Presence-absence Sampling Research Articles

Hymenopteran Parasitoids of Diamondback Moth (Lepidoptera: Ypeunomutidae) in Northern Thailand

Larvae of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Ypeunomutidae), cause severe economic damage to cabbage, Brassica oleracea L. variety capitata (Brassicaceae) and related vegetables in Thailand. Overuse of broad-spectrum insecticides for diamondback moth control is a serious problem and has obscured the contributions of indigenous parasitoids. Our objectives were to identify indigenous diamondback moth parasitoids in northern Thailand and to assess their potential for natural control. Six parasitoid species were reared from diamondback moth larvae and pupae collected in 1990 and in 2003–2004. These included the larval parasitoid Cotesia plutellae Kurdjumov (Braconidae), a larval-pupal parasitoid Macromalon orientale Kerrich (Ichneumonidae), and pupal parasitoids Diadromus collaris Gravenhorst (Ichneumonidae) and Brachymeria excarinata Gahan (Chalcididae). Single specimens of Isotima sp. Förster (Ichneumonidae) and Brachymeria lasus Walker (Chalcididae) also were reared from diamondback moth hosts. C. plutellae was the dominant larval parasitoid and was often reared from host larvae collected from fields sprayed regularly with insecticides; parasitism ranged from 14 to 78%. Average parasitism by M. orientale was only 0.5–6%. Parasitism of host pupae by D. collaris ranged from 9 to 31%, whereas B. excarinata pupal parasitism ranged from 9 to 25%. An integrated pest management (IPM) protocol using simple presence-absence sampling for lepidopterous larvae and the exclusive use of Bacillus thuringiensis (Bt) or neem resulted in the highest yields of undamaged cabbage compared with a control or weekly sprays of cypermethrin (local farmer practice). IPM programs focused on conservation of local diamondback moth parasitoids and on greater implementation of biological control will help alleviate growing public concerns regarding the effects of pesticides on vegetable growers and consumers.

Spatial Patterns and Sampling Plan forLiriomyza huidobrensis(Diptera: Agromyzidae) and Related Parasitoids on Lettuce

Field experiments were carried out in 2000 and 2001 in northern Italy, with the aim of developing a composite sampling strategy for estimating populations of Liriomyza huidobrensis (Blanchard) larvae and mines on lettuce. Larval parasitoid populations also were sampled to estimate the contribution of these beneficials to pest control. Covariance analysis and parallelism test indicated that there were not significant differences in the coefficient of Taylor’s power law between treatments (untreated versus treated) and between seasons (2000 versus 2001) for both pest and parasitoid stages. The slope of each regression was significantly >1 for L. huidobrensis mines and larvae, and endoparasitoid and ectoparasitoid larvae, indicating a clumped distribution of both pest and parasitoids. Constant precision level stoplines for mines and larvae of L. huidobrensis and for endoparasitoid and ectoparasitoid larvae were calculated, by using the common a and b derived from Taylor’s power law. Wilson and Room binomial sampling was used to estimate the mean number of L. huidobrensis mines or live larvae from the ratio of leaves with mines. In this way, it is possible to estimate the mean density of L. huidobrensis by counting the leaves with mines, an index parameter easy to obtain in field sampling. Validation of the presence-absence sampling plan by using field data collected in 2002 and 2003 seasons, showed that the Wilson and Room model fits very well empirical data. Statistical analysis does not show any significant difference between observed and predicted data.

Oversight probability in presence-absence sampling for detection of fish eggs

: Presence–absence sampling (PAS) is a sampling technique that observes only the presence or absence of objects, such as eggs, in sampling units. The purpose of the present paper was to study the oversight probability in a PAS study for detecting fish eggs in connection with the spatial distribution of eggs. It was shown that the oversight probability of presence of eggs under no-eggs observation is a monotone decreasing function of the parameter of the degree of contagion.

Evaluation of sequential presence-absence sampling plans for the diamondback moth (Plutellidae: Lepidoptera) in cruciferous crops in Australia.

