Effects of putrescine on diapause induction and intensity,and post‐diapause development of Helicoverpa armigera

Effects of putrescine on diapause induction and intensity, and post‐diapause development in Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) from Wuhan, Hubei, China were studied in the laboratory at different temperatures and photoperiod conditions. The results showed a generally higher incidence of diapause in putrescine‐feeding groups. Putrescine feeding distinctly restricted the development of non‐diapause‐destined and diapause‐destined larvae, except at 0.01% putrescine concentration, which accelerated the development of larvae at 21 °C. Putrescine had no significant effect on the duration of diapause, although it inhibited the post‐diapause development of pupae. Photoperiod played a different role in diapause induction and post‐diapause development between 21 and 23 °C. Putrescine played a definite role in diapause induction and intensity, and post‐diapause development in H. armigera, and a significant interaction between putrescine, photophase, and temperature is to be expected.     

Effects of diapause on post‐diapause reproductive investment in the moth Ostrinia scapulalis

Diapause is a strategy used by many insect species to survive adverse environmental conditions. However, diapause incurs costs that may have adverse effects on post‐diapause development and reproduction. We herein investigated the effects of diapause on the post‐diapause reproductive investment of males and females in a multivoltine moth, the adzuki bean borer, Ostrinia scapulalis (Walker) (Lepidoptera: Crambidae). We found that (1) post‐diapause males and females were smaller and had lower mating success than non‐diapause individuals, (2) post‐diapause females had lower fecundity and shorter longevity than non‐diapause females, (3) post‐diapause males transferred similar numbers of eupyrene and apyrene sperm as non‐diapause males, (4) the fecundity and longevity of non‐diapause females mated with post‐diapause males and those mated with non‐diapause males were not significantly different, and (5) no significant relationship was found between diapause duration (short and long) and post‐diapause reproductive investments in both males and females. These results suggest that post‐diapause males did not reduce reproductive investment in spite of the cost of diapause, and the significant decline in reproductive output in post‐diapause females was due to their reduced body weight and longevity, which appeared to be direct consequences of the cost of diapause.     

Hormonal control of diapause and overwintering traits in a leaf beetle, Aulacophora nigripennis

To elucidate whether Juvenile Hormone (JH) regulates physiological status in relation to diapause and cold hardiness, we investigated various physiological and biochemical changes in diapause adults of Aulacophora nigripennis after treatment with exogenous pyriproxyfen, an analogue of JH. Topical application of pyriproxyfen at high dose (≥0.05 μg) caused the diapause adults not only to consume more oxygen and mate earlier, but also to suppress enhancement of chill tolerance at 0°C and accumulation of myo‐inositol. By contrast, a lower dose of pyriproxyfen (0.01 μg) did not, suggesting that the amount of pyriproxyfen between 0.01 and 0.05 μg is a critical dose breaking both diapause and cold hardening. Pyriproxyfen‐treated post‐diapause adults lost triacylglycerols, but not glycogen, more rapidly than the acetone control. It is suggested that triacylglycerols are the main energy resource in both diapause and post‐diapause adults, but are consumed more by the latter because of their higher metabolic rate. Glycogen may be converted mainly into myo‐inositol during diapause, but consumed as an energy fuel for basal metabolism during post‐diapause development. Thus, various physiological and biochemical traits in relation to diapause and cold tolerance in this beetle may be at least in part under the control of JH.     

Termination of pupal diapause in the pine processionary moth Thaumetopoea pityocampa

Diapause development is a complex process involving several eco‐physiological phases. Understanding these phases, especially diapause termination, is vital for interpreting the life history of many insect species and for developing suitable predictive models of population dynamics. The pine processionary moth is a major defoliator of pine and a vertebrate health hazard in the Mediterranean region. This species can display either univoltine or semivoltine development, with a pupal diapause extending from a few months to several years, respectively. Although the ecological and applied importance of diapause is acknowledged, its physiological regulation in either case remains obscure. In the present study, we characterize pre‐termination, termination and post‐termination phases of pupae developing as univoltine or remaining in prolonged diapause. Changes in metabolic activity are monitored continuously using thermocouples, comprising a novel method based on direct calorimetry, and periodically by use of O₂ respirometry. The two methods clearly detect diapause termination in both types of pupae before any visible morphological or behavioural changes can be observed. Univoltine individuals are characterized by an increase in metabolic activity from pre‐termination through to termination and post‐termination, ultimately resulting in emergence. Remarkably, a synchronous termination is observed in individuals that enter prolonged diapause instead of emerging; however, in these pupae, the increased metabolic activity is only transient. The present study represents a starting point toward understanding the eco‐physiology of diapause development processes in the pupae of the pine processionary moth.     

