Diapause Intensity Research Articles

Resonance in photoperiodic regulation of larval diapause in Ostrinia nubilalis

Nanda-Hamner experimental photoperiodic regimes (Xh dark-8h light, in which X was from 8 to 88 h) were employed to demonstrate circadian resonance in the induction of larval diapause in Ostrinia nubilalis. Measured in terms of per cent incidence of diapause, manifestation of circadian resonance was shown to be dependent upon ambient temperature; resonance was not apparent at a rearing temperature of 30°C, was equivocally detected at 25°C, but strongly manifested at both 19 and 22°C. The period of the circadian resonance was 24 h at each temperature, demonstrating temperature compensation. Circadian resonance was also demonstrated between duration of the scotophase of the rearing regime and the number of days of long days (8 h dark-16 h light, 30°C) required to terminate diapause. Such resonance was detected when the temperature of the rearing regime was either 19 or 22°C, but not at 25°C. The implications of resonance in photoperiodic determination of apparent initial intensity of diapause is discussed briefly.

Changing responses to temperature and moisture of diapausing and developing eggs of Allonemobius fasciatus (Orthoptera: Gryllidae)

A portion of the Allonemobius fasciatus eggs laid in September averated embryonic diapause when transferred from 20 to 27°C in the first 12 days, but this proportion decreased if the transfer was delayed until day 16 or 20. This response may be explained by the interacting effects of low and high temperatures on the two types of diapause: Incubation at 20°C decreases the incidence of summer diapause during early embryonic stages but increases the incidence of winter diapause at a later stage. The intensity of winter diapause at 20°C was greatly increased by a 5-day exposure to 27°C occurring around the diapause stage. Exposure of eggs in winter diapause to different temperatures indicates that the thermal optimum for diapause development is relatively high (16-11°C) at the beginning and decreases to 6°C later. In the field, diapause development occurred rapidly in autumn but slowly during the winter. A short exposure of eggs to dry conditions (4–6 days) increased the incidence of summer diapause at 30°C but a long exposure (≥ 15 days) terminated summer diapause. In this cricket, the effects of different temperature and moisture conditions on diapause regulation thus change during the course of morphogenetic and diapause development.

The in vitro biosynthesis and secretion of glycerol by larval fat bodies of chilled Ostrinia nubilalis

Fat bodies from diapausing fifth-instar larvae of Ostrinia nubilalis were incubated in vitro at 5 or 23°C in Grace's medium and the glycerol contents of the organ and incubation medium determined. Fat bodies from diapausing larvae chilled 3 weeks at 5°C secreted glycerol into the medium at 5°C at a net rate of approx. 0.75 nmol/mg fat body dry wt/h for at least 96 h while the tissue levels remained essentially constant. Depending upon the experiment, from 6 to 15 times more glycerol was produced in 24 h at 5°C by these fat bodies than by those taken from diapausing unchilled larvae and incubated at either 5 or 23°C. A minimal chilling period of 10–12 days was recognized as necessary for chilled larval fat bodies to demonstrate rates of glycerol synthesis greater than those of unchilled larvae and the lag showed a temporal correlation with changes in haemolymph glycerol concentrations. These results suggest that this response to chilling by O. nubilalis is relatively slow. While incubation, at 23°C, of fat bodies from previously chilled larvae did not result in cessation of glycerol secretion, the rate of its appearance in the culture medium decreased during the 24-h incubation period. Although the ability of chilled fifth-instar larvae to accumulate glycerol is not dependent upon the diapause state results show that clearance of glycerol from the haemolymph by rewarmed O. nubilalis is related to diapause intensity.

The effect of photoperiod on the development of Amblyomma triguttatum triguttatum (Acari: Ixodidae).