Two sets of sequential presence-absence sampling plans for decision-making in the management of diamondback moth, Plutella xylostella (L.), were developed and evaluated. One set of sampling plans targeted the classification of proportions of infested plants, and the other set of sampling plans targeted the classification of larval density. The action thresholds investigated were 0.15, 0.25, 0.35, and 0.45 proportion of plants infested with larvae, and 0.2, 0.4, 0.6, and 0.8 larvae per plant. They are representative of the action thresholds currently practiced by Australian crucifer growers. For each sampling plan, the population range within which a minimal correct decision rate of 95% can be expected at a maximal average sample size of 50 plants (OC95ASN50) was specified. The closeness of an OC95ASN50 range to the target action threshold is a measure of the expected performance of the sampling plan. A closer distance reflects better performance. The OC95ASN50 ranges of the proportion-classification sampling plans were within 33-53% of the target action thresholds. The width of these OC95ASN50 ranges represents 73-87% of the entire population range (0-1). For the classification of larval density, an empirical proportion-density model was first established using data from different states and different cruciferous crops. The OC95ASN50 ranges of the density-classification sampling plans were within 57-75% of the target action threshold. Simulated sampling of 20 independent data sets showed that for most data sets the correct classification rate was at least 98% and the matching average sample size was <50 plants.

Evaluation of Sequential Presence-Absence Sampling Plans for the Diamondback Moth (Plutellidae: Lepidoptera) in Cruciferous Crops in Australia

Two sets of sequential presence-absence sampling plans for decision-making in the management of diamondback moth, Plutella xylostella (L.), were developed and evaluated. One set of sampling plans targeted the classification of proportions of infested plants, and the other set of sampling plans targeted the classification of larval density. The action thresholds investigated were 0.15, 0.25, 0.35, and 0.45 proportion of plants infested with larvae, and 0.2, 0.4, 0.6, and 0.8 larvae per plant. They are representative of the action thresholds currently practiced by Australian crucifer growers. For each sampling plan, the population range within which a minimal correct decision rate of 95% can be expected at a maximal average sample size of 50 plants (OC95ASN50) was specified. The closeness of an OC95ASN50 range to the target action threshold is a measure of the expected performance of the sampling plan. A closer distance reflects better performance. The OC95ASN50 ranges of the proportion-classification sampling plans were within 33-53% of the target action thresholds. The width of these OC95ASN50 ranges represents 73-87% of the entire population range (0-1). For the classification of larval density, an empirical proportion-density model was first established using data from different states and different cruciferous crops. The OC95ASN50 ranges of the density-classification sampling plans were within 57-75% of the target action threshold. Simulated sampling of 20 independent data sets showed that for most data sets the correct classification rate was at least 98% and the matching average sample size was <50 plants.

Presence–absence sampling for Tetranychus urticae and its predator Neoseiulus californicus (Acari: Tetranychidae; Phytoseiidae) on strawberries

We propose a systematic presence–absence sampling plan for estimating densities of both Tetranychus urticae Koch (Acari: Tetranychidae) and its predator Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) on strawberries. It is based on the synchrony and spatial coincidence between prey and predator. Active stages of both species on each leaflet and the proportion of T. urticae-free leaflets were recorded from 87 samples collected during two growing seasons on five commercial farms. Seventy to 160 leaflets in a sample were taken at intervals of 5 – 10 m in each row. The distribution-free equation Ln(m) = a + b Ln(-Ln(p)) was used to describe the relationships between the mean number (m) of T. urticae and N. californicus per leaflet and the proportion (p) of T. urticae-free leaflets. We devised the following density estimators: T. urticae: Tu = exp(2.78 + 1.31Ln(−Ln p)) and N. californicus: Nc = exp(− 0.04 + 0.76 Ln(−Ln p)). These estimates, complemented with the knowledge of the economic level of damage and the number of predators necessary to control different densities of T. urticae, are likely to help reduce the use of acaricides in the context of integrated pest management of T. urticae on strawberry.

