Diapause In Autumn Research Articles

Effect of Precipitation and Temperature on Larval Survival of Cephus cinctus (Hymenoptera: Cephidae) in Barley Cultivars.

Host plant traits strongly affect survivorship of insect herbivores, and host suitability is especially important for the wheat stem sawfly, Cephus cinctus Norton, which spends its entire egg, larval, and pupal periods in a single stem. Measuring larval survival inside stems from egg hatch through diapause-mediated dormancy is a potential measure of population size for the next year but is also useful in assessing effects of growing season precipitation and temperature. Larval growth is synchronized with host plant growth, and the larva cannot switch hosts. Thus, incorporating plant physiological time, as growing degree days (GDD), may yield a better prediction of larval survival. Therefore, we assessed wheat stem sawfly survival from early larval growth to the beginning of autumnal diapause in barley cultivars selected from across feed, forage, and two- or six-row malt groups. Field experiments were conducted in Gallatin and Chouteau counties, Montana, in 2016 and 2017. We used Kaplan-Meier estimation to assess larval survival among cultivars. We found that the survival of pre-diapause larvae was greatest in 'Hockett' (36.5%) and lowest in 'Celebration' (15.4%). Precipitation and temperature during the growing season affected temporal patterns for larval survival across study sites. Adjusting survivorship curves using site-specific GDD accumulation allowed cultivar-specific survivorship to be estimated more precisely for each site, despite differing environmental influences. Our findings suggest that measuring wheat stem sawfly survival across barley cultivars and standardizing by site-specific GDDs may provide better recommendations on barley cultivars that impede wheat stem sawfly population growth and reduce economic losses.

Adaptive significance of the recurrent photoperiodic response in a spring‐breeding carabid beetle, Carabus yaconinus

AbstractSeasonal changes in the photoperiodic sensitivity for reproduction in adults of a spring‐breeding carabid beetle, Carabus yaconinus (Coleoptera: Carabidae), were examined by transferring adults from outdoor to photoperiodic conditions in various seasons. Newly‐emerged adults transferred to the laboratory in September to December showed a long‐day photoperiodic response, but lost photoperiodic sensitivity gradually during winter. In late April, overwintered adults were not sensitive to the photoperiod, with females continuing to have mature eggs under both long‐day and short‐day conditions. In contrast, in late June and late July, the adults were sensitive to the photoperiod, with only those kept under short‐day conditions re‐entering reproductive diapause. This recovery of photoperiodic sensitivity appears to play a definitive role in maintenance of diapause in autumn for adults that have reproduced. The adults collected in late April regained photoperiodic sensitivity in two months even after being kept under unchanged conditions. Therefore, no environmental cue is required for recovery of photoperiodic sensitivity, which apparently recovers with the lapse of time. Our results suggest that the recurrent photoperiodic response is required in long‐living adults of C. yaconinus to regulate the timing of reproduction, and also indicate a difference in photoperiodic sensitivity in summer between overwintered and newly‐emerged adults.

Seasonal occurrence and diapause induction of a predatory bug Andrallus spinidens (F.) (Heteroptera: Pentatomidae)

AbstractThe bug Andrallus spinidens (F.) (Heteroptera: Pentatomidae) is a polyphagous predator of insect larvae, which is distributed in tropical and warm temperate zones worldwide. Seasonal occurrence and diapause induction of this bug were studied in a population in Miyazaki, southern Kyushu, Japan. The field research showed that A. spinidens produces three or four generations a year and is most abundant from mid‐summer to autumn. Reproductive activity of field‐collected adults decreased from late summer to autumn, indicating that this bug enters adult diapause in autumn. Only adults were found in early spring and these were reproductive. Laboratory experiments showed that, irrespective of photoperiod, adult diapause is induced at lower temperatures (≤22.5°C), whereas it is avoided at higher temperatures (≥25°C). Ambient temperature falls across the critical range from late summer to autumn. Thus, the bug clearly overwinters in adult diapause induced by low temperatures and this diapause is terminated during the course of winter.

