16L 8D Research Articles

Photoperiodic induction of reproductive diapause and life-history traits of a tortoise beetle, Laccoptera nepalensis (Coleoptera: Chrysomelidae), a range-expanding pest of southern origin

The tortoise beetle, Laccoptera nepalensis Boheman (Coleoptera: Chrysomelidae), is an important insect pest of the sweet potato, and is naturally distributed in southern to eastern Asia. The species has recently been expanding its range to the main islands of Japan, where it had previously not been distributed. In this study, the life-history traits of a local population in southern Kyushu, Japan were examined. The adults showed a long-day photoperiodic response at 20 and 25 °C with critical photophases of 13.97 and 12.52 h/day, respectively: female adults reared under long-day conditions laid eggs, whereas those reared under short-day conditions did not and entered diapause. When adults that had been reared under 16L–8D at 20 °C were transferred to 12L–12D at 20 °C, they ceased laying eggs. These results, together with the developmental threshold temperature and thermal constant obtained for each stage, suggest that the beetle overwinters in the adult stage in a state of diapause and produces a maximum of three generations per year in southern Kyushu.

Circadian rhythm of expression of core clock genes in the photosensitive pineal organ of catfish, Clarias gariepinus under different photoperiodic regimes

ABSTRACT Effects of different regimes of photoperiod (12L–12D, 16L–8D, 8L–16D, LL and DD) were studied on the circadian rhythm of expression of core clock genes (clock, bmal1, per1, per2, per3, cry1 and cry2) in the photosensitive pineal organ of air-breathing catfish, Clarias gariepinus during summer and winter seasons under both in vivo and in vitro conditions using qPCR. Our findings indicate that all major core clock genes are expressed in the photosensitive pineal organ of C. gariepinus, and exhibit significant circadian rhythm of their expression under both in vivo and in vitro conditions irrespective of photoperiods and seasons. However, photoperiods had season-dependent differential effects on mesor (24 h average), amplitude, and acrophase (peak) of the circadian rhythm of expression of the clock genes under both in vivo and in vitro conditions. Based on these findings, we suggest that the photosensitive pineal organ of the fish possesses internal autonomous clockwork composed of clock genes, and different photoperiods deferentially affect rhythm parameters of the rhythmic expression of the pineal clock genes in a season-dependent manner.

Food plant, larval bionomics, and diagnosis of the Alpine Silver-Y, Syngrapha ottolenguii (Lepidoptera: Noctuidae)

Information on the biology of the alpine moth, Syngrapha ottolenguii, is very limited. On the main island of Japan, Honshu, we determined a natural host plant of S. ottolenguii to be Empetrum nigrum in alpine fields; the larvae showed a characteristic nocturnal feeding behavior on this plant. During daytime, the moths hid in the lower layer of the dense E. nigrum shrub . S. ottolenguii exhibited a univoltine life cycle with hibernation at the second or third instar larval stage under deep snow, where the temperature stayed stable at 0 °C for about 6 months. They could be reared with a generation time of about 60 days on an artificial diet under 16L–8D at 20 °C. The larva was classified as a monosetose with subventral (SV) setae on the second and third thoracic segments.

Effects of temperature on the development and reproduction of the predatory bug Joppeicus paradoxus Puton (Hemiptera: Joppeicidae) reared on Tribolium confusum eggs

Abstract The development and reproductive capacity of Joppeicus paradoxus Puton (Hemiptera: Joppeicidae) reared on Tribolium confusum Jaquelin du Val (Coleoptera: Tenebrionidae) eggs, which is one of major pests of stored grain, were investigated at five constant temperatures (25, 28, 30, 32 and 34 °C), 70–80% RH and a 16L–8D photoperiod. The duration of pre-adult (egg to adult) stage ranged from 60.2 days at 32 °C to 142.9 days at 25 °C. Emergence rates were more than 55.6% at 25–32 °C, but only 27.2% at 34 °C. Female lifetime fecundity was greatly reduced at 34 °C, and reached a maximum at 30 °C. Female longevity ranged from 72.5 days at 28 °C to 118.5 days at 32 °C. The net reproductive rate ( R 0 ) and the intrinsic rate of natural increase ( r m ) were the highest at 30 °C. It was estimated that the optimum temperature conditions for population increase of J. paradoxus , when fed with T. confusum eggs, lie around 30 °C.

