Evidence for widespread genomic methylation in the migratory locust, Locusta migratoria (Orthoptera: Acrididae)

The importance of DNA methylation in mammalian and plant systems is well established. In recent years there has been renewed interest in DNA methylation in insects. Accumulating evidence, both from mammals and insects, points towards an emerging role for DNA methylation in the regulation of phenotypic plasticity. The migratory locust (Locusta migratoria) is a model organism for the study of phenotypic plasticity. Despite this, there is little information available about the degree to which the genome is methylated in this species and genes encoding methylation machinery have not been previously identified. We therefore undertook an initial investigation to establish the presence of a functional DNA methylation system in L. migratoria. We found that the migratory locust possesses genes that putatively encode methylation machinery (DNA methyltransferases and a methyl-binding domain protein) and exhibits genomic methylation, some of which appears to be localised to repetitive regions of the genome. We have also identified a distinct group of genes within the L. migratoria genome that appear to have been historically methylated and show some possible functional differentiation. These results will facilitate more detailed research into the functional significance of DNA methylation in locusts.     

Fecal volatile components elicit aggregation in the oriental migratory locust,Locusta migratoria manilensis (Orthoptera: Acrididae)

Abstract The aggregation components from fecal volatiles of the oriental migratory locust, Locusta migratoria manilensis were identified with gas chromatographic/electroantennographic detector (GC‐EAD), GC‐MS (mass spectrometry) analyses and behavioral bioassays. Both last instar nymphs and adults of the oriental migratory locust have similar aggregation pheromones in their volatiles. A total of 11 electrophysiologically active compounds, namely, hexanal, cyclohexanol, heptanal, phenol, 2,5‐dimethyl‐pyrazine, benzyl alcohol, benzaldehyde, guaiacol, nonanal, 2,6,6‐trimethyl‐2‐cyclohexene‐1,4‐dione and decyl aldehyde were identified in the fecal volatiles of 2‐day‐old immature adult male locusts. Only hexanal, nonanal, benzaldehyde, cyclohexanol and 2,5‐dimethyl‐pyrazine elicited significant aggregation responses in immature 2‐day‐old adult males. However, adult males had significantly lower behavioral responses to synthetics of five single compounds than the blend of cyclohexanol, 2,5‐dimethyl‐pyrazine, benzaldehyde, nonanal, hexanal in ratios of 100: 100: 2: 60: 30 in the range of 30–60 μg/mL. We propose that it is the blend of these five compounds that plays a key role in eliciting and sustaining aggregation in gregarious oriental migratory locusts. These results also showed that the aggregation pheromones of the oriental migratory locust are significantly different from those found in the desert locust.     

东亚飞蝗耐高温能力及其体温调节行为

为明确东亚飞蝗Locusta migratoria manilensis的耐高温能力和体温调节行为, 采用高温饲养、提供辐射热源和风力等方法, 对东亚飞蝗各发育期的高温耐受能力、体温（body temperature, Tb）与环境温度（air temperature, Ta）和辐射温度（radiant temperature, Tr）的关系、飞蝗对辐射热的选择行为、体温升高速率以及辐射角度和风力对体温的影响进行了研究。结果表明: 东亚飞蝗44℃下饲养, LT90 最长为326.4 h; 50℃下, LT90可达20.6 h。无辐射热条件下, Tb随Ta的上升而升高, 当Ta升至32℃, 蝗虫出现体温调节行为; Ta以0.5℃/min速率上升时, 出现体温波动的个体数占试虫总数的53.7%, Tb平均波动温差为1.15℃, 平均波动时间为5.2 min, Tb平均波动起始温度为47.2℃, 成虫致死时间略长于若虫。有辐射热条件下, 随笼顶辐射温度的逐渐升高, 飞蝗趋向选择温度相对较低的笼底, 试虫体温调节较无辐射热条件下强; 辐射角度和风力均对飞蝗的体温有显著影响。结果显示东亚飞蝗对高温的耐受能力较强, 并且具有明显的体温调节行为, 可调节体温达到最佳生理状态。     

Chill injury in the eggs of the migratory locust, Locusta migratoria （Orthoptera： Acrididae）： the time-temperature relationship with high-temperature interruption

Abstract Mortality of the overwintering egg of the migratory locust, Locusta migratoria L. , was attributed to chill injury because of its occurrence well above the egg's super cooling point. In this study, two parameters, upper limit of chill injury zone (ULCIZ) and sum of the injurious temperature (SIT), were used to examine the locust egg's cold hardiness. The value of ULCIZ for the locust egg is 1.06 ± 0.54°C, and the SIT is -329.7 (hour · degree). The superoxide dismutase (SOD) and catalase (CAT) activities changed dramatically after cold stress, indicating that oxygen and hydroxide free radicals are probably efficiently detoxified at low temperatures. It was suggested that the nature of chill injury in locust egg might be a complex of metabolic disorder and a non-proportional decrease in enzymatic reaction and transports, because the LDH activity at low temperature increased significantly and the ATPase activity decreased with prolonged duration of exposure to low temperatures. The results from high temperature interruption revealed that the high temperature intervals significantly increased the survival of locust eggs.     

