Development of economic thresholds and monitoring systems for Helicoverpa armigera (Lepidoptera: Noctuidae) in tomatoes.

Field sampling methods and economic thresholds were developed to provide management recommendations for Helicoverpa armigera (Hübner) on processing tomatoes, based on a commercially acceptable damage level of 5% fruit damage. Population estimates from destructive sampling and a rapid 1-min plant scouting method were related to fruit damage, and a nominal economic threshold of one larva per plant was derived. The economic threshold was confirmed in a designed trial where it resulted in acceptable levels of fruit damage. The 1-min scouting method and economic threshold was validated in 17 commercial crops in the Gisborne, Poverty Bay region of New Zealand. Scouting in these fields was based on 10 plants in each of four quadrants proportionally representing the topography of each field. In unsprayed areas, egg and larval populations were usually below the economic threshold in early-planted crops but often exceeded thresholds in late-planted crops. In commercial demonstration trials where standard calendar spraying practice was compared with no spraying, calendar-based applications maintained fruit damage below 3.4%, but insecticide was applied unnecessarily to more than half the crops. Larval populations were a significant predictor of damage in these commercial crops. In 12 implementation trials, where spraying recommendations were based on the 1-min scouting threshold of one larva per plant, the worst fruit damage observed was 2.3%. The definition of an economic threshold, scouting methods, and establishment of parasitoids have reduced spray applications and contributed to the implementation of an integrated pest management program for processing tomatoes in New Zealand.     

萧氏松茎象幼虫的空间分布型和抽样技术

萧氏松茎象Hylobitelus xiaoi Zhang是我国近年来发现的危害松林的新害虫。该文利用1wao等7种方法对萧氏松茎象幼虫的空间分布型进行了测定。结果表明,萧氏松茎象幼虫在林间呈聚集分布,且符合负二项分布,由此得出了林间理论抽样数公式,其抽样方式以对角线最佳;其有虫株率与平均虫口密度之间的关系可用冥函数曲线方程：Y=2．916X^0.887来进行描述。     

An under-appreciated difficulty: sampling of plant populations for analysis using molecular markers

Results of studies using molecular markers for determining demographic and genetical population parameters especially in plants or sessile animals under field conditions are strongly dependent on the sampling strategy adopted. There are two critical decisions to make when determining this strategy: (i) what is the unit to be sampled?, (ii) how should units to be sampled in the field be selected? For the first decision, there are two conceptually different approaches: sampling ramets of clonal plants as units (to get information about within-genet parameters, such as genet sizes or numbers) and sampling genets of clonal or non-clonal plants as units (to get information of the genetic structure of the population). For the second decision, it is critically important to make the goal of the study explicit. We argue that in this case fully random sampling is needed only when an estimate of the true value of the population parameter is needed; if a comparison between populations is the goal, however, other sampling schemes may be adopted. The efficiency of different types of sampling strategies to recover relative values in a spatially extended population is studied by means of a spatially explicit simulation model. The results show that a regular pattern of sampling is best for obtaining information on genet sizes or inbreeding coefficients; in contrast, random or hierarchical sampling strategies are better for obtaining information on parameters that are based on comparison of pairs of individuals, such as distribution of genet sizes or autocorrelation in genetic structure. A set of recommendations is provided for designing a good sampling strategy.     

Efficiency of variable-intensity and sequential sampling for insect control decisions in cole crops in the Netherlands

A total of 24 commercial fields of cabbages and Brussels sprouts were sampled in a grid fashion with 20–25 equally spaced cells with four plants per cell. Using this data base of 80–100 plants, we conducted computer stimulations to compare the treatment decisions that would be made for the major insect pests using published sequential sampling programs and a newly developed variable-intensity sampling program. Additionally, we compared the number of samples required to make the decision. At low thresholds (10–20%) for both Lepidoptera and cabbage aphids, variable intensity-sampling required a smaller sample size and provided more reliable decisions, while at high thresholds (40–50%) sequential sampling provided more reliable decisions. In both procedures, the occurrence of incorrect decisions was minimal. The number of cases in which a decision would not be reached after a 40-plant sample was lower for variable-intensity sampling. Considering the number of samples required to make a correct decision and the greater need for reliable decisions at lower thresholds, variable-intensity sampling was superior to sequential sampling. Additionally, variable-intensity sampling has the advantage of requiring samples to be taken in a greater area of the field and thus increases the probability of detecting localized infestations. Although variable-intensity sampling was not designed to classify pest populations for treatment decisions but rather to achieve sampling precision around the population mean, our present studies indicate that it can also be an effective method to aid in treatment decisions.     

