Cold tolerance of the invasive oak lace bug,Corythucha arcuata

1. The North American oak lace bug (OLB), Corythucha arcuata, is an invasive species in Europe and a serious threat to oak-dominated forests.
2. Survival at low temperatures is one major factor determining the spread of invasive insects. Thus, we studied key traits, that is, cold-tolerance strategy, supercooling points (SCP) and chilling-related mortality, of overwintering adults to assess their potential to withstand harsh winters.
3. Samples for SCP measurements were collected once a month from November 2020 until March 2021 at three different locations in Hungary; specimens for chilling experiments were sampled in November 2020, January 2021 and March 2021.
4. SCPs of overwintering adults ranged from −29.68 to −7.49 °C, with only moderate variation among months; C. arcuata is a freeze-avoidant species.
5. Mortality rates of adults exposed to two sub-zero temperatures above the SCP (−3 and −5 °C) for 1, 2 and 3 weeks ranged between 0% and 69.1%, suggesting that OLB has a moderate risk to die from chilling injuries. Exposure time and sampling date affected mortality, with lowest survival rates after 3 weeks, collected in March 2021.

     

Factors affecting pupal survival and eclosion in the pine beauty moth,Panolis flammea (D&S)

Summary The proportion of adult Panolis flammea emerging from the overwintering pupae was markedly affected by pupation substrate, waterlogging, temperature and relative humidty. Pupae which had spent the winter in needle litter had a significantly greater survival rate than those in either soil or peat.The greater the length of time spent waterlogged the greater the mortality rate of P. flammea pupae. At temperatures of-20° C, there was 100% pupal mortality within 24 h of exposure.Pupal weight loss was proportional to the length of time spent as a pupa. Female pupae lost proportionately more weight than male pupae. Pupae of both sexes lost more weight at a low relative humidity than at a high relative humidity. At low relative humidities female pupal mortality was higher than that of male pupae.     

Cold tolerance strategy and cold hardiness of the invasive zigzag elm sawfly Aproceros leucopoda (Hymenoptera: Argidae)

1. The invasive sawfly Aproceros leucopoda causes severe defoliation of various elm species and thus can be a major pest in forest stands and urban environments.
2. The overwintering biology of A. leucopoda has not been investigated so far; therefore, the aim of this study was to determine the cold tolerance strategy and cold hardiness of hibernating A. leucopoda eonymphs.
3. The supercooling points (SCPs) of overwintering individuals varied geographically, monthly and interannually and ranged between ?12.14 °C and ?24.22 °C.
4. As none of the eonymphs survived once the SCP had been reached, A. leucopoda is classified as a freeze‐avoidant species.
5. Survival rates of overwintering eonymphs exposed to different sub‐zero temperatures above the SCP (?1.6 °C and ?4.0 °C for 10, 20 and 30 days and ?10.5 °C for 9 days) ranged between 89.2% and 100%, suggesting that A. leucopoda is not a chill‐susceptible species.
6. Our results suggest that low winter temperatures may not be expected to be an important limiting factor for the overwintering success of A. leucopoda.

     

Cold hardiness and sugar content in photo‐insensitive individuals of the cotton bollworm Helicoverpa armigera

Abstract A proportion of Helicoverpa armigera collected from fields in Okayama Prefecture (Western Japan; 34.6°N, 134.1°E) does not enter diapause when reared under a short days at 20 °C during the larval stages. However, diapause in such photo‐insensitive individuals can be induced when they are reared at moderately low temperatures, such as 15 °C, regardless of photoperiod. To determine whether such photo‐insensitive individuals can survive overwintering in fields, the present study compares the cold hardiness and sugar content between nondiapausing and diapausing pupae of photo‐insensitive individuals selected over several generations at 20 °C under a short day photoperiod (LD 10 : 14 h). Diapausing and nondiapausing pupae are obtained under the short days by rearing at 15 and 20 °C, respectively, during larval and pupal stages. These pupae are stepwise acclimated at a reduction of 5 °C every 5 days to 0 °C. Maximum survival periods of nondiapausing and diapausing pupae at 0 °C are approximately 30 and 90 days, respectively. Trehalose content in diapausing pupae increases, reaches a maximum level (1.95 mg 100 mg^?1 in males and 2.1 mg 100 mg^?1 in females) 28 days after exposure to 0 °C and then decreases. On the other hand, glucose content in diapausing pupae increases (maximum level: 0.32 mg 100 mg^?1 in males and 0.21 mg 100 mg^?1 in females) with decreasing trehalose content 42 days after exposure to 0°C. The decrease in trehalose content and the increase in glucose content may be linked to termination of diapause in H. armigera. These results suggest that, in Japan, the photo‐insensitive individuals can only survive in the mild winters of southern regions, and not in the severe winters of northern regions.     

