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%.      

Temperature and photoperiod effects on dormancy status and life cycle parameters in Aedes albopictus and Aedes aegypti from subtropical Argentina

Aedes albopictus (Diptera: Culicidae) distribution is bounded to a subtropical area in Argentina, while Aedes aegypti (Diptera: Culicidae) covers both temperate and subtropical regions. We assessed thermal and photoperiod conditions on dormancy status, development time and mortality for these species from subtropical Argentina. Short days (8 light : 16 dark) significantly increased larval development time for both species, an effect previously linked to diapause incidence. Aedes albopictus showed higher mortality than Ae. aegypti at 16 °C under long day treatments (16 light : 8 dark), which could indicate a lower tolerance to a sudden temperature decrease during the summer season. Aedes albopictus showed a slightly higher percentage of dormant eggs from females exposed to a short day, relative to previous research in Brazilian populations. Since we employed more hours of darkness, this could suggest a relationship between day‐length and dormancy intensity. Interestingly, local Ae. aegypti presented dormancy similar to Ae. albopictus, in accordance with temperate populations. The minimum dormancy in Ae. albopictus would not be sufficient to extend its bounded distribution. We believe that these findings represent a novel contribution to current knowledge about the ecophysiology of Ae. albopictus and Ae. aegypti, two species with great epidemiological relevance in this subtropical region.     

Metabolic rate in diapause and nondiapause brown locust eggs correlated with embryonic development

Insects use dormancy to survive adverse conditions. Brown locust Locustana pardalina (Walk.) eggs offer a convenient model to study dormancy (diapause and quiescence), which contributes to their survival under arid conditions. The metabolic rates of developing nondiapause, diapause and quiescent eggs are compared in the present study using closed‐system respirometry. The embryo becomes committed to continue development and hatch or to enter diapause 6 days after the eggs are placed on moist soil. The metabolic rate of nondiapause eggs increases exponentially until hatching, whereas that of diapause eggs is low and stable. The metabolic rate of diapause laboratory eggs (1.9 ± 0.6 µL CO₂ mg^?1 h^?1) is significantly higher than that of field eggs (0.5 ± 0.3 µL CO₂ mg^?1 h^?1), although the ranges of metabolic rate overlap and the embryos are all in late anatrepsis. The metabolic rate of quiescent eggs is similar to that of diapause eggs but decreases with time. Low metabolic rates during arrested development allow eggs to persist over long periods before hatching.     

Resting stages in the life cycle of Eudiaptomus graciloides (Lill.) (Copepoda: Calanoida) in Lake Glubokoe

Seasonal changes in the abundance, age composition, vertical distribution, lipid and protein body content, development rates in the older copepodids (CIV and CV) and reproduction characteristics were studied in Eudiaptomus graciloides in the mesotrophic Lake Glubokoe (Moscow) region). Two periods of reproduction were observed: spring and late summer/autumn. The older copepodids, having accumulated lipid reserves during phytoplankton bloom, descended into the meta- and hypolimnion at the beginning of the summer. These copepods did not feed, but instead consumed their lipid reserves. A considerable delay in development (up to 40-60 days) of CIVs and CVs was found. The descended CIVs and CVs incubated under ambient temperature developed 4-5 times slower than their surface counterparts, while temperature dependence could only account for a 2-fold slow down. The descended copepods are believed to form a summer resting stock. In October, females began to produce resting eggs. The period of switching from subitaneous to resting egg production was very brief, not longer than 2-3 weeks. The percentage of subitaneous eggs produced in mid-October tended to increase when females were exposed to an increased photoperiod. At the beginning of February, latent eggs kept in a cooling container in the darkness started hatching. This process could be speeded up under natural photoperiod and increased temperature. The over-wintering population consisted largely of adults. Thus, E.graciloides includes three types of diapause in the life cycle: resting eggs, summer resting stage at CIV-CV, and overwintering adults.      

