:9D during the final larval instar reversed inductive effects of 14 to 15 12L:12D cycles. Photoperiodic sensitivity extended from the late embryo to the end of larval feeding but showed considerable fluctuation during development with maximum sensitivity occurring just before egg hatch and during larval growth.Light breaks applied at different times during the dark period of 12L:12D cycles generated different response curves, depending on the number of cycles in which light breaks were repeated. When repeated for 6 cycles, a unimodal response curve was obtained; 10 cycles produced a bimodal curve and light breaks given for 18 cycles throughout the sensitive period averted diapause regardless of time of night applied. It is suggested that diapause is regulated by a photo- and thermolabile substance that accumulates during long nights (11 hr or more) and acts during the early pupal stage to inhibit the translocation and release of development-promoting neurosecretion from the brain.     

草地螟阿格姬蜂的滞育诱导和滞育茧的低温贮藏

为了阐明环境因子对草地螟阿格姬蜂Agrypon flexorium (Thunberg)滞育诱导作用, 测定了5个光周期和4个温度处理对阿格姬蜂的滞育诱导和该蜂感受光周期的敏感虫态以及不同时间段低温贮藏对滞育虫茧的影响。结果表明： 在17~23℃、 光照时间10~14 h范围内, 随着温度的降低和光照时间的缩短, 滞育率明显提高。高温能抵消短光照对滞育诱导的影响, 在26℃下, 短光照不能诱导滞育。因此, 低温和短光照是诱导草地螟阿格姬蜂滞育的主要因子。草地螟阿格姬蜂感受滞育信号的敏感虫态为卵和1龄幼虫。卵和1龄幼虫感受滞育信号以后, 需要在滞育环境中发育到老熟幼虫才能全部进入滞育。将室内诱导的滞育茧在4℃左右环境条件下冷藏80 d, 成蜂的羽化率和寄生能力与没有冷藏的非滞育茧差异不显著, 冷藏120 d, 滞育茧仍有71.7%可以正常羽化。结果说明,可在17℃,光周期8L∶16D条件下对寄生后3 d内的草地螟Loxostege sticticalis幼虫进行滞育诱导, 滞育后的虫茧最佳贮藏时间为80 d, 不宜超过120 d。本研究为室内扩繁、 防止蜂源退化、 控制寄生蜂发育时间以便适时释放提供了参考依据。     

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.     

Effect of photoperiod on the development and diapause of the green lacewing Chrysopa pallens (Neuroptera: Chrysopidae)

To investigate the physiology of Chrysopa pallens, the effect of photoperiod on diapause and development was examined in a Japanese population (33.4°N). The response stage for diapause of C. pallens was considered to be the prepupal stage. The critical photoperiod for diapause induction at 20.0°C was between 13 h light : 11 h dark (LD 13:11) and LD 14:10. The larval developmental period was affected by photoperiod: larvae in diapause took longer to complete their development. This difference of larval developmental period in relation to photoperiod was considered to be an adjustment of larval diapause timing.     

Silkworm strains that can be clearly destined towards either embryonic diapause or direct development by adjusting a single ambient parameter during the preceding generation

In the silkworm, Bombyx mori (Lepidoptera: Bombycidae), embryonic diapause is under maternal control and the decision between diapause and direct development in bivoltine strains depends on environmental factors such as temperature and photoperiod experienced by the preceding generation. We reared ten bivoltine silkworm strains (c10, g32, k06, n25, p21, p22, p24, p44, p50 and p63) under various thermal and light conditions and examined the incidence of embryonic diapause in the next generation to identify strains in which the incidence of diapause can be controlled within the range of 0 to 100% by adjusting a single ambient parameter. Some strains were clearly destined towards either diapause or direct development. The diapause incidence in the c10, p22 and p50 strains was controlled by temperature during the egg stage (0% at 18°C and 100% at 25°C), that in the p50 strain was also determined to be dependent on illumination during the egg stage (0% under continuous darkness and 100% under continuous illumination), and photoperiod during the larval stage regulated diapause in p44 and p50 (0% and 100% under long‐day and short‐day photoperiod, respectively), when all other external parameters remained constant under each experimental condition. These diapause‐controllable silkworm strains might serve as model systems for studies of insect diapause, especially for the differential screening of related factors.     

