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.     

Rapid cold hardening in the predatory mite Euseius (Amblyseius) finlandicus (Acari: Phytoseiidae)

A rapid cold hardening response was studied in diapause and non-diapause females of the predatory mite Euseius finlandicus. When laboratory reared diapause and non-diapause females were transferred and maintained from the rearing temperature of 20 degrees C for 2 h to -11.5 degrees C and -10 degrees C, 10 to 20% survived respectively. However, conditioning of diapause females for 4 h at a range of temperatures from 0 to 10 degrees C before their exposure for 2 h to -11.5 degrees C, increased survival to approximately 90%. Similarly, conditioning of non-diapause females for 4 h at 5 degrees C before their exposure for 2 h to -10 degrees C increased survival to 90%. A similar rapid cold hardening response in both diapause and non-diapause females was also induced through gradual cooling of the mites, at a rate of approximately 0.4 degrees C per min. The rapid increase in cold tolerance after prior conditioning of the mites to low temperatures, was rapidly lost when they returned to a higher temperature of 20 degrees C. Rapid cold hardening extended the survival time of diapause and non-diapause females at sub-zero temperatures. The cost of rapid cold hardening in reproductive potential after diapause termination was negligible. In non-diapause females, however, the increase in cold tolerance gained through gradual cooling could not prevent cold shock injuries, as both fecundity and survival were reduced.     

Photoperiod and temperature studies to determine whether diapause is found in successive generations of the African phytoseiid,Euseius fustis (Pritchard and Baker) (Acari: Phytoseiidae)

Photoperiod and temperature conditions known to induce diapause in tropical arthropods were tested on two generations (G₀ and G₁) of the phytoseiid, Euseius fustis. Failure to lay eggs or a pre-oviposition period longer than 15 days were the criteria used to determine whether females were in diapause. Females reared from egg to adult and held throughout adult life under cyclic temperatures of 29/20°C in combination with long photophases of 16L: 8D and 14L: 10D showed no indication of aestival diapause. Similarly, hibernal diapause was not induced in females reared under a constant temperature of 18°C and a photophase of 8L: 16D. Under the various test conditions, females initiated oviposition within an average of 4 days. Overall, pre-oviposition patterns for G₀ and G₁ females were similar under the same test conditions. Reproductive patterns based on the mean number of eggs per female per day varied only slightly between generations for the same treatments. No behavioural or morphological attributes associated with diapause were observed.     

Environmental and genetic control of the larval diapause of the Southwestern corn borer, Diatraea grandiosella

ABSTRACT. The interaction of photoperiod and temperature in the regulation of the induction and termination of the larval diapause of the Southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera), was examined. A population originating from south-eastern Missouri had critical daylengths for diapause induction of about 15h 5min (ecological threshold) and llh (physiological threshold). The ecological threshold was more stable than was the physiological threshold at temperatures lower than 25°C. Above 25°C the diapause response was suppressed. The insect appears to measure photoperiods in a stationary manner since a stepwise increase or decrease in photoperiod did not affect the incidence of diapause. In the critical region of the photoperiodic response curve, a higher incidence of diapause was found among females than among males. Females entered diapause later than did males, but resumed active development earlier than males. The rate of diapause development was more temperature dependent than was the rate of diapause induction, yet it was also clearly under photoperiodic control. The temperature coefficient (Q₁₀) for this process was about 4. Several other factors including sex-linkage, age, and geographic adaptations are involved in controlling the rate of diapause development, even more so than they are in controlling diapause induction. In the laboratory, the intensity of diapause declined gradually without larvae being exposed to non-diapause inducing conditions. Incubation of field-collected larvae revealed that their sensitivity to diapause maintaining photoperiods had ended by January. Three generations of selection of a Mississippi population of D. grandiosella at 30°C and LD 12:12 led to the production of an essentially diapause-free strain and a diapause strain.     

Characteristics of summer diapause in the onion maggot,Delia antiqua (Diptera: Anthomyiidae)

Characteristics of summer diapause in the onion maggot, Delia antiqua, were clarified by laboratory experiments. Temperature was the primary factor for the induction of summer diapause in this species. The critical temperature for diapause induction was approximately 24 degrees C, regardless of the photoperiod. At 23 degrees C, the development of the diapausing pupae was arrested the day after pupariation, when about 7% of the total pupal development had occurred in terms of total effective temperature (degree-days). The most sensitive period for temperature with regard to diapause induction was estimated to be between pupariation and "pupation" (i.e., evagination of the head in cyclorrhaphous flies). Completion of diapause occurred at a wide range of temperatures (4-25 degrees C): The optimal temperature was approximately 16 degrees C, at which temperature only five days were required for diapause completion. The characteristics of summer diapause in D. antiqua are discussed in comparison with those of summer dormancy in a congener D. radicum and those of winter diapause in D. antiqua.     

