Termination Of Reproductive Diapause Research Articles

Seasonal Reproductive Performance and Pre-diapausing Mating Status of Female Riptortus pedestris (Hemiptera: Alydidae) Collected in Fields.

Two unexplained phenomena are found in Riptortus pedestris (Fabricius) (Hemiptera: Alydidae): the first is that it tends to enter reproductive diapause much earlier in the season and to occur on host plants until late fall before finding hibernation site. The second is that they emerge in early spring when primary food sources such as leguminous plants are unavailable. To understand these phenological trends, the reproductive seasonality of both field-collected and laboratory-reared R. pedestris were compared under conditions of with/without food or access to mates. Females collected in spring or fall produced very few eggs in laboratory. But, when food sources were provided, all the bugs produced more eggs. Eggs also hatched normally except those produced by the females collected in fall. This indicates that females collected in the spring were already mated while those collected in the fall were not, most likely because they were in reproductive diapause. Similarly, when food was provided, all laboratory-reared bugs produced eggs, regardless of diapause status, with longer preoviposition period in diapausing bugs which might be due to the termination of reproductive diapause, but only eggs from mated females hatched. In conclusion, while spring reproduction (oviposition and egg hatch) of R. pedestris can occur in the presence of food resources, any lack of food can be limiting factor impeding these activities. In fall, reproduction is greatly reduced even when food resources are available, and under these conditions failure of females to become mated, due to reproductive diapause, is likely the limiting factor.

Dynamics of the Photo-Trophic Termination of Reproductive Diapause in Females of the Multicolored Asian Ladybird Harmonia axyridis (Pallas) (Coleoptera, Coccinellidae)

Females of certain aphidophagous ladybirds in the absence of natural protein food (aphids) enter reproductive diapause. Reactivation of diapausing beetles is possible only after consuming the food which is suitable for oogenesis of females and development of larvae. The influence of diet and photoperiod on the dynamics of weight and on the rate of reproductive maturation of reactivating females of Harmonia axyridis was studied under laboratory conditions. The experiments were conducted at combinations of two day lengths (12 and 18 h) with 6 trophic regimes with the following mean numbers of daily consumed aphids: 0 (aphids were absent over the whole experiment), 0.1 (1 aphid was provided every 10 days), 0.5 (1 aphid every second day), 1 (1 aphid every day), 10 (10 aphids every day), and 50 (about 50 aphids every day). Judging from the state of ovarian development estimated by dissection 20 days after the beginning of the experiment, the threshold of the trophic termination of reproductive diapause under the long day conditions lies between the regimes of 0.1 and 0.5 aphids per day, which is approximately equal to the earlier investigated threshold of the trophic induction of diapause. Short day slowed reactivation and has increased the threshold of the trophic response up to 1-10 aphids per day. Based on these data, we conclude that under natural conditions females which entered reproductive diapause because of the absence of aphids are capable of reactivation in the presence of even a minimal amount of natural protein food. Moreover, in spring and summer (when the probability of the increase in aphid abundance is relatively high) reactivation starts at lower prey population density than in autumn, when the appearance of the stable aphid colony (which is necessary to complete the development of the emerged larvae) is less probable.

Adaptive strategies of overwintering adults: Reproductive diapause and mating behavior in a grasshopper, Stenocatantops splendens (Orthoptera: Catantopidae)

To understand the adaptive strategies of the overwintering adults of Stenocatantops splendens, the mechanism of maintenance and termination of the reproductive diapause, the variation in mortality between overwintering females and males, and the mating strategy of the males were investigated. The results indicated that the adult reproductive diapause in natural conditions was mainly regulated by photoperiod in the fall - long photoperiods promoted reproductive development and short photoperiods maintained reproductive diapause, and the sensitivity of the overwintering adults to photoperiod was over before the end of the winter. When transferred from natural conditions to controlled laboratory conditions on dates from September through February, pre-oviposition became increasingly shorter with increasingly deferred transfer dates regardless of photoperiod conditions. The adults treated with low temperature for 30 days in September through November had significantly shorter pre-oviposition, suggesting that low temperatures in winter had an important role in the termination of reproductive diapause. The female had a significantly lower supercooling point than the male, which was related to their lower mortality after winter. In addition, observations of wild populations of the species indicated that mating behavior prior to winter and the duration of pre-mating period were not affected by photoperiod; mating and sperm transfer were mostly completed by November. Compared with females only mating before winter, females mating in the spring had shorter life span, longer pre-oviposition, lower hatching rate and laid fewer egg pods while showing no significant difference with regard to ovipositional interval, per pod number of eggs and nymph dry weight.