The natural history ofPetrobia (Tetranychina) harti (Ewing) andPetrobia (Mesotetranychus) tunisiae Manson (Acari: Tetranychidae) in the laboratory

Petrobia harti (Ewing) developed more rapidly, deposited more eggs and lived longer onOxalis corniculata than onO. articulata. No development took place on several other recorded host plants. In the field this mite was most abundant during early summer. Males made up less than 10% of the population, and no diapause eggs were seen in the field.Petrobia tunisiae Manson developed on various winter Gramineae, produced about 17 non-diapause eggs during its first generation and mostly diapause eggs in the second. A few diapause eggs kept in the laboratory and dipped in chloroform hatched even after 3 years. A summer diapause is postulated for this species.     

Effects of Blue Light Pretreatments on Internode Extension Growth in Mustard Seedlings after the Transition to Darkness: Analysis of the Interaction with Phytochrome

The effects of blue light (B) pretreatments on internode extensiongrowth and their possible interaction with phytochrome mediatedresponses were examined in Sinapis alba seedlings grown for11 d under 280 µmol m^–2 s^–1 of continuousblue-deficient light from low pressure sodium lamps (SOX). SupplementaryB (16 µmol m^–2 s^–1) caused no detectable inhibitionof the first internode growth rate under continuous SOX, butgrowth rate was inhibited after transfer to darkness. This effect,and the growth promotion caused by far-red bend-of-day' lightpulses were additive. The addition of B at 16 µmol m^–2s^–1 during 11 d, or only during the first 9 or 10 d orthe latest 0.75, 1 or 2 d of the SOX pretreatment caused approximatelythe same extent of inhibition after the transition to darkness.A single hour of supplementary B before darkness caused morethan 50% of the maximum inhibition. However, 24 h of lower fluencerates of B (4 or 7 µmol m^–2 s^–1) were ineffective.Covering the internode during the supplementary B period didnot prevent the response to B after the transition to darkness.Far-red light given simultaneously with B (instead of the SOXbackground) reduced the inhibitory effect of B. Above a given threshold fluence rate, B perceived mainly inthe leaves inhibits extension growth in subsequent darkness,provided that high phytochrome photo-equilibria are presentduring the irradiation with B. Once triggered, this effect doesnot interact significantly with the ‘end-of-day’phytochrome effect. Key words: Blue light, extension growth, phytochrome     

Bi- and trivoltine complex life cycles in a Kanto (Japan) population of a wild bruchid Kytorhinus sharpianus

The partial trivoltinism and overwintering of Kytorhinus sharpianus Bridwell (Coleoptera: Bruchidae) was studied in the Kanto district, Japan. The later in the summer eggs were laid by the first-generation adults, the higher was the incidence of larval diapause in the second generation. The incidence of diapause also fluctuated between years, influencing the abundance of third-generation larvae. A relatively large proportion of third-generation larvae did not attain the diapause stage by the beginning of winter. The diapause development of larvae in diapause was completed by mid-January. Immature larvae of the third generation also overwintered and emerged as adults in the spring.     

Altitudinal variation in life cycle syndromes of California populations of the grasshopper,Melanoplus sanguinipes (F.)

Summary Life cycles of California populations of the grasshopper, Melanoplus sanguinipes, varied along an altitudinal gradient. Temperature records indicate a longer season at low altitude on the coast, based on computation of degree days available for development, even though summer air temperatures are cooler than at high altitude; this is a result of warm soil temperatures. At high and low altitudes there was a high proportion of diapause eggs oviposited, while intermediate proportions of diapause eggs occurred at mid altitudes. The low altitude, and especially sea level, populations diapaused at all stages of embryonic development, while at high altitudes most diapause occurred in the late stages just before hatch. Diapause was more intense at high altitudes. One result of diapause differences was delayed hatching in the sea level population. Nymphal development and development of adults to age at first reproduction were both accelerated at high altitude relative to sea level. At lower temperatures (27° C) there was a tendency for short days to accelerate development of sea level nymphs, but not high altitude nymphs. In both sea level and high altitude grasshoppers, short days accelerated maturation of adults to onset of oviposition at warm temperature (33° C); there was little reproduction at 27° C. Population differences for all traits studied appear to be largely genetic with some maternal effects possible. We interpret diapause variation at low and mid altitudes to be responses to environmental uncertainty and variations in development rates to be adaptations to prevailing season lengths.     

