Oviposition, development, and reproduction of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) fed on different hosts of economic importance

The host selection for oviposition by Spodoptera frugiperda (J.E. Smith) among corn, millet, cotton and soybean, and its relationship with the biological characteristics were investigated. Free and non-choice tests for oviposition using plots containing five plants each, from each host in plastic greenhouse, resulted in similar oviposition preference among the host plants. In addition, selected biological characteristics of S. frugiperda were determined in the laboratory with larvae feeding on host leaves, and the combination of leaf and cotton boll. Neonate larvae exhibited low success of colonization on cotton boll compared to the leaves of all other hosts. Spodoptera frugiperda fed only on cotton bolls exhibited longer larval and pupal development, and longer adult life span; however with similar egg production. Larvae fed cotton leaves during six days and then transferred to cotton bolls, however, exhibited development and reproduction similar to those reared on corn or only on cotton leaves. Therefore, the variations on immature stages of S. frugiperda were not related with host selection for oviposition which was similar among the studied hosts. Based on our data, the millet as a winter, rotational, and cover crop is a potential host for S. frugiperda, while leaves and cotton bolls were diets of intermediate suitability as compared to corn and soybean leaves.     

Molecular variability of Spodoptera frugiperda (Lepidoptera: Noctuidae) populations associated to maize and cotton crops in Brazil

The molecular variability among 10 populations of Spodoptera frugiperda (J.E. Smith), collected from maize, Zea mays L., or cotton Gossypium hirsutum L. crops located at distinctive geographical regions in Brazil, was assessed through random amplification of polymorphic DNA (RAPD)-polymerase chain reaction (PCR). In total, 208 RAPD markers were evaluated, and 98% of them were polymorphic. The mean genetic similarity was 0.6621 and 0.2499 by the Simple Matching and Jaccard matrices, respectively. In general, the unweighted pair-group method with arithmetic average dendrograms separated the populations into clusters related to the geographical origin of the samples. No branch of the dendrograms underpinning a molecular association of S. frugiperda has been identified to either of the two host plants. The molecular variance analysis showed that 18 and 82% of the genetic variation was distributed among and within the groups of populations, respectively. The principal coordinate analysis reinforced the pattern of population clustering found with the unweighted pair-group method with arithmetic average method. These results suggest the occurrence of considerable gene flow between S. frugiperda populations from maize and cotton fields located in the same region in Brazil. Therefore, for an effective management of this pest, there is an urgent need for a better understanding of the gene flow of S. frugiperda populations associated to different host plants along the distribution range of this pest over time in a specific cropping system.     

广东省草地贪夜蛾冬季发生特征及周年繁殖区域研究

广东省是草地贪夜蛾入侵我国的桥头堡和主要的北迁虫源地之一,明确该虫在广东省的冬季发生特征及越冬存活情况,对广东省乃至全国草地贪夜蛾的预测预报及源头治理意义重大。为准确掌握广东省草地贪夜蛾的周年繁殖区范围及冬季发生为害情况,2020年1-3月在粤东、粤西、粤北及珠三角地区,利用成虫性诱、挖土查蛹、幼虫密度及植株为害率普查等方法,分析广东省草地贪夜蛾冬前、冬后种群发生为害情况及冬季发生特征。调查结果表明:(1)广东省冬玉米种植区主要分布在湛江、茂名、阳江、惠州等地,冬玉米种植区均发现草地贪夜蛾幼虫为害,主要为害冬玉米,极少为害甘蔗;(2)不同地区冬种玉米上草地贪夜蛾的发生程度差异较大,湛江、茂名、阳江发生为害较为严重,平均为害率30%左右,而珠三角及粤东地区发生较轻,为害率低于10%;较冬前调查,冬后草地贪夜蛾发生量和为害程度出现不同程度的下降;(3)广东省大部分地区的冬种玉米田和空闲地均可持续诱捕到草地贪夜蛾成虫,而挖土调查发现草地贪夜蛾蛹密度较低。本调查明确了草地贪夜蛾在北回归线以南的冬玉米区可以周年繁殖,无明显的滞育越冬现象,粤西茂名、阳江以南至雷州半岛一带为典型冬种玉米区,草地贪夜蛾发生为害较为严重,珠三角及粤东大部分地区草地贪夜蛾种群数量相对较低,调查结果为广东省乃至全国草地贪夜蛾的早期预警和精准防控提供了重要参考。     