Chemosensory proteins of Locusta migratoria (Orthoptera: Acrididae)

We describe a family of proteins abundantly expressed in the chemoreception sensory organs, the antennae and legs, of the desert locust, Locusta migratoria (Orthoptera, Acrididae). Using polymerase chain reaction-based approaches and homology screenings, "OS-D"-like proteins were identified in L. migratoria. The different sub-types (LmigOS-Ds) are very similar to each other and share about 50-70% identity with OS-Ds from Drosophila melanogaster and Periplaneta americana. A similar degree of identity was also observed with moth OS-Ds. Northern blot analysis revealed a strong expression of the LmigOS-Ds in the antennae and legs, suggesting their involvement in chemosensory processes. Despite the lack of direct evidence for their role in chemosensation, LmigOS-Ds and their homologs seem to constitute a large protein family, characterized by a striking abundance and diversity among insect chemosensory organs.     

Structure of identified neurons innervating the lateral cardiac nerve cords in the migratory locust,Locusta migratoria migratorioides (Reiche and Fairmaire) (Orthoptera,Acrididae)

Our knowledge about the morphology of neurons innervating the lateral cardiac nerve cords (LCNCs) in migratory locusts, Locusta migratoria migratorioides (R. and F.) (Orthoptera, Acrididae) has increased considerably during recent years, mainly owing to immunocytochemical studies using antisera directed against members of insect neuropeptide families. In principle, there are three morphological types of neurons located within the CNS, which innervate the LCNCs in locusts: abdominal ganglia contain (i) bilaterally projecting, possibly unpaired neurons (BPNs) and (ii) paired, unilaterally projecting neurons. In addition, (iii) the LCNCs receive innervation from a pair of neurons, which is located within the suboesophageal ganglion. The axons of all three types of neurons project into the LCNCs via the segmental heart nerves, the most distal extensions of the dorsal segemental nerves of abdominal ganglia. When estimating the number of axons contained in one segmental heart nerve and formed by all central neurons so far identified, this number exceeds the number of axon profiles previously seen using the electron microscope. This indicates that most, or perhaps all central neurons projecting into the LCNCs, have been identified in these insects.     

Occurrence and genetics of black‐eyed migratory locusts,Locusta migratoria (Orthoptera: Acrididae)

Black‐eyed Locusta migratoria appeared in albino locusts as a result of crossing between a short‐winged strain originating from Tsushima Island, Japan, and an albino strain originating from Okinawa Island. The black eye trait was recessive to the white eye trait because the crosses between black‐ and white‐eyed albino locusts produced only individuals with white eyes in the F₁ generation. In the F₂ generation, black‐ and white‐eyed individuals appeared in a ratio of 1:3, indicating that the black eye trait was controlled by a simple Mendelian unit. The black eye trait showed no genetic association with other traits including wing morph, adult body dimensions and classical morphometric ratios such as hind femur length / head width and forewing length / hind femur length.     

Geographic variation in embryonic diapause,cold‐hardiness and life cycles in the migratory locust Locusta migratoria (Orthoptera: Acrididae) in China

To investigate geographic adaptation of the migratory locust Locusta migratoria in China, locusts were collected from six localities, ranging from 47.4°N to 19.2°N. Using offspring from the various populations, we compared embryonic diapause, reproductive traits, cold‐hardiness and adult body size. The incidence of embryonic diapause was influenced by the genetic makeup, parental photoperiod, and incubation temperature of the eggs. The northern strain (47.4°N) produced diapause eggs under all photoperiodic conditions, whereas the other strains produced a higher proportion of diapause eggs when exposed to a short photoperiod. The incubation temperature greatly influenced diapause induction. At a low temperature, all eggs entered diapause, even some of those from a tropical strain (19.2°N) in which no diapause was induced at high temperatures. Photoperiodic changes during the parental generation affected the incidence of embryonic diapause. Diapause intensity decreased with decreasing original latitude. Cold hardiness was compared by exposing eggs in diapause to either ?10 or ?20°C for various periods; the northern strain was more cold‐hardy than the southern strain, although some eggs in the tropical strain were probably not in a state of diapause. Adult body size and head width showed a complicated pattern of variation along the latitudinal gradient, whereas egg pod size (egg pod width and egg number) and hatchling weight tended to decrease with decreasing latitude. These results reveal that L. migratoria has adapted to local environments and that the latitudinal gradient appears to play an important role in shaping L. migratoria life cycle and development.     

