Time of the season: the effect of host photoperiodism on diapause induction in an insect herbivore,Leptinotarsa decemlineata

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Dimerization of Proline Dehydrogenase from Thermus thermophilus Is Crucial for Its Thermostability

Thermus thermophilus proline dehydrogenase ( TtProDH) catalyzes the first step in proline catabolism. The thermostable flavoenzyme consists of a distorted triosephosphate isomerase (TIM) barrel and three N‐terminal helices: αA, αB, and αC. Using maltose‐binding protein (MBP) fused constructs, it has been recently demonstrated that helix αC is crucial for TtProDH catalysis and for tetramerization through positioning of helix α8. Here, the structural features that determine the thermostability of TtProDH are reported. Selective disruption of two ion pairs in the dimerization interface of several MBP‐TtProDH variants result in the formation of monomers. The newly created monomers have improved catalytic properties but their melting temperatures are decreased by more than 20 °C. Sequence comparison suggests that one of the ion‐pairs involved in dimerization is unique for ProDHs from Thermus species. In summary, intermolecular ion‐pairs improve the thermostability of TtProDH and a trade‐off is made between thermostability and catalytic activity.     

Responses in metabolic rate to changes in temperature in diapausing Colorado potato beetle Leptinotarsa decemlineata from three European populations

Many insects survive adverse periods in seasonal environments by entering diapause, a deep resting stage, during which energy consumption is typically low and gas exchange is in the form of a discontinuous gas exchange cycle (DGC). Because insects in high‐latitude environments are severely time constrained during summer, an effective diapause termination with careful regulation of metabolic rate is important. The present study examines whether diapausing Colorado potato beetles Leptinotarsa decemlineata Say originating from three latitudinally different regions in Europe differ in their quantitative or qualitative gas exchange patterns in response to an increasing temperature. Overall production of gaseous CO₂, as well as qualitative patterns relating to the DGC, are measured at a late stage of diapause at four different temperatures in increasing order from 13, 18, 23 to 28 °C. Overall CO₂ production is found to be lower in the two northern populations (61°49′N and 55°75′N) compared with the southernmost population (45°48′N) but increases as a function of temperature in all populations in a similar way. However, in the northern populations, raising the temperature increases the amount of CO₂ discharged during single DGC peaks, whereas the DGC frequency remains relatively unchanged. By contrast, in the southernmost population, the amount of CO₂ discharged during individual DGC peaks remains relatively unchanged, whereas the DGC frequency increases as a function of temperature. The observed differences may relate to water retention benefits or, alternatively, energetic benefits relating to heightened gas exchange efficiency in hypoxic or hypercapnic environments. Overall, the results suggest that, although populations of L. decemlineata may have similar thermal sensitivities, they have different qualitative strategies to regulate metabolic re‐activation at diapause termination.     

Random movement pattern of fed and unfed adult Colorado potato beetles in bare‐ground habitat

• 1 Although the successful management of the Colorado potato beetle Leptinotarsa decemlineata (Say) depends on the prevention of its dispersal, its walking pattern in the landscape remains poorly understood. In the present study, post‐diapause, early summer, late summer and colony adult beetles, both fed and unfed before release, were tracked with a harmonic radar to establish their walking movement pattern in a bare‐ground field.
• 2 The random walk model successfully described the dispersal of all beetle types, whether fed or unfed.
• 3 The diverse life history of this species was manifested by an increased distance travelled and deviations of individual paths from the random model. Starved post‐diapause beetles travelled furthest and individual paths deviating from random were both local and directed, probably aiming to maximize opportunities for host colonization. Starved early summer beetles also travelled further than fed beetles but relied more on random movement to disperse in the habitat. Starving had little impact on the distance travelled or the path deviations of late summer beetles that are searching for overwintering site rather than hosts.
• 4 The increased displacement of starving beetles over fed beetles corresponded with an increased walking step and index of straightness.
• 5 The impact of starvation on travel distance was greater than expected from laboratory tests.
• 6 In conclusion, the results obtained in the present study suggest a random walking pattern to search arable land until host volatile or visual impulses trigger a more directed walk or flight.

     

Screening of l‐histidine‐based ligands to modify monolithic supports and selectively purify the supercoiled plasmid DNA isoform