Molecular cloning,developmental expression and tissue distribution of diapause hormone and pheromone biosynthesis activating neuropeptide in the bamboo borer Omphisa fuscidentalis

Diapause, an arrested period of post‐embryonic development in insects, is under the control of hormonal interactions. In the bamboo borer Omphisa fuscidentalis Hampson (Lepidoptera: Crambidae), larvae remain in diapause for as long as 9 months during the dry season, from September to the following June, although the factors that regulate larval diapause are poorly understood. The present study describes the cloning and expression analysis of the diapause hormone and pheromone biosynthesis activating neuropeptide (DH‐PBAN) precursor of O. fuscidentalis (Ompfu‐DH‐PBAN cDNA), aiming to reveal how it may be involved regulating larval diapause in this species in combination with environmental factors. The open reading frame (ORF) of the cDNA encodes a 199‐amino acid precursor protein that contains DH, PBAN and three other neuropeptides, all of which share a conservative C‐terminal pentapeptide motif FXPR/KL (X = G, T or S). The Ompfu‐DH‐PBAN is highly similar (74%) to the DH‐PBAN of the legume pod borer (Maruca vitrata). A quantitative real‐time polymerase chain reaction reveals that Ompfu‐DH‐PBAN mRNA is expressed only in neural tissues and that expression is highest in the suboesophageal ganglion. In addition, the expression level of Ompfu‐DH‐PBAN mRNA in the suboesophageal ganglion is consistently high during the fifth larval instar, increasing moderately in early diapause before reaching a peak during late diapause. After pupation, expression of the Ompfu‐DH‐PBAN precursor decreases to a low level. In addition to endocrine factors, the results demonstrate that photoperiod increases the expression level of Ompfu‐DH‐PBAN mRNA in larval diapause. These results also suggest that the expression of the Ompfu‐DH‐PBAN gene correlates with larval diapause development and may be activated by photoperiod in O. fuscidentalis.     

Obligate annual and successive facultative diapause establish a bet‐hedging strategy of Rhagoletis cerasi (Diptera: Tephritidae) in seasonally unpredictable environments

To cope with temporal and spatial heterogeneity of habitats, herbivorous insects in the temperate zone usually enter diapause that facilitates synchronization of their life cycle with specific stages of host plants, such as fruit ripening. In the present study, we address those factors regulating dormancy responses as part of a ‘longer strategy’ to persist and thrive in temperate environments, focusing on Rhagoletis cerasi, a univoltine, oligophagous species, which overwinters as pupae and emerges when host fruits are available for oviposition at local scale. To ensure population survival and reproduction at habitats with ecological heterogeneity, R. cerasi has evolved a sophisticated diapause strategy based on a combination of local adaptation and diversified bet‐hedging strategies. Diapause duration is determined both by (i) the adaptive response to local host fruit phenology patterns (annual diapause) and (ii) the plastic responses to unpredictable inter‐annual (temporal) climatic variability that drives a proportion of the populations to extend dormancy by entering a second, successive, facultative cycle of prolonged diapause as part of a bet‐hedging strategy. Besides the dormant periods, post‐diapause development (which varies among populations) exerts ‘fine tune’ adjustments that assure synchronization and may correct possible errors. Adults emerging from pupae with prolonged diapause are larger in body size compared with counterparts emerging during the first year of diapause. However, female fecundity rates are reduced, followed by an extended post‐oviposition period, whereas adult longevity remains unaffected. Overall, it appears that R. cerasi populations are adapted to ecological conditions of local habitats and respond plastically to unpredictable environmental (climatic) conditions.     

Genetics of diapause supression in the two-spotted spider mite,Tetranychus urticae Koch

Starting from the Sambucus strain of the two-spotted spider miteTetranychus urticae Koch, the strains ND₁ and ND₂ were selected for lack of diapause under a short-day regimen (LD 1014, 18°C). The genetic basis of the suppression of diapause in ND₁ and ND₂ was analysed by means of mendelian crosses and backcrosses, using the photoperiodic cycle LD 1014 as diagnostic for the distinction of diapausing and non-diapausing phenotypes. Suppression of diapause is inherited as a recessive trait. From backcross analysis it was concluded that the suppression of diapause in ND₁ and ND₂ is under monogenic control. The major genes for suppression of diapause in ND₁ and ND₂ are alleles at a locus designated asd. A mutation for albinism of the locusa-p is pleiotropic for suppression of diapause. It was shown from crosses between ND₁ and the albino strain, thatd anda-p are distinct loci.     

Metabolism of hydrogen peroxide between diapause and non‐diapause eggs of the silkworm,Bombyx Mori during chilling at 5°C

When diapause and non‐diapause eggs of the same bivoltine strain of Bombyx mori were chilled at 5°C for more than 30 days, the hatchability of diapause eggs increased while that of non‐diapause eggs decreased, respectively. To investigate the relationship between effects of chilling on the hatchability and the metabolism of hydrogen peroxide (H₂O₂), content of H₂O₂ and activities of superoxide dismutase (SOD), xanthine oxidase (XO), and catalase (CAT) between diapause and non‐diapause eggs were determined during the chilling at 5°C. The significant enhancement of H₂O₂ occurred prior to the quick increase of the hatchability in diapause eggs and coincided with the quick decline of the hatchability in non‐diapause eggs, respectively. Diapause eggs contained significantly higher H₂O₂ and XO activity and lower CAT activity compared to non‐diapause eggs. Our results showed that there were significant differences in the metabolism of H₂O₂ between diapause and non‐diapause eggs during chilling and that significant enhancement of H₂O₂ may be involved in the diapause termination of diapause eggs and the cell damage of non‐diapause eggs. © 2010 Wiley Periodicals, Inc.     

