Postharvest disinfestation of diapausing and non-diapausing twospotted spider mite (Tetranychus urticae) on persimmons: hot water immersion and coolstorage

The mortality response of diapausing and non-diapausing twospotted spider mite (Tetranychus urticae Koch) on persimmons to hot water immersion treatments between 44 and 54 °C was examined, for potential as a quarantine treatment. The mean immersion time for mean 99% mortality (LT₉₉) of diapausing mites at 44 °C was 211 min, and this time decreased with increasing temperature to 3.6 min at 54 °C. Non-diapausing mites were found to be less tolerant to temperatures below 48 °C, with an estimated LT₉₉ of 102 min at 44 °C, but had similar thermotolerance above 48 °C. In 47 °C water the immersion time required to kill 99% of diapausing mites was estimated at 67 min. This time was not reduced by subsequent coolstorage at 0 °C for up to eight weeks. Rather, coolstorage had the effect of keeping mites alive, relative to LT₉₉ estimates calculated for mites stored at 20 °C. Similarly the thermotolerance of mites did not change with increased time in diapause, even though mites in diapause for 12 weeks had high control mortality. Hot water immersion appears to be a potentially useful disinfestation method for persimmons.     

Cold-Hardiness and Supercooling Capacity in Diapausing and Nondiapausing Stages of the Cabbage Root Fly Delia radicum

Supercooling point (SCP) values and cold-hardiness were measured in individual ontogenetic stages of Delia radicum (Diptera:Anthomyiidae) in various physiological states (winter diapause, summer quiescence, and normal development). Winter diapause-destined mature third-instar larvae had a lower SCP (-9.9 degrees C) than their nondiapause counterparts (-5.2 degrees C), and more of them survived exposure to -10 degrees C for 5 h to pupariation and adult emergence. Values of SCPs were equal in both diapause and nondiapause states of prepupal and pupal stages. The lowest SCP (ca. -20 degrees C) was found in the stage of phanerocephalic pupa (PCP) regardless of the physiological state. The cold-hardiness of PCP corresponded with a low SCP value only in diapausing pupae stored for 80 days at 3 degrees C and in pupae which had terminated their diapause and whose further development was inhibited by storage at low temperatures (3 degrees C). Such pupae survived exposure to temperatures close to their SCP (14 days at -17 degrees C). However, this high cold-hardiness was only acquired after some time and/or exposure to 3 degrees C, as the PCP at the beginning of diapause showed significantly impaired cold-hardiness despite the fact that their SCP was low. The cold-hardiness of nondiapausing PCP did not correspond at all to that of low SCP, as no pupa survived the exposure to -17 degrees C for 1 day; survival rates at temperatures of -13.5 and -10 degrees C were also remarkably lower than those in diapausing pupae. Cold-hardiness in D. radicum was closely connected with the diapause syndrome but the changes in SCP value corresponded rather with the ontogeny of this insect. Copyright 1993, 1999 Academic Press.     

Effects of acclimation and diapause on the thermal tolerance of the two-spotted spider mite Tetranychus urticae

The two-spotted spider mite, Tetranychus urticae, is a worldwide pest species that overwinters as diapausing females. Cold hardening is presumed to start during diapause development to ensure the successful overwintering of this species. To address this hypothesis, we compared cold tolerance between non-diapausing and diapausing females. We measured supercooling point (SCP) and survival to acute cold stress by exposing the mites at a range of sub-zero temperatures (from −4 to −28 °C for 2 h). The mean SCPs of non-diapausing and diapausing females were −19.6±0.5 and −24.7±0.3 °C respectively, and freezing killed the mites. Diapausing females were significantly more cold tolerant than non-diapausing ones, with LT₅₀ of −19.7 and −13.3 °C, respectively. Further, we also examined the effects of cold acclimation (10 d at 0 or 5 °C) in non-diapausing and diapausing females. Our findings indicated that diapause decreased SCP significantly, while cold acclimation had no effect on the SCP except for non-diapausing females that were acclimated at 5 °C. Acclimation at 5 °C enhanced survival to acute cold stress in diapausing and non-diapausing females, with LT₅₀ of −22.0 and −17.1 °C, respectively. Altogether, our results indicate that T. urticae is a chill tolerant species, and that diapause and cold acclimation elevate cold hardiness in this species.     