Within-plant distribution of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), on ivy geranium: development of a presence-absence sampling plan.

The twospotted spider mite, Tetranychus urticae Koch, is an important pest of ivy geranium and other ornamental plants. As a part of our long-term goal to develop an integrated crop management program for ivy geraniums, the focus of this study was to produce a reliable sampling method for T. urticae on this bedding plant. Within-plant mite distribution data from a greenhouse experiment were used to identify the young-fully-opened leaf as the sampling unit. We found that 53% of the mites on a plant are on the young-fully-opened leaves. On average 22, 37, and 41% of the leaves belonged to the young, young-fully-opened, and old leaf categories, respectively. We then developed a presence-absence sampling method for T. urticae in ivy geranium using generic Taylor's coefficients for this pest. We found the optimal binomial sample sizes for estimating populations of T. urticae at densities of between 0 and 3 mites/leaf to be quite large; therefore, we recommend the use of numerical sampling within this range of T. urticae densities. We also suggest that population estimates of T. urticae on ivy geranium be done based on mite density/unit area of greenhouse space, both for conventional greenhouse pest management, and for determining how many phytoseid predators to release when using biological control.

Sampling Plan forDicyphus hesperus(Heteroptera: Miridae) on Greenhouse Tomatoes

Dicyphus hesperus Knight has good potential as a biological control agent for greenhouse pests in greenhouse tomato crops. The spatial distribution of D. hesperus was studied and a sampling plan was developed to monitor this species in greenhouse-grown tomatoes. Adults and nymphs are distributed in a more aggregated pattern among plants than within plants. The strong, significant relationship between the mean population density and the proportion of occupied sample units (leaves or plants) makes it possible to use a binomial or presence-absence sampling approach. Presence-absence sampling is an efficient method for crop management purposes because less time is needed to process the samples compared with a method where all insects are counted. At high densities, considering a sample unit to be occupied only when there are more than a determined number of individuals reduces considerably the optimum sample size required.

An assessment of some improved techniques for estimating the abundance (frequency) of sedentary organisms

The traditional sampling method for estimating frequency (the number of sub-quadrats containing a basal part of the organisms) is compared, using both computer simulations and direct comparison in the field, to two new methods that use a compound series of variable-sized concentric sub-quadrats. Both the new frequency-score and the new importance-score methods are closer approximations of density than is the standard frequency method, and the estimates produced by both of the new methods are less affected by the choice of sub-quadrat size and the spatial distribution (dispersion) of the organisms (i.e. clumping and regularity). Thus, the two nested-quadrat methods appear to ameliorate the usual frequency limitations associated with sub-quadrat size and organism dispersion, by the use of a range of different sub-quadrat sizes. This is important in community studies, where the component species may show a wide range of densities and dispersions. Both of the new methods are easily employed in the field. The importance-score method involves no more sampling effort than does standard qualitative (presence-absence) sampling, and it can therefore be used to sample a larger quadrat area than would normally be used for frequency sampling. This makes the method much more cost-effective as a means of estimating abundance, and it allows a greater number of the rarer species to be included in the sampling. The frequency-score method is more time-consuming, but it is capable of detecting more subtle community patterns. This means that it is particularly useful for the study of species-poor communities or where small variations in composition need to be detected.