Life table and age-dependent reproduction of the predatory bug Orius niger Wolff (Heteroptera: Anthocoridae) at three constant temperatures: a demographic analysis

The predatory bug Orius niger Wolff occurs throughout Iran in various climatic zones. Because of its apparent adaptation to these different climates, it is being considered as a potential biological control agent of the pest Thrips tabaci Lind. in various crops in Iran. We measured the basic life-history parameters of O. niger on a diet of corn pollen and eggs of the moth Ephestia kuehniella Zeller at 3 constant temperatures (26, 29 and 32°C under 16L–8D) to assess the possibility of culturing this predator for mass releases. Bean pods were supplied as oviposition sites. The intrinsic rate of increase was 0.113, 0.127 and 0.157 daughters/female/day at 26, 29, and 32°C respectively. Analysis of the mortality of eggs, juveniles and adults suggests that the population growth rate is restricted most by juvenile mortality. This mortality is probably caused by cannibalism, the occurrence of which should therefore be minimized in mass cultures.

アカヒゲホソミドリカスミカメの休眠卵率の季節的な推移と休眠卵産下に関与する環境要因

Seasonal changes in egg diapause induction and the effects of photoperiod and temperature on egg diapause in the rice leaf bug, Trigonotylus caelestialium (Kirkaldy), were examined using a population in Joetsu, Niigata Prefecture. The bugs were reared from egg to adult at five temperatures, ranging from 22 to 34°C, combined with eight photoperiods, ranging from 9L–15D to 16L–8D. The critical photoperiod for egg diapause induction fell between 13L–11D and 14L–10D at 25°C. However, the females reared at 28, 31 and 34°C deposited a large proportion of non-diapause eggs even if the photophase was shorter than 14 h. When the females laying diapause eggs were transferred to 11L–13D at 31°C, the number of females laying non-diapause eggs increased gradually on and after five days. Therefore, it is concluded that the females reared at a high temperature from the egg stage produce non-diapause eggs regardless of the photoperiod, and that a high temperature at the adult stage causes females laying diapause eggs to deposit non-diapause eggs. Seasonal changes in the proportion of diapause eggs produced by females collected in the fields were examined for three years, from 1999 to 2001. In 1999 and 2001, the percentage of diapause eggs increased gradually in September. However, the percentage of diapause eggs produced by the females collected on 20 September, 2000, decreased to less than 10%. It is considered that this phenomenon was caused by high temperatures for 4 days in the previous week.

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Trissolcus plautiae is a solitary and dominant parasitoid of the brown-winged green bug, Plautia crossota stali. The development of immature stages of T. plautiae in the eggs of P. crossota stali at 25°C, 16L–8D and 50±10% RH was investigated. T. plautiae was comfirmed to have three larval instars, and the mandibles were the characteristic of the 1st-instar larvae. The developmental period in males and females was estimated at 16.4 (in hours) and 16.3 in eggs, 40.0 and 39.4 in the 1st instars, 15.8 and 18.5 in the 2nd instars, 48.1 and 57.3 in the 3rd instars, 16.9 and 20.8 in prepupae, and 118.6 and 152.1 in pupae, respectively. The volume of parasitoid eggs reached their maximum 18 h after oviposition, just before hatching. The body length of larvae increased till the end of the 2nd instar, and decreased slightly in the 3rd instar. The egg volume and the body length were not significantly different between males and females of T. plautiae. Adult males first emerged 264 h after oviposition, and females emerged 48 h later than males.

