Daylength and humidity as environmental cues for diapause termination in a tropical beetle

ABSTRACT. Photoperiod is the primary factor controlling termination of adult diapause in the fungus beetle, Stenotarsus rotundus Arrow (Endomychidae: Coleoptera), in a tropical lowland forest. at 9 N. An LD 13:11 h cycle stimulated rapid development of the gonads and flight muscles in both sexes: development was eventually initiated in an LD 12:12 h cycle but was slower. Beetles showed a graded response to intermediate photoperiods. Males consistently initiated gonad development earlier than females, but both sexes developed flight muscles at the same time.
Moisture also influences development: oocytes and flight muscles developed more rapidly at high humidity than at the naturally prevailing low humidity during the dry season. Testis development was less influenced by humidity.
In the field, male gonad development began in late January, suggesting that the beetle can perceive an extremely slight increase in daylength. Ovaries did not contain any visible oocytes before March, but oocyte development was apparent in all females by April. Egg maturation was completed after dispersal from the aggregation site. Females have larger corpora allata than males. These glands increased in size in March when oocyte and/or flight muscle development was initiated. The timing of full development of flight muscles varied slightly from year to year.
Thus, the increase in daylength occurring during the dry season appears to be the cue primarily responsible for development of the reproductive systems and flight muscles. High humidity enhances this response and further prepares the beetles for an active reproductive period at the onset of the wet season.     

Reproductive status and flight activity of the overwintered Colorado potato beetle

Mating behavior of post-diapause Colorado potato beetles, Leptinotarsa decemlineata (Say), was observed within an overwintering site, a rotated potato field, newly colonized potato plants, and under laboratory conditions. The influence of spring mating on beetle flight in the presence and in the absence of host plants was investigated using a computer-linked flight mill system. Diapause was terminated simultaneously in male and female beetles, and the first matings were observed as early as within the first 24 h after the beetles emerged from the soil (60–90 DD accumulated). The beetles mated within the overwintering site, the potato field, and the fields rotated out of potatoes. Mating status did not affect flight behavior of overwintered beetles; however, unfed beetles displayed higher flight activity than fed beetles. Most flight activity took place soon after flight muscle regeneration, and then declined sharply by the 5th day after flight initiation. Mating in or near overwintering sites soon after diapause termination might be an important factor in providing gene flow between insecticide-resistant and insecticide-susceptible Colorado potato beetle populations, and should be considered in designing resistance management plans.     

Diapause development in frozen larvae of the goldenrod gall fly, Eurosta solidaginis fitch (diptera: tephritidae)

Seasonal changes in metabolic rate and the potential for morphological development demonstrated that third-instar larvae of the goldenrod gall fly, Eurosta solidaginis Fitch, exhibit a distinct winter diapause. Metabolic rate (CO2 production) was significantly lower from 15 October to 9 February than in early autumn (9 September) and spring (1 March) samples. The induction of diapause coincided with the development of cold-hardening, maximum larval mass, and gall senescence, but our experiments did not identify specific cues triggering diapause induction. We examined the influence of exposure to 0 degrees C and -20 degrees C on diapause development. Diapause development in larvae stored at 0 degrees C occurred at approximately the same rate as in nature. Until 15 December the larvae were in the refractory phase of diapause (incapable of morphological development, even at permissive temperatures), but afterward moved to the activated phase within which diapause intensity decreased until termination in February. Diapause development occurred in larvae collected during the winter and stored at -20 degrees C for periods of 1 week to 3 months. Diapause intensity decreased in frozen larvae through the winter but at a slower rate than in larvae stored at 0 degrees C.     

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.     

A trade-off between diapause duration and fitness in female parasitoids

Abstract 1. Diapause allows insects to cope with adverse weather conditions but also poses substantial fitness costs, e.g. through reduced survival of the diapausing stage or sublethal effects in the following season.
2. The energetic costs of diapause in females of the parasitoid Asobara tabida Nees (Hymenoptera: Braconidae) were assessed using experimental manipulation of diapause duration.
3. An increase in diapause length not only led to higher mortality among diapausing pupae but also caused a significant decrease in egg load, fat reserves, and dry weight of the emerging adult females.
4. Only larvae with sufficient resources were able to survive the entire diapause period and there was a trade-off between the metabolic costs of diapause and adult fitness components.
5. In contrast, the size (tibia length) of emerging females increased with increasing diapause duration. It is proposed that this may be due to a genetic correlation between larval dry weight and adult size, so that selection for heavier larvae would result in larger adults even when resources are limited.
6. Ultimately, the evolution of diapause duration and its consequences for adult performance will depend on the costs of overwintering and the ecological conditions in the habitat.     