Assessing abundance and distribution of an invasive thrips Frankliniella schultzei (Thysanoptera: Thripidae) in south Florida

Within-plant and within-field distribution of larvae and adults of an invasive thrips species, Frankliniella schultzei (Trybom) on cucumber, Cucumis sativus L. was studied in 2008 and 2009 in Homestead, Florida. The majority of thrips were found inhabiting flowers of cucumber plants and little or none was found on the other parts of the plant. Thrips were aggregated in the field, as indicated by the two regression models, Taylor's power and Iwao's patchiness regression. Iwao's patchiness regression provided a better fit than Taylor's power law. The distribution was clumped during the initial stages of infestation at the edges of the field and became random thereafter. However, with increase in population density, thrips again formed aggregates in the field. Based on the average pest density per flower in a ～0.25-ha field, minimum sample size (number of flowers) required at the recommended precision level (0.25) was 51. The number of samples required at two levels of predetermined pest density was also calculated, which would help growers in collecting optimum number of samples required to determine the correct threshold level of pest in fields. Results from seasonal abundance indicated that density of thrips peaked during the fifth week of sampling with an average of 25 and 34 adults per ten flowers during autumn 2008 and 2009, respectively. Results from these studies will help growers and extension personnel in understanding the abundance and distribution of F. schultzei in the field, which are important components required in developing a sound management program.     

Toward an optimal sampling protocol for Hemiptera on understorey plants

There are no standardised sampling protocols for inventorying Hemiptera from understorey or canopy plants. This paper proposes an optimal protocol for the understorey, after evaluating the efficiency of seven methods to maximise the richness of Hemiptera collected from plants with minimal field and laboratory time. The methods evaluated were beating, chemical knockdown, sweeping, branch clipping, hand collecting, vacuum sampling and sticky trapping. These techniques were tested at two spatial scales: 1 ha sites and individual plants. In addition, because efficiency may differ with vegetation structure, sampling of sites was conducted in three disparate understorey habitats, and sampling of individual plants was conducted across 33 plant species. No single method sampled the majority of hemipteran species in the understorey. Chemical knockdown, vacuum sampling and beating yielded speciose samples (61, 61 and 30 species, respectively, representing 53, 53 and 26% of total species collected). The four remaining methods provided species-poor samples (<18 species or <16% of total species collected). These methods also had biases towards particular taxa (e.g., branch clipping and hand collecting targeted sessile Hemiptera, and sticky trapping were dominated by five species of Psyllidae). The most time-efficient methods were beating, sweeping and hand collecting (200 minutes of field and laboratory time yielded >7 species for each technique). By comparison, vacuum sampling, sticky trapping, branch clipping and chemical knockdown yielded <5 species for the same period. Chemical knockdown had further disadvantages; high financial cost and potential spray drift. The most effective methods for a standardised sampling protocol to inventory Hemiptera from the understorey are beating and vacuum sampling. If used in combination, these methods optimise the catch of understorey hemipteran species, as their samples have high complementarity.     

Sampling to determine density of arthropods in intensively grazed grasslands

Arthropod population field studies undertaken to understand the impacts and population dynamics of the target organism rely on sampling methods that provide accurate measurements of population density. Unsuitable methods may underestimate or provide widely variable measures of population density. The suitability of three vacuum sampling methods: a domestic vacuum cleaner, Vortis™, and blower-vac (G-vac), plus heat extraction of turves were compared for sampling common species in an intensively grazed irrigated dairy pasture. Each method used a different approach to sampling with the number of samples per method based on protocols that had been used in grasslands. Overall, for adults of the weevil Listronotus bonariensis, no method provided a consistently high mean density, while for adults of the weevil Sitona obsoletus, the vacuum cleaner and turf heat extraction methods gave generally higher mean densities. For predatory beetles and lacewings, heat extraction was the most effective for density measurements, while for ladybirds and spiders, the Vortis™ provided the best estimate of mean density. Increasing pasture dry matter (kg Dm/ha) generally had a significant negative effect on S. obsoletus density but not for L. bonariensis. While no method was consistently superior than another, the vacuum cleaner and heat extraction methods generally provided higher mean densities. The G-vac generally produced the lowest density estimates, but the sampling protocol meant a larger collection area per unit effort and therefore the probability of detection was higher compared with the three other methods. In conclusion, the study showed that the optimal sampling method depends on the taxa targeted, and more than one method may be required to measure density and diversity of species in both natural and modified grasslands.     