Effect of temperature on development of Theocolax elegans (Westwood) (Hymenoptera: Pteromalidae) parasitizing larvae of the maize weevil Sitophilus zeamais (Coleoptera: Curculionidae) in brown rice

The development and adult longevity of Theocolax elegans (Westwood) were investigated at six temperatures (20, 25, 28, 30, 32 and 35°C), 70–80% RH and a 16L–8D photoperiod. Fecundity was also investigated at 25°C and 30°C. The hosts were larvae of Sitophilus zeamais Motschulsky reared on brown rice. As the temperature was increased from 20°C to 32°C, the developmental period decreased from 54.4 to 16.2 days for females and from 53.8 to 15.6 days for males. The developmental period at 35°C was longer than at 32°C. Males developed faster than females. Adult longevity decreased with increasing temperature from 14.5 to 4.5 days for females and from 20.6 to 3.6 days for males. The mean number of progeny produced per female over a lifetime was 161.0 at 25°C and 110.1 at 30°C. The intrinsic rate of natural increase (rm) was 0.131 females per female per day at 25°C and 0.169 females per female per day at 30°C.

Effects of temperature on oviposition and development of Amphibolus venator (Klug) (Hemiptera: Reduviidae), a predator of stored product insects.

The egg production and development of Amphibolus venator (Klug) were investigated at five temperatures (25, 27.5, 30, 32.5 and 35°C), 70% r.h. and 16L–8D photoregime. The optimum temperature for multiplication and development of A. venator was around 32.5°C. Pre-oviposition period decreased with increasing temperature. Temperature in the range 25–35°C had no effect on oviposition period. The average numbers of egg laid per ovipositing female increased with increasing temperatures, however differences were not significant. The percentages of ovipositing females at 32.5 and 35°C were the same (95.8%), but higher than in other temperatures. Total oviposition number was highest at 35°C. Egg incubation period decreased with increasing temperature, however, hatchability was not affected. The development period of nymphs decreased with increasing temperature. The lower developmental thresholds and total effective temperatures were calculated as 16.9°C and 126.6 degree-days for eggs, respectively. The corresponding values for nymphs were 20.7°C and 714.3 degree-days.

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Life history parameters of apterous viviparous Myzus persicae reared on qing-geng-cai were measured at constant temperatures of 15, 20, 25 and 30°C under a 16L–8D photoperiod. Mean developmental times from 1st instar to adult emergence decreased as the temperature increased. Survival rates were over 90% at all temperatures and showed no significant difference between each temperature. The lower developmental threshold and total effective temperature were calculated as 5.6°C and 113.1 degree-days. The adult fertility and longevity reached a maximum at 20°C, but the intrinsic rate of population increase was highest as 0.420 at 25°C.

Effect of light condition on the insecticidal activity of BT (Bacillus thuringiensis) formulations to the silkworm, Bombyx mori (L.).

The insecticidal activity of BT (Bacillus thuringiensis) formulations to the silkworm, Bombyx mori, reared under dark conditions was reduced significantly when the insects were reared under two different light conditions (80–120 and 1,500–2,000 lx: 16L–8D). The neonates reared with no illumination showed significantly lower sensitivity (20.7% mortality) than insects reared under the two illuminated conditions (50.3 and 52.1% mortality, respectively) (p>0.05). The LC50 of BT to insects reared under dark conditions (3.77 μg/g diet) was lower than for insects reared under the two light conditions (2.57 and 2.45 μg/g diet, respectively). These results strongly suggest that a protocol for rearing insects under dark will conditions reduce the insecticidal activity of BT formulations, and it is not appropriate to evaluate natural sensitivity to BT formulation of insects reared under dark conditions.

Life history parameters during immature stage of Aphidius gifuensis Ashmead(Hymenoptera: Braconidae) on green peach aphid, Myzus persicae(Sulzer)(Homoptera: Aphididae).

In order to evaluate the efficiency of an indigenous aphid parasitoid Aphidius gifuensis as a biological control agent against Myzus persicae, its oviposition rate, developmental time and survival rate on M. persicae were investigated in the laboratory. The oviposition rate was 84.9% at 25°C, and no aphids in which more than one A. gifuensis progeny were oviposited by one A. gifuensis female were observed. The survival rates and developmental times of immature A. gifuensis were examined at four constant rearing temperatures of 15, 20, 25 and 30°C with a photoperiod of 16L–8D. The survival rates from egg to adult emergence were more than 80% at all temperatures tested. The developmental times decreased with increasing temperatures in both sexes, except that the periods at 30°C were slightly longer than those at 25°C. The lower developmental threshold (T0) and total effective temperature (K) of A. gifuensis were 5.5°C and 188.6 degree-days for the females, and 5.7°C and 181.0 degree-days for the males. The oviposition rate, survival rates and the developmental times were similar to those of commercially produced Aphidius colemani.