Modifications in dispersal and oviposition of Bt-resistant and Bt-susceptible Colorado potato beetles as a result of exposure to Bacillus thuringiensis subsp. tenebrionis Cry3A toxin

Laboratory strains of Colorado potato beetle, Leptinotarsa decemlineata (Say), physiologically resistant and susceptible to Bacillus thuringiensis (Berliner) subsp. tenebrionis Cry3A toxin were reared to adults on caged potato plants. Influence of three different diets (transgenic potatoes, regular potatoes, and regular potatoes followed by the transgenic potatoes) on beetle mortality, fecundity, and flight behavior were tested under laboratory conditions. A computer-linked flight mill system was used to quantify beetle flight, and dissections were performed to determine the level of flight muscle development. Susceptible beetles continuously fed on transgenic foliage suffered heavy mortality, did not develop flight muscles, and did not produce any eggs. Resistant beetles continuously fed on transgenic foliage were capable of flight and reproduction; however, it took them longer to initiate flight behavior, and their fecundity was lower than fecundity of other treatments. In both strains, detrimental effects became significantly less severe when the beetles were allowed to feed on regular foliage prior to toxin ingestion. In the resistant strain, ingestion of Cry3A toxin significantly increased flight activity, indicating that physiological resistance was probably reinforced by the behavioral escape from toxic environments. No such response was observed for susceptible beetles. When fed on regular foliage, resistant Colorado potato beetles engaged in significantly fewer flights than susceptible beetles. Behavioral differences between resistant and susceptible beetles observed in the present study are likely to affect gene flow between transgenic crops and adjacent refugia, and should be taken in consideration when designing resistance management plans for transgenic potato crops.     

双季稻区稻水象甲一代成虫的滞育

对浙江省双季稻区稻水象甲（ＬｉｓｏｒｈｏｐｔｒｕｓｏｒｙｚｏｐｈｉｌｕｓＫｕｓｃｈｅｌ）夏季种群的研究表明,光照和温度可排除在一代成虫夏季滞育的诱导因子之外,而不同的食料条件是引发滞育的主导因素．在自然状态下,即使是强迫滞留,早稻田内的一代成虫也不转入正常发育,但取食稻秧能使新羽一代成虫和稻田内外处于生殖滞育状态的一代成虫的卵巢正常发育,并能解除已进入夏蛰的一代成虫的生殖滞育;同时,不论是新羽成虫还是夏蛰成虫,取食稻秧后卵巢和飞行肌同时发育;若这种食料条件能持续下去,则飞行肌消解而卵巢发育产卵．     

The effects of temperature and moisture on the inception of diapause in eggs of the Australian plague locust,Chortoicetes terminifera Walker (Orthoptera: Acrididae)

Chortoicetes terminifera lays a mixture of diapause and non-diapause eggs during the autumn months of March and April. Diapause eggs cease development in late anatrepsis when kept in moist soil at 32.5°C. These conditions favour rapid embryogenesis and hatching in non-diapause eggs. Significant reductions in the incidence of diapause were obtained when newly-laid eggs were kept for 40 days at either 15.5°C or 32.5°C in conditions that prevented the uptake of water. In eggs held for a similar period in moist soil at 15.5°C, diapause was virtually eliminated. These eggs did not develop to the stage at which water uptake occurs. It is suggested that the inception of diapause is dependent upon the occurrence of warm, moist conditions at the time of laying and that these requirements are an integral part of the overall inductive process, which also involves the temperature and photoperiod at which the parent insects are reared. A flow-diagram illustrating the development of diapause eggs in relation to temperature and moisture is discussed in relation to the survival of the species.     