Different light regimens had no effect on preoviposition periods, egg prehatch periods, or larval molting success of Amblyomma triguttatum triguttatum at 25 °C and 2–3 mm saturation deficit. More than 85% of nymphs molted when exposed to 14 h of light daily; with shorter light regimens the percentage molting declined markedly. The mean premolt periods of nymphs were shortest with ticks exposed daily to 14 h of light and longest with 10 h; results with 12 h of light were intermediate. Diapause (lack of molting after 50 days postdetachment) did not occur in nymphs held under 14-h light regimens, but most underwent diapause when held at 10-h or 0-h light regimens. The intensity of diapause in nymphs was strongly affected by the light conditions they experienced both before and after engorgement.

Diapause Survival of Overwintering Populations of the Horn Fly, Haematobia irritans (Diptera: Muscidae), in South-central Texas

The horn fly, Haematobia irritans (L.), overwinters by diapausing as a pharate adult within the puparium. In south-central Texas the flies enter diapause in October and November. The peak in production of diapausing pharates occurs during the first 2 weeks of November, when there is an optimal combination of pupa production and diapause induction. Adult flies emerge from diapause from late February to early May. Those entering diapause later tend to emerge slightly earlier relative to the total spring emergence pattern, indicating a more intense diapause development. There is a substantial mortality due to pupa parasites of the genus Spalangia. The wasps overwintered within puparia of the host and entered quiescence coincident with onset of diapause in the fly.

Diapause in Platynota idaeusalis (Lepidoptera: Tortricidae): Effects of Temperature, Photoperiod, and Time of Inoculation in the Field on Diapause Termination

Termination of larval diapause in the tufted apple budmoth, Platynota idaeusalis (Walker), is a dynamic process in which insect development is influenced by both the nature and the timing of the various stimuli to which it is exposed. Parameters investigated in this study with respect to diapause termination included time of inoculation (egg hatch) in the field, temperature, and photoperiod. Each factor was shown to affect significantly diapause development in diapausing larvae. However, the magnitude of the effect of each consistently diminished as the season progressed. Comparisons of laboratory and field strains of P. idaeusalis, reared under similar conditions, showed no significant differences in their respective diapause responses to each of the factors investigated. Larvae inoculated out of doors earlier in autumn exhibited a less intense diapause than those inoculated later. Diapause termination was accelerated when larvae were exposed to higher constant temperatures and longer stationary daylengths, or both. Because natural temperatures rarely rise above 27°C (the optimum temperature tested for diapause termination) between November and March in North Carolina, larval diapause in P. idaeusalis is most likely terminated by increasing daylengths in the spring, with temperature acting as a modifying influence in the overall rate of diapause development.

Seasonal variation in embryonic diapause of the striped ground cricket, Allonemobius fasciatus

ABSTRACT. The incidence and intensity of embryonic diapause in the striped ground cricket, Allonemobius fasciatus DeGeer (Gryllidae), is influenced by the date of oviposition and the incubation temperature. At 20d̀C, embryos develop normally until the end of the appendage‐formation stage when diapause occurs. The intensity of ‘winter’ diapause at this stage is greatest in eggs laid early in the season. Incubation at higher temperature induces a different and earlier ‘summer’ diapause. The higher the temperature the earlier the stage at which this developmental suppression is imposed. At 27 and 30d̀C, some individuals develop without any interruption and hatch within 20 days. The proportion of these fast‐developing eggs is low in summer but increases towards the end of the laying season. In nature, this species is univoltine and precocious hatching before winter is unlikely.When embryos diapausing at an early stage at 27d̀C are transferred to low temperatures, they resume development and enter winter diapause. The time required to reach the winter‐diapause stage after transfer is inversely related to the temperature (30‐30d̀C). At 30d̀C, sunmer diapause is neither induced nor maintained.