Differences in pupal cold hardiness and larval food consumption between overwintering and non‐overwintering generations of the common yellow swallowtail,Papilio machaon (Lepidoptera: Papilionidae), from the Osaka population

To clarify differences in pupal cold hardiness and larval food consumption between overwintering and non‐overwintering generations of the common yellow swallowtail, Papilio machaon, we reared larvae from the Osaka population under photoperiods of 16 h light : 8 h dark (LD 16:8) (long day) or LD 12:12 (short day) at 20°C. We examined the relationship between food consumption and weight during the final larval stadium and pupae, and measured the pupal supercooling point (SCP). Although the ratio of assimilation to consumption did not differ significantly between photoperiods, the ratio of assimilation to pupal weight differed significantly between individuals reared under long and short days. All diapausing pupae were brown, whereas 56% of non‐diapausing pupae were green with the remainder brown. The mean pupal body length (L), dorsal width (W₁) and lateral width (W₂) were larger in non‐diapausing than in diapausing pupae, and the W₁/L and W₁/W₂ ratios differed significantly between non‐diapausing and diapausing pupae. SCP was approximately –20°C and did not differ among pupae 5, 15 and 30 days after pupation under long‐day conditions. However, under short‐day conditions, mean SCP gradually decreased, stabilizing at approximately –24 to –25°C by 30 days after pupation. After freezing, some diapausing pupae emerged as adults, whereas all non‐diapausing pupae died. Both egestion and assimilation were greater under long‐day conditions. The results revealed that pupae of this papilionid exhibit seasonal polyphenism in physiological and morphological traits. Energy from food appears to be expended on increasing cold hardiness in the overwintering generation and on reproduction in the non‐overwintering generation.     

Timing of diapause termination in relation to variation in winter climate

In temperate insects, winters are typically endured by entering diapause, which comprises a deep resting stage. Correct timing of diapause termination is vital for synchronization of emergence with conspecifics and for mobilizing resources when conditions for growth and reproduction become favourable. Although critical to survival, the intrinsic and extrinsic drivers of diapause termination timing are poorly understood. In the present study, we investigate diapause development under a range of durations (10–24 weeks) spent at different temperatures (?2 to 10 °C) in the pupal diapausing butterfly Pieris napi Linnaeus (Lepidoptera:Pieridae). We determine: (i) the maximum cold temperature for diapause development; (ii) if pupae in diapause count cold days or cold sums; and (iii) whether diapause termination is distinct or gradual. The results indicate large and idiosyncratic effects of high and low nonlethal temperatures on diapause development in P. napi. Although all temperatures tested lead to diapause termination, a thermal optimum between 2 and 4 °C is observed. Lower temperatures lead to decreased eclosion propensity, whereas higher temperatures slow down development and increase emergence desynchronization. These data suggest that, rather than a simple cold‐summing process with a distinct diapause termination point, there are trade‐offs between time and temperature at the low and high end of the thermal range, resulting in a nonlinear thermal landscape showing a ridge of increasing eclosion propensity at moderate temperatures. The present study suggests that the effects of temperature on diapause development should be included in projections on post‐winter phenology models of insects, including pest species.     