Adult diapause ofCybocephalus nigriceps nigriceps [Col.: Cybocephalidae]

During autumn and winter (October–February)Cybocephalus nigriceps nigriceps (J. Sahlberg) adults undergo a facultative diapause. The diapausing adults agregate in hiding places, development of the ovaries is arrested, and prey consumption is lowered. Diapause can be prevented by exposure to a long-day photoperiod (16 hr light) at high temperatures (29° and 32°C). Diapause is induced mainly by short-day conditions, but the termination of diapause is affected by both photoperiod (long-day conditions) and temperature (29°, 32° and 34°C). In mature females, diapause induction causes ovarian degeneration. The induction or inhibition of adult diapause is affected by photoperiods occurring during larval development as well as during adult life.     

Trade-off between diapause and other life-history traits in the spider mite Tetranychus urticae

1. Diapause is generally believed to entail costs that manifest themselves as decreased survival, rate of development, and/or reproduction after diapause completion. The present study is a first step in investigating such diapause costs in the spider mite Tetranychus urticae.
2. The relationship was assessed between diapause duration and the post-diapause life-history traits of longevity and egg production, under six photoperiods at 19 °C.
3. The relationship between diapause duration and longevity was negative under five out of six treatments; in three cases this negative relationship was significant.
4. Most evident were the negative correlations between diapause duration and rate of oviposition, peak rate of oviposition, and total egg production. These phenotypic correlations suggest that there may be a trade-off between diapause duration and post-diapause reproduction.     

Effects of photoperiod and temperature on the development and diapause of the bark beetle Ips typographus

Abstract:  Diapause was induced in a Central European population of Ips typographus grown at 20°C when the day length decreased below 16 h [50% diapause incidence occurred in the 14.7:9.3 h L:D (light:dark) regime]. The non-diapausing adults fed on days 2–6 and 10–14 after the ecdysis and swarmed after the second feeding bout with chorionated eggs in the ovaries and sperm in the spermiducts. Neither gonads nor the flight muscles matured and no swarming occurred in the diapausing adults. The development from egg to adult took about 34 days in both 18:6 h (no diapause) and 12:12 h L:D (diapause) regimes, but it was extended by up to 30% without diapause induction when only larvae or pupae were exposed to L:D 12:12 h. Diapause was induced in insects reared at L:D 12:12 h through the last larval and the pupal instars and/or in the adult stage. Temperature ≥ 23°C prevented diapause induction at L:D 12:12 h but diapause occurred at L:D 14:10 h associated with 26:6°C thermoperiod. The effect of thermoperiods on the developmental rate requires further research. Exposure of the non-diapausing adults to 5°C for several days blocked feeding and evoked a diapause-like state, whereas diapausing adults fed and their gonads slowly developed at this temperature. Diapausing adults exposed in forest to low night temperatures and transferred in October to 20°C readily reproduced at 18:6, but not 12:12 h L:D photoperiods. After 2-months at 5°C and darkness, they became insensitive to the photoperiod, matured and most of them also swarmed at 20°C in the 12:12 h L:D regime. In a Scandinavian population, diapause occurred at 18:6 h L:D and was terminated either by exposure to 5°C or by very long photoperiod (L:D 20:4 h) combined with high temperature (23°C).     

Laboratory studies of egg development and diapause in Isoperla obscura (Plecoptera) from a mountain stream in Norway

SUMMARY 1. A laboratory study of egg development of the stonefly Isoperla obscura (Zetterstedt) collected from the stream Flybekken (southern Norway, 61°25'N, 8°48'E, 1373 m a.s.l.) showed a short diapause followed by a prolonged period of postdiapause quiescence.
2. Diapause occurred over a wide range of temperatures (−20°C to +8°C), but 0–1°C was the most favourable for fast diapause development and successful hatching. Diapause development required temperatures below 12°C, but sub-zero diapause temperatures increased mortality during the postdiapause phase, as well as reducing hatching success.
3. The threshold for initiation of postdiapausal development was about 1–2°C. Development rate increased and variation in development time decreased at higher water temperatures. These may be important characteristics to ensure seasonal and geographical synchrony of development in individual populations. Low postdiapausal temperatures were unfavourable, despite a subsequent increase in water temperature. No response to postdiapausal photoperiod was detected.
4. The results agreed well with conditions noted in the natural environment, and with the abundance of this species at high altitudes and latitudes in Fennoscandia. Nevertheless, Isoperla obscura also occurs in streams in the maritime parts of western Norway. The results of the present study suggest that egg development in these populations will prove to be different.     