The growing demand of pharmaceutical‐grade plasmid DNA (pDNA) suitable for biotherapeutic applications fostered the development of new purification strategies. The surface plasmon resonance technique was employed for a fast binding screening of l ‐histidine and its derivatives, 1‐benzyl‐l ‐histidine and 1‐methyl‐l ‐histidine, as potential ligands for the biorecognition of three plasmids with different sizes (6.05, 8.70, and 14 kbp). The binding analysis was performed with different isoforms of each plasmid (supercoiled, open circular, and linear) separately. The results revealed that the overall affinity of plasmids to l ‐histidine and its derivatives was high (K_D > 10⁻⁸ M), and the highest affinity was found for human papillomavirus 16 E6/E7 (K_D = 1.1 × 10⁻¹⁰ M and K_D = 3.34 × 10⁻¹⁰ M for open circular and linear plasmid isoforms, respectively). l ‐Histidine and 1‐benzyl‐l ‐histidine were immobilized on monolithic matrices. Chromatographic studies of l ‐histidine and 1‐benzyl‐l ‐histidine monoliths were also performed with the aforementioned samples. In general, the supercoiled isoform had strong interactions with both supports. The separation of plasmid isoforms was achieved by decreasing the ammonium sulfate concentration in the eluent, in both supports, but a lower salt concentration was required in the 1‐benzyl‐l ‐histidine monolith because of stronger interactions promoted with pDNA. The efficiency of plasmid isoforms separation remained unchanged with flow rate variations. The binding capacity for pDNA achieved with the l ‐histidine monolith was 29‐fold higher than that obtained with conventional l ‐histidine agarose. Overall, the combination of either l ‐histidine or its derivatives with monolithic supports can be a promising strategy to purify the supercoiled isoform from different plasmids with suitable purity degree for pharmaceutical applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Inheritance patterns of photoperiodic diapause induction in Leptinotarsa decemlineata

Photoperiod is a reliable indicator of season and an important cue that many insects use for phenological synchronization. Undergoing range expansion insects can face a change in the local photoperiod to which they need to resynchronize. Rapid range expansion can be associated with rapid photoperiodic adaptation, which can be associated with intense selection on strongly heritable polygenic traits. Alternatively, it is proposed that, in insects with an XO sex‐determination system, genes with large effect residing on the sex chromosome could drive photoperiodic adaptation because the gene or genes are exposed to selection in the sex carrying only a single X‐chromosome. The present study seeks to understand which of these alternatives more likely explains the rapid photoperiodic adaptation in European Colorado potato beetles Leptinotarsa decemlineata Say. Diapause induction is assessed in beetles from a northern and a southern population, as well as from reciprocal hybrid crosses between the northern and southern population, when reared at an intermediate length photoperiod. The crosses within population display the expected responses, with the northern and southern populations showing high and low diapause propensity, respectively. The hybrids show intermediate responses in all studied traits. No clear difference in the responses in hybrids depending on the latitudinal origin of their father or mother is detected, even though partial paternal line dominance is seen in the responses of male beetles in one hybrid cross. These results therefore indicate that, in L. decemlineata, photoperiodic diapause induction is strongly heritable, and has an additive polygenic autosomal background.     

Potential of a synthetic aggregation pheromone for integrated pest management of Colorado potato beetle

Abstract

• 1 The relative number of colonizing adult Colorado potato beetles (CPB) Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) coming to pitfall traps baited with the aggregation pheromone (S)‐3,7‐dimethyl‐2‐oxo‐oct‐6‐ene‐1,3‐diol [(S)‐CPB I] and the use of the pheromone in a trap crop pest management strategy were evaluated in the field for the first time.
• 2 More than five‐fold more adult L. decemlineata were caught in pitfall traps baited with the pheromone compared with controls. However, attraction to the pheromone diminished after 5 days in the field.
• 3 In the trap crop management strategy, more colonizing adults were present in pheromone‐treated rows of potatoes compared with untreated middle rows.
• 4 Significantly fewer L. decemlineata egg masses and larvae were found in potato plots that were bordered by pheromone‐treated rows, or bordered by imidacloprid + pheromone‐treated rows, or rows treated at‐planting with imidacloprid compared with untreated (control) potato plots.
• 5 Densities of L. decemlineata egg masses and larvae and percentage defoliation were significantly lower, and marketable tuber yield significantly higher, in conventional imidacloprid‐treated potatoes compared with all other treatments.
• 6 Although our results demonstrate the potential for use of the aggregation pheromone in the management of L. decemlineata in the field, more research is needed to optimize the release rates of the attractant and incorporate control methods for cohabiting pests.

     

Two New Chromone Glycosides from the Roots of Saposhnikovia divaricata

Five chromone glycosides were isolated from the water‐soluble portions of 70% EtOH extract of the roots of Saposhnikovia divaricata, including two new chromone glycosides 1 and 2 . The structures of the chromone glycosides were identified as (3′S)‐3′‐O‐β‐d ‐apiofuranosyl‐(1 → 6)‐β‐d ‐glucopyranosylhamaudol ( 1 ), (2′S)‐4′‐O‐β‐d ‐apiofuranosyl‐(1 → 6)‐β‐d ‐glucopyranosylvisamminol ( 2 ), 3′‐O‐glucopyranosylhamaudol ( 3 ), 4′‐O‐β‐d ‐glucopyranosylvisamminol ( 4 ), and 4′‐O‐β‐d ‐glucopyranosyl‐5‐O‐methylvisamminol ( 5 ) on the basis of extensive spectroscopic methods, and the absolute configurations of the new compounds were elucidated by the electronic circular dichroism (ECD) calculation and acid hydrolysis. The cytotoxic activities of the glycosides 1 – 5 against three human cancer cell lines (PC‐3, SK‐OV‐3, and H460) were evaluated. The result showed that compounds 1 – 5 had weak cytotoxic activities against the human cancer cell lines with IC₅₀ values in the range of 48.54 ± 0.80 – 94.25 ± 1.45 μm .     