Inheritance of diapause induction and intensity in Papilio zelicaon

Five generations of mass selection reduced “obligate” diapause, critical photo-period, and diapause intensity in a strain of the anise swallowtail, Papilio zelicaon Lucas. Reciprocal crosses made between the selected line and unselected uni-and multivoltine populations produced hybrids with diapause induction and intensity intermediate to parental values. The results suggest polygenic inheritance of induction and intensity. Differences in response between reciprocal hybrids indicate the presence of maternal effects on diapause induction. It is proposed that the genetic variance underlying the diapause trait and the switch to non-native host plants have facilitated the evolution of multivoltinism in P. zelicaon.

Altitudinal adaptation of the life cycle in Allonemobius fasciatus DeGeer (Orthoptera: Gryllidae)

Allonemobius fasciatus DeGeer maintains a univoltine life cycle with an embryonic diapause over an altitudinal gradient of as large as 1100 m. Hatching time differs by more than 1.5 months between the highest and lowest altitudes studied. Little or no genetic difference was detected between populations from different altitudes when physiological traits such as diapause intensity, postdiapause development, and nymphal development were compared in the laboratory. Photoperiod influenced the duration of the nymphal stage and the number of instars, compensating for the shorter growing season at higher elevations. This photoperiodic regulation of nymphal development would also serve as a mechanism synchronizing adult emergence within a population of this species.

Egg and larval diapause in two populations of Aedes geniculatus (Diptera: Culicidae).

Aedes geniculatus mosquitoes diapause either as eggs (mature embryos) or as 4th- (last-) instar larvae. Photoperiod and temperature effects on induction and termination of egg and larval diapause were studied in populations from near Orgosolo, Sardinia (MTSGIOV strain), and Brighton, England (SUSSEX strain). A percentage of each population undergoes “obligate” egg diapause. In the facultative diapause portion of the population, short-day photoperiods induced diapause, while long-day photoperiods maintained egg hatchability. Warm temperatures and long days were most effective in promoting a return to hatchability among diapause eggs. MTSGIOV had a relatively weaker embryonic diapause than SUSSEX. Larval diapause was induced by short-day, cool conditions and prevented by long days in both populations. Diapause was terminated by long days. Compared to MTSGIOV, SUSSEX larvae had a longer critical photoperiod for diapause induction, stronger diapause intensity (i.e., less easily terminated), and a greater sex-related difference in intensity. Sex-related differences were present in both the induction and the intensity of egg and larval diapause. Males were less likely to enter either diapause state and had a less intense diapause than females.

Pupal Diapause in Battus philenor (Lepidoptera: Papilionidae)

Environmental factors involved in the induction, maintenance, and termination of the pupal diapause of Battus philenor (L.) were examined. Induction is strongly temperature dependent. Higher temperatures promoted continuous development, although significant numbers of diapause pupae occurred at all temperatures studied. Photoperiod had little effect on diapause induction, but once in diapause, pupae were responsive to both temperature and photoperiod. Warm temperatures and long photoperiods were most effective in promoting diapause development. Pupae were sensitive to both length and directional change of photoperiod. Age influenced the effect of chilling on diapause pupae. Diapause intensity was relatively weak the first 3 weeks after pupation, peaked in 5- to 7-week-old pupae, and then gradually declined. Under controlled laboratory conditions, males were less likely to enter diapause than females. Male pupae had a less intense diapause than females and emerged sooner under all photoperiods tested.

Observations on the intensity of diapause and cold tolerance in larvae from twelve populations and two reciprocal crosses of the Indian meal moth, Plodia interpunctella

ABSTRACT. The duration of diapause in larvae of Plodia interpunctella (Hübner) (Lepidoptera, Pyralidae) was assessed at 20°C in LD 11:13. Mean times from hatch to pupation for diapausing larvae from different populations ranged from 88 to 236 days. Most non‐diapausing larvae pupated within 70 days at this temperature. Transferring diapausing larvae to 25°C and LD 9:15, or to 20°C and LD 15:9, 70 days after hatch reduced the subsequent mean time to pupation by 18–82% and 9–63% respectively. Only two population samples terminated diapause faster under LD 15:9 at 20°C than under LD 9:15 at 25°C. The mortality of diapausing larvae caused by 6‐ or 10‐week exposures at 5, 7.5 or 10°C was generally less than 25%. Hybrids produced from a reciprocal cross between a temperate and a tropical African stock survived well. For other stocks there was some correlation between survival and diapause intensity. The low temperature regime which resulted in the greatest shortening of pupation time after return to the conditions used to induce diapause, did not always coincide with the temperature permitting the best survival. Results, however, indicate that some individuals of all stocks but one from the tropics are likely to survive in the U.K.

