Genetic variability in the diapause response of the burnet moth Zygaena trifolii (Lepidoptera: Zygaenidae)

A high degree of phenotypic variability was observed in the diapause response of the burnet moth Zygaena trifolii. In this study, we show that the observed variability is partly based on genetic differences between individuals. In a selection experiment, the larval instar at which diapause occurs was changed within six generations. Diapause instars were dependent on the time of pre-diapause development of larvae, which varied considerably between larvae. A heritability analysis indicates that a part of the variability in development time is based on additive genetic variance. The maintenance of genetic variability in the development time and the diapause response of Z. trifolii is discussed in the context of spatially and temporally changing selection pressures.     

Effect of daylength and temperature on the larval diapause of the sunflower moth, Homoeosoma electellum

The effect of daylength and temperature on the regulation of the larval diapause of a central Missouri population of the sunflower moth, Homoeosoma electellum, was examined. Fully grown fourth-instar larvae exhibit a facultative diapause. Measurements of the effect of photoperiod on diapause induction revealed critical photoperiods of about 13 h 30 min light/day at 20°C, and between 11 h 45 min and 12 h light/day at 23°C. Third and fourth-instar larvae were shown to be the main sensitive stages for diapause determination. Daylength was also shown to be an important regulator of the rate of diapause development. A short day of LD 10:14 h permitted only a low rate of diapause development, whereas long days of LD 14:10 h and LD 16:8 h accelerated diapause development at 25 and 30°C. When long days were alternated with short days at 30°C the accelerating effect of long days on diapause development was not found. Systematic transfers of chilled diapausing larvae revealed an accelerated diapause development in groups transferred from 10 to 30°C LD 10:14 h, but diapause development was not accelerated in groups transferred from 10 to 30°C LD 16:8 h.     

Influences of daylength and temperature on the period of diapause and its ending process in dormant larvae of burnet moths (Lepidoptera,Zygaenidae)

The onset of larval diapause in the burnet moth Zygaena trifolii is clearly characterized by the larva molting into a specialized dormant morph. In a potentially bivoltine Mediterranean population (Marseille) two types of diapause can occur within 1 year: firstly, a facultative summer diapause of 3–10 weeks, and secondly, an obligate winter diapause, which can be lengthened by a period of thermal quiescence to several months in temperatures of 5°C. For the first time, three successive physiological periods have been experimentally distinguished within an insect dormancy (between onset of diapause and molting to the next non-diapause stage), using chilling periods of 30–180 days at 5°C, and varying conditions of photoperiod and temperature. These stages are: (1) a continuous Diapause-ending process (DEP); (2) thermal quiescence (Q); and finally, (3) a period of postdiapause development (PDD) before molting to the next larval instar. The result of transferring dormant larvae from chilling at 5°C to 20°C depended on the length of the chilling period. After chilling for 120–180 days, molting to the next instar occurred after 6–10 days, independent of daylength. This period corresponds with the duration of PDD. After shorter chilling periods (90, 60, 30 days and the control, 0 days) the period to eclosion increased exponentially, and included both the latter part of the previous diapause process and the 6–10 day period of PDD. However, photoperiod also influences the time to eclosion after chilling. Short daylength (8 h light / 16 h dark: LD 8/16) lengthened the diapause in comparison to long daylength (16 h light / 8 h dark: LD 16/8). Short daylength had a similar effect during chilling at 5°C, as measured by the longer time to eclosion after transfer. The shorter time to eclosion resulting from longer chilling periods (30–90 days) demonstrates that the state of diapause is continuously shortened at 5°C, and corresponds to the neuroendocrine controlled DEP. Presumably the DEP has already started after the onset of diapause. When chilling was continued after the end of the DEP, which ranged between 90 and 120 days, thermal quiescence (Q) followed (observed maximum 395 days). Different photoperiodic conditions during the pre-diapause inductive period modified diapause intensity (measured as the duration of diapause), in that a photoperiodic signal just below the critical photoperiod for diapause induction (LD 15/9) intensified diapause. Experiments simulating the summer diapause showed that PDD occurred in the range of 10–25°C. Higher temperatures (15 and 20°C) shortened the DEP at LD 16/8, so that at 20°C many individuals had already terminated diapause after 10–40 days and had molted after the 6–10 days of PDD. A temperature of 25°C unexpectedly lengthened the DEP to 110 days in several individuals. The ecological consequences and the adaptive significance of variation in the duration of the diapause are discussed in relation to the persistence of local populations predictably variable and rare climatic extremes throughout the year.     