江苏沿江棉区第三代棉铃虫防治指标研究

通过人工接虫为害,获得了棉铃虫各龄期幼虫在棉花上的为害量和为害损失。并观察了不同年份棉铃虫卵和各龄幼虫的自然存活率。在此基础上．研究得出了自然状态下第3代棉铃虫的防治指标,其值为百株累计卵量100粒,或当日百株新增卵量25粒。与用固定虫量研究方法得出的指标相比,该指标更合理、更经济可行。     

A comparison of three sampling techniques to estimate the population size of caterpillars in trees

Three sampling techniques commonly used to estimate the population size of caterpillars and sawfly larvae in trees (branch samples, frass production, water basins), were compared with respect to sampling error and economic costs. At the level of tree populations (e.g. forests), on an arbitrary date, the mean caterpillar intensity per tree (expressed in numbers of larvae or their biomass per 100 shoots) was predicted from the mean frass production per tree (expressed in mg frass per m² forest floor per day). At the level of the single tree, the frass production on an arbitrary date was related to the population intensity, but, due to the large sampling error, did not provide an accurate prediction. Summing the frass produced over the whole season reduced this error and predicted the seasonal abundance of larvae in single trees, estimated as their maximum intensity or their density (numbers of larvae or their biomass per m² forest floor). The maximum population intensity was not related to the population density. The sampling techniques suffer from large errors unrelated to larval abundance. The main sources of error (i.e. weather or predation of the larvae) usually cause an underestimation of population size. Labour, the main cause of high costs, was low in the basin technique and high in the frass production technique. Possible ways of reducing errors and applications of the three techniques are discussed.     

Populations of Predaceous Natural Enemies Developing on Insect-Resistant and Susceptible Tomato in North Carolina

Naturally occurring populations of immature and adultGeocoris punctipes,adultColeomegilla maculataand immature coccinellids were monitored on field-grown tomato lines susceptible and resistant toManduca sextaandHelicoverpa zea. Helicoverpa zeaandHeliothis virescenseggs and small larvae that serve as prey for these predators also were monitored. MoreH. zeaandH. virescenseggs and small larvae were found on resistant than on susceptible plant lines. However, similar populations of largeH. zeaandH. virescenslarvae were found on resistant and susceptible plants. The number of adultGeocoris punctipes,adultColeomegilla maculataand immature coccinellids on resistant plants was always as high or higher than the number on susceptible plants. The data demonstrate no incompatibility of host-plant resistance with biological control provided by these predaceous insects, but indicate that the number ofG. punctipesand coccinellids required to provide effective biological control may develop too late in the season to be of practical value. Large populations of stilt bugs (Jalysus wickhami,Hemiptera: Berytidae) and spiders were observed to occur earlier in the growing season than eitherG. punctipesor coccinellids and may be a significant source of mortality forH. zeaeggs and small larvae.     

The efficiency of patch sampling for determination of relative tick burdens in comparison with total tick counts

Quanttative data on host tick burdens ar fundamental for the initiation of control strategies and effective management of wildlife populations, but the methods of live sampling employed for domestic animals are unsuitable for sampling wild animals. Despite advances in the use of destructive methods (the scrub and digestion techniques) to obtain measures of the total tick burden on wildlife, these methods are too involved for many field workers, who often need only measures of relative tick burden. Recently, patch sampling methods have been introduced whereby only certain predilection sites are sampled, the presumption being that the number of ticks collected gives an indiccation of the relative degree of infestation. We examined the validity of patch sampling as a measure of relative tick burden by comparing adult ticks collected from the ears, head, neck, foreleg and perianal region of impala (aepyceros melampus) with total tick burdens of the same animals derived from the digestion technique. Adult ticks from patch sampling were positively and significantly correlated with total adults and total ticks (larvae, nymphs, and adults) on impala, with ticks patch sampled from the neck showing the highest correlation with the total tick burden. Comparison of relative tick loads from patch sampling with absolute tick loads from digestion for three classes of impala (females, bachelor males and territorial males) gave qualitatively similar results. We conclude that, when measures of relative tick load are sufficient and destructive sampling is not feasible, patch sampling can provide reliable information on relative tick burdens that are positively correlated with the total tick burden.     