Effects of nutrition and methoprene treatment upon reproductive diapause in Caloptilia fraxinella (Lepidoptera: Gracillariidae)

Abstract Female Caloptilia fraxinella exhibit a prolonged reproductive diapause immediately post adult emergence in mid‐summer until the next spring when mating, egg development and oviposition on fresh Fraxinus spp. leaflets occur. Factors that effect the termination of reproductive diapause are investigated in this species. Caloptilia fraxinella diapausing adults held in overwintering conditions (2 °C, LD 0 : 24 h) for 24 weeks terminate diapause after placement for 2 weeks in simulated summer conditions (24 °C, LD 16 : 8 h) only if they are provided with 10% sugar water. Exogenous application of the Juvenile Hormone (JH) analogue methoprene to moths in both early‐ (summer) and mid‐ (autumn) reproductive diapause demonstrates that JH affects diapause termination but a carbohydrate nutrition source also mediates mating and vitellogenesis. Mating between moth pairs early in diapause occurs only after treatment with methoprene and provision with sugar water. However, there is no impact of mating on the propensity of females to produce vitellogenic oöcytes. Moths collected in the autumn in mid‐diapause respond in a dose‐dependent fashion to methoprene treatment and the response is greater than that of moths early in diapause collected in the summer. Treatment with methoprene and access to sugar water results in vitellogenic oöcytes in 18.75% of females from mid‐diapause moth pairs treated with 0.01 μg methoprene per insect and in all females from pairs treated at the two highest doses of methoprene (0.1 and 1 μg per insect). Mating occurs only between moths in mid‐diapause treated with the two highest doses of methoprene and these doses induce 91% and 100% mating, respectively. Both control and methoprene‐treated males in mid‐diapause held under summer conditions mate successfully and pass a spermatophore to their methoprene‐treated female partner. These data demonstrate that female C. fraxinella undergo a prolonged reproductive diapause in which termination is dependent on JH and further mediated by a carbohydrate nutrition source. The production of vitellogenic oöcytes is independent of mating. These data also provide evidence that response of moths in diapause to exogenous applications of methoprene differs throughout the diapause period and between male and female C. fraxinella.     

The effect of larval photoperiod on pupal colour and diapause in swallowtail butterflies

ABSTRACT.

• 1 There are significant differences in the effects of larval photo-period on diapause and pupal colour among the species Papilio polyxenes Fabr., P.troilus L., Battus philenor (L.) and Eurytides marcellus (Cramer).
• 2 Diapause and pupal colour in P.polyxenes and P.troilus are strongly influenced by larval photoperiod, short photophase eliciting brown diapausing pupae. Photoperiods of 15L:9D permit the expression of the green and brown pupal colour alternatives.
• 3 Pupal colour in B.philenor and E.marcellus is not affected by larval photoperiod, but short photophase induces diapause in these species.
• 4 All species except B.philenor show an association between brown pupal colour and diapause: Emarcellus when reared on long (midsummer) photophase, P.polyxenes and P.troilus when reared on short (autumnal) photophase.
• 5 In P.polyxenes, short photophase can affect pupal colour responses directly, whether the individual enters diapause or not.
• 6 Differences among the species are related to differences in the ecology of their natural pupation sites.

     

Nutrition,sex and season contribute to variation in fat and glycerol levels in the long‐lived moth Caloptilia fraxinella

The ash leaf cone roller Caloptilia fraxinella Ely (Lepidoptera: Gracillariidae) is an invasive leaf‐mining moth pest of horticultural ash Fraxinus spp. in the Canadian Prairie Provinces. Caloptilia fraxinella overwinter as adults in reproductive diapause and mating occurs after overwintering in the spring. The effect of a carbohydrate food source on fat and glycerol reserves throughout the long adult life stage of this moth is investigated. Insects collected as pupae are given access to either water or sugar water upon adult eclosion. Moths held under the different feeding regimes are sampled before (summer and autumn) and after overwintering in the spring. Analysis of either glycerol or lipid content is conducted for male and female moths from each collection period. Both moth weight and glycerol concentration are affected by moth sex, food regime and season of collection. Although female moths are heavier than males, a higher glycerol concentration occurs in males. Moths fed sugar are heavier and have a higher glycerol concentration than water‐fed moths late in reproductive diapause and after overwintering. Moths collected in the spring after overwintering are lighter and have a lower glycerol content than moths collected before winter. There is a significant influence of feeding regime and season on moth body lipid content, with sugar‐fed moths having more fat than water‐fed moths; however, this difference is smaller in the summer than the autumn or spring. An initial understanding of the overwintering biology and diapause of this pest is provided in the present study.     

