Egg weight, batch size and fecundity of the spotted stalk borer, Chilo partellus in relation to weight of females and time of oviposition

The egg laying pattern of the spotted stalk borer on sorghum and maize, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae) was studied during the first three nights of oviposition under laboratory conditions. More than 50% of both eggs and egg batches are laid during the first night of oviposition. Batch size decreases with time, whereas mean egg weight remains constant.Larger females lay both larger eggs and egg batches than smaller ones. They are also more fecund but it is only the second night of oviposition that contributes significantly to this difference.The reproductive effort decreases much with time. Allocation of reproductive reserves to early eggs seems more important than having eggs evenly distributed over time. Larger females use proportionally more resources to the production of late eggs. Large eggs are likely to contain more yolk which could be of importance for the ballooning behaviour of newly hatched larvae.

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Résumé La ponte de C. partellus Swinhoe a été étudiée au laboratoire pendant les trois premières nuits de la ponte. Plus de 50% des ooplaques et des oefs ont été pondus pendant la première nuit. La taille des ooplaques diminue avec le temps, tandis que le poids moyen des oeufs reste constant.Les grosses femelles pondent des ooplaques et des oeufs plus grands que les petites. Elles sont aussi plus fécondes, mais c'est seulement à la seconde nuit de ponte qu'est due cette différence.Le reproduction diminue beaucoup avec le temps. L'affectation aux premiers oeufs des réserves utilizées pour la reprodution semble plus importante que l'émission d'oeufs régulièrement répartis dans le temps. Les grosses femelles utilisent proportionnellement plus de ressources à la production d'oeufstardifs. Les gros oeufs contiennent vraisemblablement plus de vitellus que pourrait être nécessaire pour le comportement aérostatique des chenilles néonates.

     

Resistance in certain maize cultivars to first and third-instar Chilo partellus larvae

The resistance/susceptibility levels of ten maize (Zea mays L.) cultivars to neonates and 3rd-instar larvae of Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae) were measured in the field and screenhouse experiments. The maize cultivars tested were: Inbred A, Mp 704, V-37, Population 10, Hybrid 511, Katumani Composite B, ER-29 SVR, Poza Rica 7832, ICZ2-CM, and MMV 400. Most cultivars were found susceptible to 3rd-instar larvae based on the incidence of dead heart symptoms, foliar feeding and stem tunnelling caused by stem borers in both the field and screenhouse experiments. However, the maize cultivars V-37, MMV 400 and Poza Rica 7832 sustained significantly lesser damage than the other cultivars when infested with neonates or 3rd instar larvae.The screenhouse experiments conducted with five maize cultivars, i.e. Inbred A, Mp 704, V-37, ER-29 SVR, and Poza Rica 7832 showed that neonates fed less on the resistant than the susceptible maize cultivars but feeding by the 3rd instars was equally high on all the maize cultivars except Mp 704 on which the larvae fed less than the others. In the cultivars infested with neonates, the mean period for 50% moth emergence P₅₀ was longest on Mp 704 followed by Poza Rica 7832, ER-29 SVR, V-37 and Inbred A. In the cultivars infested with 3rd-instars, P₅₀ was longest for Poza Rica 7832 followed equally by the remaining cultivars.On the basis of the evidence presented we here conclude that neonates of C. partellus are sensitive to the growth inhibiting effects of the resistant maize cultivars Mp 704, V-37, and Poza Rica 7832 but the older larvae are insensitive to these effects of Mp 704 and V-37 but not of Poza Rica 7832.     