Response of Pisum sativum (Fabales: Fabaceae) to Sitona lineatus (Coleoptera: Curculionidae) infestation: effect of adult weevil density on damage, larval population, and yield loss

Sitona lineatus L. (Coleoptera: Curculionidae) is an invasive pest in North America and its geographical range is currently expanding across the Canadian prairies. Adults and larvae of S. lineatus feed upon the foliage and root nodules, respectively, of field pea, Pisum sativum L. (Fabales: Fabaceae), and may contribute to economic losses when population densities are high. Integrated pest management (IPM) programs that incorporate economic thresholds should be used to manage S. lineatus populations in a sustainable manner. The impact of nitrogen fertilizer on field pea yield and the relationships between adult weevil density and above- and below-ground damage and yield were investigated in southern Alberta, Canada using exclusion cages on field pea plots. In each cage, 32 field pea plants were exposed to weevil densities ranging from zero to one adult weevil per plant. Nitrogen-fertilized plants yielded 16% more than unfertilized plants. Nitrogen-fertilized plants had fewer root nodules than unfertilized plants, but fertilizer had no effect on foliar feeding by S. lineatus. Adult density affected foliar feeding damage, with increases in above-ground damage associated with increases in S. lineatus density. Adult density did not affect root nodule damage, larval density, foliar biomass or seed weight. Overall, these results indicate that terminal leaf damage may be used to estimate adult weevil density but cannot be used to predict larval density or yield loss. Further research is required to better understand the impact of larval damage on yield and determine if economic thresholds can be developed using data from large-scale production systems.     

基于性诱和深度学习的草地贪夜蛾成虫自动识别计数方法

【目的】探究深度学习在草地贪夜蛾Spodoptera frugiperda成虫自动识别计数上的可行性,并评估模型的识别计数准确率,为害虫机器智能监测提供图像识别与计数方法。【方法】设计一种基于性诱的害虫图像监测装置,定时自动采集诱捕到的草地贪夜蛾成虫图像,结合采集船形诱捕器粘虫板上草地贪夜蛾成虫图像,构建数据集;应用YOLOv5深度学习目标检测模型进行特征学习,通过草地贪夜蛾原始图像、清除边缘残缺目标、增加相似检测目标(斜纹夜蛾成虫)、无检测目标负样本等不同处理的数据集进行模型训练,得到Yolov5s-A1, Yolov5s-A2, Yolov5s-AB, Yolov5s-ABC 4个模型,对比在不同遮挡程度梯度下的测试样本不同模型检测结果,用准确率(P)、召回率(R)、F1值、平均准确率(average precision, AP)和计数准确率(counting accuracy, CA)评估各模型的差异。【结果】通过原始图像集训练的模型Yolov5s-A1的识别准确率为87.37%,召回率为90.24%,F1值为88.78;清除边缘残缺目标图像集训练得到的模型Yolov5s-A2的识别准确率为93.15%,召回率为84.77%,F1值为88.76;增加斜纹夜蛾成虫样本图像训练的模型Yolov5s-AB的识别准确率为96.23%,召回率为91.85%,F1值为93.99;增加斜纹夜蛾成虫和无检测对象负样本训练的模型Yolov5s-ABC的识别准确率为94.76%,召回率为88.23%,F1值为91.38。4个模型的AP值从高到低排列如下：Yolov5s-AB>Yolov5s-ABC> Yolov5s-A2>Yolov5s-A1,其中Yolov5s-AB与Yolov5s-ABC结果相近;CA值从高到低排列如下：Yolov5s-AB>Yolov5s-ABC>Yolov5s-A2>Yolov5s-A1。【结论】结果表明本文提出的方法应用于控制条件下害虫图像监测设备及诱捕器粘虫板上草地贪夜蛾成虫的识别计数是可行的,深度学习技术对于草地贪夜蛾成虫的识别和计数是有效的。基于深度学习的草地贪夜蛾成虫自动识别与计数方法对虫体姿态变化、杂物干扰等有较好的鲁棒性,可从各种虫体姿态及破损虫体中自动统计出草地贪夜蛾成虫的数量,在害虫种群监测中具有广阔的应用前景。     