Qualitative and quantitative studies on the compounds of the larval defensive secretion of Zygaena trifolii (Esper, 1783) (Insecta, Lepidoptera, Zygaenidae)

Beside the known existence of cyanoglucosides (linamarin and lotaustralin) and proteins the neurotoxin beta-cyanoalanine has been demonstrated for the first time in the defensive secretions of animals. It is proposed that beta-cyanoalanine is produced by metabolizing cyanide from the cyanoglucosides. The methanolic precipitated protein fraction contains high amounts of aspartic acid, glycine, alanine, leucine and serine, thus being similar to the composition of larval silks in Lepidoptera. The defensive secretion contains 85% water, 8% proteins, 7% cyanoglucosides, 0.3% beta-cyanoalanine and beta-glucosidase while beta-cyanoalanine-synthetase could only be detected in the haemolymph.     

Genital Morphology and Copulatory Mechanism in Zygaena trifolii (Esper, 1783) (Insecta,Lepidoptera, Zygaenidae)

The coremata and male genital structures together with the associated muscles of Zygaena trifolii are described and illustrated in detail. Of the female genitalia only the external parts are dealt with. The closure of the male coremata pouch was found to be effected by a special muscle. Mating pairs were quickly fixed while in copula and dissected afterwards in order to examine the mechanism of copulation. It turns out that the female is held by the male at three points: first, the gonopods (= valvae) grip the female abdominal tip laterally. Secondly, the praephallus together with the everted endotheca (= vesica) are tightly locked inside the female ductus bursae. Thirdly, female postvaginal structures become evaginated and are then held between the spined anellus and the eighth abdominal tergum of the male.     

温周期对不同地理种群棉铃虫幼虫发育及蛹滞育的影响

为了探明不同地理种群棉铃虫Helicoverpa armigera (Hiibner)对温周期的反应,本研究系统调查了棉铃虫广东广州种群(23.08°N,113.14°E)、江西水修种群(29.04°N,115.82°E)、山东泰安种群(36.15°N,116.59°E)和辽宁喀佐种群(41.34°N,120.27°E...     

Volatiles from the burnet moth Zygaena filipendulae (Lepidoptera) and associated flowers,and their involvement in mating communication

The burnet moth Zygaena filipendulae L. contains the cyanogenic glucosides linamarin and lotaustralin, which can be degraded to the volatiles hydrogen cyanide (HCN), acetone and 2‐butanone. Linamarin and lotaustralin are transferred from the male to female during mating and thus are considered to be involved in mating communication. Because volatile semiochemical cues play a major role in mating communication in many insect species, the emissions of HCN, acetone and 2‐butanone from Z. filipendulae are characterized in the present study, aiming to determine the interplay between the degradation products of cyanogenic glucosides and pheromones. The volatile emissions from Z. filipendulae and flowers inducing mating are measured using headspace solid‐phase micro‐extraction and gas chromatography‐mass spectrometry analysis. All Z. filipendulae life stages emit HCN, acetone and 2‐butanone. Virgin females show higher emissions than mated females, whereas mated males have higher emissions than virgin males. Hydrogen cyanide is only rarely detected in the course of male–female copulation. These observations indicate a role for the cyanogenic glucoside derived volatiles in female calling and male courtship behaviours, although not as a defence during copulation. Males rejected for mating by a female are accepted after injection of linamarin or lotaustralin, demonstrating that cyanogenic glucosides are also important for female assessment of the fitness of the male. Volatiles from flowers occupied during mate calling are also analyzed, and emissions from males and females result in the identification of novel putative pheromones for Z. filipendulae.     

Molecular biogeography of the arctic-alpine disjunct burnet moth species Zygaena exulans (Zygaenidae, Lepidoptera) in the Pyrenees and Alps