不同释放密度和高度对稻螟赤眼蜂防控两种水稻螟虫效果的影响

稻螟赤眼蜂Trichogramma japonicum Ashmead是二化螟Chilo suppressalis(Walker)和稻纵卷叶螟Cnaphalocrocis medinalis(Guenée)的优势卵寄生蜂。为优化稻螟赤眼蜂田间释放技术,作者分别在安徽、福建和贵州进行了稻螟赤眼蜂不同释放高度和密度对防控两种水稻螟虫效果影响的田间试验。结果表明,对于防控稻纵卷叶螟,释放量一定时,赤眼蜂在稻株顶部以上5 cm高度、8点/0.07 hm 2释放密度的防治效果优于其他释放密度和高度的处理。而对于防控二化螟,不同释放高度对赤眼蜂防治效果差异不显著。     

A chromosome‐level genome assembly reveals the genetic basis of cold tolerance in a notorious rice insect pest,Chilo suppressalis

The rice stem borer, Chilo suppressalis, is one of the most damaging insect pests to rice production worldwide. Although C. suppressalis has been the focus of numerous studies examining cold tolerance and diapause, plant–insect interactions, pesticide targets and resistance, and the development of RNAi‐mediated pest management, the absence of a high‐quality genome has limited deeper insights. To address this limitation, we generated a draft C. suppressalis genome constructed from both Illumina and PacBio sequences. The assembled genome size was 824.35 Mb with a contig N₅₀ of 307 kb and a scaffold N₅₀ of 1.75 Mb. Hi‐C scaffolding assigned 99.2% of the bases to one of 29 chromosomes. Based on universal single‐copy orthologues (BUSCO), the draft genome assembly was estimated to be 97% complete and is predicted to encompass 15,653 protein‐coding genes. Cold tolerance is an extreme survival strategy found in animals. However, little is known regarding the genetic basis of the winter ecology of C. suppressalis. Here, we focused our orthologous analysis on those gene families associated with animal cold tolerance. Our finding provided the first genomic evidence revealing specific cold‐tolerant strategies in C. suppressalis, including those involved in glucose‐originated glycerol biosynthesis, triacylglycerol‐originated glycerol biosynthesis, fatty acid synthesis and trehalose transport‐intermediate cold tolerance. The high‐quality C. suppressalis genome provides a valuable resource for research into a broad range of areas in molecular ecology, and subsequently benefits developing modern pest control strategies.     

Molecular characterization and functional analysis of the vitellogenin receptor in the rice stem borer,Chilo suppressalis

As a member of the low-density lipoprotein receptor (LDLR) superfamily, vitellogenin (Vg) receptor (VgR) is responsible for the uptake of Vg into developing oocytes and is a potential target for pest control. Here, a full-length VgR complementary DNA (named as CsVgR) was isolated and characterized in the rice stem borer, Chilo suppressalis. The composite CsVgR gene contained an open reading frame of 5,484 bp encoding a protein of 1,827 amino acid residues. Structural analysis revealed that CsVgR contained two ligand-binding domains (LBDs) with four Class A (LDLR_A) repeats in LBD1 and seven in LBD2, which was structurally different from most non-Lepidopteran insect VgRs having five repeats in LBD1 and eight in LBD2. The developmental expression analysis showed that CsVgR messenger RNA expression was first detectable in 3-day-old pupae, sharply increased in newly emerged female adults, and reached a peak in 2-day-old female adults. Consistent with most other insects VgRs, CsVgR was exclusively expressed in the ovary. Notably, injection of dsCsVgR into late pupae resulted in fewer follicles in the ovarioles as well as reduced fecundity, suggesting a critical role of CsVgR in female reproduction. These results may contribute to the development of RNA interference-mediated disruption of reproduction as a control strategy of C. suppressalis.     

Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae) a new invasive species in Israel

Chilo partellus, the spotted stem borer (SSB), is reported for the first time from the fields of sorghum and corn in Israel. Spotted stem borer larvae were first discovered in July 2010 on sorghum and corn plants in the Western Galilee. The new pest had spread all over northern Israel by the end of 2011. The identity of the new pest was confirmed using the morphology of the dissected male genitalia and its attraction to SSB sex pheromone.     