Effects of constant and changing temperature conditions on diapause induction in Helicoverpa armigera (Lepidoptera: Noctuidae)

The effects of photoperiod and temperature on the induction and termination of facultative pupal diapause in Helicoverpa armigera (Lepidoptera: Noctuidae) were investigated under laboratory conditions. Exposing H. armigera larvae to both constant and fluctuating temperature regimes with a mean of 25°C and 20°C resulted in a type-III photoperiodic response curve of a short-long day insect. The long-day critical daylengths for diapause induction were ten hours and 12 hours at the constant temperatures of 25°C and 20°C, respectively. Higher incidences of diapause and higher values both for the longer and the shorter critical photoperiods for diapause induction were observed at fluctuating regimes compared with the corresponding constant ones. At alternating temperatures, the incidence of diapause ranged from 4.2% to 33.3% and was determined by the temperature amplitude of the thermoperiod and by the interaction of cryophase or thermophase with the photoperiod. Helicoverpa armigera larvae seem to respond to photoperiodic stimuli at temperatures >15°C and <30°C; all insects entered diapause at a constant temperature of 15°C, whereas none did so at a constant temperature of 30°C under all the photoperiodic regimes examined. Although chilling was not a prerequisite for diapause termination, exposure of diapausing pupae to chilling conditions significantly accelerated diapause development and the time of adult emergence. Therefore, temperature may be the primary factor controlling the termination of diapause in H. armigera.     

Influence of photoperiod on low temperature acclimation for cold-hardiness in Drosophila auraria

ABSTRACT. Imagines of Drosophila auraria Peng, a reproductive diapause species, developed cold-hardiness at low temperatures to a greater extent when exposed to a diapause-inducing photoperiod (LD10:14 h) than when exposed to a diapause-preventing photoperiod (LD 16:8h). Imagines kept at 18°C, which was the temperature at which they were reared to eclosion, did not survive a test exposure to -5°C for 8 days regardless of age or photoperiod. When transferred to 10 or 5°C, either from eclosion or from 8 days after eclosion, the survival rate, on testing, rose with time since transfer and rose faster and higher with a photoperiod of LD 10:14h than with LD16:8h. Flies transferred to 15°C only showed improved ability to survive the test if they were kept in LD 10:14h. When cultured at 18°C to the age of 8 days after eclosion, diapause was terminated in about 30% of females even at LD 10:14h. In these post-diapause females the ability to develop cold-hardiness at lower temperatures was somewhat less than in the diapausing females, but apparently greater than in the non-diapause females. These results suggest that the physiological mechanism which promotes cold-hardiness under a diapause-inducing photoperiod is not directly linked to the process causing reproductive diapause.
In Sapporo, flies from a natural population became tolerant to cold in October when they entered diapause and daily mean temperature fell below 15°C and the light/dark cycle fell below LD 12:12h.     

Diapause induction in the codling moth, Cydia pomonella: effect of prediapause temperatures

The effect of four prediapause temperatures (18, 22, 26 and 30°C) on the photoperiodic response of the codling moth, Cydia pomonella (L.), was studied under controlled conditions. The highest rates of diapause were recorded, for all day-lengths, at temperatures of 22 and 26°C while relatively lower rates of diapause were elicited at 18 and 30°C. The same trend was demonstrated by projecting the values of the critical photoperiod which induces 50% diapause (=CPhP₅₀) over the prediapause temperature. The change in diapause incidence as a function of photoperiod, at all prediapause temperatures, exhibited a response characteristic of long-day insects, i.e. high rates of diapause at short days (12–13.5 h) and a decrease in diapause incidence at long days (14–15 h). The results for temperatures 22, 26 and 30°C support the view that lower prediapause temperatures enhance diapause induction, at a give photoperiod, while higher temperatures tend to avert or diminish the process. On the other hand, the low rates of diapause obtained at 18°C contradict this view. Nevertheless, high correlation was found between the laboratory evidence and field data, indicating the adaptability of the Israeli codling moth to subtropical climate.     

