Laboratory evaluation of the virulence of Beauveria bassiana isolates to the sorghum shoot borer Chilo partellus Swinhoe (Lepidoptera: Pyralidae) and their characterization by RAPD-PCR

Beauveria bassiana has long been used as a mycopesticide. It has a wide host range; isolates have been reported to differ in host range and virulence to a given insect species. Identification of a molecular marker linked to a virulent phenotype to a target pest would be useful in screening for isolates effective against it. Twenty B. bassiana isolates were tested for their virulence to the second instar larvae of Chilo partellus Swinhoe in laboratory bioassays and their DNA fingerprints were generated by RAPD-PCR. Three arbitrary categories of aggressiveness were chosen; isolates that caused >70%, between 70 and 40% and <40% larval mortality were grouped as highly, medium and less aggressive types, respectively. In the random amplified polymorphic DNA (RAPD) analysis a 30% variability was observed among the isolates; which clustered into three major groups. The groups based on virulence rating did not match with the RAPD clusters. One of the highly aggressive isolates clustered with less aggressive isolates in one cluster and the other grouped along with the medium aggressive isolates in a different cluster. The B. bassiana isolates were classified phenotypically based on the taxonomic order of the original insect host and the climatic zone (tropical/temperate) from which they were isolated. No correlation between the aggressiveness of the isolate and the relatedness of the original insect host to the tested insect was observed; both the highly aggressive isolates were from coleopteran insects. A correlation was found between the RAPD grouping and the phenotypic classification of the isolates. All the lepidopteran isolates grouped into one major cluster, most sub clusters were constituted by isolates from the same climatic zone.     

二化螟种群空间格局的经典分析与地统计学比较研究

为揭示二化螟幼虫空间格局特征并阐明经典格局分析的局限性与地统计分析的优越性,从2个原始样本出发,另构建了一系列格栅样本、随机样本和顺序样本并进行了比较研究。结果表明,经典格局分析不能有效区分频次分布相同但分布型或聚集程度不同的样本,存在受样方大小、格栅初始点位置和样本容量大小影响等许多局限性,其中受格栅初始点位置影响是首次报道;而地统计学半变异函数能有效刻划二化螟种群空间分布格局,表征其聚集强度和空间异质性,且受样方大小、格栅初始点位置和样本容量大小的影响较小,二化螟种群在低密度下呈随机分布;在高密度下呈聚集分布,聚集强度为0．1056,空间依赖范围为193cm,在高密度下二化螟种群空间分布存在几何异向性,行方向上的聚集强度（0．2716)明显高于列方向(0．0867),但行方向上的空间依赖范围(115cm)小于列方向(264cm)。     

二化螟乙酰胆碱受体α亚基的基因克隆与序列分析

烟碱型乙酰胆碱受体(nAChR)在昆虫的兴奋性突触传递中起着重要的作用,同时也是杀虫剂作用的重要靶标。近年来,二化螟对作用于昆虫nAChR的沙蚕毒素类杀虫剂杀虫单产生了高抗性。为了研究可能存在的靶标不敏感机制,我们采用RT-PCR技术,对二化螟nAChR-α亚 基全长cDNA进行了分子克隆。序分析表明,这是1个新的α亚基基因,定名为Cs α 1。基 因全长为1997个核苷酸,包含了1个开放阅读框,编码1个509氨基酸的成熟蛋白和1个24氨基酸的信号肽。Cs α 1与其他昆虫nAChR α亚基之间有52%-94%的同源性,高于与脊椎动物nAChR α亚基之间的同源性。     

Do differences in life‐history traits and the timing of peak mating activity between host‐associated populations of Chilo suppressalis have a genetic basis?

The development of host races, genetically distinct populations of the same species with different hosts, is considered to be the initial stage of ecological speciation. Ecological and biological differences consistent with host race formation have been reported between water‐oat and rice‐associated populations of Chilo suppressalis. In order to confirm whether these differences have a genetic basis, we conducted experiments to determine the extent to which various life‐history traits and the time of peak mating activity of these populations were influenced by the species of host plant larvae were raised on. Individuals from each population were reared for three consecutive generations on either water‐oat fruit pulp or rice seedlings. Descendants of both populations had higher larval survival rates, shorter larval developmental periods, higher pupal weight, and longer adult forewings, when reared on water‐oats than when reared on rice. The time of peak of mating activity differed between the descendants of each population, irrespective of whether they were raised on water‐oats or rice. These results indicate that although some life‐history traits of host‐associated populations of C. suppressalis are influenced by the host plant larvae are raised on, time of peak mating activity is not. Because it is a stable, objective, phenotypic trait, further research on difference in the time of peak mating activity between host‐associated populations of C. suppressalis should be conducted to clarify the mechanism responsible for host race formation in this species.     