Foraging Activity inPlebeia remota, a Stingless Bees Species, Is Influenced by the Reproductive State of a Colony

Colonies of the Brazilian stingless beePlebeia remotashow a reproductive diapause in autumn and winter. Therefore, they present two distinct reproductive states, during which colony needs are putatively different. Consequently, foraging should be adapted to the different needs. We recorded the foraging activity of two colonies for 30 days in both phases. Indeed, it presented different patterns during the two phases. In the reproductive diapause, the resource predominantly collected by the foragers was nectar. The majority of the bees were nectar foragers, and the peak of collecting activity occurred around noon. Instead, in the reproductive phase, the predominantly collected resource was pollen, and the peak of activity occurred around 10:00 am. Although the majority of the foragers were not specialized in this phase, there were a larger number of pollen foragers compared to the phase of reproductive diapause. The temperature and relative humidity also influenced the foraging activity.

Seasonal activity-profiles of enzymes involved in cryoprotectant biosynthesis in Pyrrhocoris apterus (Heteroptera: Pyrrhocoridae)

The activities of three enzymes involved in polyol biosynthesis (aldose reductase, AR; ketose reductase, KR; and polyol dehydrogenase, PDH) were studied in adult females of the linden bug, Pyrrhocoris apterus, collected from the field during 2005/2006. While the activities of three enzymes were low in reproductive females, activities greater by one or two orders were seen in reproductively arrested females. AR and KR showed similar seasonal trends in activity. Activities were low during diapause initation and later increased and stabilized during autumnal diapause development. Further increases of AR and KR activities were seen during low temperature quiescence and finally the activities sharply decreased during vernal resumption of direct development. The activity of PDH was relatively high (but fluctuating) during diapause, then decreased in quiescent insects and almost disapeared in reproductively active females. Insects collected in February were subjected to laboratory de-acclimation (exposure to high temperatures) followed by re-acclimation (exposure to low temperatures) which resulted in loss of activity in all three enzymes and no regain. High activities of AR, KR and PDH in reproductively arrested females thus conform well with their previously observed high capacity to synthesize and accumulate polyol cryoprotectants.

Life History Traits of <I>Pseudasphondylia rokuharensis</I> (Diptera: Cecidomyiidae) Affecting Emergence of Adults and Synchronization with Host Plant Phenology

To identify adaptive strategies of gall-inducing cecidomyiids, we studied the life history traits of Pseudasphondylia rokuharensis (Diptera: Cecidomyiidae), a univoltine species inducing fruit galls on a deciduous shrub, Viburnum dilatatum. Although univoltine gall midges that are associated with trees or shrubs are usually difficult to rear from immature stages under artificial conditions, we successfully reared P. rokuharensis from first instar to adult. Mature larvae entered diapause in autumn, and the diapause terminated after low temperature treatment (4 mo of incubation at 5 degrees C). The adults emerged within a shorter period of time than those without low temperature treatment. Thus, the diapause provides better synchronization of adult emergence in the spring. Because adults live for only a few days, this synchronization improves the chances of adults finding a mate. This is the first report on the mechanism of larval diapause termination for univoltine and tree- or shrub-associated gall midges. The numbers of days needed for adults to emerge under laboratory conditions after low temperature incubation were significantly different between two different localities. This result might suggest the possible existence of ecoclines in their life history parameters.

Voltinism and larval growth pattern in Coenagrion mercuriale (Odonata: Coenagrionidae) at its northern range margin

Voltinism and larval growth pattern were investigated in an edge-of-range population of Coenagrion mercuriale. Coenagrion mercuriale is semi-voltine in Britain and growth is inhibited in winter. The 2nd year group overwinters in a range of instars between the antepenultimate and final instar consistent with the early, asynchronous emergence pattern of this species. A facultative autumnal diapause in the penultimate instar is the most likely mode of seasonal regulation. The broad size distribution of larvae produced by this growth pattern was wider than that found in co-occurring populations of Pyrrhosoma nymphula, a spring species with synchronous emergence. The broad size distributions may lead to considerable intraspecific interference between C. mercuriale larvae. Sex ratio in the last three larval instars of C. mercuriale did not differ significantly from unity. A laboratory investigation of the effect of temperature and photoperiod on growth and diapause in C. mercuriale is recommended to determine whether high minimum temperature thresholds for development limit both the width of the temporal niche and microhabitat use by this species at its range margin.