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.     

Some aspects of induction and termination of diapause in a Greek strain of the miteTetranychus cinnabarinus (Boisduval) Boudreaux, 1956 (Acari: Tetranychidae)

A Greek strain of the miteTetranychus cinnabarinus, collected from ivy (Hedera spec.) in Thessaloniki (41 °N), exhibits a facultative, imaginal diapause. Diapause is induced by photoperiod and the photoperiodic response is of the long-day type. The critical daylength is 12.5 h at 19 °C. A period of chilling is not necessary for the termination of diapause under long-day conditions. Diapausing females are sensitive to photoperiod at least during the first 11/2 month of diapause.     

Life-History Variation inChrysoperla carnea:Implications for Rearing and Storing a Mexican Population

A population ofChrysoperla carneafrom San Pedro, Coahuila, Mexico, showed phenological responses that differ from those of previously studied North American biotypes. Short daylengths that induce diapause in other biotypes resulted in low incidences of diapause in the San Pedro population. Diapause induction required a decrease in daylength (from long to short days). Constant long days produced variable reproductive responses, whereas an increase in daylength (from short to long day) resulted in high incidences of reproduction. Providing prey to adults that had been reared under short days consistently increased the incidences of reproduction. Storage of either diapausing or nondiapausing adults at low temperature (5°C) for 13 weeks yielded better survivorship and reproductive performance than in unstored (24°C) controls. For efficient production, the San Pedro population ofC. carneamay be reared either with an increase in daylength or with the regular intervention of a storage period. To induce diapause in individuals destined for storage, larvae may be reared under long-day photoperiod and the prepupae transferred to short days.     

Timing of diapause induction outside the natural distribution range of a species: an outdoor experiment with the bean bug Riptortus clavatus

The phytophagous bug Riptortus clavatus (Thunberg) (Heteroptera: Alydidae) produces two or three generations per year in Central Japan and overwinters in the adult stage. In bugs from the Kyoto population (35°00 N, 135°45 E), we studied (1) the effects of day-length on the nymphal and preoviposition periods under constant photoperiod at 20.5 °C, and (2) photoperiodic induction of adult diapause at 20.5 °C and under a combination of constant photoperiod and natural daily rhythm of temperature in the forest-steppe zone of Russia (50°38 N, 35°58 E). Then, we examined (3) the timing of diapause induction under quasi-natural conditions in the same region, far outside the species' natural geographical range. At 20.5 °C, the nymphal period in both males and females was significantly longer under regimes with shorter photophases than under those with longer photophases. The preoviposition period in females was significantly longer under the near-critical long-day regime L14:D10 than under typical long-day regimes (L15:D9, L16:D8, and L17:D7). The critical day-length for diapause induction was shorter under conditions of natural daily rhythm of temperature than those reported at constant 20, 25, and 30 °C. Under quasi-natural conditions in the forest-steppe zone, R. clavatus entered diapause in September, much later than the local populations of true bugs studied to date. This experiment showed that R. clavatus was maladapted to new environmental conditions: diapause was induced too late with the result that all or most nymphs hatched in late August or early September will die.     

Response of diapausing eggs hatching to changes in temperature and the presence of fish kairomones

It has been hypothesized that the production of diapausing eggs in Daphnia can be induced by fish kairomones. A population of Daphnia could survive severe predation using this predator avoidance strategy. However, in changing environments, diapausing eggs experience various temperature conditions, and hatchlings at emergence may be exposed to the same predation risks as their mothers. Therefore, staying in diapause or an immediate response upon hatching to available environmental information could be important for hatchling survival. For this study, we investigated the impact of water temperature (10, 15, 20, and 25°C) in the presence and absence of fish kairomones (Lepomis macrochirus) on the hatching success of resting eggs (D. galeata). Results show that no diapausing eggs hatched at the lowest temperature (10°C), and the highest hatch percentage occurred at 15°C. Although higher water temperatures reduced hatching success, diapausing eggs hatched more quickly. The number of hatchlings was significantly higher after exposure to fish kairomones, and this was more noticeable at higher temperatures (20 and 25°C). The present results suggest that the diapausing eggs were produced as a predator avoidance strategy in Daphnia; however, the presence of fish works as a positive signal to increase hatchlings when the diapausing stage is terminated.     