Sampling for Liriomyza huidobrensis (Diptera: Agromyzidae) Larvae and Damage in Celery

A sampling plan to estimate population levels of Liriomyza huidobrensis (Blanchard) larvae and total mining damage was developed for use in celery. Dispersion indices from Taylor's power law were calculated from 1992 data obtained from whole plant samples collected from commercial fields at two times during the cropping season and utilizing one of three different leafminer management strategies. Analysis of covariance indicated that variance–to–mean relationships were consistent among petiole position among plants, pest management strategies, and time of growing season for live L. huidobrensis larvae and total numbers of mines per petiole. In an attempt to develop a presence–absence sampling plan, all equation was derived to relate the proportion of petioles infested, P(l), to the mean number of live larvae or the mean number of mines per petiole. However, predicted frequencies of infested petioles delivered from this equation were significantly greater than the frequencies of petioles infested with live larvae or infested with mines observed in validation studies. This lack of fit between predicted and expected frequencies precludes use of a presence–absence sampling plan to predict mean densities from the proportion of leaves infested. The results from Taylor's dispersion analysis were also used to evaluate a constant precision–level sampling plan. Validation tests of this sampling plan indicated that the formula used to ca1culate critical stoplines accurately predicted the observed cumulative totals of live larvae or total numbers of mines. Implementation of a sequential sampling plan for L. huidobrensis larvae with a 0.25 level of precision and with a possible maximum sample size of 100 petioles (to compensate for the prohibitively large sample sizes necessary at low densities) should greatly reduce the amount of labor necessary to achieve accurate estimates of population densities and to facilitate the use of action thresholds based upon these estimates.

Gypsy Moth (Lepidoptera: Lymantriidae) Egg Mass Distribution and Sampling in a Residential Setting

The spatial distribution of gypsy moth, Lymantria dispar (L.), egg masses was determined in 60 developed lots in a residential community in Greenbelt, Md. The community was divided into low and high gypsy moth density sections, with average densities of 393.3 and 2,656.3 egg masses per ha, respectively. In the high-density lots, the proportion of egg masses found on trees, man made objects, and houses was 73.9, 21.6, and 4.5%, respectively. The distribution in the low density lots was similar. Oaks, Quercus spp., received the highest proportion of egg masses out of all tree species subcategories at both low and high population densities. The cost effectiveness of a number of potential sampling units, including entire lots, back yards, fixed area plots, and individual trees, was evaluated. The entire lot sampling units required the fewest samples to achieve a predetermined level of precision. However, cost (= sampling time) for these sampling units was also the highest, resulting in relatively low cost effectiveness. Fixed-area plot samples (0.01 ha) were in general the most cost effective sampling units. A binomial (presence-absence) sampling approach, in which the percentage of trees in each lot with >5 egg masses is determined, was nearly as cost effective as fixed-area plots, but its usefulness is limited because it does not provide direct estimates of absolute gypsy moth population density.

Determining Population Characteristics and Sampling Procedures for the Western Flower Thrips (Thysanoptera: Thripidae) and the Predatory Mite Amblyseius cucumeris (Acari: Phytoseiidae) on Greenhouse Cucumber

Distribution characteristics of the western flower thrips, Frankliniella occidentalis (Pergande), and the predatory mite Amblyseius cucumeris (Oudemans) were studied on greenhouse cucumber and used in developing presence–absence sampling procedures. The variance-mean relationship was described by Taylor's power law and resulted in aggregation indices on middle leaves of 1.62 for thrips larvae and 1.31 for thrips adults and A. cucumeris . Tables are presented for estimating population density from percentage of leaves infested and for determining sample size required at different population densities and precision levels. Thrips density correlated with leaf damage but not with fruit damage.

Presence-Absence Sampling for Fisheries Management

It is often important to estimate the abundance of a fish stock when the stock is somewhat depleted. For pelagic species this presents great operational difficulties, because adult surveys may be prohibitively expensive and time consuming. Here we introduce a method for estimating the spawning biomass of a stock by means of egg or larval surveys. In particular, we develop a series of models for presence-absence sampling of eggs or larvae and show how presence-absence data can be used to estimate adult spawning biomass. The models are based on an underlying probabilistic description of the aggregation of eggs or larvae, a search process, and a description of habitat structure. Methodologies are given for estimating the distribution of the size of the spawning biomass from presence-absence data. A case study of sardine is used to justify a number of the assumptions. The methods are applied to a 1985 survey for sardine eggs and are compared to an alternative method based on egg production.