低温和光周期对绿盲蝽越冬卵滞育解除和发育历期的影响

为了探讨温度和光周期对绿盲蝽Apolygus lucorum Meyer-Dür越冬卵滞育解除和发育历期的影响, 系统调查了绿盲蝽越冬卵在不同温度和不同光照组合下的孵化率和孵化时间, 结果显示：绿盲蝽的越冬卵均为滞育卵,低温和光周期对绿盲蝽越冬卵的滞育解除均有影响。2℃的低温处理能够显著促进其滞育解除,在0~65 d范围内,随着低温处理时间增长,其滞育解除时间缩短,未经低温处理的越冬卵T₅₀为68.5 d,低温处理65 d的T₅₀为12.25 d,绿盲蝽越冬卵在2℃低温处理65 d后完全解除滞育;在0~40 d范围内,低温处理时间越长,绿盲蝽越冬卵的孵化率越高,在25℃、全光照的条件下不经低温处理的孵化率为68.65%,低温处理40 d后在25℃的条件下的孵化率达到99.46%。在20~26℃范围内,绿盲蝽越冬卵的滞育后发育历期随着温度的上升而缩短, 随着光周期的延长而缩短。结果说明低温处理能够提高绿盲蝽越冬卵滞育解除率,但不是其滞育解除的必要条件,低温处理与自然变温对绿盲蝽滞育解除的作用相似;高温和长光照能够促进绿盲蝽的滞育解除,缩短发育历期。     

中华通草蛉自然越冬成虫在两种光周期下滞育解除过程中的生理生化变化

摘要: 光周期在昆虫滞育中起重要作用, 而昆虫光敏感性差异导致了光在昆虫滞育解除过程中作用机制的多样性。为明确光周期在中华通草蛉Chrysoperla sinica (Tjeder)滞育解除过程中的调控机制, 本研究测定了长光周期（15L∶9D）和短光周期（9L∶15D）条件下, 中华通草蛉自然越冬种群成虫在滞育解除过程中的干重、 含水量、 过冷却点（supercooling point, SCP）、 结冰点（freezing point, FP）及蛋白质和糖原含量变化。结果表明： 雌成虫干重在长光照下处理30 d低于短光照下, 其他处理时间的干重均高于短光照下, 但处理间差异不显著（P>0.05）; 雄成虫在长光照下处理5 d的干重高于短光照下, 其余处理时间的干重均低于短光照下, 其中处理30 d 时差异显著（P<0.05）。雌、 雄成虫含水量总体呈上升趋势, 长光照下上升显著（P<0.05）, 短光照下上升不显著（P>0.05）。雌、 雄成虫的SCP、 FP在短光照下处理不同时间均无显著性差异（P>0.05）, 而长光照下表现出先降后升的趋势且处理间差异显著（P<0.05）。成虫蛋白含量在短光照条件下雄虫处理10 d以及雌虫处理15 d均显著低于长光照（P<0.05）, 其他处理之间没有显著性差异。短光照处理成虫体内糖原含量均高于长光照, 且有显著性差异（P<0.05）。多因素方差分析表明, 不同光周期对中华通草蛉成虫滞育解除过程中的SCP、 FP、 糖原变化均有显著性影响（P<0.05）, 而对干重、 含水量及蛋白质含量影响不显著;性别只对成虫FP与糖原有显著影响（P<0.05）; 处理时间对干重、 含水量、 SCP、 FP、 蛋白及糖原含量均有显著影响（P<0.01）。3种因素的交互作用对SCP、 FP、 蛋白及糖原含量均有显著影响, 对干重及含水量影响不显著。初产卵成虫体内物质含量变化测定发现, 长光照（处理10 d）下雌、 雄成虫体内蛋白和糖原含量极显著低于短光照（处理25 d）下（P<0.01）, 雄成虫体内含水量显著高于短光照下（P<0.05）。结果说明, 中华通草蛉自然越冬成虫在长、 短两种光周期下均逐渐解除滞育, 但在滞育解除过程中呈现出不同的生理生化变化。     

Imidazole derivative KK-42 boosts pupal diapause incidence and delays diapause termination in several insect species