Expression of the maize proteinase inhibitor (mpi) gene in rice plants enhances resistance against the striped stem borer (Chilo suppressalis): effects on larval growth and insect gut proteinases

The maize proteinase inhibitor (mpi) gene was introduced into two elite japonica rice varieties. Both constitutive expression of the mpi gene driven by the maize ubiquitin 1 promoter and wound-inducible expression of the mpi gene driven by its own promoter resulted in the accumulation of MPI protein in the transgenic plants. No effect on plant phenotype was observed in mpi-expressing lines. The stability of transgene expression through successive generations of mpi rice lines (up to the T(4) generation) and the production of functional MPI protein were confirmed. Expression of the mpi gene in rice enhanced resistance to the striped stem borer (Chilo suppressalis), one of the most important pests of rice. In addition, transgenic mpi plants were evaluated in terms of their effects on the growth of C. suppressalis larvae and the insect digestive proteolytic system. An important dose-dependent reduction of larval weight of C. suppressalis larvae fed on mpi rice, compared with larvae fed on untransformed rice plants, was observed. Analysis of the digestive proteolytic activity from the gut of C. suppressalis demonstrated that larvae adapted to mpi transgene expression by increasing the complement of digestive proteolytic activity: the serine and cysteine endoproteinases as well as the exopeptidases leucine aminopeptidase and carboxypeptidases A and B. However, the induction of such proteolytic activity did not prevent the deleterious effects of MPI on larval growth. The introduction of the mpi gene into rice plants can thus be considered as a promising strategy to protect rice plants against striped stem borer.     

Gene cloning and expression of aminopeptidase N and cadherin from midgut of the rice stem borer,Chilo suppressalis

The rice stem borer,Chilo suppressalis Walker is one of the most importantinsect pests on rice in Asia,north Africa and southern Europe.Transgenic Bt rice has beendeveloped in the laboratory with good resistance to this pest and other Lepidopteran insects,which will provide a possible alternative tool for this pest control.The full-length cDNAsencoding an aminopeptidase N (CsAPN) and a cadherin (CsCad) were cloned from C.suppressalis.CsAPN showed common features of,and high identities to,other insect AP...     

用甜玉米粒饲养二化螟实验种群

介绍一种能够继代饲养二化螟Chilo suppressalis(Walker)实验种群的天然饲料---"甜玉米粒"及相应饲养方法。结果显示,甜玉米粒和马蹄的饲养成绩皆不同程度地高于稻苗、甘蔗和田间种群。取食甜玉米粒的幼虫存活率达92.0%,显著高于其余3种天然饲料。平均蛹重为60.7mg,单雌产卵量达197.4,除性比为0.9∶1之外,其重要生物学指标和此前报道的饲养成绩最好的马蹄没有显著差异,但成本更低,且更利于清洗消毒等加工处理,因而更适于在实际生产中大量饲养二化螟实验种群。     

Yield loss due to the stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) at different nitrogen application rates to maize

Field trials were conducted at Kibaha and Morogoro in eastern Tanzania during two seasons to evaluate the effect of nitrogen fertilization (0, 50, 75, 100 kg [N]/ha) on pest abundance, plant damage and yield loss of maize due to stemborers. In general, ear and grain weights increased linearly with nitrogen level. In the infested plot, grain weight increased 2.5 and 1.8 fold from 0 to 100 kg [N]/ha in the short and long rainy season, respectively, at Kibaha, and 1.4 and 1.6 times at Morogoro. Yield loss decreased with an increase in nitrogen application and the effect was stronger under high than low borer infestation levels. The results show the beneficial effect of nitrogen on the plant’s ability to compensate for borer damage. Analysis of economic benefits of applying fertilizer and insecticide treatment indicated that using insecticides is not profitable under high-pest-low-soil fertility conditions.     

水稻-二化螟系统模型研究

选影响水稻-二化螟系统产量输出的主要环境要素:氮肥、磷肥、栽插密度、二化螟卵量和幼虫入侵时的叶龄,设计5因子5水平的二次正交旋转组合设计试验。建立了各要素与产量关系的数学模型:Y_Y=0.853-6.77x_1-4.47x_3-13.15x_4 5.92x_1x_3-11.36x_2x_4-5.85x_1~2-3.76x_3~2-4.29x_4~2±0.005;虫口主效应对产量损失的预测模型:Y_L=-13.15x_4-11.36x_2x_4-4.29x_4~2。通过对数学模型的分析得出在中等肥力田块,1m~2施纯氮3.75—7.5g和过磷酸钙75g作底肥,每丛插中苗2株,1m~2有4.05—8.1个卵时能得到0.825kg/m~2以上的高产。也建立了各因素与亩穗数的数学模型,并进行了分析讨论。     

CO_2倍增和转Bt水稻对二化螟幼虫的生理影响

通过开顶式气室研究了CO2浓度倍增(750vs.375μL/L)对取食转Bt水稻及其对照亲本秀水11的二化螟Chilo suppressalis(Walker)幼虫体内代谢酶乙酰胆碱酯酶(AChE)和保护酶(超氧化物歧化酶SOD、过氧化物酶POD和过氧化氢酶CAT)活力的影响,以期明确该类害虫对大气CO2浓度升高及转Bt水稻的生理响应。研究结果表明:(1)AChE受CO2浓度水平影响显著,与对照CO2处理相比,高CO2条件下该酶活力显著降低;(2)高CO2水平及水稻中Bt毒素蛋白的存在均会导致二化螟幼虫体内POD活力显著降低,SOD初期活力显著升高,但不能维持较长时间,CAT活力表现为先升后降的特点;(3)当受到水稻品种、CO2浓度水平和取食时间的综合影响时,以上代谢酶和保护酶活力会发生显著变化。短时间内二化螟幼虫可通过体内以上生理代谢调节减缓受CO2浓度升高和水稻中Bt毒素蛋白的不利影响,但长时间环境胁迫下这种应对不利环境的响应机制将会失去作用,最终导致种群适合度的降低。