Dissecting insect responses to climate warming: overwintering and post‐diapause performance in the southern green stink bug,Nezara viridula,under simulated climate‐change conditions

The effect of simulated climate change on overwintering and post‐diapause reproductive performance is studied in Nezara viridula (L.) (Heteroptera: Pentatomidae) close to the species' northern range limit in Japan. Insects are reared from October to June under quasi‐natural (i.e. ambient outdoor) conditions and in a transparent incubator, in which climate warming is simulated by adding 2.5°C to the ambient temperatures. Despite the earlier assumption that females of N. viridula overwinter in diapause, whereas males do so in quiescence, regular dissections show that the two sexes overwinter in a state of true diapause. During winter, both sexes are dark‐coloured and have undeveloped reproductive organs. Resumption of development does not start until late March. During winter, the effect of simulated warming on the dynamics and timing of physiological processes appears to be limited. However, the warming significantly enhances winter survival (from 27–31% to 47–70%), which is a key factor in range expansion of N. viridula. In spring, the effect of simulated warming is complex. It advances the post‐diapause colour change and transition from dormancy to reproduction. The earlier resumption of development is more pronounced in females: in April, significantly more females are already in a reproductive state under the simulated warming than under quasi‐natural conditions. In males, the tendency is similar, although the difference is not significant. Warming significantly enhances spring survival and percentage of copulating adults, although not the percentage of ovipositing females and fecundity. The results suggest that, under the expected climate‐warming conditions, N. viridula will likely benefit mostly as a result of increased winter and spring survival and advanced post‐diapause reproduction. Further warming is likely to allow more adults to survive the critical cold season and contribute (both numerically and by increasing heterogeneity) to the post‐overwintering population growth, thus promoting the establishment of this species in newly‐colonized areas.     

Patterns of diapause frequency and emergence in swede midges of southern Ontario

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On the factors inducing the inhibition of diapause in the progeny of diapause females of Trichogramma telengai

The ability to enter diapause in the progeny of Trichogramma Westw. (Hymenoptera: Trichogrammatidae) females that have undergone diapause is markedly reduced or even completely absent. This maternal inhibition of diapause can result from three types of factors: (i) environmental factors that induce maternal diapause; (ii) maternal diapause itself; and (iii) diapause‐terminating environmental factors. The present study aims to determine the factors that prevent diapause in the progeny of a Trichogramma telengai Sor. generation that has undergone diapause. Different tendencies to enter diapause in the maternal generation are induced by different photoperiods (LD 12 : 12 h, 16 : 8 h and 18 : 6 h) during development of the grandmaternal generation and different temperatures (from 10 to 15 °C) during larval development of the maternal generation. To terminate diapause, prepupae of the maternal generation are kept at 4–5 °C in the dark. To estimate the ability to enter diapause, the progeny generation is incubated at 14 °C. The results suggest that the inhibition of the tendency to enter diapause in the progeny of T. telengai females that have undergone diapause is caused by diapause itself rather than by diapause‐inducing or diapause‐terminating environmental factors. This result can be used to clarify the mechanism of the inhibition of diapause in the progeny of females that have undergone diapause.     

Differences in the pre‐diapause and pre‐oviposition accumulation of critical nutrients in adult females of the beetle Colaphellus bowringi

In many insect species, the differentiation of development between diapause and reproduction first becomes obvious during the diapause preparation (pre‐diapause) and pre‐oviposition phases. However, the differentiation of nutrient accumulation between these two phases remains unclear. We compared the weights of pre‐diapause and reproductive adult female Colaphellus bowringi Baly (Coleoptera: Chrysomelidae), and measured their triacylglycerol (TAG), protein, and carbohydrate content from emergence until they had fed for 4 days post‐eclosion. We also compared the ovarian development and accumulation of lipid droplets between pre‐diapause and reproductive adult females in order to determine whether we could visually detect differences in nutrient allocation. The weights of both pre‐diapause and reproductive females increased with duration of feeding. The fresh weight and water content of pre‐diapause females was significantly lower than that of reproductive females after feeding for 3 days post‐eclosion. Pre‐diapause females channeled their reserves into TAG in the fat body, whereas reproductive females converted nutrients into proteins and carbohydrates for egg development. These results quantify differences in nutrient accumulation between pre‐diapause and reproductive adult female C. bowringi, and provide clues for understanding the molecular mechanisms underlying differences in the allocation of nutrients between diapause and reproduction in insects.