Sequential sampling protocols for Spodoptera frugiperda (Lepidoptera: Noctuidae), on Zea mays fields: influence of sampling unit size

Spodoptera frugiperda (J.E. Smith) is a major pest in maize fields in Argentina. However, a sampling method that accounts for spatial pattern and allows reliable pest density estimations is still lacking. This paper addresses the issue of how sampling unit size can influence the characterization of S. frugiperda spatial pattern and the performance of sampling plans. An intensive sampling programme for S. frugiperda larvae was carried out in maize fields from October until March in four growing seasons. On each sampling date, 12 to 20 sampling units were taken at random. Each unit consisted of 1, 2, 4, 6, 8, 10 or 12 consecutive plants along a row. The linearized version of the Taylor's power law (TPL) was fitted to mean and variance estimated for each sampling date and data set through least squares regression. In general, b values from TPL were significantly >1 (P<0.05), indicating an aggregated sampling distribution. Regression slopes (b) ranged from 1.28 to 1.48 in small larvae and from 1.06 to 1.24 in large larvae, indicating stronger clumping in the former. TPL parameters were used to develop constant precision sampling plans. The efficiency of these plans in terms of expected total cost (searching and handling sampling units) was very sensitive to the size of the sampling units with small larvae but not with large larvae. The influence of sampling unit size and spatial pattern on TPL parameters and sampling costs is discussed.     

Haplotype identification within Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) corn and rice strains from Colombia

The fall army worm Spodoptera frugiperda (Smith) is a migratory important pest of corn, sorghum, rice, grass and bermudagrass in North and South America. This species has diverged into two genetically differentiated but morphologically identical strains, "the rice" and "the corn". They have been analyzed by sequencing the genes cytochrome oxydase I, II and ITS1 from populations from the United States and Brazil. However, no such studies were performed in Colombia. In here, we identified 43 haplotypes by sequencing a fragment of the COI gene from 102 individuals, of which 40 had already been identified as the "corn" and "rice" strains or to their hybrids from Tolima, and the rest were collected from corn, cotton, sorghum, grass and rice fields in other regions of Colombia. The corn strain haplotype H1 was the most frequently found in this country, representing the main target for FAW monitoring programs. AMOVA analysis confirmed the population structure between Colombian and North American S. frugiperda haplotypes (F(ST) = 0.76812, P < 0.001), but not within the different Colombian regions, suggesting high gene flow within the country. The ML trees obtained for Tolima and for Colombia as a whole did not generate clustering amongst S. frugiperda sequences, neither via host-plant association nor by geographical areas. The minimum spanning network for Colombia corroborated our finding that the haplotype H1 has the highest frequency in the country. Our data suggest that haplotype frequency determination will be useful in the establishment of a monitoring system for this species.     

Aggregative oviposition behaviour of Helicoverpa spp. (Lepidoptera: Noctuidae) in contaminated chickpea crops

Abstract Aggregative egg distribution by Helicoverpa spp. within experimental field plots of chickpea containing various contaminant plant species was documented at different stages of plant growth. More eggs were laid on contaminant faba and wheat plants than on the surrounding chickpea. The level of egg aggregation on faba and wheat plants increased with general crop growth, becoming evident before a significant disparity in growth rates between these species and the surrounding chickpea became apparent. In chickpea plots contaminated with canola, aggregative oviposition activity on the contaminant plants was observed in the early seedling stage whilst a clear height differential between the two species was evident. Total Helicoverpa egg density on contaminant plants was not correlated with height above chickpea for any of the contaminant species. It is proposed that the aggregative oviposition behaviour of Helicoverpa spp. in contaminated chickpea results from differential apparency of the contaminant plants to ovipositing moths. Differential apparency may result from several factors including growth rate and morphological differences between chickpea and the contaminants. Physiological changes in chickpea, including growth stage-related changes in acid production by the foliage, may also contribute to the greater apparency of contaminant plants in chickpea plots. The implications of differential host plant apparency for insect pest management are discussed.     