Cumulative induction of diapause in successive generations of Trichogramma species (Hymenoptera,Trichogrammatidae)

The ability of two Trichogramma species (Trichogramma telengai Sor. and T. principium Sug. et Sor.) to accumulate the effect of the maternal photoperiodic response during 5 consecutive generations reared in the laboratory under the short day (12 h) conditions was investigated. Control individuals developed at the same temperature of 20°C, but under the long day (18 h) conditions. The tendency to diapause was estimated by the proportion of progeny that entered diapause under the short day conditions at the temperatures of 13, 14 and 15°C. Trichogramma principium manifested an evident transgenerational cumulative photoperiodic response: the development of 1, 2, and 3 consecutive generations under the short day conditions caused a gradual increase in the proportion of diapausing progeny. In T. telengai, the progeny of the females that developed under the short day conditions also entered diapause more often than the progeny of those that developed under the long day conditions, but the number of preceding generations which developed under short day had no effect on the tendency to diapause. This interspecific difference can be possibly explained by the different natural geographic ranges of the two studied species. Trichogramma principium occurs in Southern Europe, Southern Kazakhstan, and Central Asia where the autumnal decrease in temperature is very slow and thus two or even more generations can develop under the short day conditions, whereas T. telengai is distributed over Central and North-Western Europe and in Siberia, where the autumnal decrease in temperature is rather fast, the development of one more “autumnal” generation is risky, and thus even the first “short-day signal” induces a very strong tendency of the progeny to diapause.     

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.     

Seasonal development of the lacewing Chrysopa dorsalis Burmeister (Neuroptera, Chrysopidae) in the forest-steppe zone of Russia

Seasonal adaptations of Chrysopa dorsalis Burmeister were studied in Belgorod Province of Russia (50°N, 36°E). It was found that in the forest-steppe zone two generations may be produced, but from 76 to 100% of the prepupae of the first generation entered diapause, about 40% of them having an obligate diapause. In the rest of the population, seasonal development was controlled by photoperiod and temperature. The critical day length was about 17 h at 20°C. Some prepupae were found to require two or three years to complete the diapause. This prolonged diapause seems to be a permanent element of the life cycle of the studied species. The proportion of the prepupae that remain in diapause after the first winter positively correlated with the percentage of diapausing prepupae of the first generation in the previous season (r = 0.8). The offspring from eggs laid by females simultaneously collected under the natural conditions emerged in successive years, and the tendency to enter a long-term diapause was not inherited. The rate of the larvae development and the prepupae weight were not different in individuals which had one-year-long and prolonged diapause. However, the weight loss due to dehydration and respiration during the first winter was slightly lower in the prepupae with the prolonged diapause. The expression of the prolonged diapause was independent of the photoperiod during the diapause induction, but it was increased at a high temperature (28°C). Probably, the prolonged diapause increases polymorphism of local Ch. dorsalis populations, ensuring their survival under unpredictable conditions.     

Involvement of ERK/MAPK in regulation of diapause intensity in the false melon beetle, Atrachya menetriesi

Embryonic diapause is commonly terminated by exposure to low temperature for a certain duration. Previous studies using the silkworm, Bombyx mori, showed that extracellular signal-regulated kinase (ERK), a member of the mitogen-activated protein kinase family, was activated by cold exposure and regulated diapause termination. The involvement of ERK in regulation of diapause termination was investigated in the false melon beetle, Atrachya menetriesi. Embryonic diapause of this beetle is terminated both by cold exposure and by mercury. Phospho-ERK levels remained high during the pre-diapause period but decreased after the eggs entered diapause. Exposure to 7.5 degrees C, which was effective for diapause termination, increased phospho-ERK levels, and these levels were maintained under 7.5 degrees C at least for 100 d. Incubation at 25 degrees C after the eggs were kept at 7.5 degrees C for 20 d, which intensified diapause, decreased the phospho-ERK level. An insufficient cold treatment, i.e., incubation at 0 degrees C for diapause termination did not activate ERK. However, incubation at 0 degrees C after cold treatment at 7.5 degrees C, which is effective for diapause termination, induced high phospho-ERK levels. Moreover, mercury treatment also increased phospho-ERK. Therefore, changes in the phospho-ERK level correlated well with diapause intensity. The results suggest that ERK plays a key role in the regulation of embryonic diapause.     