The imidazole derivative KK-42 is a synthetic insect growth regulator known previously to be capable of averting embryonic diapause in several Lepidoptera, but whether it also affects diapauses occurring in other developmental stages remains unknown. In the present study, we examined the effect of KK-42 on pupal diapause in two species of Lepidoptera, the Chinese oak silkworm Antheraea pernyi and the corn earworm Helicoverpa zea, and in one species of Diptera, the flesh fly Sarcophaga crassipalpis. In A. pernyi, KK-42 delayed pupal diapause termination under the long day conditions that normally break diapause in this species. Likewise, in H. zea, KK-42 delayed termination of pupal diapause, a diapause that, in this species, is normally broken by high temperature. KK-42-treated pupae of these two species eventually terminated diapause and successfully emerged as adults, but the timing of diapause termination was significantly delayed. KK-42 also significantly increased the incidence of pupal diapause in H. zea and S. crassipalpis when administered to larvae that were environmentally programmed for diapause, but it was not capable of inducing pupal diapause in H. zea if larvae were reared under environmental conditions that do not normally evoke the diapause response. Experiments with H. zea showed that the effect of KK-42 on pupal diapause was dose- and stage-dependent, but not temperature-dependent. Results presented here are consistent with a link between KK-42 and the ecdysteroid signaling pathway that regulates pupal diapause.     

Regulation of heat shock proteins in the apple maggot Rhagoletis pomonella during hot summer days and overwintering diapause

Abstract Developing larvae of the apple maggot Rhagoletis pomonella are frequently exposed to summertime apple temperatures that exceed 40 °C and, during their overwintering diapause, pupae are exposed to sub‐zero soil temperatures for prolonged periods. To investigate the potential involvement of heat shock proteins (Hsps) in response to these environmental extremes, the genes encoding Hsp70 and Hsp90 in R. pomonella are cloned and expression monitored during larval feeding within the apple and during overwintering pupal diapause. Larvae reared in the laboratory at constant temperatures of 25, 28 or 35 °C express Hsp90 but very little Hsp70. Larvae do not survive rearing at 40 °C. The temperature cycles to which larvae were exposed inside apples in the field, ranging 16–46.9 °C over a 24‐h period, elicit strong Hsp70 and Hsp90 expression, which begins at mid‐day and reaches a peak in late afternoon, coinciding with peak air and apple temperatures. Heat shock proteins are also expressed strongly by pupae during their overwintering diapause. Hsp70 is not expressed in nondiapausing pupae but is highly expressed throughout diapause. Hsp90 is constitutively expressed in both diapausing and nondiapausing pupae. Rhagoletis pomonella thus strongly expresses its Hsps during pupal diapause, presumably as a protection against low temperature injury, and during larval development to cope with natural temperature cycles prevailing in late summer.     

Effects of terrigenous organic substrates and additional phosphorus on bacterioplankton metabolism and exoenzyme stoichiometry