飞蝗研究进展

飞蝗作为农业重大害虫,其分布遍及欧洲、亚洲、非洲和澳洲。全世界共有10个亚种,我国有3个亚种。飞蝗不但分布广,而且数量多、发生频率高,危害极为严重。作者在查阅了国内外近20年文献资料的基础上,结合我国蝗害情况,分别从形态、组织、生理、生化、遗传、毒力及分子系统学等方面综述了国内外飞蝗的研究进展,以期对我国飞蝗的基础及应用研究提供参考。     

东亚飞蝗胚胎体节的形成过程

体节形成是昆虫胚胎发育过程中的关键问题.东亚飞蝗Locusta migratoria manilensis(Meyen)是一种重要的农业害虫,其体节形成的时序过程尚无详细报道.本研究采用免疫组化和品红染色方法研究了室内人工饲养东亚飞蝗的体节形成过程.结果表明:完成受精后,细胞核开始分裂并向卵表面迁移.细胞核到达卵表面的...     

Influence of soil moisture on egg cold hardiness in the migratory locust Locusta migratoria (Orthoptera: Acridiidae)

Abstract.  The present study investigates the influence of environmental moisture on cold hardiness of the migratory locust, Locusta migratoria . The water content of locust eggs kept in soil at 30 °C varies according to the moisture content of the substrate. In turn, it can significantly affect the supercooling point of locust eggs (range from −26 to −14.8 °C) and the mortality when exposed to subzero temperatures. Environmental moisture influences the supercooling capacity of eggs and their survival at low temperature. When locust eggs of the same water content are exposed to subzero temperatures under different soil moistures, their mortality varies between short-time exposure and long-time exposure at subzero temperatures. Given a short-time exposure, mortality in wet soil is lower than in dry soil due to the buffering effect of soil water against temperature change. The pattern of egg mortality is reversed after long-time exposure at low temperature, suggesting that inoculative freezing may be an important mortality factor. It is suggested that interactions between soil moisture and low temperature can influence the cold hardiness of locust eggs, and partial dehydration is beneficial to over-wintering eggs of the migratory locust.     

东亚飞蝗山西两地理种群酯酶特性的比较研究

对东亚飞蝗山西临猗和永济2个地理种群的酯酶特性进行了比较研究.非变性聚丙烯酰胺凝胶电泳图谱显示:以a-乙酸萘酯为底物染色,2个东亚飞蝗种群谱带差别不明显.但是,酯酶动力学研究结果表明:以a-乙酸萘酯和α-丁酸萘酯为底物时,永济种群的酯酶活性分别是临猗种群的1.81倍和1.20倍.永济种群酯酶活性的增高可能与非变性聚丙烯酰胺凝胶电泳图谱显示出较临猗种群多出的酶带有关.体外酯酶抑制动力学研究表明:永济和临猗2种群所含酯酶大都为B型酯酶,其含量分别为84.94%和91.47%.永济种群对对氧磷的耐受性要高于临猗种群,我们推测可能与2种群马拉硫磷使用背景不同有关.     

东亚飞蝗山西两地理种群酯酶特性的比较研究

对东亚飞蝗山西临猗和永济2个地理种群的酯酶特性进行了比较研究。非变性聚丙烯酰胺凝胶电 泳图谱显示：以α-乙酸萘酯为底物染色,2个东亚飞蝗种群谱带差别不明显。但是,酯酶动力 学研究结果表明：以α-乙酸萘酯和α-丁酸萘酯为底物时,永济种群的酯酶活性分别是临猗 种群的1.81倍和1.20倍。永济种群酯酶活性的增高可能与非变性聚丙烯酰胺凝胶电泳图谱显 示出较临猗种群多出的酶带有关。体外酯酶抑制动力学研究表明：永济和临猗2种群所含酯酶大 都为B型酯酶,其含量分别为84.94%和91.47%。永济种群对对氧磷的耐受性要高于临猗种群 ,我们推测可能与2种群马拉硫磷使用背景不同有关。     

Differences in egg thermotolerance between tropical and temperate populations of the migratory locust Locusta migratoria (Orthoptera: Acridiidae)