Different photoreceptor organs are used for photoperiodism in the larval and adult stages of the carabid beetle, Leptocarabus kumagaii

The role of the two distinct retinal photoreceptor organs in photoreception for photoperiodism was examined in the carabid beetle, Leptocarabus kumagaii, by surgical removal. This beetle shows long-day and short-day photoperiodic responses in the larval and adult stages, respectively. Larval diapause in the final instar is induced under short-day conditions whereas pupation occurs without diapause under long-day conditions. Adult reproductive diapause is terminated under short-day conditions but maintained under long-day conditions. The stemmata of the larvae and compound eyes of the adults were removed and the responses of the animals to photoperiod were compared to those of intact beetles. When all the stemmata were removed, larvae pupated without entering diapause under both long-day and short-day conditions, indicating that the larvae lacking stemmata were incapable of photoreception for photoperiodism. As in other holometabolous insects, the stemmata migrated into the brain during metamorphosis and remained rudimentarily in the optic lobe of the adult brain. However, these stemmata-derived organs were found to be no longer necessary for photoperiodism, because adults lacking the stemmata-derived organs responded to photoperiod normally. By contrast, removal of the compound eyes in adults resulted in the termination of reproductive diapause under both long-day and short-day conditions, indicating that photoreception for photoperiodism in the adult stage is performed by the compound eyes. Therefore, the site of photoperiodic photoreception in L. kumagaii appear to change from the stemmata to the compound eyes during metamorphosis.

Effect of photoperiod and temperature on reproductive diapause of Scotinophara lurida (Burmeister) (Heteroptera: Pentatomidae)

This study was carried out to investigate the effects of photoperiod and temperature on induction and termination of reproductive diapause in the black rice bug, Scotinophara lurida (Burmeister). Newly ecdysed fourth-instar nymphs and emerged adults of S. lurida adults did not enter reproductive diapause when reared at 30 °C in any photoperiod used. However, they exhibited the threshold photoperiod between 9 and 10 h at 25 °C and between 12 and 16 h at 20 °C adults overwinter in a state of reproductive diapause induced by short photoperiod and/or low temperature.

Termination of reproductive diapause in the rice water weevil with particular reference to the effects of temperature

The period of diapause termination in adults (collected in Yueqing 120.94°E, 28.14°N, Zhejiang) of the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), were determined by initially exposing diapausing adults to various constant temperatures (25–5°C) as well as to room temperatures (33–−1°C), and then transferring them at intervals to a climatically controlled chamber (26±1°C, using rice seedlings as adult hosts) where the dynamics of oviposition onset and the numbers of eggs deposited were observed. Under room temperature, the diapause in 1st- and 2nd-generation adults terminated around late September and early December, respectively, i.e. at ca. 2.5 and 2.0 months after collection. Diapause in both 1st- and 2nd-generation adults was significantly affected by temperature. When exposed to 10, 15 and 20°C, the diapause in most 1st-generation adults terminated after 75, 25 and 50 days, respectively, while in 2nd-generation adults it terminated after 50 days at each of these temperatures. The associated adaptive significance and geographical variation of diapause termination in this insect are discussed.

Overwintering strategy in Pyrrhocoris apterus (Heteroptera): the relations between life-cycle, chill tolerance and physiological adjustments

Seasonal dynamics of ecophysiological parameters are described which are relevant to overwintering in field-collected adults of a Czech population of the red firebug, Pyrrhocoris apterus. Five life-cycle phases were distinguished using the duration of pre-oviposition period as a criterion: reproductive activity (spring–early summer), intensification of reproductive diapause (RD) (peak of summer), maintenance of RD (late summer–early autumn), termination of RD (late autumn–early winter), and low temperature quiescence (LTQ) (winter). The supercooling capacity and chill tolerance (c.t.) increased simultaneously with the termination of RD and all three processes were triggered/conditioned by autumnal decrease in ambient temperatures. Maximum supercooling capacity and c.t. ‘outlived’ the end of diapause and persisted throughout the LTQ state. The limits of c.t. were estimated as −15°C/1–2 weeks for 50% survival. Ribitol, sorbitol, arabinitol, and mannitol were accumulated in the winter-sampled insects. Relatively low concentrations of polyols (dominating ribitol reached ca. 1% FW) indicate that they do not function as colligative cryoprotectants. However, because their seasonal occurrence coincided with the highest c.t., their non-colligative cryoprotectant effects would merit further study. Although the overwintering microhabitat of P. apterus is buffered, the temperatures may fall to −13°C during exceptionally cold winters and thus, the parameters of c.t. seem to be just appropriately tuned to the local overwintering conditions.