Effect of photoperiod and temperature on diapause in a Florida strain of the tropical warehouse moth Ephestia cautella

A photoperiodically-controlled diapause of the long-day, short-day type was identified in a brown-winged, yellow-eyed strain of Ephestia cautella (Walker). The proportion of larvae diapausing in very long photoperiods was less than in short photoperiods. The mean critical photoperiod, here defined as that photoperiod giving half the maximum percentage of insects that diapause in response to photoperiod at a given temperature, was between 12 and 13 hr for the long-day reaction at both 20 and 25°C. The principal sensitive phase occurred near the time of the last larval moult. The mean duration of diapause was 2–3 months at 20°C and slightly longer at 25°C. The optimum temperature for diapause development was near 15°C, all larvae pupating within 24 days after a 45-day exposure at this temperature. Diapause could be terminated whenever larvae diapausing at 20°C were exposed to as few as five long (15 hr) photoperiods at 25°C. Long photoperiods at 20°C, or short photoperiods (9 hr) at 25°C were less effective in terminating diapause.     

Factors governing the induction of diapause in Ephestia elutella and Plodia interpunctella (Lepidoptera)

Diapause in fully grown larvae of Ephestia elutella and Plodia inferpunctella was induced by low temperature and short photoperiods. Light intensities below 1 lx affected the induction of diapause in both species. At 20 and 25d?C, the critical photo-period for E.elutella was c. 14 h, and for P.interpunctella c. 13 h. The sensitive phase in both species occurred at about the time of the fourth larval moult. In E.elutella about seven short photoperiods were required for larvae to enter diapause. In P.interpunctella high population density during larval development increased the proportion of larvae entering diapause. The conditions inducing diapause in laboratory stocks, and in stocks collected from the field, were different. Laboratory stocks of both species did not enter diapause at 25d?C and required short photoperiods for diapause at 20d?C. Some larvae of the field stock of E.elutella entered diapause in constant darkness at 30d?C, the number being increased at low R.H., and almost all did in short photoperiods at 25°C. At 20T, most larvae of this stock entered diapause regardless of photoperiod, and at 15°C all did. In P.interpunctella up to one-third of larvae of the field stock entered diapause in short photoperiods at 25d?C, and all did if transferred to short photoperiods at 20d?C. In unheated premises, falling temperatures normally induce diapause in E.elutella each autumn, photoperiod only being important if temperatures are high. In P.interpunctella, photoperiod is a more important factor because it can override the effect of falling temperature to a greater extent than in E.elutella. In both species, however, different field populations may respond in different ways.     

Intra‐population genetic variation in diapause incidence of adult‐diapausing Tetranychus pueraricola (Acari: Tetranychidae)

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Induction and termination of diapause inOrius predatory bugs

Photoperiodic induction of reproductive diapause at 18°C was investigated in fourOrius [Heteroptera: Anthocoridae] species.Orius insidiosus (Say) displayed a long-day response with a critical photoperiod between L11:D13 and L12:D12. Diapause in this species was terminated rapidly when the temperature and/or the daylength were increased.Orius majusculus (Reuter) also displayed a long-day response. The critical photoperiod fell between L14:D10 and L16:D8. Diapause in this species was not terminated within 14 days when both temperature and daylength were increased. InOrius albidipennis (Reuter) no diapause could be induced at photoperiods varying from L8:D16 to L16:D8. InOrius tristicolor (White) a high proportion of diapause was found at all photoperiods tested. The effect of temperature on photoperiodic induction of diapause was studied inO. insidiosus at L10:D14. Diapause occurred at 18°C, 21°C and 25°C, but not at 30°C. Again, diapause was terminated rapidly after transfer to 25°C/L16:D8. Exposing only the nymphal instars 1–5 to short daylength was not enough to induce diapause in the whole population ofO. majusculus. Orius predatory bugs are used as biocontrol agents against western flower thrips,Frankliniella occidentalis (Pergande) [Thysanoptera: Thripidael, in greenhouses. The consequences of photoperiodic induction of diapause for the success of early season releases ofOrius are discussed.     