Photoperiodic and temperature control of diapause induction and colour change in the southern green stink bug Nezara viridula

Abstract. The effect of photoperiod and temperature on the duration of the nymphal period, diapause induction and colour change in adults of Nezara viridula (L.) (Heteroptera: Pentatomidae) from Japan was studied in the laboratory. At 20 °C, the developmental period for nymphs was significantly shorter under LD 10 : 14 h (short day) and LD 16 : 8 h (long day) than under intermediate photoperiods, whereas at 25 °C it was slightly shorter under intermediate than short- and long-day conditions. It is assumed that photoperiod-mediated acceleration of nymphal growth takes place in autumn when day-length is short and it is unlikely that nymphal development is affected by day-length under summer long-day and hot conditions. Nezara viridula has an adult diapause controlled by a long-day photoperiodic response. At 20 °C and 25 °C in both sexes, photoperiodic responses were similar and had thresholds close to 12.5 h, thus suggesting that the response is thermostable within this range of temperatures and day-length plays a leading role in diapause induction. Precopulation and preoviposition periods were significantly longer under near-critical regimes than under long-day ones. Short-day and near-critical photoperiods induced a gradual change of adult colour from green to brown/russet. The rate of colour change was significantly higher under LD 10 : 14 h than under LD 13 : 11 h, suggesting that the colour change is strongly associated with diapause induction. The incidences of diapause or dark colour did not vary among genetically determined colour morphs, indicating that these morphs have a similar tendency to enter diapause and change colour in response to short-day conditions.     

Geographic variation of diapause intensity in the spider mite Tetranychus urticae

Abstract. Eight strains of the spider mite Tetranychus urticae, originating from different localities in western and central Europe, with latitudes ranging from 40.5 to 60^oN, displayed marked differences in the period of chilling at 4^oC required for diapause termination under a diapause-maintaining short-day photoperiodic regime at 19^oC, to which the mites were transferred after the cold period. The higher the latitude from which the strains originated the longer was the period of chilling required for diapause termination, suggesting the presence of a gradient in diapause intensity, diapause being deeper the more northern the origin of the strains. Two strains originating from higher altitudes appeared to have a much deeper diapause than expected from their latitudinal origin. In addition, these two mountain strains showed mutual differences in diapause intensity, notwithstanding the fact that they originated from similar latitudes and altitudes; local climatic conditions probably act as strong selective forces with regard to diapause depth. All strains appeared to be sensitive to photoperiod during the period of diapause development. Diapause was quickly completed by a long-day photoperiod (LD 17:7 h), but was maintained by a short-day photoperiod (LD 10:14h). However, even under the latter regime sensitivity to photoperiod gradually diminished and eventually disappeared, thus leading to ‘spontaneous’ termination of diapause. The length of the period of diapause development, as measured by the sensitivity to photoperiod of diapausing mites, varied between strains; it was shorter in the southern strains and longer in the northern strains. The results indicate great variation in diapause intensity between strains, which is probably genetically determined and may have adaptive significance for this widespread species. When young females which had just entered diapause were kept for ever longer periods of time under the diapause inducing short-day regime at which they had been reared, before being transferred to the cold room, the duration of the period of chilling required for diapause termination was found to decrease proportionally in all three strains tested. These results suggest that intensification of diapause does not occur in T. urticae; diapause intensity seems to be highest at the beginning of diapause and to diminish gradually during diapause development.     