Fumigant toxicity of Carum copticum L. (Apiaceae) essential oil on Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) adults under greenhouse conditions

Greenhouse whitefly Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) is one of the most injurious pests of greenhouse crops and ornamental plants in worldwide, both outdoor and indoor. This insect, feeding on plant sap, producing honeydew and transmitting plant viruses, causes quantitative and qualitative damages in plants. For controlling this pest in greenhouse, plant essential oils are mentioned instead of chemical insecticidal. So, in this research, fumigant toxicity of Carum copticum L. (Fam.: Apiaceae) plant oil on mentioned adult pest was surveyed. Dry ground seeds were subjected to hydrodistillation using a modified Clevenger-type apparatus and the resulting oil contained Thymol (50.07%), Gama-Terpinene (23.99%), P-Cymene (22.9%), Myrcene (0.51%) and 1,8-Cineole (0.5%). All bioassay tests were conducted at 27?±?2?°C, 65?±?5 RH and a photoperiod of 16:8?h (light: dark). This research was performed with a completely random design with six treatments (five different concentrations of essential oils plus control). Each concentration includes of three replicates and each replicate consisted of 20 adult of pests. The results showed that aforementioned essential oil shows significant mortality of adults 24?h after exposure. The value LC₅₀ of mentioned plant oil on T. vaporariorum was 1.03?μl?L/L air. And mortality percentage shows higher sensitivity of T. vaporariorum against application of essential oil. The value LT₅₀ estimated for T. vaporariorum in concentration of 1.03?μl?L/L air was 7.18?h. Fumigant toxicity this essential oil has had an ordered relationship with the concentration and time exposure. The results of this research showed that mentioned plant oil had appropriate insecticidal effects on these greenhouse pests. The findings showed that C. copticum L. oil has high impact on the above-mentioned pests and it is suggested because of its high potential in fumigant toxicity and its use in integrated pest management programmes in greenhouses is mentioned.     

广东省草地贪夜蛾种群周年动态及发生特征

为了明确广东省草地贪夜蛾Spodoptera frugiperda(J. E. Smith)种群周年消长动态及发生特征,根据2020年和2021年广东省草地贪夜蛾性诱监测及田间调查数据,分析不同生态区草地贪夜蛾成虫及幼虫种群周年发生动态。结果表明：(1)草地贪夜蛾在广东省大部分冬种玉米区可以周年繁殖,仅在清远、韶关、河源等地未发现幼虫为害;不同地区之间草地贪夜蛾越冬虫源基数差异较大,粤西发生为害较重,珠三角及粤东地区发生相对较轻;(2)周年繁殖区草地贪夜蛾成虫和幼虫全年均可发生为害,而季节发生区一般于3-4月才零星始见草地贪夜蛾成虫和幼虫,且诱蛾量、幼虫种群数量及为害程度均相对较低;(3)广东省草地贪夜蛾种群消长动态呈多峰型,发生高峰期主要集中于5-10月,期间出现多个大小不等的高峰,但峰期、蛾量和虫量在不同地区之间差异较大。本研究明确了广东省不同生态区草地贪夜蛾种群的周年消长动态及发生特征,为广东省乃至全国草地贪夜蛾的早期预警和精准防控提供重要参考。     

不同寄主对草地贪夜蛾生长发育和繁殖的影响

草地贪夜蛾是入侵我国的重大农业害虫,严重威胁我国粮食安全。为明确该虫在不同寄主植物上的适合度,本文系统研究了草地贪夜蛾取食花生、荞麦和生姜3种寄主生长发育和繁殖情况,组建了实验种群生命表。结果表明:草地贪夜蛾在3种寄主植物上的繁殖力高低为花生(771.73粒)>荞麦(477.13粒)>生姜(209.22粒),卵的孵化率无显著差异,幼虫和蛹重均是花生>荞麦>生姜。草地贪夜蛾取食花生、荞麦和生姜后的净增殖率(R 0)分别为226.36、102.45和20.75,内禀增长率(r m)分别为0.16、0.13和0.06。研究发现,草地贪夜蛾在花生、荞麦和生姜3种寄主植物上均能实现种群繁殖,其中,花生是最适宜的寄主,荞麦次之,生姜相对较不适宜。     

Field evaluation of a Helicoverpa zea (Lepidoptera: Noctuidae) damage simulation model: effects of irrigation, H. zea density, and time of damage on cotton yield