Aim The phylogeography of ‘southern’ species is relatively well studied in Europe. However, there are few data about ‘northern’ species, and so we studied the population genetic structure of the arctic‐alpine distributed burnet moth Zygaena exulans as an exemplar. Location and methods The allozymes of 209 individuals from seven populations (two from the Pyrenees, five from the Alps) were studied by electrophoresis. Results All 15 analysed loci were polymorphic. The mean genetic diversities were moderately high (A: 1.99; H_e: 11.5; P: 65%). Mean genetic diversities were significantly higher in the Alps than in the Pyrenees in all cases. F_ST was 5.4% and F_IS was 10%. Genetic distances were generally low with a mean of 0.022 between large populations. About 62% of the variance between populations was between the Alps and the Pyrenees. The two samples from the Pyrenees had no significant differentiation, whereas significant differentiation was detected between the populations from the Alps (F_ST = 2.8%, P = 0.02). Main conclusion Zygaena exulans had a continuous distribution between the Alps and the Pyrenees during the last ice age. Most probably, the species was not present in Iberia, and the samples from the Pyrenees are derived from the southern edge of the glacial distribution area and thus became genetically impoverished. Post‐glacial isolation in Alps and Pyrenees has resulted in a weak genetic differentiation between these two disjunct high mountain systems.     

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.     

Maternal temperature has different effects on the photoperiodic response and duration of larval diapause in blow fly ( Calliphora vicina ) strains collected at two latitudes

Abstract .The blow fly Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae) has a wide distribution across northern and temperate Europe. It has a facultative, maternally-induced larval diapause in response to short days. The photoperiodic response, measured at 15 and 20°C, of two populations was compared. A southern population (originating at 51° N) was sensitive to temperature at all daylengths; the incidence of diapause was greatly reduced at 20°C compared with 15°C. The photoperiodic response of a northern population (from 65° N) was sensitive to temperature only in long days; in short days (< 14 h of light) the response of this strain was identical at each temperature.
Variation in parental photoperiod and temperature were found to affect the duration of larval diapause, indicating a role for maternal effects in diapause intensity as well as incidence. However, the between-strain variation was greater than that within strains, indicating qualitative differences in diapause response. These differences may arise from the ecological conditions at the points of origin of the two strains. The northern strain from the harsher climate has a more intense diapause that follows a relatively temperature-insensitive photoperiodic response. In contrast, the southern strain has a shallow diapause and its photoperiodic response may be overridden by the experience of concurrent high temperature.     

Effect of an ecdysteroid agonist, tebufenozide, on the completion of diapause in susceptible and resistant strains of the codling moth, Cydia pomonella

Codling moth Cydia pomonella (L.) (Lepidoptera, Tortricidae) larvae kept under a short photoperiod enter a diapause which can be broken by exposure to 25°C following an extended chilling period. We investigated the effects of the ecdysteroid agonist tebufenozide on the diapause of this species, both on a laboratory strain susceptible to insecticides and two strains selected for resistance to diflubenzuron or deltamethrin. The treatment induced moulting by breaking diapause of the susceptible strain when applied at the end of the growth period, or by reducing the pre-emergence period when applied after chilling. The strains exhibiting resistance in the neonate instar were also resistant to the ecdysteroid agonist applied to diapausing larvae, indicating that mechanisms of resistance remained active during this arrest of development. High doses of tebufenozide were lethal for the most resistant insects, but neither reduced the pupation delay nor produced the larval-pupal moults which occur in the susceptible strain. As diapausing larvae of C. pomonella can be easily collected, the expression of resistance to tebufenozide both in the target instar, i.e. neonates, and during diapause may contribute to early detection of resistance to this insecticide in field populations.     

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.     

Geographic variation in photoperiodic diapause induction and diapause intensity in Sericinus montelus (Lepidoptera: Papilionidae)

Abstract Due to the risk of extinction and ornamental value of the swallowtail butterfly, Sericinus montelus Gray (Lepidoptera: Papilionidae) in China, knowledge about local adaptations is important for the conservation and economical utilization of the species. In the present study, photoperiodic diapause induction and diapause intensity of S. montelus populations from Jiamusi (46°37′N), Beijing (40°15′N), Zibo (36°48′N), Fangxian (32°36′N), Wuhan (30°33′N) and Huaihua (27°33′N) were characterized at 25°C. Logistic regression analysis revealed a significant population × hours of light interaction, confirming that photoperiodic responses varied among populations. The critical photoperiod was positively correlated with latitude and increased toward the north at a rate of about 1 h for each 6.67 degrees of latitude. Survival analyses indicated that survival time of diapausing pupae before adult eclosion differed significantly among populations at 25°C and 16 : 8 L : D h. The mean duration of pupal diapause was also positively correlated with latitude. Our study reveals geographic variation in the critical photoperiod for diapause induction and in diapause intensity of S. montelus. These results provide useful information for our general understanding about seasonal adaptation in insects and may also be used to predict how geographic populations respond to climate warming.     