Temperature-dependent development, diapause and cold tolerance of Gratiana graminea, a potential biological control agent of Solanum viarum in Florida, USA

The objectives of this study were to examine temperature-dependent development, diapause and cold tolerance of Gratiana graminea Klug (Chrysomelidae), a candidate biological control agent of tropical soda apple, Solanum viarum Dunal (Solanaceae). Immature development was examined at six constant temperatures ranging from 15°C to 30°C. Diapause induction was determined by exposing adults to either long or short photoperiods at 20°C and cold tolerance was assessed by exposing adults to 0°C. G. graminea completed development at temperatures ranging from 20°C to 30°C. Linear regression estimated a lower temperature threshold of 11.7°C and 312 degree-days were required to complete development. Diapause was induced when adults were exposed to short photoperiods (10:14 L:D h) at 20°C. The lethal times for diapausing adults of G. graminea at 0°C (LT₅₀?=?19?days, LT₉₀?=?41?days) were two times higher compared to Gratiana boliviana Spaeth, a biological control agent already established in south and central Florida, USA. The presence of diapause and the greater cold tolerance suggest that G. graminea may establish and perform better than G. boliviana in northern Florida.     

Inheritance of photoperiodic induction of larval diapause in the Asian corn borer Ostrinia furnacalis

The Asian corn borer Ostrinia furnacalis (Guenée) enters facultative diapause as fully‐developed larvae in response to short‐day conditions. As a consequence of geographical variation in photoperiodic response, moths from Nanchang (28°46′N, 115°50′E) enter diapause in response to short day‐lengths (D strain), even at the high temperatures whereas moths from Ledong (18°47′N, 108°89′E) exhibit almost no diapause under the same conditions (N strain). In the present study, crosses between the two strains are used to evaluate the inheritance of diapause under different photoperiods at temperatures of 22, 25 and 28 °C. The moths, both reciprocal crosses and backcrosses, show a clear long‐day response, similar to that of the D strain, suggesting that the photoperiodic response controlling diapause in this moth is heritable. However, the critical day‐length for induction of diapause is shorter in hybrids than in the D strain. The N strain also shows a short‐day photoperiodic response at the lower temperature of 22 °C, indicating that the N strain still has the capacity to enter a photoperiodically‐induced diapause, depending on the rearing temperature. The incidence of diapause in all crosses is highest with D strain fathers or grandfathers and lowest with N strain fathers or grandfathers, indicating that the male parent has significantly more influence on the incidence of diapause of subsequent progeny than the female. The results obtained from all crosses under LD 12 : 12 h or LD 13 : 11 h photocycles at 25 °C show that inheritance of diapause in O. furnacalis does not fit an additive hypothesis and that the capacity for diapause is transmitted genetically in the manner of incomplete dominance.     

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.     

Photoperiodic induction of larval diapause and temperature-dependent termination in a wild multivoltine bruchid,Kytorhinus sharpianus

A wild bean weevil,Kytorhinus sharpianus Bridwell (Coleoptera: Bruchidae), has a multivoltine life cycle and enters a hibernal larval diapause at the fourth instar under a short daylength (Shimada & Ishihara, 1991). Here, we investigated their diapause incidence under different photoperiods at 24°C and 27°C. The critical photoperiods for diapause induction were 14.5 h at 24°C and 14 h at 27°C. The stages susceptible to diapause-inducing stimuli were estimated by transferring larvae of various instars from long days to short days and vice versa. Then we investigated the incidence of larval diapause. The sensitive stage was estimated to be from the third to early fourth instar. Though larval diapause, which was induced under a short daylength, was terminated only by increasing the daylength, the termination was more synchronized by an exposure to a low temperature followed by increasing temperature, irrespective of photoperiod.     

Effects of low temperature on diapause termination and body colour change in adults of a stink bug, Plautia stali