Temperature and photoperiodic regulation of diapause of the southwestern corn borer,Diatraea grandiosella

The effect of temperature and photoperiod on the onset and termination of the mature larval diapause of the southwestern corn borer, Diatraea grandiosella, was examined. The results showed that diapause induction was an extremely temperature-dependent process. Larvae reared at 23°C under short days all entered diapause whereas 90 per cent of those reared at 27°C developed continuously. A photoperiodic response was only demonstrable at 25°C, when diapause was instituted following larval exposure to daily photophases ranging from 8 to 14 hr. An examination of the sensitivity of immature larvae to low temperatures revealed that all instars showed some susceptibility to low temperature induction of diapause. No intermediate instar was found in which the developmental programme could be switched entirely from a diapause to a non-diapause one, or vice versa.Diapause development was also found to be primarily temperature regulated. The rate of termination of diapause at 30°C was significantly higher than that at 25 or 23°C. Continuous exposure to light rather than a daily photoperiod produced the highest rate of diapause development. It was also shown that a period of chilling (5°C) did not accelerate diapause development. The significance of the results in relation to the evolution and geographical distribution of the species is discussed.     

Photoperiodic induction in the silkworm, Bombyx mori, reared on artificial diet: Evidence for extraretinal photoreception

When a bivoltine race of the silkworm, Bombyx mori, was reared on artificial diets, the silkworm became photoperiodically responsive during larval development. The response curve for the embryonic-diapause induction of the next generation was of the long-day type, showing a sharply defined critical day-length of 16.5 hr. Complete blindness caused by covering the larval stemmata with black paint was confirmed electrophysiologically. It did not influence the diapause incidence. Vitamin A deficiency, which produced a similar defect in visual function in the stemmata, was also without effect on diapause. These observations show that extraretinal photoreception is involved in photoperiodic induction in the silkworm.     

Role of specific activators of intestinal amino acid transport in Bombyx mori larval growth and nutrition.

Nutrient absorption and its modulation are critical for animal growth. In this paper, we demonstrate that leucine methyl ester (Leu-OMe) can greatly increase the activity of the transport system responsible for the absorption of most essential amino acids in the larval midgut of the silkworm Bombyx mori. We investigated leucine uptake activation by Leu-OMe in brush border membrane vesicles and in the apical membrane of epithelial cells in the midgut incubated in vitro. Moreover, the addition of this strong activator of amino acid absorption to diet significantly affected larval growth. Silkworms fed on artificial diet supplemented with Leu-OMe reached maximum body weight 12-18 h before control larvae, and produced cocoon shells up to 20% heavier than those of controls. The activation of amino acid absorption plays an essential role in larval development so that larval growth and cocoon production similar to controls reared on an artificial diet with 25% of dry mulberry leaf powder were observed in silkworms fed on an artificial diet with only 5% of mulberry powder. Arch.     

不同饲料饲养家蚕其肠道微生态优势菌群类型的组成及差异性

为探讨鳞翅目昆虫的生长发育及抗病性与肠道微生态状况的关系,以不同的桑科植物柘叶与桑叶分别饲养家蚕,采用纯培养分离检测技术、16S rDNA序列测定和系统发育分析方法,对4、5龄家蚕肠道优势菌群的类型进行了鉴定和差异性分析。结果表明:柘叶与桑叶饲养家蚕共有的优势菌群有短波单胞杆菌属(Brevundimonas)、寡养单胞菌属(Stenotrophomonas)、肠杆菌属(Enterobacter)和葡萄球菌属(Staphylococcus)4个类群。从桑叶饲养家蚕肠道中检索到的优势菌群还有气单胞菌属(Aeromonas)、短杆菌属(Brevibacterium)、柠檬酸杆菌属(Citrobacter)、埃希氏菌属(Escherichia)和克雷伯氏菌属(Klebsiella)5个类群,而从柘叶饲养家蚕肠道中检索到的优势菌群仅有假单胞菌属(Pseudomonas)和土壤杆菌属(Agrobacterium)2个类群。饲料的改变导致家蚕肠道微生态细菌种群组成的变化,从柘叶饲养家蚕肠道中分离出的优势菌群与桑叶饲养的家蚕相比,出现较大差异且不如桑叶饲养家蚕的菌群丰富。推测这种改变可能与柘叶饲养家蚕生长发育不良、容易患病具有相关性。     

光周期和温度对草地螟滞育诱导的影响

草地螟Loxostege sticticalis以老熟幼虫滞育越冬。在室内通过人工诱导的方法对其滞育的光周期和温度诱导条件进行了研究。结果表明:草地螟是一种典型的长日照发育型种类。光周期、温度及其交互作用均对草地螟滞育诱导具有重要影响, 其中光周期起主导作用, 温度伴随着光周期起作用。对幼虫滞育诱导最有效的光周期是L12∶D12; 随着温度的升高, 临界光周期呈缩短趋势（18℃除外）。18, 22, 26和30℃条件下幼虫滞育的临界日长依次为13.97, 14.48, 13.92 和12.88 h。光敏感实验揭示:21℃时草地螟对光照反应最敏感时期为幼虫孵化后的11～17 d（约5龄幼虫）, 但孵化后7～11 d（约4龄幼虫）的短光照积累对提高滞育率也有重要作用, 可以将滞育率从40.0%提高到90.0%。     