Repeated cycles of chilling and warming effectively terminate prolonged larval diapause in the chestnut weevil, Curculio sikkimensis

Curculio sikkimensis (Coleoptera: Curculionidae) requires one or more years to complete its life cycle, owing to prolonged larval diapause. To compare the effects of temperature cycles and total periods of chilling on the termination of prolonged diapause, larvae were subjected to different chilling (5 degrees C) and warming (20 degrees C) cycles ranging from 30 to 720 days, and all cycles were repeated until the sum of chilling and warming periods reached 720 days. The prolonged diapause of C. sikkimensis was more effectively terminated by repeated cycles of chilling and warming than by prolonging the continuous chilling period. However, extremely short temperature cycles were not highly effective in enhancing diapause termination, even when such cycles were repeated many times. To examine the role of warming periods on diapause termination, diapause larvae were subjected to a sequence of chilling (120 days at 5 degrees C) and warming (240 days at 20 degrees C) with a warming period (0-120 days at 20 degrees C) inserted in the chilling period. Diapause larvae that were not reactivated in the first chilling period required exposure to a certain period of warming before they were able to complete diapause development in the subsequent chilling. Thus, C. sikkimensis appears to spread its reactivation times over several years in response to seasonal temperature cycles.     

马尾松毛虫越冬代滞育与非滞育幼虫过冷却点的研究

测定了在恒温和自然温度处理下饲养的马尾松毛虫滞育与非滞育幼虫的过冷却点。结果表明 ,2 7℃恒温饲养的滞育幼虫的平均过冷却点较非滞育幼虫的平均过冷却点低 ,但无显著差异 ;而自然温度下饲养的滞育幼虫的过冷却点较非滞育的过冷却点也低 ,然而 ,滞育开始时差异不显著 ,之后差异显著。相应滞育状态下 ,自然温度下饲喂的幼虫较 2 7℃恒温下饲喂的平均过冷却点低 ,但在滞育开始阶段和结束阶段两者之间的差异显著。自然温度下滞育和非滞育幼虫的抗寒能力都随气温的降低而增强 ,而 2 7℃下滞育与非滞育幼虫的抗寒能力均出现先增后减的趋势     

Seasonal dynamics of oviposition in non-autogenous population of Culex pipiens pipiens (Diptera: Culicidae) in the Leningrad province

Seasonal patterns of oviposition in a synanthropic unautogenous population of Culex pipiens pipiens mosquitoes from 69 suburban settlements (60 degrees 30' N, 30 degrees E') of the Leningrad province were studied during the period 1998-2002 years. The numbers of egg rafts laid in six artificial pools (barrels) were counted every day; altogether 692 rafts were collected. The general patterns of oviposition activity were similar for all studied years, in spite of their differences in the summer temperature regimes. The first peak of oviposition was observed during the second decade of July, the second peak--during the third decade of July--the first decade of August. The first and second summer generations of mosquitoes were responsible for these oviposition peaks, whereas the third generation completely entered the reproductive diapause. Thus, the oviposition activity was successfully used for populational monitoring of C. p. pipiens, that was for the first time recommended by Madder and co-authors (1980), taking into consideration the simplicity and economy of this technique. The differences in the attractiveness of distinct reservoirs for oviposition were recorded. The females preferred the barrels located on open sun-lit space and waters with organic pollution settled by mosquito larvae. Windly and rainy weather and also low (below 10 degrees C) night temperatures suppressed mosquito oviposition.     

Multigenerational maternal inhibition of prepupal diapause in two Trichogramma species (Hymenoptera: Trichogrammatidae)

It is known that in some insect species the incidence of diapause among the progeny of females that had undergone diapause is relatively low or zero even under strong diapause-inducing conditions. Moreover, the maternal inhibition, preventing the induction of a maladaptive diapause in spring, can persist over several generations. This multigenerational effect based on hypothetical ‘interval timer’ was thoroughly studied in Aphididae. We first described a similar phenomenon in Hymenoptera: laboratory experiments demonstrated that the proportion of diapausing progeny of Trichogramma females that had undergone diapause was practically zero independently of photoperiodic and temperature conditions used (day lengths of 12 and 18 h and temperatures of 12–15 °C). Then the ability to enter diapause recovered gradually and returned to the normal level over two (in Trichogramma telengai) or even five (in Trichogramma principium) generations. We conclude that the observed effect may be based on an interval timer similar to that in aphids.     

