Rapid Identification of Helicoverpa armigera and Helicoverpa zea (Lepidoptera: Noctuidae) Using Ribosomal RNA Internal Transcribed Spacer 1

Rapid identification of invasive species is crucial for deploying management strategies to prevent establishment. Recent Helicoverpa armigera (Hübner) invasions and subsequent establishment in South America has increased the risk of this species invading North America. Morphological similarities make differentiation of H. armigera from the native Helicoverpa zea (Boddie) difficult. Characteristics of adult male genitalia and nucleotide sequence differences in mitochondrial DNA are two of the currently available methods to differentiate these two species. However, current methods are likely too slow to be employed as rapid detection methods. In this study, conserved differences in the internal transcribed spacer 1 (ITS1) of the ribosomal RNA genes were used to develop species-specific oligonucleotide primers that amplified ITS1 fragments of 147 and 334 bp from H. armigera and H. zea, respectively. An amplicon (83 bp) from a conserved region of 18S ribosomal RNA subunit served as a positive control. Melting temperature differences in ITS1 amplicons yielded species-specific dissociation curves that could be used in high resolution melt analysis to differentiate the two Helicoverpa species. In addition, a rapid and inexpensive procedure for obtaining amplifiable genomic DNA from a small amount of tissue was identified. Under optimal conditions, the process was able to detect DNA from one H. armigera leg in a pool of 25 legs. The high resolution melt analysis combined with rapid DNA extraction could be used as an inexpensive method to genetically differentiate large numbers of H. armigera and H. zea using readily available reagents.     

Differential efficacy of three commonly used pyrethroids against laboratory and field‐collected larvae and adults of Helicoverpa zea (Lepidoptera: Noctuidae) and significance for pyrethroid resistance management

BACKGROUND: Helicoverpa zea (Boddie) pyrethroid resistance monitoring programs typically utilize cypermethrin in the adult vial test. Here we investigated if differences in insect growth stage and pyrethroid structure affect resistance ratios and discuss implications for pyrethroid resistance management. RESULTS: Vial bioassays with cypermethrin, esfenvalerate and bifenthrin were conducted on H. zea third instars and male moths from a susceptible laboratory colony and the F1 generation of a pyrethroid‐resistant field population. In the susceptible population, both growth stages were most sensitive to bifenthrin and adults were more sensitive to esfenvalerate than cypermethrin. LC₅₀ resistance ratios for the larvae and adults of the resistant population were approximately two times higher for bifenthrin than cypermethrin or esfenvalerate. CONCLUSION: For the resistant population, vial assays using either growth stage gave similar resistance ratios for each of the three pyrethroids, respectively, proving the adult vial test accurately reflects larval resistance. However, as resistance ratios varied considerably depending on the pyrethroid used, resistance ratio values obtained with one pyrethroid may not be predictive of resistance ratios for other pyrethroids. Our results suggest that carefully chosen pyrethroid structures diagnostic for specific mechanisms of resistance could improve regional monitoring programs. Copyright © 2009 Society of Chemical Industry     

Pest-damage relationships for Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on soybean (Glycine max) and dry bean (Phaseolus vulgaris) during pod-fill

The response of soybean (Glycine max) and dry bean (Phaseolus vulgaris) to feeding by Helicoverpa armigera during the pod-fill stage was studied in irrigated field cages over three seasons to determine the relationship between larval density and yield loss, and to develop economic injury levels. H. armigera intensity was calculated in Helicoverpa injury equivalent (HIE) units, where 1 HIE was the consumption of one larva from the start of the infestation period to pupation. In the dry bean experiment, yield loss occurred at a rate 6.00 ± 1.29 g/HIE while the rates of loss in the three soybean experiments were 4.39 ± 0.96 g/HIE, 3.70 ± 1.21 g/HIE and 2.12 ± 0.71 g/HIE. These three slopes were not statistically different (P > 0.05) and the pooled estimate of the rate of yield loss was 3.21 ± 0.55 g/HIE. The first soybean experiment also showed a split-line form of damage curve with a rate of yield loss of 26.27 ± 2.92 g/HIE beyond 8.0 HIE and a rapid decline to zero yield. In dry bean, H. armigera feeding reduced total and undamaged pod numbers by 4.10 ± 1.18 pods/HIE and 12.88 ± 1.57 pods/HIE respectively, while undamaged seed numbers were reduced by 35.64 ± 7.25 seeds/HIE. In soybean, total pod numbers were not affected by H. armigera infestation (out to 8.23 HIE in Experiment 1) but seed numbers (in Experiments 1 and 2) and the number of seeds/pod (in all experiments) were adversely affected. Seed size increased with increases in H. armigera density in two of the three soybean experiments, indicating plant compensatory responses to H. armigera feeding. Analysis of canopy pod profiles indicated that loss of pods occurred from the top of the plant downwards, but with an increase in pod numbers close to the ground at higher pest densities as the plant attempted to compensate for damage. Based on these results, the economic injury levels for H. armigera on dry bean and soybean are approximately 0.74 HIE and 2.31 HIE/m², respectively (0.67 and 2.1 HIE/row-m for 91 cm rows).     