Helicoverpa zea (Boddie) is an important pest of cotton, Gossypium hirsutum L., for which many economic injury and population models have been developed to predict the impact of injury by this species on cotton yield. A number of these models were developed using results from simulated damage experiments, despite the fact that no studies have demonstrated that simulated damage is comparable to real H. zea damage. Our main objective in this study was to compare the effect on yield of H. zea larvae feeding on cotton fruiting structures at different irrigation levels, larval densities, and cotton physiological ages with damage produced artificially by removing fruiting structures by hand using simulated estimates of H. zea injury. To accomplish this, we used two irrigation levels, each divided into real and simulated damage plots. In real damage plots, H. zea larvae were placed on plants and allowed to feed; whereas in simulated damage plots, fruiting structures were removed by hand using a simulation model of H. zea damage to determine numbers and amounts of fruiting structures to remove. Each of these plots was further divided into one undamaged control plot and nine treatment plots. Each treatment plot was randomly assigned one of three damage times (early, middle, or late season) and one of three H. zea densities. In 1998, we found that only artificial H. zea damage (performed by hand removal of fruiting structures) at the highest density and during the late season decreased yield; whereas real damage caused by H. zea larvae placed on plants, and artificial damage occurring at earlier time periods and lower H. zea densities did not affect yield. In 1999, both real and artificial damage decreased yield at the higher H. zea densities compared with the lowest density, but, as in 1998, this was only true when damage occurred late in the season. The most important finding of this study was that high H. zea densities had no effect on cotton yield unless they occurred late in the season. In particular, this was true for artificial H. zea damage. The second most important finding of this study was that, with the exception of late in the season, our model for simulating H. zea damage to cotton through removal of fruiting structures resulted in similar yields as real H. zea larvae damage to cotton.     

Probability distribution of Orthezia praelonga Douglas (Hemiptera: Sternorrhyncha: Ortheziidae) in citrus

The probability distribution of the orthezia scale, Orthezia praelonga Douglas, was studied in plots of commercial orange orchards (Citrus sinensis L., var. "Pêra Rio"), with 5, 9 and 15 years of age, during one year. The survey of presence or absence of the pest in the plants was carried through twenty samplings in the total area of each plot visually inspecting each plant. The dispersion indexes used were: variance/mean relationship (I), index of Morisita (Id), coefficient of Green (Cx) and k exponent of negative binomial distribution for each sampling. The negative binomial distribution was more representative of the frequency distribution data of this scale in citrus, since the variance was superior to the average in all samplings. The analysis of the aggregation index showed that the majority of the samplings presented aggregate distribution for the scales.     

Host plant association and genetic differentiation of corn and rice strains of Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) in Colombia

Spodoptera frugiperda (Smith) is a polifagous insect of major economic impact in the western hemisphere and exhibits two strains (i.e., corn and rice) that are morphologically identical but differ in ecology, genetics and physiology. In this work we identified these strains and their respective hybrids by using a PCR-RFLP of the COI gene and PCR of the tandem region FR. Moreover, we performed a population structure analysis by using 253 larvae from Tolima, a region where S. frugiperda is a pest on corn, rice, sorghum and cotton. Corn strain was found on 42% in corn, 34% in cotton, 19% in sorghum and 0.04 % in rice and rice strain on 35% in corn, 0.06% in cotton, 0.06% in sorghum and 53% in rice, demonstrating that corn strain specificity is superior to rice strain. Hybrids between these strains were more abundant in corn. The distributions on their host plants reflect a population genetic differentiation in S. frugiperda with values of PhiPT (COI) = 0.31, P < 0.0001, PhiPT (FR) = 0.17, P < 0.0001 for all crops and PhiPT (COI) = 0.42, P < 0.01, PhiPT (FR) = 0.13, P < 0.01 for the sixteen sampled farms. The dendrograms showed two clusters representing both strains. The results obtained in this study suggest that the management of this insect must differ on each host plant, given the specialization that both strains present, particularly in corn and rice.     