Egg development and diapause: ecophysiological and genetic basis of phenological polymorphism and adaptation to varied hosts in the green oak tortrix, Tortrix viridana L. (Lepidoptera: Tortricidae)

Experiments concerned 8 tortrix populations associated with varied oak species. They showed that the egg development included a phase of diapause. Completion of embryogenesis at 20°C was used as a criterion for whether diapause was completed. Under semi-natural conditions diapause terminated in late autumn or early winter, then eggs developed continuously, without postdiapause winter quiescence, even in severe cold. The eggs from the populations associated with holm or cork oak completed diapause then hatched later than those from the populations associated with sessile or pubescent oak. Reciprocal crossbreedings confirmed that this phenological polymorphism was genetically determined. Under constant temperatures the physiological state of diapausing eggs, assessed by measuring their cold requirements to complete diapause by exposure to 8°C, varied gradually with increasing age. This diapause development was strongly temperature-dependent. Cold requirements of diapausing eggs were much higher in a late-hatching than in an early-hatching population. This explains the phenological polymorphism of the tortrix: the more eggs need cold, the later they complete diapause in autumn, and the later they hatch in spring. Egg cold requirements varied widely within populations too, which resulted in large variations in the date of diapause end among individuals. The date of egg hatch was influenced by the temperatures occurring during diapause and postdiapause, but apparently not by photoperiod.

Dormancy in the Strawberry Leafroller (Lepidoptera: Tortricidae)

A 2-yr study of strawberry leafroller, Ancylis comptana (Froelich), populations in central Iowa showed that short daylengths and low temperatures maintain diapause during autumn and that this autumnal diapause ends without a specific cue by the end of December. The completion of diapause does not require chilling. The postdiapause developmental rate of A. comptana is linearly related to temperatures between 14 and 30°C; adult emergence requires 154 degree-days (DD) above a lower thermal threshold ( t ) of 10.5°C. Field cage studies demonstrated that 50% emergence of adult A. comptana from overwintering larvae can be predicted accurately based upon the accumulation of approximately 150 DD > 10°C.

Diapause termination in eggs of the stonefly Arcynopteryx compacta (McLachland) in relation to dehydration and cold hardiness

In the alpine regions of Southern Norway, eggs of the stonefly Arcynopteryx compacta are oviposited in small streams and lake outlets. During ice enclosure, eggs avoid freezing by supercooling and lose about two-thirds of their water content by shrinkage due to osmotic outflux of body water. The eggs enter diapause in autumn at an early stage of embryogenesis. The termination of diapause in 50–55% of eggs kept at 3°C for 3 or 6 months, arises from the effect of chilling on diapause development. The dehydration, however, serves as a diapause-terminating cue. For water contents down to 41%, the termination of diapause seems directly correlated with the degree of dehydration. Treatments with juvenile hormone were also effective in terminating diapause. The termination may therefore be linked to a temporary elevation in juvenile hormone titre by dehydration. Fully hydrated eggs supercool to about −26.5°C, and withstand ice enclosure for 3 days at −22°C. The elevation of supercooling point, water content and depletion of thermal hysteresis-producing proteins correspond with the initiation of postdiapause development. Also ice-enclosure for 3 days at −15 and −18°C proved fatal at this embryonic stage. The loss of cold hardiness could not be related to termination of diapause per se. Eggs remained cold hardy at 3°C as long as the postdiapause development was prevented during the thermally controlled quiescence. The physiological and biochemical mechanisms which underlie adaptation to cold, however, are specific for an early stage of embryogenesis.

Interspecific and Geographic Variation of Diapause Intensity and Seasonal Adaptation in the Drosophila auraria Species Complex (Diptera: Drosophilidae)

Species of the Drosophila auraria complex entered reproductive diapause in autumn in response to short daylengths. Their diapause ended even at short daylengths without special stimuli. For D. auraria Peng, D. triauraria Bock & Wheeler and D. subauraria Kimura, duration of diapause was longer at a shorter daylength but such a relationship was not clear in D. biauraria Bock & Wheeler. High temperature or continuous illumination broke diapause but chilling had a small or no effect in terminating diapause. In outdoor cultures of D. auraria and D. triauraria, diapause was almost terminated by spring in individuals which had eclosed in early autumn, but not in most individuals which had eclosed in midor late autumn. Excluding D. biauraria (below), for sympatric populations D. subauraria had the deepest diapause, D. auraria had the shallowest one and D. triauraria had the intermediate one. It was proposed that the deeper diapause of D. subauraria or D. triauraria was an adaptation to the earlier start of its diapause in autumn. Also in these three species, diapause was deeper in northern populations. This variation may occur because northern populations enter diapause earlier and experience relatively longer daylengths which are less effective in maintaining diapause. D. biauraria had rather deep diapause compared with the other three species and this species did not show clinal variation in the diapause intensity. Key-words: Drosophila auraria species complex, reproductive diapause, diapause intensity, seasonal adaptation