Diapause development in the chestnut weevilCurculio elephas

Larval diapause development in the chestnut weevilCurculio elephas (Coleoptera, Curculionidae) was studied in the laboratory at different temperatures. The results proved that exposure to low temperatures (3–6°C) in the period December–February is not required to complete diapause. The diapause is terminated in December and from January on, the larvae can initiate post-diapause morphogenesis in the laboratory, if temperatures allow it. In the field developmental rates are negligible during winter cold (4–6°C) and only after March morphogenesis can proceed with no interruption until adult emergence. Diapause and post-diapause quiescence contribute to individual synchronization for initiation of development. The observed spread of adult emergence was 30 days in the laboratory. This variability produced during post-diapause development may be a response to annual variation in the phenology of the chestnuts.     

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.     

Survivability and post‐diapause fitness in a scolytid beetle as a function of overwintering developmental stage and the implications for population dynamics

1. It has recently been suggested that expected increases in temperature might lead to an additional generation per season in bark beetles. Thus, populations would grow more rapidly. However, an additional but not fully developed generation could lead to high winter mortality in the pre‐imaginal stages. 2. Winter survivability and post‐diapause fitness as a function of the overwintering developmental stage of the spruce bark beetle Ips typographus L. were studied along an altitudinal cline. Fitness was tested in terms of weight, lipid content and flight capacity. 3. Mortality was significantly lower and emergence per brood system significantly higher for fully developed adults that entered overwintering than for larvae, pupae or callow adults. 4. Post‐diapause fitness in terms of dry weight and flight capacity was significantly higher in individuals that completed development before winter, and lipid contents also showed a trend for being higher in those individuals. 5. In conclusion, in a scenario where effective temperature sums are not adequate for the complete development of an additional generation, models may overestimate population growth by neglecting increased mortality and reduced post‐diapause fitness. The results highlight the importance of considering life‐history traits and indirect effects in addition to abiotic factors such as temperature when modelling population dynamics.     

The effect of a seasonal time constraint on development time, body size, condition, and morph determination in the horned beetle Allomyrina dichotoma L. (Coleoptera: Scarabaeidae)

Abstract.  1. In horned beetles selection favours males that adjust their investment in horn development in relation to cues that predict adult body size. Here it is shown that in the Japanese horned beetle, Allomyrina dichotoma . There is a significant discontinuity in the horn length body size allometry. This can be described as a linear relationship that is shifted towards an increased horn length to body length ratio in males with horns longer than 16 mm.
2. Larval nutrition explains morph determination in A. dichotoma . However, unlike other species, variation in larval nutrition was the result of a seasonal time constraint that limits the time available for feeding prior to the onset of winter diapause.
3. Even when eggs were reared with an ad libitum food supply, minor morphs were still observed. Individuals that were oviposited later in the season had less time to feed, shorter development times, eclosed as smaller individuals and, in the case of males, were more likely to be hornless. Major morphs, minor morphs, and females all reduced their body size in response to seasonal time constraints in the same way. However, males that were laid later in the season had faster development times than females laid at the same time, but showed no reduction in their size relative to females, suggesting seasonal time constraints increase growth rates in males but not in females.
4. No evidence was found that seasonal time constraints resulted in a reduction of size-corrected fat reserves at eclosion, or that minor morphs gained any developmental advantage by reducing investment in horn length.     

Seasonal regulation of dormancy in Chrysopa carnea (Neuroptera)

In Ithaca, New York, diapause incidence in Chrysopa carnea exceeds 50 per cent among adults emerging between 31 August and 3 September. Apparently, decreasing late summer day lengths, which exceed the stationary critical photoperiod in the laboratory, act on the sensitive stages and induce diapause. Full diapause intensity occurs about 2 weeks after adult emergence; complete winter coloration appears approximately 2 weeks later. Photoperiodic stimili in combination with the geographic strain largely determine diapause depth.Decreasing autumn day lengths decelerate diapause development and maintain diapause until the winter solstice. Subsequently, short day lengths and cold temperatures slow diapause development. In nature, neither long days, increasing day lengths, nor chilling hasten diapause termination. Diapause duration is largely determined by the interaction between inducing photoperiod, maintaining photoperiodic and thermal stimuli, and geographic strain. In Ithaca, diapause ends (all response to photoperiod ceases) between 22 January and 12 March.After diapause ends, the animals retain their diapause characteristics until temperatures exceed 4°C. Post-diapause reproductive development in females requires approximately 100 heat units above 4°C; however, below 8°C mating and oviposition are absent. Although the winter coloration remains, mating occurs within 1 day after transfer from 4 to 24°C. Temperature determines the rate at which the green summer colour returns.     