Coexistence of Tetranychus urticae (Acarina: Tetranychidae) with different capacities for diapause: comparative life-history traits

Summary Individuals of the two-spotted spider mite, Tetranychus urticae Koch (Acarina: Tetranychidae), with and without a capacity for diapause, coexist in central Japan. Diapause appears to be adaptive because females in diapause suffered less mortality than non-diapausing individuals when frozen at –24°C for more than 4 h. However non-diapausing females showed good survival up to 4 h of freezing. Active non-diapausing mites survived on rose leaves in Kyoto (35°N) throughout the winters of 1988–1989 and 1989–1990. Cultures of mites with low (LD) and high (HD) diapause capacities at 18°C and 9L-15D photoperiod were successfully selected from the rose population and from a population on chrysanthemum in Nara (34.4°N). Their life-history traits at 15, 20, 25 and 30°C were characterized. HD and LD mites from both populations were of similar ages at first reproduction at 15–30° C. However, at temperatures 20° C, HD individuals produced more eggs than LD individuals, resulting in higher fecundity and intrinsic rate of natural increase. These traits allow HD individuals, which stop breeding between October and April, to increase faster in summer than LD individuals. This provides a mechanism, together with climatic fluctuations, in maintaining the coexistence of diapausing and non-diapausing T. urticae in Kyoto where winter conditions are rarely lethal to the non-diapausing individuals.     

Behavioural response and winter survival of mated and unmated diapausing females of the Tetranychus atlanticus-urticae complex (Acari, Tetranychidae)

Behavioural responses were studied in mated and unmated females of a Dutch strain of the spider mite Tetranychus urticae which were destined to enter diapause. Observations were confined to the period between acquirement of the winter coloration by the females (a few days after the last moult) and their entering of artificial hibernation sites offered to the mites on the host leaves. Unmated females were found to stay longer on the leaf surface than mated females; they entered the hibernation sites significantly later than mated females. The delay in the search for hibernation sites shown by unmated females may be seen as a behavioural adaptation to enhance the chance of being fertilized before hibernation. Winter survival of mated and unmated diapausing females of the same strain of mites was studied both in the laboratory at a constant temperature of 2±1°C and outdoors under natural climatic conditions in Amsterdam during the winter of 1990–1991. Survival was high under both conditions for mated as well as unmated females; no significant differences in survival were found between both types of female. Observations on post-diapause females of Tetranychus atlanticus (a mite belonging to the T. urticae complex) sampled from strawberry fields near Moscow in spring, showed that at most 10% of the females of this natural spider mite population were unmated. Both mated and unmated females had survived winter temperatures of -28 to -30°C.     

Cold-hardiness and development of eggs of Rhopalosiphum insertum

Abstract. 1. The eggs of Rhopalosiphum insertum (Walker) showed a seasonal increase in cold-hardiness under field conditions. Their supercooling point fell from -35°C in November to below -40°C in January, then rose to-35°C or above by March.
2. Laboratory experiments demonstrated that both temperature and date affected cold-hardiness of the eggs. The supercooling points of eggs kept at 16 h photoperiod or in darkness did not, however, differ significantly.
3. Eggs brought from the field into warm, long-day conditions would not hatch until after mid-January. After this date, per cent hatch was significantly greater in 16 h photoperiod than in darkness; it did not differ between eggs kept at 5 or 0°C, but was reduced at -5°C.
4. It is concluded that eggs of Rinserturn are in diapause until mid-January, and that hatching rate and cold-hardiness are determined by separate environmental factors.     

Effect of hydration,photoperiod and temperature on diapause termination in eggs ofPetrobia (Tetranychina) harti (Acari: Tetranychidae)

Petrobia harti (Ewing) displays a facultative summer diapause in the egg stage. An adult female will lay only either diapause or non-diapause eggs throughout her life. In the laboratory, diapause eggs are laid by females which develop on detachedOxalis articulata leaves under long-day photoperiods and a relatively low temperature of 19±1°C.Diapause occurs in a stage of advanced embryonic development, in which the embryo appears U-shaped when observed from the egg's ventral side. Embryonic development ceased at this stage, and no further growth occurred when the eggs were kept under a relative humidity of about 70% in various photoperiod and temperature conditions. However, when the eggs were hydrated by placing them on wet cotton wool, development in some embryos (apparently in those which had completed their diapause development) proceeded beyond the U-stage at a rate similar to that in non-diapause embryos and the eggs hatched.Under LD 168 and 19±1°C or 26±1°C, the later from oviposition the period of egg hydration started, the higher the percentage of diapause termination. Under LD 168 and 26±1°C, diapause termination occurred mostly during the first week of hydration, while at 19±1°C mostly during the second and third week.At 26±1°C, in eggs hydrated 15 days but not 30 days from oviposition, the percentage of diapause termination was higher under a long-day than under a short-day photoperiod.Under LD 168, when the eggs were hydrated continuously from oviposition or starting 15, 30 and 45 days from it, the percentage of diapause termination was higher at 26±1°C than at 19±1°C.The percentage of diapause-laying adult females and the intensity of egg diapause were higher when the pre-imaginal mites grew at LD 1212 and 19±1°C, than when they grew at LD 168 and 26±1°C. This maternal effect on egg diapause intensity was expressed when the eggs were maintained at LD 1212 and 19±1°C but not at LD 168 and 26±1°C.     