Effect of anoxia on diapause termination in eggs of the false melon beetle, Atrachya menetriesi

The effect of anoxia on diapause development in the leaf beetle Atrachya menetriesi was investigated to elucidate the role of oxygen in regulation of egg diapause. While anoxia alone had no effect on diapause termination, it decreased diapause intensity before chilling. Such an effect reached a maximum level when anoxia lasted for about 10 days. Anoxia applied during the pre-diapause stage also reduced diapause intensity. On the other hand, anoxia terminated diapause when the diapause intensity had been lowered by sufficient duration of chilling (50 days at 7.5 degrees C). The effect of anoxia was temperature dependent; the larger effect was elicited when anoxia was combined with a higher temperature. A 50-day chilling caused more than 20% of eggs to terminate diapause upon transfer to warm conditions. However, when this chilling period was interrupted on the 20th day by a 5-day exposure to a high temperature of 20, 25 or 30 degrees C, the effect of the former chilling was cancelled partially or completely, suggesting that warming reversed diapause development. This reversing effect of a high temperature, however, was not manifested when the warming was combined with anoxia. The results suggest that anoxia inhibits diapause reversal and facilitates a certain process of diapause development. The sequence of exposure to anoxia and chilling is not important.     

马尾松毛虫的光周期反应

马尾松毛虫Dendrolimus punctatus Walker和油松毛虫 Dendrolimus tabulaeformisTsai et Liu都属于长日照型昆虫。它们的光周期反应却存在着明显的差开。马尾松毛虫初龄幼虫对光照时数虽然敏感,可是只有在整个幼虫期都处在短光照周期条件下才能维持幼虫的滞育。 而且, 幼虫的滞育强度明显较弱,解除滞育所要求的条件也不如油松毛虫严格。在较高温度条件下,幼虫的滞育更不稳定,一般仅表现为生长的短暂停滞和幼虫历期的相对延长。温度和光周期还可影响到幼虫的存活和性比。马尾松毛虫幼虫呈典型的浅滞育现象。正是由于这一特性,在环境条件的影响下,长江沿岸省份不同年份马尾松毛虫二、三代分化的比例才有较大的波动,这直接关系着当地的种群动态,也是当年当地高虫口区二代虫能否成灾的关键。     

Interaction between photoperiod, temperature, and chilling in dormant larvae of the tree-hole mosquito, Toxorhynchites rutilus Coq.

1. Unchilled, diapausing larvae of Toxorhynchites rutilus rely on photoperiod for the maintenance of diapause. The photoperiodic clock is temperature-compensated between 16.5 degrees and 25 degrees C, maintaining both a similar set-joint and inherent accuracy over this range. The rates of development among larvae terminating diapause are dependent upon both temperature and photoperiod. 2. Chilling of dormant Toxorhynchites rutilus can promote response to progressively shorter daylengths, thus decreasing the critical photoperiod. Chilling can also accelerate response to long days, thereby decreasing the depth of diapause and, after prolonged exposure, can eventually terminate diapause directly, leaving subsequent morphogenesis independent of photoperiod. 3. The optimal temperature for these effects of chilling is above 4 degrees C, below 16.5 degrees C, and may lie around 7 degrees C. 4. Temperatures between 5 degrees and 15 degrees C are vernal and autumnal rather than hibernal. The interaction between chilling and photoperiod may then represent an adaptive compromise between selection due to long-term climatic trends and the vagaries of spring weather.     

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.     

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.     

The environmental regulation of adult diapause in Drosophila littoralis

Drosophila littoralis overwinters in the adult stage in a reproductive diapause. During the warm season there are one or two generations in Finland. The diapause appears to be a prolongation of the post-eclosion immaturity of young females. The termination of diapause is controlled by a combination of adequate temperature and sufficiently long photophases. The diapausing status of females is ascertained by inspecting the developmental stage of their ovaries. In laboratory experiments the maturity of ovaries is not closely correlated with the receptivity of females.