Studies on the Relationship between Occurrence Degree of Cotton Boll-worm and Rainfall

[Objective] The aim of the study is to investigate the factors causing the outbreak of cotton boUworm and to provide effective measures for con-trolling cotton bollworm. [Method] Based on the analysis of the data about insect and weather situation in Luyi County in 32 years, the meteorological pre-diction model was established for monitoring the quarterly or monthly, occurrence trend of cotton bollworm. [Result] The cotton bnflworm oceurred slightly in the years with rainfalls of 3 months over 500 nm and severely in the years with rainfalls of 3 months less than 400 nm. The results of correlation analysis show that annual occurrence degrees of cotton bollworm and occurrence degrees of 4th generation of cotton bollworm are extremely negatively correlated with rainfall during June - August ; the occurrence degrees of 3rd and 4th generations of cotton bollworra are also extremely negatively correlated with rainfall in July. [Condusion] The occurrence of cotton bollworm in field is heavily influenced by rainfall in at its occurrence stage, moreover, the rainfall during June - August is the decisive factors influencing the occurrence of cotton bollworm.     

棉铃虫发生程度与降雨量关系的研究(英文)

[Objective] The aim of the study is to investigate the factors causing the outbreak of cotton bollworm and to provide effective measures for controlling cotton bollworm. [Method] Based on the analysis of the data about insect and weather situation in Luyi County in 32 years,the meteorological prediction model was established for monitoring the quarterly or monthly occurrence trend of cotton bollworm. [Result] The cotton bollworm occurred slightly in the years with rainfalls of 3 months over 500 nm and severely in the years with rainfalls of 3 months less than 400 nm. The results of correlation analysis show that annual occurrence degrees of cotton bollworm and occurrence degrees of 4th generation of cotton bollworm are extremely negatively correlated with rainfall during June-August; the occurrence degrees of 3rd and 4th generations of cotton bollworm are also extremely negatively correlated with rainfall in July. [Conclusion] The occurrence of cotton bollworm in field is heavily influenced by rainfall in at its occurrence stage,moreover,the rainfall during June-August is the decisive factors influencing the occurrence of cotton bollworm.     

控制棉铃虫猖獗危害的区域性综合防治关键技术体系的研究

在跟踪推广应用“六五”以来所形成的综防技术基础上,进一步研究改进关键技术、加强病虫监测预报、组建综防技术体系。在1992、1993年棉铃虫猖獗发生的情况下,于河南省新乡棉花病虫害综防示范区0.67万hm#+2棉田上实施后,有效控制了棉铃虫危害。这套控制棉铃虫猖獗危害综合防治关键技术主要是：研究改进了棉铃虫中期预报方法;提出“一代监测、二代保顶、三代保蕾、四代保铃”为主的防治策略;制定推广适用于不同世代、不同水肥条件的科学防治指标;协调应用多种配套措施保护、利用自然天敌控害;系统监测和治理害虫抗药性;利用棉花种质资源和品种的抗病虫性;诱杀成虫;组建大面积综防技术体系。     

转基因棉Bt毒性表达的时空动态及对棉铃虫生存、繁殖的影响

转Ｂｔ基因棉３１０品系在不同发育阶段,对棉铃虫的毒性表达测定表明,（１）棉株各空间组织在不同发育阶段均能强力阻止棉铃虫取食,表达出较高的抗虫效果。（２）棉株不同空间组织在同一时期,毒性表达存在差异,以营养组织,中、小蕾高于大蕾和铃。（３）同一组织毒性表达随着棉株生长、发育、成熟、衰老逐渐呈动态下降。（４）前后各阶段,同一组织饲喂棉铃虫,死亡所需要天数呈动态增加,但最终生存率降低到一个较低水平。存活老熟幼虫重量、蛹重及蛹羽化率比对照棉铃虫下降３０％～５０％,羽化的蛾子进行自交或异交均能产下受精率、孵化率很高的卵。取食Ｂｔ转基因棉的雌蛾产卵量比对照减少５０％～７０％。     

阿维菌素对棉铃虫毒力及增效剂的作用

采用浸债法测定了阿维菌素对棉铃虫卵孵化抑制作用,0．1,1,10,I10μg·mL－1阿维菌素对卵孵化抑制率分别为州,51％,63％,71％。采用饲料混药法测定了阿维菌素对不同龄期棉铃虫的毒力。结果表明,处理后96h对初孵、1龄、3龄、4龄幼虫的致死中浓度LC500分别为0．005,0．021,0．64,1．13μg·mL－1,对照药剂甲基对硫磷、水胺硫磷、灭多威对3龄幼虫的致死中浓度分别为22,39,72μg·mL－1;同时还观察到1龄幼虫经处理96h后幼虫体长抑制率与药剂浓度成正相关,当药剂含量为0．00625,0．0125,0．025,0.05μg·mL－1时,体长抑制率分别为9．5％,57．1％,71．4％,90．5％;处理14d后,对照幼虫为6龄,处理组0．05μg·mL－1的为2～3龄,0．00625μg·mL－1的为3～5龄;低含量阿维菌素饲喂5龄幼虫8d后化蛹率、死蛹或畸形蛹率、蛹重对照组分别为68％,13％,0．48g·头-1,处理组分别为3％,56％,0．26g·头-1;采用点滴法和饲料混药法测定的PBO和TPP对阿维菌素的增效作用,结果表明PBO有一定的增效作用。文中还讨论了PBO增效作用的机理。     

棉铃虫二代成虫高峰期预测研究

通过资料整理和研究,弄清了影响棉铃虫（Helicoverpa armigera Hibner)二代成虫高峰期的三个主导因子,在此基础上,利用模糊列联表法进行了15年的回顾测和2年的预测,结果达到93．33％,可提前半月作出预测。