杨扇舟蛾卵和幼虫的空间分布型及抽样技术

研究了杨扇舟蛾Clostera anachoreta(Fabricius)卵和幼虫的空间分布型及抽样技术,结果表明杨扇舟蛾卵和幼虫在杨树林的分布型均为聚集型中的负二项分布。几种抽样方法中,卵以棋盘式最好,幼虫以平行线法最好。同时建立了杨扇舟蛾卵的下层抽样模型为y=2.4481x 0.4243;幼虫的中、下层抽样模型为y=2.4605x 3.9126。     

Possible effect of genetically modified cotton on foraging habits of early instar Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae

Abstract  We estimated survival and final location of neonate Helicoverpa armigera after 72 h on both genetically modified (GM) and conventional cotton at the squaring stage. On average, about 2.5% out of a total of 1620 initial larvae survived on two gene GM cotton (CS × 450, 289BGII®) compared with 39.5% out of a total of 810 initial larvae on Sicot 189, a conventional cotton variety. A disproportionate number of larvae were collected on squares of GM cotton, assuming they behave the same way on GM plants as on conventional plants but suffer higher rates of mortality. Our results imply that the behaviour of neonates on GM plants in terms of finding squares (and/or better survival on squares) may be contributing to the continued pest status of Helicoverpa on GM cotton from time to time. Experiments to determine if selection for changed behaviour in the field has or is occurring are urgently required.     

Probability Range in Damage Predictions as Related to Sampling Decisions

The risk involved in basing a nematode management decision on predicted crop loss is related to the uncertainty in the crop damage function and error in measuring nematode population density. The sampling intensity necessary to measure a nematode population with specified precision varies with population density. Since the density is unknown prior to sampling, optimum sampling intensity for a management decision is calculated for the economic threshold population level associated with the management cost. Population densities below the threshold are measured with greater precision than required; those above the threshold are less precisely measured, but invoke management. The approach described provides resolution to sampling strategies and allows assessment of the risk associated with the management decision.     

刺槐叶瘿蚊越冬幼虫空间格局及抽样调查技术

本文采用聚集指标法分析了刺槐叶瘿蚊Obolodiplosis robiniae(Haldemann)越冬幼虫的空间分布格局,结果表明:刺槐叶瘿蚊越冬幼虫在林间呈聚集分布;其聚集的原因与刺槐叶瘿蚊自身的行为习性有关或由刺槐叶瘿蚊本身与环境的异质性共同作用所造成。采用"z"字型、平行线、棋盘式、大五点、对角线5种抽样方法估计林间刺槐叶瘿蚊越冬幼虫虫口密度,确定对角线法调查15样方为最佳抽样方法。对土壤不同深度土层中越冬幼虫数量调查,明确最适取样深度为3cm。同时利用Iwao回归建立了理论抽样数量模型:n=t2/D2(1.1957/x珋+0.8905)。利用过筛手检和过筛水漂2种方法检数土中幼虫,对检出刺槐叶瘿蚊越冬幼虫虫量及检虫时间进行了对比分析,结果表明过筛水漂法检虫较为可取。     

华北棉区第三代棉铃虫对棉花为害损失与经济阈值的研究

通过在华北棉区棉花蕾铃期阶段,连续５ａ的田间蕾铃脱落原因的观察,明确了在第三代棉铃虫的中常发生年份,影响蕾铃期蕾铃脱落的主要因素是棉株本身的自然脱落其脱落率占总脱落的９０％以上,而因第三代棉铃虫为害造成的脱落率在５％以上。根据田间棉铃虫Ｈｅｌｉｃｏｖｅｒｐａ ａｒｍｉｇｅｒａ（ｈｕｂｎｅｒ）３龄幼虫虫量与为害力的关系研究,结合多年第三代棉铃虫田间生命表,文中提出了三代棉铃虫的经济阈值为百株累计卵量     

A comparison of live and destructive sampling methods of determining the size of parasitic tick populations

The accuracy of a general and a specific method of collecting and counting ixodid ticks on live hosts was compared with that of a destructive technique which can only be applied to dead animals. Destructive sampling provided considerably more accurate results than either of the live sampling methods when applied to domestic goats (Capra hircus) and a duiker (Sylvicapra grimmia).The smaller the life stage and the tick species the less likely it is that it will be recovered by either of the live sampling techniques. Both live and destructive sampling yielded similar results for adultAmblyomma hebraeum, a large tick.A sub-sampling method, used to estimate larval numbers, was repeatable and an accurate predictor of population size for populations ranging from 50 to 1000 of unengorgedA. hebraeum larvae.     