Abstract. Diapause adults of Plautia stali Scott maintained at 20°C under short day conditions (LD 12:12 h) were exposed to four temperatures of 5–20°C to examine the effect on diapause development which was assessed in terms of oviposition. Diapause adults kept at 20°C under short day conditions changed their body colour gradually from brown to green and started egg laying after a prolonged preoviposition period. Those transferred to either 10 or 15°C also showed colour change but did not lay eggs. Bugs exposed to 5°C underwent neither body colour change nor oviposition and died more rapidly than those kept at higher temperatures. When 30-day-old diapause adults were chilled at 5, 10 or 15°C for 30 or 60 days and returned to 20°C and long day conditions (LD 16:8 h), the preoviposition period varied primarily depending on the chilling, but not on the temperature. On the other hand, when 60day-old diapause adults chilled for 30 days were observed at 20°C and long day conditions, their preoviposition period tended to be longer as the chilling temperature was lower In this case, a temperature of 10°C appeared to intensify diapause. Therefore, the effect of chilling on diapause development varied depending on the age at which insects were chilled. When chilled bugs were transferred to short day conditions at 20°C, most females failed to lay any eggs and some turned green, then after a while, some green bugs changed to brown again. These results indicate that bugs remained sensitive to short day conditions even after a 60-day chilling at 10 or 15°C.     

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.     

Transgenerational phenotypic plasticity of diapause induction and related fitness cost in a commercial strain of the parasitoid Aphidius ervi Haliday

Diapause is an adaptation that insects have evolved to synchronize their life cycle with that of seasonal climatic changes and resources availability. However, cues for its induction are not always clear and, in some cases, a maternal effect may be involved. At the population level, just a part of the individuals may exhibit diapause with important consequences in terms of winter survival. Moreover, clear indicators of diapause state are difficult to identify. Diapause induction was thus investigated in the aphid parasitoid species Aphidius ervi Haliday (Hymenoptera: Braconidae) developing in the aphid Sitobion avenae (Hemiptera: Aphididae) at four crossed photothermal regimes (16 °C and 8 °C, 16:8 h L:D and 8:16 h L:D), and during 2 successive generations. We analyzed the reliability of changes in mummy color to assess for the diapausing state compared to dissections, and we measured parasitoid morphological and physiological traits. We observed that the proportion of dark brown mummies increased after one generation under low photothermal regime compared to other regimes. No diapause was recorded at 16 °C, 16:8 h L:D, while we observed 16.2% and 67.5% diapause incidence at 8 °C, 8:16 h L:D, at 1st and 2nd generation, respectively. Diapause induction is thus increased by short day-length conditions and low temperatures as well as by maternal effects. All parasitoid life-history traits (weight, size, fat content, water content, egg-load, and longevity) were affected by the photothermal regime and/or the generation. These results raise new questions on the environmental thresholds needed to induce diapause and on survival and adaptation potential of commercially available parasitoid strains in different environments.     

Effects of thermoperiod on photoperiodic determination of larval diapause in Ostrinia nubilalis

Some effects of thermoperiods on the photoperiodic determination of larval diapause in the European corn borer, Ostrinia nubilalis are reported. Thermoperiods and photoperiods were shown to interact to a highly significant degree in the induction of diapause. Diapause determination was found to be sensitive to the duration and temperature of the cryoscotophase of the thermophotoperiod; the thermophotophase characteristics exerted only minor influence. Cryoscotophase temperatures of 10°C or lower caused an unexpected increase in the apparent critical nightlength for diapause determination. A 0°C cryoscotophase effectively prevented the photoperiodic determination of diapause. Experimental investigation of the effects of 0°C cryoscotophases produced evidence that such low-temperature cryoscotophases may suppress the biological clock functions regulating the determination of diapause. Photoperiodic regimes in which 0°C pulses were inserted at successive points in 24-h cycle evoked responses suggesting that the early scotophase (saturation phase) was more strongly influenced by the low temperature pulse than was the later scotophase (scotonon); low temperature had little effect on the light-dependent processes (photonon) associated with the photophase.     

Termination and induction of diapause in the gypsy moth larval parasitoid, Apanteles melanoscelus

Diapause in Apanteles melanoscelus can be terminated by exposure of the diapausing last instar larvae within their cocoons to 5°C for a period of 8 or more weeks. Photoperiod has no consistent influence upon diapause termination, but is of paramount importance for diapause induction. At less than 16 hr light per day virtually all larvae diapause, and at 18 hr and above very few larvae diapause. By exposing different larval stages to different photoperiods it was found that older larvae were most sensitive to the light-dark cycle. It was also noted that cocoons of diapausing larvae are larger than those of non-diapausing larvae.     