1. Bamboo, as a pioneer vegetation, often forms forests on bare lands after catastrophic landslides. Compared to evergreen forest soil, bamboo forest soil is much more labile, with a higher percentage of microbially derived organic carbon (OC), lower molecular weight, and lower humic acid content. We hypothesised that different terrigenous organic matter (tOM) sources with varying lability and phosphorus (P) availability select for bacterioplankton with distinct metabolic pathways.
2. We incubated natural bacterioplankton assemblages with tOM leached from bamboo forest soil (BOM) and evergreen forest soil (EOM) and compared these to a lake water control. To test if microbial metabolism would be limited by OC or P availability of each tOM treatment, we used acetate as an extra labile OC source and phosphate as an inorganic P source. Bacterial metabolism was measured by analysing respiration via O₂ consumption and production via tritiated thymidine (TdR) assimilation.
3. Bacterioplankton metabolism is limited by the availability of P in BOM substrates. When using BOM, bacteria had higher enzymatic activities for phosphatase. The nutrients required for bacterial biomass seemed to be derived from organic matter. Under BOM treatment, bacterial production (BP) (0.92 ± 0.13 μg C L⁻¹ hr⁻¹) and cell specific TdR assimilation rates (0.015 ± 0.002 10^–18 M TdR cell⁻¹ hr⁻¹) were low. Adding P enhanced BP (BOM_+P 1.52 ± 0.31 and BOM_+C+P 2.25 ± 0.37 μg C L⁻¹ hr⁻¹) while acetate addition had no significant effect on BOM treatment.
4. This indicated that the bacteria switched to using added inorganic P to respire a P-limited BOM substrate, which increased total BP and abundance, resulting in even more active respiration and lower growth efficiency. We also found higher activities for chitin-degrading enzyme β-N-acetylglucosaminidase, which is associated with N mining from aminosaccharides.
5. Microbes using EOM, however, did not change metabolic strategies with additional acetate or/and inorganic P. This is due to higher concentrations of organic P in EOM substrates and the presence of inorganic N in the EOM leachates an alternative nutrient source. Bacteria produced β-glucosidase and leucyl-aminopeptidase in order to utilise the humic substances, which sustained greater bacterial abundance, higher BP (2.64 ± 0.39 μg C L⁻¹ hr⁻¹), and lower cell-specific respiration. This yielded a much higher bacterial growth efficiency (15 ± 9.2%) than the lake water control.
6. Our study demonstrated the aquatic metabolic discrepancy between tOM of different forest types. Bacterioplankton in BOM and EOM exhibit distinct metabolic responses. Bacterial metabolic strategy when using BOM implied that the supposedly stabilised biomass OM might be efficiently used by aquatic bacterioplankton. As the labile and nutrient-deficient BOM is more susceptible to the influence of additional nutrients, fertiliser residues in bamboo forest catchments might have a stronger effect on aquatic bacterial metabolic pathways. Thus, it is important to take tOM differences into consideration when building models to estimate soil carbon turnover rates along a terrestrial–aquatic continuum.

     

Identification and characterization of an ecdysiotropic peptide from brain extracts of the gypsy moth,Lymantria dispar

A peptide (Lymantria TE) was isolated from brains of the gypsy moth, Lymantria dispar, which stimulates synthesis of ecdysteroid in the testes of larval and pupal insects. This ecdysiotropic peptide was purified and its structure determined to be NH₂-IIe-Ser-Asp-Phe-Asp-Glu-Tyr-Glu-Pro-Leu-Asn-Asp-Ala-Asp-Asn-Asn-Glu-Val-Leu-Asp-Phe-OH using protein sequence analysis and electrospray mass spectrometry. The peptide was biphasic in activity, with maximal activity in the pupal testes at 10⁻¹³ M and 10⁻⁹ M, with a minimum at 10⁻¹⁰ M, and with maxima at 10⁻¹⁵ M and 10⁻¹⁰ M and minimum at 10⁻¹³ M for larval testes. Arch. Insect Biochem. Physiol. 34:175–189, 1997. © 1997 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

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.     

Local outbreaks of Operophtera brumata and Operophtera fagata cannot be explained by low vulnerability to pupal predation

• 1 One of the unresolved questions in studies on population dynamics of forest Lepidoptera is why some populations at times reach outbreak densities, whereas others never do. Resolving this question is especially challenging if populations of the same species in different areas or of closely‐related species in the same area are considered.
• 2 The present study focused on three closely‐related geometrid moth species, autumnal Epirrita autumnata, winter Operophtera brumata and northern winter moths Operophtera fagata, in southern Finland. There, winter and northern winter moth populations can reach outbreak densities, whereas autumnal moth densities stay relatively low.
• 3 We tested the hypothesis that a lower vulnerability to pupal predation may explain the observed differences in population dynamics. The results obtained do not support this hypothesis because pupal predation probabilities were not significantly different between the two genera within or without the Operophtera outbreak area or in years with or without a current Operophtera outbreak.
• 4 Overall, pupal predation was even higher in winter and northern winter moths than in autumnal moths. Differences in larval predation and parasitism, as well as in the reproductive capacities of the species, might be other candidates.