Role of temperature in diapause response to fish kairomones in crustacean Daphnia

The effect of non-lethal thermal conditions on the diapause response to a simulated threat of fish predation was tested in the freshwater planktonic crustacean Daphnia magna.From an early developmental stage, female Daphnia were either exposed or not exposed to fish kairomones that notified of the threat of fish predation at the benign growth temperatures of 18, 22 or 26 °C. The proportion of females switching from the production of subitaneous to diapausing eggs and their rate of reproduction were recorded.Besides the faster development and more intense reproduction observed at higher temperatures, a smaller proportion of the females formed protective, diapausing eggs when exposed to fish kairomones than was the case in colder conditions. The production of diapausing eggs was not observed when the threat of fish predation was absent. These results indicate an interactive effect of fish kairomones and thermal conditions on diapause induction in D. magna.We interpret these findings in the context of strategies for the maximisation of reproductive success. The production of well protected diapausing eggs (which assures low yet stable gains under diverse thermal conditions) may be a more beneficial life history strategy at lower temperatures, where the chances of survival of active individuals until maturation and successful reproduction are low. Higher temperatures permit faster maturation and more intensive reproduction that may surpass numerical losses of active descendants due to predation, making diapause a less rewarding option.     

Photo-thermal regulation of diapause in Trichogramma piceum Djur. (Hymenoptera, Trichogrammatidae)

Interaction of the photoperiodic conditions of development of maternal females (day lengths of 2 to 22 h at 20°C) with the thermal regime of development of their progeny (temperature of 12 to 15°C at day length of 12 h) in determination of prepupal diapause in Trichogramma piceum was studied under laboratory conditions. At 15°C the diapause was practically absent. At lower temperatures, the proportion of diapausing prepupae was maximal (25% of larvae at 14°C, 70% of larvae at 13°, and 80% of larvae at 12°C) if the maternal females developed under short day conditions (10–12 h). When maternal females developed at day lengths of 18–20 h, diapause was rarely recorded at all temperatures, while ultra-short (less than 8–10 h) days also caused a decrease in the proportion of diapausing progeny. The right (ecologically important) threshold of this maternal long-day photoperiodic response was about 14–15 h independently of the temperature during the progeny development. These results make it possible to clarify the mechanism of the “maternal photoperiodic correction of the progeny thermal response.” Although the impact of the maternal photoperiodic response can be revealed only within a very narrow thermal range, the relative strength of the diapause-inducing effect of different day lengths is independent of the temperature regimen of the progeny development.     

Cold-hardiness: a component of the diapause syndrome in pupae of the flesh flies, Sarcophaga crassipalpis and S. bullata

ABSTRACT. Diapausing pupae of Sarcophaga crassipalpis Macquart and S. bullata Parker reared at 20 or 25C readily survive exposure to - 10C for at least 25 days. In contrast, non-diapausing pupae produced by a variety of means are consistently intolerant of the low temperature. Non-diapausing pupae are not immediately killed by exposure to -10C: pupae exposed to the low temperature for up to 3 days proceed with pharate adult development but ultimately die before adult eclosion. Unlike many temperate zone insects, diapausing flesh fly pupae do not require a period of chilling for induction of cold-hardiness, and the attribute of cold-hardiness cannot be separated from other features of the diapause syndrome. Some cold-hardiness is already acquired during the third larval instar: diapause-destined larvae exposed to -10C are more successful in pupariating than non-diapause-destined larvae of the same age.