Standardized sampling plan for Aphis gossypii based on the cotton cultivar,plant phenology and crop size

A standardized sampling plan is the starting point for developing a decision‐making system for pest control. Aphis gossypii (Hemiptera: Aphididae) is a destructive sap‐feeding pest on cotton worldwide. However, research addressing cotton cultivar, plant phenology and field size with the aim of developing a sampling plan for A. gossypii has not been done. Therefore, in this study, we developed a standardized sampling for A. gossypii as a function of these factors. To accomplish this, A. gossypii densities in four experimental cotton cultivars were sampled weekly during year one to determine the ideal aphid characteristic to sample (by individual or colony). During year one and two, A. gossypii densities were sampled weekly in the same cultivars to determine sampling unit, sampling technique and the number of samples for an A. gossypii sampling plan. Using the sample number determined, the sampling time was recorded for cotton field size of 1, 5, 10, 50, 100 and 150 ha in order to estimate the sampling cost. In cotton, the count of individuals was the best characteristic for the assessment of A. gossypii. Leaves of the most apical branches for the vegetative and reproductive cotton plant stage were the best sampling units. The best sampling technique was direct counting. The cotton cultivar did not affect the development of the sampling plan. The A. gossypii sampling plan involved the evaluation of 58 samples per zone and required 20 min (<0.35 min/sample) for the evaluation of these samples. However, the walking time between samples was the main factor responsible for the total sampling time and cost in cotton fields, and this factor strongly depends on the size of the cotton field.     

Testing the reliability of noninvasive genetic sampling by comparing analyses of blood and fecal samples in Barbary macaques (Macaca sylvanus).

Genetic studies of wild animal populations are often hindered by difficulties in obtaining blood samples. Recent advances in molecular biology have allowed the use of noninvasive samples as sources of DNA (e.g., hair or feces), but such samples may provide low-quality DNA and prevent the determination of true genotypes in subsequent DNA analysis. We present a preliminary study aimed at assessing the reliability of using fecal samples for genotyping in Barbary macaques (Macaca sylvanus). The test was performed on samples of blood and feces from 11 captive animals, using three dinucleotide microsatellites. The CTAB DNA extraction method was found to be the most relevant for Barbary macaque feces, yielding successful amplification at all loci for 70% of PCRs. All the fecal samples tested gave correct genotypes at least once for each locus when referenced against blood-derived genotypes. An average of 18.3% of PCRs displayed spurious genotypes (false homozygous or false allele). The minimum theoretical probability required to obtain a 100% accurate genotype is 0.74, based on the criterion that a correct genotype is assessed only if it was observed at least twice. The observed probability of obtaining a correct genotype from three PCRs, based on our genotyping results, was greater (0.81 on average) than the minimum threshold. In conclusion, our comparison of blood and fecal samples showed that fecal sampling is a reliable tool for the further study of wild Barbary macaque populations.     

Effect of count duration on abundance estimates of Black-capped Vireos

ABSTRACT.   Distance sampling applied to point count surveys (point transects) has become a common method for estimating the absolute abundance of birds. When conducting point transects, detections of focal species are typically recorded during a fixed time interval. However, count duration has varied among studies and the effect of such variation on the resulting abundance estimates is unclear. My objective was to examine the effect of count duration on abundance estimates of male Black-capped Vireos ( Vireo atricapilla ). The abundance of these vireos in a 349-ha area in central Texas was estimated using 3-, 5-, and 6-min point transects and results were then compared to actual number present as determined by banding and territory mapping. The 3-min counts provided an estimate that was 26% greater than the actual number of male Vireos present ( N = 201), but this number was within the corresponding 95% confidence interval ( N = 157–413). Confidence intervals for the 5- and 6-min counts did not include the actual number of vireos present. The shortest count duration may have provided the most accurate abundance estimate because male Black-capped Vireos are typically active, sing intermittently, and sometimes move tens of meters between songs. Thus, shorter-duration counts may also yield the most accurate abundance estimates for other species that exhibit similar behavior. However, because behavior varies among species, I recommend that investigators collect preliminary data to establish an appropriate count duration when accurate estimates of absolute, rather than relative, abundance are important.