Phenological adaptations of a colonizing insect: The southwestern corn borer, Diatraea grandiosella.

The developmental rate, critical photoperiod, and diapause intensity were determined for three populations of the southwestern corn borer, Diatraea grandiosella, from Missouri, Mississippi and Kansas. Mississippi larvae grew at the highest rate and Missouri larvae grew at the lowest rate. The zero developmental temperatures (°C) for the Missouri population were estimated from regression lines as follows: 10.5° (eggs), 10.8° (diapausing larvae), 13.3° (non-diapausing larvae) and 11.4° (pupae). The required heat units were: 85° (eggs), 588° (diapausing larvae), 333° (non-diapausing larvae) and 149° days (pupae). However, the observed low temperature limit for larval growth under constant temperature regimes was approximately 17°C.The critical day lengths for diapause induction observed at 25°C were: 15 h 11 min (Missouri); 15 h 20 min (Mississippi); and 15 h 22 min (Kansas). The photoperiodic response of the Mississippi larvae was more or less retained at 30°C, whereas the response of the Missouri larvae was completely suppressed at this temperature. Diapause was most easily terminated in the Kansas larvae. The most intense diapause was observed in the Mississippi larvae.Model seasonal life cycles of the three geographic populations were constructed using photothermograms. Although the models showed good agreement with the field situation for the Missouri and the Kansas populations, some unknown factor(s) remains to account for an extremely long critical photoperiod in the Mississippi population.

Larval Diapause in the Eastern Tree-Hole Mosquito, Aedes triseriatus1: Latitudinal Variation in Induction and Intensity

Larvae of Aedes triseriatus (Say) from 26 to 46°N latitude undergo 4th-instar diapause in response to short-day cool conditions. Both subtropical and northern populations have relatively greater incidence of continuous development at short photoperiods, whereas northern populations exhibit greater diapause at long photoperiods as well. Diapause intensity is relatively stronger in females and in the central area of the latitudinal range; intrapopulation variance is greatest at range extremes. The critical photoperiod (CP) for larval diapause increases only slightly with population latitude and much less than the corresponding CP increase for embryonic diapause. Embryonic diapause CP exceeds larval diapause CP, within populations, by at least 1 h from Atlanta, Ga., north, indicating that eggs are the primary overwintering stage. Larval diapause may be maintained in the North by the selective effects of unpredictable spring weather, whereas in southern populations having incomplete embryonic diapause, progressively milder winter conditions favor larval diapause and continuous development.

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.

STUDIES ON THE ADULT REPRODUCTIVE DIAPAUSE OF THE MONARCH BUTTERFLY,DANAUS PLEXIPPUS

Monarch butterflies obtained at monthly intervals during the annual adult cycle were held in summer conditions for 5, 10, and 20 days. Examination of these revealed in both sexes an adult reproductive diapause characterized by depressed growth of those reproductive organs sensitive to juvenile hormone. Diapause began for both sexes in late August or early September; female diapause ended in Dc cember while male diapause ended in November. Diapause intensity, maximal in September—October, appeared to be greatest in females. In summer conditions, reproductive tract growth in postdiapause females, but not males, was comparable to that observed in prediapause animals. Previously mated postdiapause, but not diapause, females showed a greater response to summer conditions than did virgins. Storing prediapause monarchs in winter conditions for up to 5 months did not induce diapause, indicating that diapause may be induced in a preadult stage. Diapause monarchs of both sexes responded to juvenile hormone with pronounced growth of the pertinent reproductive organs, suggesting that decreased production of juvenile hormone may be a characteristic of adult diapause. The possible ad vantages of diapause to the survival of the adult population are discussed.