Melatonin Does Not Prevent Long Photoperiod Stimulation of Secondary Sexual Characters in the Male Three-Spined SticklebackGasterosteus aculeatus

Breeding in the three-spined stickleback is stimulated by long but not by short photoperiods in many seasons. The aim of the present study was to test the hypothesis that melatonin plays a role in the inhibitory effect of short photoperiod in this species. Adult nonbreeding males were kept either under constant light (Experiment 1) or under a stimulatory long photoperiod (16L 8D, Experiment 2), in water containing 0, 20, or 80 μg/liter melatonin for 16 hr/day for 28 days during the spring. These melatonin treatments were intended to simulate the daily melatonin pattern of a nonstimulatory short photoperiod. In the second experiment, fish were also kept under a nonstimulatory short photoperiod (8L 16D). In the natural breeding season the only germ cells found in the stickleback testes are spermatozoa and spermatogonia, a condition found in many fish under all treatments. In the first experiment, spermatogenesis was not influenced by melatonin. However, testes also containing spermatocytes and spermatids were more common in fish kept under 8L 16D and fish treated with 80 μg/liter melatonin than in 16L 8D controls in Experiment 2. Kidney hypertrophy, an androgen-dependent male secondary sexual characteristic in the stickleback, appeared in most males kept under constant light or 16L 8D and was not influenced by melatonin treatment. In contrast, control males kept under 8L 16D in Experiment 2 did not display kidney hypertrophy. Therefore, the presence of an extended period of elevated melatonin did not prevent the stimulatory effects of long photoperiod on development of this secondary sexual characteristic in the stickleback.

Effects of Day Length and Temperature on Gonadal Development, Body Mass, and Fat Depots in White-Crowned Sparrows, Zonotrichia leucophrys pugetensis

We tested the effects of ambient temperature (5°, 20°, and 30°) on photoperiodically induced reproductive functions in male and female white-crowned sparrows, Zonotrichia leucophrys pugetensis.Transfer from short days (9L 15D) to long days (16L 8D) resulted in rapid testicular growth and partial ovarian development in all three temperature treatments. There were no differences in sizes of testes and cloacal protuberance following 30 or 70 days of exposure to long days at the different temperatures. However, brood patch and follicular development were enhanced in females at 30° compared with the 5° and 20° groups. Many of these females exposed to 30° had large yolky follicles by Day 70. This enhancement was evident only when females were housed in the same room with males, however. Despite the effects of high temperature on ovarian development, there were no differences among groups in plasma levels of follicle-stimulating hormone or luteinizing hormone, suggesting that differential ovarian development may have been mediated by gonadal sensitivity to gonadotropins rather than by differential secretion of these hormones. We examined circulating levels of corticosterone (B) and both tri-iodothyronine (T 3) and thyroxine (T 4) as possible regulators of this differential ovarian sensitivity to gonadotropins. Plasma B levels showed transitory increases in males at 5° and 20°, but were suppressed in males at 30°. Titers of B were not influenced by temperature treatments in females. Circulating T 4increased following photostimulation in both sexes, but this increase was reduced at 5°. T 3concentrations in plasma were highly variable and not influenced by either photoperiod or temperature in males, but were significantly lower in females exposed to 30° by Day 70. Thus, B and T 4levels do not appear to help explain differential ovarian development, but circulating T 3levels cannot yet be excluded as a regulator of ovarian sensitivity to gonadotropins. Long days resulted in no change, or a gradual decrease, in body mass and fat deposit in males and females, and temperature regimes had no further effects on fattening or body mass. Thus, reproductive development under long days appears to be resistant to naturally relevant temperature extremes in male Z.l. pugetensis,whereas follicular development (i.e., yolk deposition in follicles leading to ovulation and onset of nesting) can be enhanced by high temperature. Reasons for the dimorphism in this response are unknown, but may be explained by the role of females in determining onset of final ovarian maturation and nesting in relation to favorable environmental conditions. In a second experiment, in which the sexes were isolated from one another, we determined the effects of the same treatments on Z.l. pugetensis.Again there was no effect of temperature on photoperiodically induced testicular growth, and the enhancement of follicular development in females at 30° was greatly reduced in the absence of males. We also continued this experiment up to 116 days of treatment to investigate effects on onset of photorefractoriness (spontaneous gonadal regression) and onset of prebasic moult. In both sexes it was clear that low temperature (5°) retarded gonadal regression and high temperature (30°) advanced it. Similarly, the prebasic moult score was greater at 30° and less at 5° in both sexes. There were no effects of temperature on plasma levels of LH at Day 116 of treatment, but plasma levels of T 4were higher in the 5° group of both males and females sampled at Day 116. Clearly, the effects of temperature can have different effects on gonadal recrudescence, onset of breeding (yolk deposition), andtermination of breeding. Whether these influences of temperature on reproductive function at different stages in the breeding cycle have different mechanisms remains to be determined.