Density–Damage Relationship and Presence–Absence Sampling of the Elm Leaf Beetle (Coleoptera: Chrysomelidae) in Northern California

The relationship between density of elm leaf beetle, Xanthogaleruca luteola (Muller), and damage to English elm, Ulmus procera Salisbury, and Siberian elm, Ulmus pumila L., was studied in seven northern California cities in 1986 and 1987. Peak first-generation elm leaf beetle egg or larval densities were good predictors of cumulative foliage damage to English elm and to a lesser extent predicted Siberian elm damage. Egg density on both hosts was highly associated with the proportion of samples infested with eggs. The maximum proportion of presence-absence samples infested with first generation eggs predicted cumulative damage to English but not to Siberian elm. When no effort was made to control beetle populations most English elm trees sustained more than 40% damage to retained foliage, whereas damage to most Siberian elms was less.

Within-plant distribution of Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) on cassava: effect of clone and predation on aggregation

AbstractA presence-absence sampling procedure is presented which relates the proportion of leaves infested with the mite Mononychellus tanajoa (Bondar) at a given node of cassava to the mean number of mites per leaf at that node. The procedure incorporates Taylor's variance-mean density relationship, taking into account mite aggregation behaviour. Aggregation of M. tanajoa was greater in plants where mite predators were excluded, on a resistant (CG5-79) rather than a susceptible cassava clone (MCol 22) and on leaves arising from the lower nodes rather than the higher ones. The implications of the effect of mite mortality factors on aggregation are discussed.

Sampling Program for Fall Armyworm in Maize

A sampling program for fall armyworm (FAW), Spodoptera frugiperda (Smith), in Honduran maize, Zea mays (L.), is described. Presence-absence sampling was used to monitor FAW infestations and insecticide treatment decisions were made against predetermined action thresholds. Simplification of the sampling program for grower acceptance required standardization of sample size. Two methods for estimating sample size were compared. Sample sizes needed to maintain a level of sample precision were larger than sample sizes needed to make control decisions. By reducing sampling effort and standardizing sample size, we provide a sampling program more appropriate for local grower needs and skills.

Sampling mites in almonds: II. Presence-Absence Sequential Sampling forTetranychusMite Species

A practical monitoring program for spider mites, Tetranychus spp., in almond orchards is proposed. It is possible to determine densities of the Tetranychus mites after they disperse through each tree by using the proportion of leaves infested with one or more mites rather than counting the actual number of mites per leaf. This presence-absence (binomial) sampling technique may be used in conjunction with sequential sampling to further reduce sampling time. Provisional control action thresholds developed are 0.436 (mean proportion infested leaves) in the presence of the predatory mite Metaseiulus occidentalis, and 0.220 in its absence. Optimal numbers of trees to be sampled at various confidence levels are determined for a range of mite densities with leaf samples of 5, 15, and 40 per tree.

Breeding Avifauna of a Mediterranean Succession: The Holm oak and Cork Oak Series in the Eastern Pyrenees, 1. Analysis and Modelling of the Structure Gradient

Within the Mediterranean level of the Alberes chain, 186 samples were taken in different formations from grassland to forest, with presence-absence sampling of the bird and plant species, and estimation of the relative cover of 7 vegetation layers, plus the rock itself. After multidimensional ordination (Correspondence Analysis) of the birds x stations matrix, and multiple correlation of the first factor F1 of C.A. with the 8 cover values, a model results which, (1) proves that F. is the expression of a progressive evolution of the vegetation structure, (2) shows that there is a logarithmic relationship between this structural evolution and bird species turnover, (3) permits a calculation, for any station of the studied region, of optimal indices of avifaunistic gradient and of structure gradient, (4) allows one to predict semi-quantitatively, from the vegetation structure, the probable avifauna of any station, and vice versa. This gradient analysis is a good alternative to the classical model (unidimensional sequence of discrete classes), especially when an ecological succession is reconstructed from the simultaneous comparison of different stations.