Induction and development of winter larval diapause in a drosophilid fly,Chymomyza costata

Photoperiodic response during induction of larval hibernal diapause of Chymomyza costata was characterized and the course of diapause development was analyzed in the laboratory. C. costata becomes sensitive to photoperiodic stimuli during an unspecified stage of its early development (embryo, 1st larval instar); the sensitivity gradually increases during the 2nd and early 3rd larval instars and reaches its maximum just before the moment when it abruptly ceases at the age of 15-19 days after oviposition. Diapause intensifies during a period of 2-3 weeks after induction and, later, is maintained without apparent development until death (between 150 and 250 days) under 18 degrees C and a short-day photoperiod (L10:D14, SD). Diapause may be terminated in a horotelic process by exposure to a low temperature (2 degrees C) during which larvae subsequently (1) synchronize their post-diapause development (requires up to 14 days of chilling), (2) lose photoperiodic sensitivity (2 months), and finally (3) terminate diapause (5 months). Alternatively, diapause may be terminated in a tachytelic process by exposure to a high temperature (18 degrees C) and long-day photoperiod (L16:D8, LD) during which no synchronization occurs and pupariation takes place after a mean of 25.2 days (with a broad range from 8 to more than 50 days). Larvae that are transferred from LD to SD during their sensitive period switch their developmental programming from pupariation to diapause. Proliferation of adult primordial structures (imaginal discs, neuroblasts) slows down within 1 day after transfer. In contrast, whole body growth continues for at least 3 days before its rate slows down and matches the rate characteristic for SD conditions.     

Colonisation ability of the threatened tenebrionid beetle Oplocephala haemorrhoidalis and its common relative Bolitophagus reticulatus

Abstract. 1. Life-history traits associated with colonisation ability were compared in the threatened tenebrionid beetle Oplocephala haemorrhoidalis and its common relative Bolitophagus reticulatus . Both species feed and breed exclusively in fruiting bodies of the wood-decaying fungus Fomes fomentarius .
2. The presence and status of flight wings, flight muscles, and mature eggs were determined by dissection. Flight willingness was studied in a field experiment, and flight duration in a flight-mill experiment.
3. Females of O. haemorrhoidalis had fewer but larger eggs in their abdomen than B. reticulatus females.
4. All beetles of both species had fully developed flight wings but a larger proportion of B. reticulatus than O. haemorrhoidalis had developed flight muscles.
5. Bolitophagus reticulatus was more willing to take off than O. haemorrhoidalis , however both species, especially O. haemorrhoidalis , were powerful fliers, with many individuals being able to fly several kilometres. Oplocephala haemorrhoidalis tended to make few flights of long duration whereas B. reticulatus made several, but mostly shorter, flights.
6. The results indicate that B. reticulatus has a suite of life-history traits that makes it better adapted than O. haemorrhoidalis to exploit the scattered trees with fruiting bodies present in managed forests. This may explain why O. haemorrhoidalis is restricted primarily to sites with a high density of suitable substrates that have been available continuously for a long time.     

Some aspects of overwintering in southern England of the mosquitoes Anopheles atroparvus and Culiseta annulata (Diptera: Culicidae)

Abstract. 1. Overwintering of the mosquitoes Anopheles atroparvus van Thiel and Culiseta annulata Schrank, both of which feed on blood throughout the year, is compared.
2 The aquatic stages, males and gonoactive females of A.atroparvus disappear before winter, leaving a generation of inseminated, nulliparous, diapausing females to overwinter. Blood meals taken by diapausing females merely serve to maintain fat reserves. After re-activation in March–April, gonoactive life expectancy appears to be rather short. Aquatic development at this season is slow and eggs laid in the spring do not significantly affect adult densities until June.
3. Aquatic stages, males and gonoactive females of C.annulata are present throughout the year. This species appears to be able to overwinter without recourse to diapause, females passing the winter in alternating, or lasting, states of cold-induced quiescence or normal gonoactivity.