Releasing primary dormancy in <Emphasis Type="Italic">Avena fatua</Emphasis> L. caryopses by smoke-derived butenolide

The effect of smoke and smoke-derived butenolide in releasing dormancy of caryopses (referred to as seeds) of the economically important weed Avena fatua L. was studied. Seeds of A. fatua are dormant after harvest. Both smoke-water and butenolide, applied continuously, removed dormancy in darkness at 15, 20 and 25°C and slightly at 30°C. Butenolide was very active at a concentration of 10⁻⁸ M. Butenolide at 10⁻⁸ M was also able to remove dormancy at 20°C when applied for 12 or 24 h at 4°C or for 3 to 24 h at 20°C. Sensitivity to butenolide decreased with longer preincubation times in water. This compound was less effective in releasing dormancy in the light than in darkness. Dormancy release by butenolide involves induction of cell-cycle activity just before coleorhiza protrusion. Stimulatory effects of smoke-water and butenolide were also observed in respect of seedling growth and vigor.     

Immunoreactive intensity of FXPRL amide neuropeptides in response to environmental conditions in the silkworm, Bombyx mori

In the silkworm Bombyx mori, the diapause hormone-pheromone biosynthesis activating neuropeptide gene, DH-PBAN, is a neuropeptide gene that encodes a polypeptide precursor consisting in five Phe-X-Pro-Arg-Leu-NH₂ (FXPRL) amide (FXPRLa) neuropeptides; DH (diapause hormone), PBAN (pheromone-biosynthesis-activating neuropeptide) and α-, β- and γ-SGNPs (subesophageal ganglion neuropeptides). These neuropeptides are synthesized in DH-PBAN-producing neurosecretory cells contained within three neuromeres, four mandibular cells, six maxillary cells, two labial cells (SLb) and four lateral cells of the subesophageal ganglion. DH is solely responsible, among the FXPRLa peptide family, for embryonic diapause. Functional differentiation has been previously suggested to occur at each neuromere, with the SLb cells releasing DH through brain innervation in order to induce embryonic diapause. We have investigated the immunoreactive intensity of DH in the SLb when thermal (25°C or 15°C) and light (continuous illumination or darkness) conditions are altered and following brain surgery that induces diapause or non-diapause eggs in the progeny. We have also examined the immunoreactivity of the other FXPRLa peptides by using anti-β-SGNP and anti-PBAN antibodies. Pupal SLb somata immunoreactivities seem to be affected by both thermal and light conditions during embryogenesis. Thus, we have been able to identify a close correlation between the immunoreactive intensity of neuropeptides and environmental conditions relating to the determination of embryonic diapause in B. mori.     

Estivation and hibernation of Pieris brassicae (L.) in southern Spain: synchronization of two complex behavioral patterns

 The large white butterfly, Pieris brassicae, has an unusually complex life-history in its southernmost range in Western Europe. This complexity results (1) from two developmental rests, a short-day induced hibernation and a long-day induced estivation response, and (2) from the exceptionally early appearance of the first adult generation in January/February and a subsequent winter diapause in some of their progeny. It was found that in spring and autumn, different generations are faced with critical photophases which induce hibernation or estivation, with the consequence that in five out of six generations per year, only some develop directly whereas the others enter a dormancy phase. To assess the implications of this high number of optional responses on the generation succession, the development time was studied at various photoperiods and temperatures. The results showed that a threshold response determines the duration of estivation. With unchanged summer conditions (daylengths ≥15 h) estivation lasts on average 18–19 weeks, while with autumn conditions (daylengths ≤14 h) it lasts only 7 weeks. A change of photophases from ≥15 h to ≤14 h terminates estivation within about 3–5 weeks, slightly depending on the pupal exposure time in summer conditions. The duration of estivation is not affected by temperature or by the photophases experienced by the caterpillars. The winter diapause lasts 18–19 weeks on average with winter conditions (12°C/10.30 h light), but only 8–10 weeks with late spring conditions (21°C/15 h light). These results were used to assess the effects on the population phenology, with the finding that despite the different developmental pathways, a desynchronization of the generation succession is largely prevented. Estivation, hibernation, and direct development at different seasons are well adjusted to a common phenological pattern of a continuously reproducing population. This pattern of activity covers a cryptic dormant subpopulation, and could not have been deduced by field observations. Received: October 3, 2001 / Accepted: October 3, 2002     