     

D2‐like dopamine receptors mediate regulation of pupal diapause in Chinese oak silkmoth Antheraea pernyi

The present study investigated the pharmacological properties of dopamine receptors that functioned in the termination of pupal diapause in the Chinese oak silkmoth, Antheraea pernyi (Lepidoptera: Saturniidae). Dopamine receptors are classified according to their structure and function into two subfamilies as D1‐ and D2‐like receptors. D1‐like receptors activate, whereas D2‐like receptors inhibit, adenylate cyclase. We examined the effects of agonists and antagonists selective for D1‐ and D2‐like receptors on the diapause state. As A. pernyi is a long‐day species, pupal diapause is maintained during short days and can be terminated by exposure to a long‐day photoperiod. The D2‐like receptor‐selective agonist quinpirole delayed the timing of adult emergence under long days, and the D2‐receptor‐selective antagonist sulpiride terminated pupal diapause even under a short‐day photoperiod. The D1‐like receptor‐selective agonist and antagonist, SKF‐38393 and SCH‐23390, respectively, caused no significant effects on diapause pupae. These results suggest that not D1‐ but D2‐like receptors mediated diapause regulation in A. pernyi. This dopamine pathway appeared to block the termination of pupal diapause. Furthermore, the actions of the cAMP analog 8‐CPT‐cAMP and dopamine receptor antagonists upon diapause pupae were similar, which supports the notion that D2‐like receptors involved in diapause of this insect prevent adenylate cyclase from producing cAMP like vertebrate D2‐like receptors. Taken together, our findings suggest that dopamine blocked diapause termination through D2‐like receptors that inhibited adenylate cyclase in A. pernyi. During short days under which diapause was maintained in pupae, the dopaminergic mechanism might be stimulated to suppress cAMP levels in cells regulating diapause.     

Serotonin Receptor B May Lock the Gate of PTTH Release/Synthesis in the Chinese Silk Moth,Antheraea pernyi; A Diapause Initiation/Maintenance Mechanism?

The release of prothoracicotropic hormone, PTTH, or its blockade is the major endocrine switch regulating the developmental channel either to metamorphosis or to pupal diapause in the Chinese silk moth, Antheraea pernyi. We have cloned cDNAs encoding two types of serotonin receptors (5HTR_{A and B}). 5HTR_A-, and 5HTR_B-like immunohistochemical reactivities (-ir) were colocalized with PTTH-ir in two pairs of neurosecretory cells at the dorsolateral region of the protocerebrum (DL). Therefore, the causal involvement of these receptors was suspected in PTTH release/synthesis. The level of mRNA^5HTRB responded to 10 cycles of long-day activation, falling to 40% of the original level before activation, while that of 5HTR_A was not affected by long-day activation. Under LD 16:8 and 12:12, the injection of dsRNA^5HTRB resulted in early diapause termination, whereas that of dsRNA^5HTRA did not affect the rate of diapause termination. The injection of dsRNA^5HTRB induced PTTH accumulation, indicating that 5HTR_B binding suppresses PTTH synthesis also. This conclusion was supported pharmacologically; the injection of luzindole, a melatonin receptor antagonist, plus 5th inhibited photoperiodic activation under LD 16:8, while that of 5,7-DHT, induced emergence in a dose dependent fashion under LD 12:12. The results suggest that 5HTR_B may lock the PTTH release/synthesis, maintaining diapause. This could also work as diapause induction mechanism.     

Physiology of larval diapause: a tool for insect pest management

Summary

Two major pests cause damage of economic importance to maize crops in France: the European corn borer (Ostrinia nubilalis), which has a worldwide distribution, and the pink maize stalk borer (Sesamia nonagrioides), which is present all around the Mediterranean. During winter, last instar larvae of these species exhibit a facultative diapause. Early forecasting of the field emergence period and a good knowledge of the overwintering survival (both strongly dependent on conditions controlling diapause maintenance and termination) are key features for effective management of these pests. In this connection physiological studies of diapause provide us with useful information. Special emphasis is given to variations of carbohydrate metabolism, particularly glycogen, trehalose and glycerol in both species. In the European corn borer the presence of glycerol and trehalose makes it possible to forecast diapause termination 2–3 months before the first field pupal molts. These data are used for the construction of a model of the population dynamics, developed by the National Institute of Agronomic Research. In the pink maize stalk borer we demonstrate the great sensibility of this pest to low temperatures, and we propose a novel cultural pest-suppressing method which is now being tested in collaboration with the General Association of Maize Producers.