Environment modifies the testosterone levels of a female bird and its eggs.

Past studies have shown that the yolk of the canary (Serinus canaria) egg contains maternal testosterone, that its concentrations increase in the subsequently formed eggs of a clutch, and that testosterone influences development. The present study investigated 1) if the testosterone levels vary in the female during yolk formation; 2) how such putative variations may be related to the concentrations of maternal testosterone in the yolk; and 3) if environmental factors, such as day length, can modify the testosterone levels in the mother and her eggs. Maternal testosterone levels, measured in the females' feces, increased during yolk formation and egg laying, and decreased during incubation. This pattern was modified by day length. In a photoperiod of 12 h of light and 12 h of darkness (12L 12D), female testosterone levels decreased after the last egg of the clutch was laid while in a photoperiod of 16L 8D, they decreased after the first egg was laid. These different patterns were reflected in the testosterone concentrations in the egg yolk. Further, the eggs of subsequent clutches that were produced under a naturally changing photoperiod differed significantly in their testosterone concentrations. Finally, the doses of testosterone in the yolk of individual eggs were positively correlated with the concentrations of testosterone in the female during the yolk phase of each egg. I conclude that here we have a mechanism which communicates environmental conditions from the mother to the offspring, and that this mechanism serves to optimize reproduction and/or modify offspring traits.

Melatonin Does Not Modulate Testicular Responsiveness to Altered Photoperiods. A Study During Different Phases of the Annual Gonadal Cycle in Roseringed Parakeets (Psittacula krameri)

The roseringed parakeet has been shown to exhibit a variable testicular responsiveness to both altered photoperiodic regimens and to treatment with melatonin during different phases of the annual gonadal cycle. Adult male roseringed parakeets were held under either natural photoperiods (NP), or long photoperiods (LP; 16L 8D), or short photoperiods (SP; 8L 16D) for a total period of 90 days. From day 46 onward, half of the total birds in each group were administered with the vehicle of melatonin, and the other birds were injected daily in the afternoon with melatonin (25 µg/ 100 g body wt.) till the end of the experiment. An identical experimental schedule was followed during the four different (preparatory, progressive, pre-breeding, and breeding) phases of the annual testicular cycle. The testicular activities in various bird groups were evaluated by volumetric, gravimetric, histometric and karyometric measurements, and by quantitative histological studies. The findings revealed that exogenous melatonin may exert either a suppressive influence or none at all on the testicular functions in relation to the photoperiodic schedule as well as to the reproductive phase of the concerned bird, but in no case modulates gonadal responsiveness to artificially altered photoperiods.

Control of Testicular Cycles in the Song Sparrow, Melospiza melodia melodia: Interaction of Photoperiod and an Endogenous Program?