Selection for an optimal monovoltine life cycle in an unpredictable environment. Studies on the beetleCatops nigricans Spence (Col., Catopidae)

Summary Catops nigricans reproduces in the autumn. Pre-imaginal development is temperature-dependent and takes place during the winter, followed by aestivation in the early adult stage. This summer diapause is obligatory and temperature independent. It synchronizes the monovoltine life cycle with the annual cycle. In three populations collected near Kiel (54°22′ N, 10°6′ E), K?ln (50°54′ N, 7°6′ E), and Paris (49°25′ N, 2°20′ E), pre-imaginal development slowed and the duration of summer diapause decreased with increasing latitude. Synchronization of the critical breeding interval with the appropriate environmental conditions was achieved through temperature- and photoperiod-dependent sensitivity of ovipositing adults, through different thermal thresholds in eggs, larvae, and pupae, and through sensitivity to photoperiod in third-instars larvae.C. nigricans copes with the unpredictability of climatic conditions in different ways. The local populations have evolved a mean diapause length which probably adjusts the life cycle in most years to the optimal date for reproduction. The mean diapause length was 77 days for Kiel, 98 days for K?ln and 138 days for Paris at 10°C, short-day (=SD).C. nigricans also spreads the risk by varying diapause length. Amongthe progeny of single females the range of diapause duration covered about 70% of the total range of the whole population. The oviposition rate of females confined to subterranean life was the same as females confined to subterranean life was the same as in those living under the influence of a varying photoperiod.C. nigricans should therefore be able to live both in the litter layer of forests and also in the nests and galleries of small mammals.     

The Insect Growth Regulator Pyriproxyfen Terminates Egg Diapause in the Asian Tiger Mosquito,Aedes albopictus

The Asian tiger mosquito, Aedes albopictus, is a highly invasive mosquito species that transmits chikungunya and dengue. This species overwinters as diapausing eggs in temperate climates. Early diapause termination may be a beneficial strategy for winter mosquito control; however, a mechanism to terminate the diapause process using chemicals is not known. We tested the hypothesis that a hormonal imbalance caused by the administration of juvenile hormone analog would terminate egg diapause in A. albopictus. We tested the insect growth regulator pyriproxyfen on all developmental stages to identify a susceptible stage for diapause termination. We found that pyriproxyfen treatment of mosquito eggs terminated embryonic diapause. The highest rates of diapause termination were recorded in newly deposited (78.9%) and fully embryonated (74.7%) eggs at 0.1 and 1 ppm, respectively. Hatching was completed earlier in newly deposited eggs (25–30 days) compared to fully embryonated eggs (71–80 days). The combined mortality from premature diapause termination and ovicidal activity was 98.2% in newly deposited and >98.9% in fully embryonated eggs at 1 ppm. The control diapause eggs did not hatch under diapausing conditions. Pyriproxyfen exposure to larvae, pupae and adults did not prevent the females from ovipositing diapausing eggs. There was no effect of pyriproxyfen on diapausing egg embryonic developmental time. We also observed mortality in diapausing eggs laid by females exposed to pyriproxyfen immediately after blood feeding. There was no mortality in eggs laid by females that survived larval and pupal exposures. In conclusion, diapausing eggs were the more susceptible to pyriproxyfen diapause termination compared to other life stages. This is the first report of diapause termination in A. albopictus with a juvenile hormone analog. We believe our findings will be useful in developing a new control strategy against overwintering mosquito populations.     