Seasonal population fluctuations of the diamondback moth,Plutella xylostella (L.) (Lep.: Plutellidae) on different cauliflower cultivars

The diamondback moth, Plutella xylostella (L.) (Lep.: Plutellidae) is one of the most important pests of cruciferous plants throughout the world. In recent years, it has been identified as a serious pest of the cauliflower fields in Tehran province. Resistance of P. xylostella to all main groups of insecticides has been recorded and it is ranked in the 20 most resistant pest species reported until now. According to many researchers, to solve the problem of pest resistance to chemical pesticides, an integrated pest management programme should be used. Despite this condition, it seems that the use of resistant cauliflower cultivars is an appropriate policy for integrated control of the pest in the field. In order to identify the most resistant cultivar in the field, eight cauliflower cultivars in a completely randomised design with five replicates were planted at the Shahed University research field (south of Tehran). Density of eggs, larvae and pupae of P. xylostella were measured every 10 days in these cultivars. The results showed that there is no significant difference between numbers of eggs per plant on different cultivars. But number of larvae and pupae per plant were significantly different among different cultivars. Smilla and Snow mystique cultivars had the highest number of larvae and pupae. On the other hand, Buris and Snow crown cultivars had the lowest number of pupae and Snow crown and SG cultivars had the lowest number of larvae per plant. According to the results, the Buris and Snow crown cultivars had the lowest infestation and had a kind of resistance to pest.     

Plant resistance and its effect on the peritrophic membrane of southwestern corn borer (Lepidoptera: Crambidae) larvae

The southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera: Crambidae), is a serious pest of corn, Zea mays L., in the southern United States. Corn germplasm lines with conventional genetic leaf-feeding resistance to this pest, the fall armyworm, Spodoptera frugiperda (J.E. Smith), and other lepidopterans have been released to the public by USDA-ARS scientists located in Mississippi. Recent studies suggest the insect resistant lines disrupt the integrity of the peritrophic membrane of the fall armyworm. The objectives of this study were to investigate any morphological differences in the structure of the peritrophic membrane of southwestern corn borer larvae feeding on resistant and susceptible corn hybrids and to quantify the damage. Larvae were reared under field and laboratory conditions on three corn hybrids (two resistant and one susceptible). Scanning electron microscopy was used to examine the peritrophic membrane for abnormalities such as holes or tears and to count the holes or tears in the membrane. Differences in the degree of damage to peritrophic membrane of larvae fed on resistant and susceptible plants were not detected. Up to five distinct layers of the membrane were observed in each larva. Variation in the amounts of damage to the peritrophic membrane observed from larvae feeding on all plant material was high. Plant resistance adversely affects growth and development of southwestern corn borer larvae, and further investigations are needed to explain the role of plant resistance and its relation to peritrophic membrane in southwestern corn borer larvae.     

Importance of host plant species, Neotyphodium endophyte isolate, and alkaloids on feeding by Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae

Three grass host species--tall fescue, Festuca arundinacea Schreber; meadow fescue, Festuca pratensis Hudson; and perennial ryegrass, Lolium perenne L.--each infected with a number of different Neotyphodium endophyte isolates, were investigated for their effects on fall armyworm, Spodoptera frugiperda (J.E. Smith). Alkaloid profiles varied among associations. Choice and no-choice tests comparing feeding and early development of S. frugiperda larvae on endophyte-infected and endophyte-free leaf blade material were performed. Endophyte-mediated resistance to S. frugiperda was greatest in meadow fescue and weakest in tall fescue. Some endophyte isolates, particularly in perennial ryegrass and meadow fescue, had a major effect on feeding and development of S. frugiperda, whereas others had no effect or were only weakly efficacious. In tall fescue, some associations deterred S. frugiperda from feeding in choice tests but had no effect on development, whereas larvae reared on other associations weighed significantly more than control larvae fed endophyte-free grass. It was concluded that the deleterious consequences of endophyte infection were easily masked by other factors in tall fescue. Relative leaf age had no effect on feeding preferences in the three host species. Chemical analysis of herbage from the plants used, and results from a no-choice study using spiked artificial diets, failed to individually implicate any of the major known alkaloids (peramine, lolitrem B, ergovaline, and lolines) in the observed effects on S. frugiperda. Hypotheses explaining these observations, and their impact on creating desirable grass-endophyte associations for use in pastures, are discussed.     