The migratory locust Locusta migratoria L., which is widely distributed throughout the world, exhibits within- and between-population variation in cold tolerance. To understand physiological adaptation in populations, we studied the genetic basis of thermotolerance in Hainan (tropical) and Liaoning (temperate) populations and measured expression of Hsp70 and Hsp90 mRNA in both populations at low (0 degrees C) and high temperatures (40 degrees C). Phenotypic variation of thermotolerance is heritable. Heritable characteristics differed among different stages of locust egg development, as well as among different measures of thermotolerance. Nuclear genetic factors, rather than cytoplasmic factors, contribute to differences in cold tolerance between the tropical and temperate populations of the migratory locust; for heat tolerance, maternal effects were involved in three stages of egg development. Expression of Hsp90 mRNA was induced in temperate population after heat shock (40 degrees C x 12h), whereas expression of Hsp70 and 90 was induced in tropical population after cold shock (0 degrees C x 12h). We suggest that thermotolerance of locust eggs has a complex genetic basis and heat shock proteins may be involved in differences of thermotolerance between locust populations.     

Characterization of cuticular proteins from the migratory locust,Locusta migratoria

Proteins were extracted from the still unhardened (teneral) cuticle of the migratory locust, Locusta migratoria. The proteins are soluble only at extreme pH-values and at low ionic strength, the solubility increases with decreasing temperature. The unhardened cuticle contains approx. 100 different proteins according to two-dimensional polyacrylamide gel electrophoresis. The majority of the proteins are very basic. The basicity and solubility properties of the proteins have necessitated development of modified electrophoretic procedures. The amino acid composition of the bulk protein shows that alanine, proline, glycine, valine and tyrosine constitute two thirds of the total amino acid content and that cysteine, methionine and tryptophan are absent.The proteins have been extracted from various parts of the cuticle and analysed by two-dimensional electrophoresis. Characteristic protein compositions were found for cuticle from the different body parts. Amino acid analyses of these extracts are strikingly similar. The only significant difference is in the glycine-alanine ratio. Cuticles that are destined to become hard are extremely rich in alanine, whereas the flexible parts of the cuticle are enriched in glycine. The results indicate that the proteins of locust cuticle constitute a group of structural proteins different from other known structural proteins.     

东亚飞蝗fem-1基因的克隆与表达分析

秀丽隐杆线虫Caenorhabditis elegans fem-1基因是性别决定的关键基因。本研究基于生物信息学方法从东亚飞蝗Locusta migratoria manilensis的转录组数据库中克隆出了线虫fem-1的3个同源基因, 将其分别命名为Lmfem-1a, Lmfem-1b和Lmfem-1c (GenBank登录号分别为AB698670, AB698671和AB698672)。其cDNA序列长度分别为2 233, 2 625和2 142 bp, 分别编码662, 642和638个氨基酸。生物信息学分析显示, Lmfem-1a, Lmfem-1b和Lmfem-1c分别含有6, 8和8个典型的锚蛋白重复序列模体。组织表达谱分析发现, Lmfem-1a, Lmfem-1b和Lmfem-1c基因在检测的所有组织中都有表达, 但均在精巢中的表达水平最高, 说明Lmfem-1a, Lmfem-1b和Lmfem-1c基因可能参与东亚飞蝗的多种生理过程, 并受到严格的表达调控。而且, 随着精巢的发育, Lmfem-1a, Lmfem-1b和Lmfem-1c的表达均逐渐增强, 可能与东亚飞蝗的精子形成有关, 但这3个基因是否参与东亚飞蝗的性别决定还有待进一步研究。     

First record of Aspergillus oryzae (Eurotiales: Trichocomaceae) as an entomopathogenic fungus of the locust,Locusta migratoria (Orthoptera: Acrididae)

A novel entomopathogenic fungus of Locusta migratoria was identified as Aspergillus oryzae using a comparative sequence analysis of the internal transcribed spacer regions, aflatoxin B₁ detection and morphological analysis. The fungus isolated from a dead locust collected in northwestern China was found to be pathogenic to the insect. Phylogenetic experiments revealed a 99% similarity between the fungus and those of three species, A. oryzae, Aspergillus flavus and Aspergillus parvisclerotigenus which are in the same branch of the Flavi section of the genus Aspergillus. Tests to detect aflatoxin B₁ demonstrated that this fungus is a non-aflatoxin B₁ producer, unlike A. parvisclerotigenus. Furthermore, morphological comparison with A. oryzae and A. flavus revealed that Aspergillus sp. XJ-1 belongs to A. oryzae, and named as A. oryzae XJ-1. The results of bioassays against third-instar locusts showed that mortality was dose-dependent and its median lethal concentrations were 3.3 × 10⁸, 1.7 × 10⁷ and 7.2 × 10⁶ conidia/ml on the 10th-, 13th- and 15th-day post-inoculation. Therefore, the A. oryzae XJ-1 may have biocontrol potential against locusts.