Diapause in the calanoid freshwater copepod Eudiaptomus graciloides

The seasonal appearance and the intensity of diapausing-eggproduction in Eudiaptomus graciloides in five lakes of differentsize and trophic level were studied. In all lakes, diapausingeggs were produced in autumn. In the large mesotrophic lakeSelenter See, the population’s shift to the productionof diapausing eggs was more complete than in other lakes. Weexamined day length, temperature and food as proximate factorsfor the production of diapausing eggs with laboratory experiments.Eudiaptomus graciloides produced diapausing eggs in all treatments,but a significantly higher percentage of diapausing eggs wasfound under short day conditions except when algal food wasabundant and temperature was high. To investigate the adaptivesignificance of diapause in E. graciloides, we compared thesurvival of adult and juvenile at different temperatures forE. graciloides with Eudiaptomus gracilis, a sympatric speciesthat does not exhibit diapause. At 8°C, adult E. graciloidessurvived better than adult E. gracilis and exhibited reducedgut contents and accumulation of storage lipids, traits characteristicof adult diapause. Eudiaptomus graciloides nauplii did not reachthe copepodid stage at 6°C, but E. gracilis nauplii exhibitedhigh mortality and developed very slowly. We hypothesize thatadult diapause and production of diapausing eggs facilitatethe survival of E. graciloides during cold periods and enhancecoexistence with its congener, E. gracilis, in temperate zones.     

Diapause and prolonged development in the embryo and their ecological significance in two cicadas, Cryptotympana facialis and Graptopsaltria nigrofuscata

The seasonal timing mechanism of egg hatching was examined in two cicadas, Cryptotympana facialis and Graptopsaltria nigrofuscata, with different but overlapping geographical distributions. These species lay eggs in summer, and nymphs hatch in the summer of the following year after egg durations of 10-12 months. When eggs were maintained at 25 °C from oviposition, both the species entered embryonic diapause within 60 days irrespective of photoperiod, but at different developmental stages between the two species. The optimal temperature for diapause development was approximately 15 °C in both the species. The development rate for postdiapause morphogenesis increased linearly with temperature in the range of 20-27.5 °C in C. facialis, and of 15-25 °C in G. nigrofuscata. The lower development threshold and the sum of effective temperatures were computed as 14.3 °C and 715.3 day-degrees in C. facialis and 12.1 °C and 566.6 day-degrees in G. nigrofuscata, respectively. The hatching dates predicted by these large thermal constants accorded with the hatching dates observed in the field, i.e., late June and mid-July in G. nigrofuscata and C. facialis, respectively. Therefore, the high thermal requirements for postdiapause development compel the cicadas to hatch in summer.     

Characteristics of summer diapause in the onion maggot,Delia antiqua (Diptera: Anthomyiidae)

Characteristics of summer diapause in the onion maggot, Delia antiqua, were clarified by laboratory experiments. Temperature was the primary factor for the induction of summer diapause in this species. The critical temperature for diapause induction was approximately 24 degrees C, regardless of the photoperiod. At 23 degrees C, the development of the diapausing pupae was arrested the day after pupariation, when about 7% of the total pupal development had occurred in terms of total effective temperature (degree-days). The most sensitive period for temperature with regard to diapause induction was estimated to be between pupariation and "pupation" (i.e., evagination of the head in cyclorrhaphous flies). Completion of diapause occurred at a wide range of temperatures (4-25 degrees C): The optimal temperature was approximately 16 degrees C, at which temperature only five days were required for diapause completion. The characteristics of summer diapause in D. antiqua are discussed in comparison with those of summer dormancy in a congener D. radicum and those of winter diapause in D. antiqua.     