Adult male song sparrows, Melospiza melodia melodia, underwent testicular development accompanied by increases in plasma levels of follicle-stimulating hormone (FSH) and lutenizing hormone (LH) regardless of photoperiods tested. Although gonadal development progressed rapidly in birds exposed to long days, males subjected to short day lengths also showed testicular growth between 90 and 200 days. Onset of photorefractoriness during exposure to continual long days was highly variable among individuals. Short days were not required to regain photosensitivity, and thus spontaneous testicular recrudescence occurred in birds held on long days for prolonged periods. However, cycles of testicular mass, length of cloacal protuberance, and prebasic-type molt in birds held on continuous long days became dissociated and were erratic. If males held on short days were exposed to 1 long day (18L 6D) and then returned to short days, a rapid increase in testicular mass and plasma levels of LH and FSH followed. The effect of 1 long day was greater if males had been exposed to short days for 2 months or longer. Thus, although short days were not absolutely required for dissipating photorefractoriness, they apparently accelerate the process. Female song sparrows showed a similar response to 1 long day. Input from changing day length was also important for triggering testicular regression. Male song sparrows held on 16L 8D for 10 months showed no signs of prebasic molt or testicular regression. When half of the males in this group were then exposed to 14L 10D (a shorter day length but still photostimulatory in spring), there were rapid declines in testis mass and FSH levels. These results are consistent with the phenomenon of "relative photorefractoriness," in which decreased day length results in gonadal regression despite the fact that similar day lengths would have been photostimulatory earlier in spring. It is suggested that song sparrows have "programs" of gonadal activity and molt that are not usually expressed in captivity as part of a complete cycle. The annual change in day length may act to drive the cycle, as continual environmental input for entraining endogenous programs to exactly 1 year and for scheduling the correct temporal sequence of events. Such a combination of continual environmental input and endogenous rhythms may be widespread.

Effect of temperature and photoperiod on sexual maturation and spawning of the common carp: II. Under conditions of low temperature

Carp were reared at a constant cool temperature (16°C) combined with either short (12L–12D) or long (16L–8D) photoperiods. The fish showed similar, continuous increases in the number of matured oocytes and body weight increment during the first 5–6 months (August–January). Loss of matured oocytes and a reduction in body weight, probaly indicating repeated partial spawnings, were observed from time to time commencing in February. These changes became more significant after 9 months. Fish ovulated one month earlier at 16L–8D than at 12L–12D later changed to 16L–8D. Fish from the long photoperiod group spawned totally when the temperature was raised to 22°–25°C, while fish of the short photoperiod group ovulated at 20°–24°C. Photoperiodism is probably involved, although slightly, in ovarian maturation even under cool temperatures.

Effect of temperature and photoperiod on sexual maturation and spawning of the common carp: I. Under conditions of high temperature

Common carp or “Magoi”, Cyprinus carpio (Linnaeus), were reared under constant 24°C and different photoperiod conditions following induced spawning in July. Under a 12L–12D photoperiod, half of the females spawned partially within 6 months, and by the tenth month two of 14 females had spawned totally twice and eight on one occasion. Under a 16L–8D photoperiod, 12 of 15 females spawned totally after 3 months, and six of them spawned again in another 3 months. During the first 10–11 months, the fish were in an “active spawning phase”. Females retained on these regimes for another year did not spawn again although they held matured oocytes. They were in a “passive spawning phase”, because temporary cooling of the tank water to 16°C was effective in inducing immediate spawning. In the “active spawning phase”, gonadal maturation was accelerated when fish were transferred from 12L–12D to 16L–8D, but not when they were transferred from 16L–8D to 22L–2D. In the “passive spawning phase”, lengthening of the photoperiod was not effective.

Breeding-related growth of captive Sparus aurata (Teleostei, Perciformes)

Growth is arrested in male and female Sparus aurata during gonadal recrudescence and spawning. Growth and feeding rates of fish exposed to a constant long photoperiod ( 16L 8D ) were significantly higher than those of fish under a natural photoperiod. When the experimental photoperiod was shortened, fish underwent gonadal recrudescence and reduced feeding, and their growth was arrested. Fish under the long photoperiod regime reached the commercial weight of 350 g six months earlier than the controls.