The hormonal regulation of the larval diapause in the codling moth, Laspeyresia pomonella (Lep. Tortricidae)

The hormonal control of the facultative diapause of the codling moth has been investigated. The diapause can be divided into 4 phases or periods: (1) diapause induction by short-day conditions (SD) in young larvae, (2) initiation of the diapause in the early last larval instar by a high titre of juvenile hormone, (3) onset and maintenance of diapause with inactivity of the neuroendocrine system, as evidenced by the results of neck-ligation experiments, (4)termination of diapause by the production of ecdysteroid.Diapause-induced larvae pupated after spinning the cocoon, if the state of induction was changed by injection with the anti-juvenile hormone precocene II at the beginning of the last larval instar and subsequent results of neck-ligation experiments, (4) termination of diapause by the production of ecdysteroid. treated with juvenile hormone during the first 1.5 days after the last larval moult and subsequently reared under SD. Under LD, continuous application of juvenile hormone during the last larval instar and after spinning did not prevent the insects from moulting to either a supernumerary larva, a pupa or a larval-pupal intermediate. Termination of diapause, i.e. pupation, was achieved by injecting diapausing larvae with 20-hydroxyecdysone. Although juvenile hormone was found to have a prothoractropic effect in diapausing larvae, no pupal moult could be induced by the application of the hormone. Contrary to the hormonal situation before pupation of nondiapausing larvae, no juvenile hormone could be detected before or during the pupation of larvae after diapause.     

Termination of the facultative diapause in the codling moth, Laspeyresia pomonella (Lepidoptera, Tortricidae)

The abiotic factors regulating the termination of the facultative diapause of the mature larva of the codling moth, Laspeyresia pomonella (L.), are described. The termination of diapause under long-day conditions (LD) is influenced by: (i) the rearing temperature of the larvae during prediapause development, (ii) the duration of the preincubation period, i.e. the time for which the diapausing larvae remain under prediapause rearing conditions, (iii) the reactivating incubation, i.e. the period for which the larvae are chilled, and (iv) the complementary incubation (LD and, except in one experiment, 26°), i.e. the period after the chilling needed for the pupation of the insects. The complementary incubation is distinctly shorter if the prediapause development of the larvae takes place at rearing temperatures below 26°, i.e. 21° or 19°. The latter conditions led to 100% pupae and pupation could be accelerated by prolonging the preincubation period. In larvae reared at 26°, the prolongation of the preincubation period raised the rate of pupation to a maximum of only 56% and also caused higher mortality. On the other hand, diapause was terminated under short-day conditions if the temperature was raised to 26° after a rearing temperature of 19° and a preincubation period of 90 days.

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Beendigung der fakultativen diapause des apfelwicklers, Laspeyresia Pomonella (Lepidoptera, Tortricidae)

Zusammenfassung Es wurde untersucht, welche abiotischen Faktoren die Beendigung der fakultativen Diapause ausgewachsener Apfelwicklerlarven (Laspeyresia pomonella) steuern. Die Beendigung der Diapause unter Langtagbedingungen (LT) wird beeinflusst durch: 1. die Zuchttemperatur der Larven während der Prädiapauseentwicklung; 2. die Dauer der Präinkubation, d.h. die Zeit, während der diapausierende Larven unter Prädiapause-Zuchtbedingungen bleiben; 3. die Reaktivierungs-inkubation, d.h. eine Periode von 70 d, während der die Larven auf 4° gekühlt werden und 4. die Komplementärinkubation (LT und, ausser in einem Experiment, 26°), d.h. die nach der Kühlung bzw. dem Wechsel in der Photoperiode benötigte Zeitdauer bis zur Verpuppung. Die Komplementärinkubation ist deutlich kürzer, wenn die Prädiapauseentwicklung der Larven bei Temperaturen unter 26° stattfindet. Bei 19° verpuppten sich 100% der Larven, wobei der Zeitpunkt der Verpuppung durch die Verlängerung der Präinkubationszeit beschleunigt wurde. Bei Larven, die bei 26° gezüchtet wurden, erreichte die Verpuppungsrate lediglich 56% bei einer relativ langen Präinkubationsdauer, wobei deren Verlängerung auch die Larvenmortalität erhöhte. Nach einer Zuchttemperatur von 19° und einer Präinkubationsdauer von 90 Tagen konnte die Diapause unter Kurztagbedingungen beendet werden, wenn die Temperatur auf 26° erhöht wurde.