Comparison of three transgenic Bt rice lines for insecticidal protein expression and resistance against a target pest,Chilo suppressalis (Lepidoptera: Crambidae)

Two transgenic rice lines (T2A‐1 and T1C‐19b) expressing cry2A and cry1C genes, respectively, were developed in China, targeting lepidopteran pests including Chilo suppressalis (Walker) (Lepidoptera: Crambidae). The seasonal expression of Cry proteins in different tissues of the rice lines and their resistance to C. suppressalis were assessed in comparison to a Bt rice line expressing a cry1Ab/Ac fusion gene, Huahui 1, which has been granted a biosafety certificate. In general, levels of Cry proteins were T2A‐1 > Huahui 1 > T1C‐19b among rice lines, and leaf > stem > root among rice tissues. The expression patterns of Cry protein in the rice line plants were similar: higher level at early stages than at later stages with an exception that high Cry1C level in T1C‐19b stems at the maturing stage. The bioassay results revealed that the three transgenic rice lines exhibited significantly high resistance against C. suppressalis larvae throughout the rice growing season. According to Cry protein levels in rice tissues, the raw and corrected mortalities of C. suppressalis caused by each Bt rice line were the highest in the seedling and declined through the jointing stage with an exception for T1C‐19b providing an excellent performance at the maturing stage. By comparison, T1C‐19b exhibited more stable and greater resistance to C. suppressalis larvae than T2A‐1, being close to Huahui 1. The results suggest cry1C is an ideal Bt gene for plant transformation for lepidopteran pest control, and T1C‐19b is a promising Bt rice line for commercial use for tolerating lepidopteran rice pests.     

Olfactory cues explain differential attraction of the striped rice stem borer to different varieties of rice plant

In Iranian rice fields, different varieties of rice are cultivated which are differentially impacted by females of the rice stem borer, Chilo suppressalis. To elucidate the role odours may play in their host plant finding behaviour, female Ch. suppressalis were exposed to four varieties of rice plants and their volatiles in a four‐arm olfactometer. In whole plant tests, Ch. suppressalis were significantly attracted to the variety previously characterized as most susceptible, least attracted to one characterized as semisusceptible, and showed no attraction to those varieties characterized as semi‐ and highly resistant. Tests using headspace volatile extracts yielded similar results in the case of the most susceptible variety, but showed no attraction to the semisusceptible and highly resistant varieties, and low attraction to the semiresistant variety. Subsequent analysis of the volatile composition identified a panel of 27 components, some of which were either unique to, or abundantly present in, particular varieties, and may explain the observed variation in their attractiveness. Our findings show that rice plant volatiles can play a role in the host selection behaviour of this pest species, and we suggest compounds which may be important to this process and the future application of volatiles in rice pest management programs.     

四种鳞翅目害虫精氨酸激酶基因的表达谱及基于RNAi的功能分析

【目的】精氨酸激酶(arginine kinase, AK)(EC 2.7.3.3)是昆虫体内重要的磷酸原激酶(能量代谢调节因子),也是唯一能够形成有效ATP的磷酰基供体,起着与脊椎动物中肌酸激酶相同的作用。本研究旨在了解鳞翅目害虫AK基因的表达和功能。【方法】利用qRT-PCR方法测定AK基因在大螟Sesamia inferens、二化螟Chilo suppressalis、甜菜夜蛾Spodoptera exigua和斜纹夜蛾Spodoptera litura 这4种鳞翅目害虫不同发育阶段和3龄幼虫不同组织中的表达谱;通过终点法检测了这4种害虫不同发育阶段和幼虫不同组织中的AK酶活性;采用RNAi技术抑制该基因的表达并分析其功能。【结果】AK基因在大螟、二化螟、甜菜夜蛾和斜纹夜蛾这4种鳞翅目昆虫的不同发育阶段和3龄幼虫不同组织中均有表达,说明该基因的表达不具有发育时期和组织特异性。不同发育时期和3龄幼虫不同组织中AK酶活性与基因表达量变化趋势大体一致。注射以AK基因为靶标的dsRNA 6 d后,4种害虫体内AK基因的mRNA表达下降30%~50%,AK酶活性降低30%左右;14 d后幼虫的死亡率达50%左右,显著高于对照组幼虫的死亡率。【结论】AK基因在上述4种鳞翅目害虫中为组成型表达,RNAi抑制AK基因的表达可导致4种害虫的幼虫死亡,研究结果为开发以AK基因为靶标的鳞翅目害虫防治新技术提供了理论依据。