Diapause induction and termination in a commonly univoltine leaf beetle (Phratora vulgatissima)

Abstract The leaf beetle Phratora vulgatissima (Linnaeus 1758) is commonly univoltine in south‐central Sweden but may sometimes initiate a partial second generation. The current study was set out to investigate under what abiotic conditions the beetles initiate a second generation. Using climate chamber experiments, the beetles were shown to have a facultative reproductive diapause induced by declining day‐length. The critical day‐length (CDL) for diapause induction was estimated to be 18 h and 10 min. In the field, first‐generation beetles developing to adulthood before August in 2009 became reproductively active and produced a second generation, but most individuals emerged later and were in reproductive diapause. P. vulgatissima overwinter as adults and diapause was shown to be maintained until mid‐winter in 2008/2009. The cumulative temperature requirement for oviposition after diapause termination was estimated to be 222 day‐degrees with a 5.5°C temperature threshold. Three different day‐degree models that were developed to predict the phenology of female oviposition in the spring were validated by comparing model results with field data on the timing of oviposition in previous years. The study suggests that P. vulgatissima may initiate a second generation in Sweden if development of the first generation is completed before August. Warmer spring and summer temperatures due to ongoing climate change may cause advanced insect phenology and faster completion of insect life‐cycles at northern latitudes, which will affect the proportion of insects that initiate a second generation.     

The nature and titre of juvenile hormone in the Colorado potato beetle, Leptinotarsa decemlineata

This paper describes the nature and titre of juvenile hormone at different developmental stages of the Colorado potato beetle, Leptinotarsa decemlineata Say, determined by a selective mass-spectroscopic detection technique, High levels of juvenile hormone III were observed in long-day beetles, whereas low titres occurred in pre-diapause and diapause adults. The level of juvenile hormone III in larvae was low compared with reproductive adults, whereas hardly any juvenile hormone could be detected in pupae. We were not able to detect juvenile hormones I or II. The results agree well with previously reported data using the Galleria bioassay.     

Host‐plant quality adaptively affects the diapause threshold: evidence from leaf beetles in willow plantations

1. Voltinism of herbivorous insects can vary depending on environmental conditions. The leaf beetle Phratora vulgatissima L. is univoltine in Sweden but will sometimes initiate a second generation in short‐rotation coppice (SRC) willow plantations. 2. The study investigated whether increased voltinism by P. vulgatissima in plantations can be explained by (i) rapid life‐cycle development allowing two generations, or (ii) postponed diapause induction on coppiced willows. 3. In the field, no difference was found in the phenology or development of first‐generation broods between plantations (S. viminalis) and natural willow habitats (S. cinerea). However, the induction of diapause occurred 1–2 weeks later in SRC willow plantations. 4. Laboratory experiments indicated no genetic difference in the critical day‐length for diapause induction between beetles originating from plantations and natural habitats. Development time was unaffected by host‐plant quality but critical day‐length was prolonged by almost an hour when the beetles were reared on a non‐preferred willow species (S. phylicifolia). When reared on new leaves from re‐sprouting shoots of recently coppiced willow plants, diapause incidence was significantly less than when the beetles were reared on mature leaves from uncoppiced plants. 5. The study suggests that P. vulgatissima has a plastic diapause threshold influenced by host‐plant quality. The use of host‐plant quality as a diapause‐inducing stimulus is likely to be adaptive in cases where food resources are unpredictable, such as when new host‐plant tissue is produced after a disturbance. SRC willows may allow two beetle generations due to longer growing seasons of coppiced plants that grow vigorously.     

Enforcing temporal control of maternal mRNA translation during oocyte cell‐cycle progression

Meiotic cell‐cycle progression in progesterone‐stimulated Xenopus oocytes requires that the translation of pre‐existing maternal mRNAs occur in a strict temporal order. Timing of translation is regulated through elements within the mRNA 3′ untranslated region (3′ UTR), which respond to cell cycle‐dependant signalling. One element that has been previously implicated in the temporal control of mRNA translation is the cytoplasmic polyadenylation element (CPE). In this study, we show that the CPE does not direct early mRNA translation. Rather, early translation is directed through specific early factors, including the Musashi‐binding element (MBE) and the MBE‐binding protein, Musashi. Our findings indicate that although the cyclin B5 3′ UTR contains both CPEs and an MBE, the MBE is the critical regulator of early translation. The cyclin B2 3′ UTR contains CPEs, but lacks an MBE and is translationally activated late in maturation. Finally, utilizing antisense oligonucleotides to attenuate endogenous Musashi synthesis, we show that Musashi is critical for the initiation of early class mRNA translation and for the subsequent activation of CPE‐dependant mRNA translation.