     

Termination of diapause in the Cinnabar moth (Tyria jacobaeae) by chilling

The effect of chilling time on the termination of pupal diapause was studied in the Cinnabar moth, Tyria jacobaeae L., Lepidoptera: Arctiidae. Chilling followed by a temperature of 20°C was effective in terminating diapause. Chilling for 120 days immediately after pupation yielded the highest percentage emergence and resulted in the shortest total pupal development time (162 days). A more natural treatment, a warm period before cold treatment, did not result in a higher percentage of emergence or in a shorter total pupal development time.During hibernation this species experiences two successive processes: diapause development during the first three to four months of cold, followed by a period of quiescence. Application of high temperatures in this latter period immediately starts morphogenesis. The impact of a relative humidity of 70% during the pupal stage for complete wing unfolding is demonstrated. The underlying mechanism of diapause is discussed.

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Résumé L'effet sur la levée de la diapause de différents régimes de température infligés aux chrysalides est étudié chez Tyria jacobaeae L. (Lepidoptera: Arctiidae). Une mise au froid suivie de hautes températures lève efficacement la diapause. Un refroidissement pendant 120 jours immédiatement après la nymphose entraîne le plus grand pourcentage d'éclosions et la durée totale du développement des chrysalides la plus courte (162.3 j). Un traitement plus naturel, une période chaude avant la période froide, n'entraîne pas un plus grand pourcentage d'éclosions ni une durée plus courte de développement.Il est proposé que durant l'hibernation cette espèce passe par deux processus successifs: un diapause durant les premiers trois ou quatre mois de froid, suivie d'une période de quiescence. Le transfert à des hautes températures pendant cette derpériode déclanche immédiatement la morphogénèse. L'influence d'un taux élevé d'humidité relative durant le stade chrysalide sur le déploiement complet des ailes est démontré. Le méchanisme de diapause sous-jacent est discuté.

     

The effect of temperature and light pulses on the induction of diapause in the Toyama strain of the Indian meal moth, Plodia interpunctella

Abstract.The photoperiodic response in Plodia interpunctella collected at Toyama (36.7°N) was of long-day type and highly sensitive to temperature. The critical photoperiod giving 50% diapause was between 14 and 16 h at 20°C, between 12 and 14 h at 25°C and between 6 and 8 h at 30°C. Effects of night interruption by a 2-h light pulse on the diapause response were examined at 25°C on different background photoperiods ranging from LD 12:12 h to LD 2:22 h. Percentage diapause was very low when the middle portion of dark period was interrupted, so that U- or V-shaped response curves were obtained with background scotophases longer than 12 h. In these curves, the descending slopes were less steep than the ascending slopes. The critical dark period measured from dusk to an interrupting light pulse was about 1.5 h longer than the critical dark period ( c . 10 h) in the normal photoperiodic response. The critical dark period from the interrupting light pulse to dawn, on the other hand, was not parallel to dawn but shorter than the normal critical period in LD 12:12 h and LD 10:14 h and longer than that in LD 7:17 h to LD 4:20 h, indicating that the priming effects of the light pulse might be under the influence of the photophase.     

The role of juvenile hormone in the larval diapause of the European corn borer,Ostrinia nubilalis

The possible role of juvenile hormone (JH) in the induction and termination of larval diapause in the European corn borer, Ostrinia nubilalis, was investigated using topical applications of both JH I and a JH mimic as well as by monitoring JH titers with the Galleria bioassay. Neither JH nor the JH mimic ZR515 was capable of influencing diapause termination when administered topically. The Galleria bioassay revealed little or no JH in the hemolymph of mid diapause (>30 days) insects, indicating no demonstrable role for JH in diapause maintenance. When ZR515 was administered to nondiapause, newly ecdysed fifth instar larvae the pupal molting cycle was delayed. By use of photoperiodic regimes we were able to show that the molting delay was not equivalent to diapause induction. The Galleria bioassay showed differences in JH titer profiles between diapause and nondiapause animals during the final larval stadium. The nondiapause insects showed titers that decline rapidly to trace amounts following the molt to fifth instar then rose prior to pupation. The diapause insects had generally higher titers and exhibited a more gradual decline after the molt. No evidence was obtained to support the hypothesis that JH plays a key role in the induction, maintenance, or termination of larval diapause.