Factors influencing the duration and termination of diapause in the Indian-meal moth, Plodia interpunctella

The influence of environmental factors on the duration of diapause in Plodia interpunctella larvae reared in short photoperiods at 20 or 25° C was examined, Diapause terminated most rapidly in long photoperiods at high temperatures. Pupation was more delayed, and mortality was higher, in darkness than in the presence of light. At 20° C, LD 16: 8 hastened diapause termination only slightly in unchilled samples. Chilling for 10 weeks at 10° C greatly reduced the duration of diapause at 20 or 25° C in constant darkness, and rendered LD 16:8 effective in terminating diapause at 20° C. In addition, the quite short duration of diapause under LD 16:8 at 25° C was further shortened by holding for 6–10 weeks at 10° C or below, or by holding in an outbuilding during winter. Holding diapausing larvae at 15 or 20° C proved less effective. Temperature rises from 20 to 25 or 30° C proved effective in terminating diapause. In one stock, the temperature at which diapause was induced influenced its subsequent duration. Lighting conditions during induction had less influence on duration than had temperature, and no difference occurred between pupation times of larvae reared at different population densities, Under all conditions tested, diapause lasted longer in a recently collected field stock than in a laboratory stock.     

La diapause facultative dePimpla instigator [Hymenoptera,ichneumonidae] I. Role de la photopériode

Résumé La diapause dePimpla instigator F. (Ichneumonide) s'installe au dernier stade larvaire, en réponse aux courtes photopériodes inférieures à 12 heures. Les photopériodes plus grandes entra?nent un développement continu. La période de sensibilité à l'induction photopériodique est située entre le 6^e et le 14^e jour avec un maximum entre le 8^e et le 11^e jour de la vie larvaire (à la température de 20°C). Toutefois aucune photopériode ne permet d'obtenir 100% de diapause. La diapause peut cesser sans qu'apparement aucun facteur externe soit nécesaire comme stimulus. Cette reprise spontanée du développement est étalée dans le temps suivant les individus (entre 3 et 7 mois). La diapause dePimpla instigator, F. a deux caractéristiques particulières: le pourcentage de males en diapause est toujours supérieur de 20 à 40% à celui des femelles, la levée de la diapause par les grandes photopériodes est très rapide. 12 jours en 16 heures suffisent à déclencher la métamorphose.

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Summary The diapause ofPimpla instigator occurs in the last larval stage in reponse to the short day photoperiods less than 12 hours. With longer photoperiods, no diapause occurs. The sensitivity period at photoperiodic induction extends between the 6 th and 14 th day, with the maximum between the 8 th and 11 th of larval life (at a temperature of 20°C). However the incidence of diapause never reaches 100%. Diapause may be interrupted without any apparent external stimulus. Such a spontaneous termination of the diapause may occur between 3 or 7 months, depending on the individual. The diapause ofP. instigator shows two characteristics: the percentage diapause is always from 30 to 40% lower in males than in females; termination of the diapause by long-day photoperiods is very rapid: 12 days of 16 hours light are sufficient to induce metamorphosis.

     

Diapause induction in the thrips predatorAmblyseius cucumeris [Acarina: phytoseiidae] under greenhouse conditions

The predatory miteAmblyseius cucumeris (Oudemans) is an important biological control agent for thrips in commercial greenhouses, but its effectiveness in fall and winter is limited by reproductive diapause induced under short day conditions. Influence of photoperiod and temperature on diapause induction was investigated to provide information for successful management of the predator. Under 8∶16 (L∶D) photoperiods and 22°C photophase temperatures, diapause incidence was inversely related to scotophase temperature, decreasing from 100% diapause at 15°C to no diapause at 21°C. In continuous darkness, diapause was induced by thermoperiods of 20∶10 and 22∶17 and 22∶17 but not 25∶15°C (T∶C) (8h thermophase). Critical daylength for inducing diapause under 22∶17°C (T∶C) was 12.45 h, which was consistent with the trend in diapause incidence in mites collected from an established greenhouse population September to November. MostA. cucumeris diapaused only when exposed to diapause inducing conditions throughout their juvenile development and none stopped laying eggs when transferred from nondiapause to diapause inducing conditions as adults. After 14 generations of genetic selection for a nondiapause strain, diapause incidence was 33.3%.      