Diapause Dynamics and Host Plant Suitability of Papilio zelicaon (Lepidoptera: Papilionidae)

The swallowtail butterfly Papilio zelicaon Lucas is generally univoltine in habitats where it feeds on native species of Umbelliferae. In lowland areas of California, where it uses introduced species of Foeniculum and Citrus, it is multivoltine. Diapause induction is primarily regulated by photoperiod. Long days ( > 14 hr light) prevent pupal diapause while short days (12 hr light) induce diapause. Critical photophase varies with latitude of the population, being longest (13.5 hr light) in central California multivoltine populations and shortest (12 hr light) in multivoltine populations from southern California. Univoltine populations had more than 50% diapause at the long photophase (14L) tested. Selection at 14L1OD, 23.5 C for low diapause in a laboratory stock originating from central California multivoltine females lowered the critical photophase from 13.5L to 13.OL. Diapause development and termination are primarily regulated by temperature. A sufficient period of chilling at the optimum 11 C temperature was necessary for maximum frequency of diapause termination. Numerous pupae from the low diapause stock eclosed without a chilling treatment, but virtually no progeny from field-collected females did so. Weaker diapause intensity in the low diapause laboratory stock and southern California populations suggests that linkage exists between the genetic controls regulating diapause induction and diapause termination. Diapause incidence in progeny from females which had diapaused was significantly greater than that in nondiapause females. Consequences of adult oviposition preference for Foeniculum vulgare were examined by comparing the suitability of Foeniculum for larval growth with another introduced but nonpreferred host, Conium maculatum. Conium was less suitable in almost all respects as a host plant, producing higher larval and pupal mortality, decreased pupal weights and an increased frequency of diapause.

Geographical variation of photoperiodic adult diapause in Drosophila auraria.

The variation of photoperiodic adult diapause was studied in Drosophila auraria strains originating in Japan at latitudes from 33.8 to 43.1°N. All the differently-located geographical strains showed a photoperiodic diapause. The critical daylength of these strains fell between 12 and 14h. The diapause intensity increases with an increase in latitudes. The duration of diapause was shorter at a photoperiod of 12 or 6h than at one of 10 or 8h in all the strains. This is because the photoperiod of 12 or 6h is less effective as a stimulus for the maintenance of diapause.

OCCURRENCE OF A TWO GENERATION STRAIN OF THE EUROPEAN CORN BORER, OSTRINIA NUBILALIS (LEPIDOPTERA: PYRALIDAE), IN QUEBEC

AbstractThere are now two strains of the European corn borer, Ostrinia nubilalis (Hübner), in Quebec. The strain normally found produces one generation while the more recently introduced strain produces two generations per year. Both strains have been characterized and compared with corn borer strains from Ontario and New York State. The two attributes of the recently introduced strain that promote the development of a second generation are (1) early emergence in the spring with less intense diapause and (2) a lower critical photoperiod for diapause induction. The latter characteristic allows pupation of first generation larvae. Field and laboratory tests on the pheromone response of adult male moths demonstrated that the origin of this recent introduction was New York State.

GENETICS OF DIAPAUSE INDUCTION AND TERMINATION IN THE EUROPEAN CORN BORER, OSTRINIA NUBILALIS (LEPIDOPTERA: PYRALIDAE), IN SOUTHWESTERN ONTARIO

AbstractGrowth rate, diapause incidence, and diapause intensity were different in two strains of corn borers found in southwestern Ontario. Crosses between these two strains demonstrated that growth rate was female sex linked while diapause incidence was male sex linked. The effect of these two characteristics on hybridization is discussed.