Larval diapause in the mosquito aedes triseriatus: effects of diet and temperature on photoperiodic induction

Larval diapause was induced in both a northern (Ohio) and a southern (Alabama) strain of Aedes triseriatus by photoperiodic treatment of the larval stage itself. The effect of a short-day (10 hr) photoperiod during larval development was cumulative and resulted in failure of the fourth instar to pupate. The larvae, which had been obtained from long-day (16 hr) eggs, underwent diapause when their development was slowed by a low-quantity diet or low temperature (16°C) for a sufficient number of days to allow the short-day photoperiod to exert a visible effect.     

白蛾周氏啮小蜂滞育诱导及滞育后发育

本研究针对人工繁育白蛾周氏啮小蜂Chouioia cunea Yang过程中出现的小蜂滞育现象, 对其滞育诱导的光周期反应及敏感光照虫态进行了调查。结果表明: 沈阳地区的白蛾周氏啮小蜂属长日照型昆虫, 以老熟幼虫进入滞育状态, 但在不同的温度条件下诱导滞育的临界光周期不同, 在18℃时诱导滞育的临界光周期处于13L∶11D和14L∶10D之间; 在21℃和24℃时诱导滞育的临界光周期变短, 处于12L∶12D和13L∶11D之间。白蛾周氏啮小蜂滞育诱导的敏感光照虫态为幼虫期, 且以幼虫的后期最为敏感, 但整个幼虫期接受短光照对滞育的形成更为有利。通过观察白蛾周氏啮小蜂滞育后在18℃, 21℃, 24℃和30℃的恒温条件下的发育历期, 由最小二乘法计算出白蛾周氏啮小蜂老熟幼虫滞育后发育起点温度和有效积温分别为14.60±0.31℃和209.38±8.72日·度。这些结果可为进一步研究白蛾周氏啮小蜂的种蜂长期保存技术和指导商品蜂生产, 正确把握放蜂时机提供理论依据。     

Deuterium oxide alters pupal diapause response in the flesh fly, Sarcophaga crassipalpis

ABSTRACT. Deuterium oxide averts pupal diapause in the flesh fly Sarcophaga crassipalpis Macquart when fed to larvae or when applied topically to photosensitive embryos exposed to short daylength. Deuterium oxide was not effective in promoting diapause when presented to embryos or larvae reared at long daylength. The effect of deuterium oxide appears to be cumulative in the larval state: increasing exposure time progressively reduces diapause response. If flies reared on deuterium oxide are exposed to continuous darkness, the diapause response remains high, thus implying that the physiological capacity for diapause is not disrupted. We suggest that deuterium oxide exerts its effect on the circadian rhythm controlling diapause induction.     

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.     

Effects of photoperiod and temperature on diapause induction in Conogethes punctiferalis (Lepidoptera: Pyralidae)

The yellow peach moth, Conogethes punctiferalis (Guenée), a multivoltine species that overwinters as diapausing larvae, is one of the most serious insect pests on maize in China. Effect of photoperiod and temperature on larval diapause was examined under empirical laboratory conditions. Short‐day treatments caused larval diapause at 25°C, and the critical photoperiod was between 12 and 13 h (or 12 h 51 min) light per day. No sensitive instar was identified for diapause induction under alternated short‐ (L : D 11 : 13 h) and long‐day (L : D 14 : 10 h) treatments at different larval stages. However, accumulative treatment of three instars and 10 d under short‐day treatment was required for the induction of 50% larval diapause. All larvae entered diapause at 20°C, whereas less than 3% did so at 30°C, irrespective of the long‐ or short‐day treatment. Furthermore, under the short‐day treatment, more than 90% of larvae went into diapause with temperatures ≤ 25°C, but less than 17% did so at 28°C. In contrast, under the long‐day treatment, less than 19% of larvae went into diapause with temperatures ≥ 23°C. The forward shift (5°C) of critical temperature under the long‐day regime demonstrated the compensatory effect of temperature and photoperiod on diapause induction. In conclusion, C. punctiferalis had a temperature‐dependent type I photoperiodic diapause response; there was no sensitive instar for diapause determination, but the photoperiodic accumulation time countermeasures both of the short‐day cycles and the number of instars exposed, and the photoperiodic diapause response, was a temperature‐compensated phenomenon.