Bovine Thelaziasis in Iowa

The prevalence of developing Thelazia nematodes in face flies (Musca autumnalis) was studied for 7 yr at a beef farm in central Iowa. Juvenile nematodes were not found among flies in reproductive diapause in autumn, nor among nulliparous, overwintered flies in spring, but only among actively reproducing insects. Thus Thelazia probably do not overwinter in face flies. A mean prevalence of 2.0% infected was recorded among flies in 7 fly breeding seasons. No heterogeneity in Thelazia prevalence was detected within fly breeding seasons. The frequency distribution of Thelazia among face flies by year of occurrence was homogeneous, with a mean of 2.75 larval nematodes per infected fly. Thelazia gulosa and T. skrjabini were recovered in necropsy from the eyes of bovines from central Iowa. Prevalence among fat cattle 18-27 mo old was 15%; among cows 3-15 yr old, prevalence was only 3%. Thelazia skrjabini was found in 29 eyes and T. gulosa in 4 eyes. Infections were randomly distributed among the eyes of subject cattle. The mean worm burden was 2.3 T. skrjabini and 12 T. gulosa per infected eye. Thelaziasis is clearly enzootic in Iowa.

Seasonal Synchrony of the Parasite Perilitus coccinellae1 and its Host Coleomegilla maculata2

Dormancy is significant in determining the seasonal interactions between the thelyotokous braconid parasite Perilitus coccinellae and its coccinellid host, Coleomegilla maculata . The parasite's autumnal diapause is maintained by short daylengths and it ends in 50% of the population by the winter solstice. Low temperatures are not required to terminate diapause. The autumnal-hibernal diapause of the host is maintained by short daylengths. By the end of Mar. the photoperiodic control of diapause ends in 50% of the beetles; subsequently temperature and availability of prey determine when oviposition begins. P. coccinellae parasitizes the overwintering C. maculata population twice: during Sept., before the beetles form overwintering aggregations, and again in spring after the beetles disperse.

Some Adaptations of Limnadia stanleyana King (Crustacea: Branchiopoda: Conchostraca) to a Temporary Freshwater Environment

Limnadia stanleyana King (Crustacea: Conchostraca) which inhabits temporary rainpools near Sydney, Australia, was studied to determine how it survives in this severe environment. Drying of the pools in which the species lives frequently kills its freeswimming stages, though eggs are drought-resistant (Bishop 1968). Eggs enter diapause in autumn and do not hatch during the cooler months of the year when the animals have a reduced chance of attaining sexual maturity before pools dry (Bishop 1967). Climate has further, more profound effects as the water level of pools is controlled by the local precipitation/evaporation ratio. Near Sydney the rainfall is irregularly distributed throughout the year and it is impossible to predict when a pool will fill or for how long it will contain water. This paper discusses some adaptations that enable the species to counteract this unpredictability of the environment. Conchostracans in a pool are frequently killed by drying before they can reproduce and the species has to withstand such population crashes if it is to survive in the pool. The following strategies are theoretical possibilities: (a) The species may recolonize the pool when this has dried and then refilled. (b) Some part of the population may be kept as a drought-resistant reserve in case the rest of the animals are killed by desiccation. (c) The species may evolve mechanisms by which it increases its chances of reproducing before the pool dries. Longhurst (1955) attributed the wide distribution of some species of Notostraca to the effectiveness of their eggs as dispersive agents. Proctor (1964) found that eggs of several branchiopods survived passage through the gut of waterfowl and were dispersed by them. Dispersal of eggs could result in recolonization of pools by L. stanleyana after drying had killed previous populations. Gillett (1955a, b) investigated a genetic mechanism that restrained some eggs of mosquitoes (genus Aedes) from hatching to form a reserve in case larvae were destroyed by premature drying of the habitat. (Aedes inhabit temporary pools and the eggs of some species are drought-resistant (Clements 1963).) Some branchiopods hatch only soon after their pool habitat fills with rain-water. This has obvious adaptive value as it maximizes the period over which post-embryonic stages can grow and reproduce thereby enabling the species to make the most effective use of the time the habitat is favourable. Hall (1959, 1961) concluded that development of eggs of Chirocephalus diaphanus Prevost (Anostraca) was inhibited in water deeper than 20 cm. Moore (1963) did not find that this was the case in Streptocephalus seali Ryder and Eubranchipus holmani (Ryder) (Anostraca). He suggested that eggs of these species