Role of photoperiod and temperature in the induction of overwintering pupal diapause in the spotted tentiform leafminer,Phyllonorycter blancardella

The role of photoperiod and temperature in the induction of overwintering diapause inPhyllonorycter blancardella (F.) (Lepidoptera: Gracillariidae) was examined in the laboratory and field using leafminers from commercial apple orchards in Ontario, Canada.P. blancardella exhibited a long-day response to photoperiod: long daylengths resulted in uninterrupted development whereas short daylengths induced diapause. The estimated critical photoperiod for diapause induction was L14.25∶D9.75. The larvae of leafminers destined to enter diapause took ca. 3× longer to complete development than the larvae of non-diapausing leafminers. The development prolonging effect of photoperiod decreased with decreasing daylength. Temperature modified the diapause inducing effect of photoperiod. At L14.25∶D9.75, diapause incidence was similar at 15 and 20°C but was lower at 25°C. Photoperiod also altered the normal relationship between development rate and temperature. At L14.25∶D9.75, the duration of larval development of diapausing leafminers was similar at 15, 20 and 25°C. Temperature alone is unlikely to have a role in the induction of diapause because leafminers exposed to natural late summer and fall temperature regimes and L16∶D8 did not enter diapause.     

Determination of effective light pulse and classical Bünsow experiment in the larval diapause of the Indian meal moth Plodia interpunctella

Plodia interpunctella Hübner (Lepidoptera: Pyralidae) comprises a model insect to analyse the photoperiodic time‐measuring system controlling its larval diapause. In the present study, the effective length of light pulse in night interruption experiments is determined at 25 °C. Various lengths of light pulse are tested by inserting them at the midnight of an LD 12 : 12 h photoperiod. When the light pulse is 15 or 30 min, the incidence of diapause is 86%. To inhibit the induction of diapause effectively, a light pulse of 1.75–2 h is needed. The incidence of diapause is 12% under an LD 12 : 5 : 2 : 5 h photoperiod. To determine the precise role of the light pulse, 2‐h light pulses placed at the midnight of an LD 12 : 12 h photoperiod are disrupted systematically by darkness. When a 2‐h light pulse is disrupted by 15 min of darkness, diapause is generally prevented (< 29%) regardless of the temporal position of darkness. Longer disruption by darkness induces diapause moderately (37–67%). A Bünsow experiment is also conducted at 25 and 20 °C, in which the main photophase of 12 h of light is combined with 24–72‐h scotophases scanned by a 2‐h light pulse. The photoperiodic cycle length tested, therefore, varies in the range 36–84 h. In each cycle length, the incidence of diapause fluctuates as the light pulse moves toward dawn. However, no regular and circadian changes in the percentage diapause are observed in relation to diapause determination.     

The effect of temperature on the development times of eggs,naupliar and copepodite stages of five species of cyclopoid copepods

The duration times of eggs, combined naupliar instars and of the different copepodite stages of five species of cyclopoid copepods — Acanthocyclops robustus, Cyclops vicinus, Diacyclops bicuspidatus, Mesocyclops leuckarti, and Thermocyclops crassus — were investigated at five different temperatures. The five species can be divided in two groups: two species, C. vicinus and D. bicuspidatus, adapted to cold water conditions and three species, A. robustus, M. leuckarti and T. crassus adapted to warm water conditions. The cold water species showed a faster egg development than M. leuckarti and T. crassus at 5–15 °C. The eggs and instars of the warm water species M. leuckarti tend to develop faster than those of the former two species at higher temperatures. A. robustus showed the shortest egg and instar development at 10–25 °C. The warm water species T. crassus produced no eggs at 10 °C and temperatures below. At higher temperatures (20, 25 °C) the egg and instar duration times were similar or longer than those of the other species. When cultured in total darkness a great part of the C_IV respectively C_V copepodites of the summer forms entered arrest and the percentage of copepodites that showed an arrest of development was highest at lowest temperatures. The present results are compared with data from literature and differences are discussed.