Rice-Straw Mulch Reduces the Green Peach Aphid,Myzus persicae (Hemiptera: Aphididae) Populations on Kale,Brassica oleracea var. acephala (Brassicaceae) Plants

Organic mulches, like peel and rice-straw, besides other materials affect the UV and temperature, which cause a reduction in the aphid arrival. The aim was to evaluate the effect of covering the soil with straw on the populations of the green peach aphid, Myzus persicae on the kale, Brassica oleracea var. acephala plants. The first experiment evaluated the direct effect of the rice-straw mulch and the second its indirect effect on aphid immigration, testing the plant characteristics that could lead to the landing preference of this insect. The third experiment evaluated the direct effect of the mulch on the aphid population. In the second and third experiments, four plants, each in a 14 L polyethylene pot with holes at the bottom, were used in areas with and without soil mulching. These pots were changed between areas, after seven days, to evaluate the effects of this change on the arrival of the winged aphids to the plants. Each plant was covered with anti-aphid gauze and inoculated with one winged M. persicae. Winged and apterous adults of this insect were counted per plant after 15 days. The temperature increased in the mulched plots to a maximum of 21–36°C and to 18–32°C in the plots with or without soil covering, respectively. Plant growth reduced the numbers of the winged aphids landing before and after they were moved to the bare soil plots. The nutrient content was similar in plants in both the mulched and no mulched plots. The population growth of M. persicae was higher in the control than in the mulched plots. This was partially due to temperatures close to 30°C in these plots and changes in the plant physiology. The soil mulching with rice-straw decreased the M. persicae landing, increased the plot temperatures and improved the vegetative growth of the kale plants.     

Winter ecology of the cabbage aphid Brevicoryne brassicae (L.) (Homo., Aphididae) and its parasitoid Diaeretiella rapae (McIntosh) (Hym., Braconidae: Aphidiidae)

Abstract:  Flower strips near crops may stimulate natural enemies by the provision of nectar and hibernation sites. However, these habitats may also be beneficial for potential pest species. We investigated the dynamics of the cabbage aphid Brevicoryne brassicae (L.) (Homo., Aphididae) and its primary parasitoid Diaeretiella rapae (McIntosh) (Hym., Braconidae) in brussels sprout fields and adjoining flower plots in winter. A wide variety of 14 plant species were included in the study, each established as monoculture plots. Brussels sprout fields and flower plots were established at two sites. One site was located in an open agricultural landscape, the other in a landscape dominated by mixed forest. Brevicoryne brassicae and D. rapae were found on brussels sprout plants but not in the flower plots. Brevicoryne brassicae was initially more abundant in the open landscape, but as their densities declined rapidly in time, no living aphids were recovered at both sites by February. The density of aphids parasitized by D. rapae showed a similar trend, but densities of eight mummies per brussels sprout plant were still present by the end of February. These findings suggest that (i) flower species under investigation do not function as sources of B. brassicae and (ii) brussels sprout plants that are not harvested may not only harbour D. rapae populations that may sustain biological control, but are also likely to act as sources of B. brassicae infestation.     

Influence of Different Intensities of Pesticide Management on the Structure of Ground Beetle Communities (Coleoptera; Carabidae) During a Crop Rotation

Investigations were lead through in the years 1992 to 1995 at Halle (Saale) on a stand 24ha in size. Aim of the survey was to record the effects of graduate intensities of pest management on ground beetles. For this purpose 6 plots were installed on the field, 72 ‐ 200m each. Two plots served as control areas, without any application of pesticides. On two other plots intensive chemical pest management was applied. On the last two plots treatments were lead through considering the economic thresholds for weeds, fungal and insect pests according to the rules of integrated pest management. Ground beetles were sampled by using pitfall traps. In 1992 complementary methods to the pitfall trap catches, pick up of beetles after pesticide applications and semi-field-tests, on all plots were lead through. The graduate pest management was carried out 1992 and 1993 in winter wheat and 1994 in sugar beet stands. The last crop in 1995 was summer barley. In this year all plots were treated conventionally. In 1992 the differences between the total catches of ground beetles on the experimental sites were not high. In the following year most species were predominant on the control sites. In 1994 in sugar beet mechanical weed control was carried out on the control plots. The intensity of pesticide management between intensive and integrated plots differs only small. The amounts of ground beetles reached similar values on all experimental sites. In contrast to the expections the trap catches of ground beetles in the final investigations in summer barley were highest in the plots which had been treated integrated in the years before. The smallest amount was sampled in the former intensively managed sites. Renunciation of pesticides often is connected with economic losses which are not tolerable. If management is conducted considering the economic thresholds corresponding to the principles of integrated pest management negative effects on the economy of nature should not be expected for the longer term.