Geographical variation in photoperiodic induction of larval diapause in the bruchid beetle, Bruchidius dorsalis: polymorphism in overwintering stages

The bruchid beetle, Bruchidius dorsalis Fahraeus (Coleoptera: Bruchidae), has a multivoltine life cycle and shows geographical variation of overwintering stages in Japan. Our previous study found that B. dorsalis enters larval diapause in the final instar under short photoperiods. In cooler areas, we observed that most individuals overwinter in the final larval stage in diapause, whereas beetles at different developmental stages (non‐diapausing young instars, diapausing instars, and adults) were overwintering in warmer areas. In this study, we investigated geographical variation in the photoperiodic response for induction of larval diapause at 20 °C (three populations) and 24 °C (two populations) to clarify the overwintering strategy of B. dorsalis. We observed that (1) diapause incidence at 20 °C changed sharply from ca. 100% to 0% with a change in photoperiod in all the populations, (2) critical photoperiod was longer at 20 °C in populations from cooler areas, and (3) critical photoperiod at 24 °C was shorter than at 20 °C and a fraction of the larvae did not enter diapause, even under short photoperiods. Overwintering stages estimated from these results were consistent with those actually observed in the field. This study indicates that the geographical variation of overwintering stages is likely to reflect adaptive diapause induction in each local environment.     

The effect of temperature and light conditions on diapause induction in a Korean population of Neoseiulus womersleyi Schicha (Acari: Phytoseiidae)

To determine the condition for diapause induction of a Korean population of Neoseiulus womersleyi, combinations of constant temperatures (14, 16, 18, 20 and 25 °C) and photoperiods (0, 8, 10, 12, 14, 16 and 24 h photophase) were used from egg to adult emergence. Diapause induction was determined by reproductive cessation of adult females. Lower temperature and shorter photophase resulted in higher diapause induction. Critical photophases for diapause induction were 10 and 12 h at 18 and 16 °C, respectively. Diapause-induced N. womersleyi adult females consumed significantly fewer eggs of the two-spotted spider mite, Tetranychus urticae, than non-induced females. Field monitoring of N. womersleyi showed that there was no egg-bearing female after 282 Julian date, while a model estimated complete diapause induction at 288 Julian date. Diapause of this predatory mite occurred approximately 2 weeks before diapause of its main prey, T. urticae, in Korean apple orchards. Further study perspectives are discussed relative to the spider mite biological control system in fruit orchards.     

Critical photoperiod and daylength threshold differences between northern and southern populations of the butterfly Limenitis archippus

Laboratory studies show that different photoperiods induce diapause in northern (Vermont) and southern (Maryland) larval strains of the butterfly Limenitis archippus. The northern strain responds to $\text{1}\text{2}\text{hr}$ longer photoperiod thresholds and critical ranges than does the southern one. These responses are correlated with geographic differences in the ambient photoperiod of the two localities. In this facultative diapausing species, third instar larvae construct hibernacula within the basal portions of tubular leaves spun with silk, when daylength approaches either 13·5 hr (Vermont strain) or 13·0 hr (Maryland strain). When reared in total darkness some larvae develop directly to fourth inszar without diapause, although mortality is high. Among both strains different broods exhibit different incidences of diapause. Reciprocal inter-strain hybrids show intermediate diapause responses, suggesting that larval diapause is under the control of multiple genes.     

Inheritance of the photoperiodic response controlling larval diapause in the blow fly,Calliphora vicina

Larvae of the blow fly Calliphora vicina R-D. (Diptera: Calliphoridae) display a diapause in response to the exposure of their parents to short photoperiods. Due to geographic variation in photoperiodic response, flies from a southern, English population show a long-day response to the fixed photoperiod of L:D 15.5:8.5 whilst flies from a northern population from Finland show a short-day response to the same photoperiod. Crosses between these strains have shown previously that diapause incidence is a maternal characteristic; here we demonstrate that the hybrid female offspring of such crosses are not intermediate between the two parental strains but show a photoperiodic response biased towards their maternal line. Thus not only are males unable to influence directly the diapause incidence among their offspring but the indirect effects of inheritance down the male line are weaker than down the female. Diapause duration, in contrast, is influenced by each parent in a similar manner. Diapause lasts longer in larvae with a greater admixture of northern genes regardless of whether they were maternal or paternal.