Spatial distribution of the green peach aphid used in estimating the populations of gynoparae

Summary In 2 years, during the initial invasion of peach leaves by the green peach aphid,Myzus persicae (Sulzer), the number of gynoparae was low, and the distribution on leaves was random. Then as the mean number increased, the distribution became intermediate and could not be distinguished from either a Poisson or a negative binomial. Finally, as the mean continued to increase, the variance increased rapidly, and the population was found to fit a negative binomial distribution. Thus the aggregation response was verified because the dispersion pattern fitted a contagious distribution. A sampling plan was devised by which the dispersion parameterk was used to estimate the density of aphids per leaf based on the percentage of leaves infested. Sampling the third year of the study confirmed the validity of the sampling parameter that had been calculated from data for the 2 previous years.     

Random median sampling to enhance the precision of population estimates

We describe the characteristics of a sampling procedure called random median sampling that was proposed to enhance the precision of population estimates. In performing random median sampling, we first select a sampling item at random from the sampling area. We roughly compare the abundance of individuals in the selected item with that of the adjacent two items in order to identify the item that has median abundance, i.e., the item that has the second largest abundance among the three items. We count the number of individuals of the item having the median abundance. This procedure is repeated n times in the sampling area (i = 1, 2, ..., n). Let m _i be the ith median abundance. The estimates of the mean abundance per sampling item and the variance of estimates are given by Σm _i /n and Σ(m _i –Σm _i /n)²/n(n – 1), respectively. This method is a local application of the median ranked set sampling that was proposed by Muttlak (J Appl Stat Sci 6:245–255, 1997). Random median sampling is effective when the correlation coefficient between adjacent items is small. If the correlation coefficient is close to zero, random median sampling reduces the variance of estimates to 45 or 32% of that in simple random sampling when the distribution follows a normal distribution or a Laplace distribution, respectively. The sample size required to achieve a given precision of estimate decreases accordingly. The effectiveness of random median sampling, however, is small if the correlation coefficient is large. The condition in which random median sampling is superior to simple random sampling is also discussed.     

On fixed precision level sequential sampling

Summary It is proposed that the sequential sampling design ofKuno (1969) for estimating populations with a fixed level of precision be modified by using σ²=am ^b for the variance-mean relationship for most field distributions of organisms. This function yields a straight line “stop line” rather than a curve. An example is calculated and used with field data.     

棉花苗期棉蚜的二项式抽样设计及其精度分析

基于棉花苗期棉蚜（Ａｐｈｉｓ ｇｏｓｓｙｐｉｉ）的２４组调查数据,利用每样方虫口不超过数阈值Ｔ（为０,１,２,…,９,１０,１５,２０,３０）头蚜虫的植株比例（ＰＴ）与种群密度（ｍ,头／株）的关系,拟合经验关系式１ｎ（ｍ）＝α＋ｂ１ｎ〔－１ｎ（ＰＴ）〕设计二项式抽样。通过对不同数阈值Ｔ的决定系数（ｒ＾２）、估计方差（Ｖａｒ（ｍ））和抽样精度（ｄ估计）等进行综合分析,结果表明该蚜虫在数阈值Ｔ为１５时     

Population dynamics of the potato tuber moth on processing tomatoes in Israel

The potato tuber moth (PTM),Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is a major pest of processing tomatoes,Lycopersicon esculentum Mill. (Solanaceae), in Israel. The larvae penetrate the tomato fruit through the stem end and present a serious threat to crop quality. Foliage and fruit samples were taken in nine commercial tomato fields located in Israel's three main tomato growing areas, two of which are potato growing areas as well. PTM was not found where potatoes were absent. Potato harvest in nearby fields was found to be the most significant factor affecting seasonal trends in PTM population density in tomatoes. All four larval instars were found in foliage on all sampling dates. Significantly higher proportions of first instars were found during the population density increase which followed potato harvest. Damaged fruits did not contain first instar larvae, indicating that PTM never undergoes complete development within tomato fruit. Fruit damage levels at harvest were positively correlated to the peak mean population densities on foliage and the date they were observed. In tomato fields not adjacent to potatoes, infestation was first observed at the edge of the field. Both before and after the potato harvest in nearby fields, population density at the edge of the field was significantly higher than at the center. In tomato fields adjacent to potatoes, no significant differences were found between population densities at the edge and center before the potatoes were harvested. After the potato harvest, population density at the center of tomato fields was higher than at the edge. Deceased, October 1988     

Seasonal abundance, spatial distribution and sampling indices of thrip populations on cotton; a 4-year survey from central Greece

Abstract: Field studies were carried out in order to assess the populations of thrips on cotton leaves, by developing a sampling program to estimate the density with an acceptable level of precision. Thus, in a cotton field (1.1 ha) in central Greece, 45 leaves were collected (one leaf per cotton plant) at 10‐day intervals from May to September, for four consecutive growing seasons (1995–98). Five species of thrips were found: Frankliniella intonsa was the most abundant species followed by Thrips angusticeps, Thrips tabaci, Frankliniella occidentalis and Aeolothrips intermedius. Although considerable differences were observed in the population fluctuations among species, the highest population densities, for all species found, were recorded in July and August. As indicated by Taylor's power law estimates, all species presented aggregated distribution among sampling units. As this type of spatial pattern indicates, the accuracy obtained in estimating mean population density increased with the increase of the mean. Furthermore, the increase of the mean caused an exponential decrease in sample size. However, the precision level is acceptable only in high mean values, while at the same time the benefit from an increase in sample size is of no practical value.     

Regulatory processes and population cyclicity in laboratory populations ofAnagasta kühniella (Zeller) (Lepidoptera: Phycitidae) IV. The sequential steps in the behavioral process of host finding and parasitization by the entomophagous parasite,Venturia canescens (Gravenhorst) (Hymenoptera: Ichneumonidae)

Summary The sequential steps in the behavioral process of a California stock of the entomophagous parasite,Venturia canescens (Grav.), parasitizingAnagasta kühniella (Zeller) was studied. In host-habitat finding, food media infested with hosts were very attractive to the parasites. Host finding was not covered in detail in this paper as it is presented in subsequent papers. Briefly, in all experiments host density was the most influential factor affecting the efficiency of the parasite. When three age stages of the host were exposed to a parasite, all tests showed that the large, last instar larvae was the preferred age stage but it was not the most suitable (when parasitized) for successful parasite development. Small larvae were less preferred but more suitable for parasite development when accepted. These studies were conducted as a partial fulfillment in the Ph. D. program of one of us (B. M. Matsumoto) and form a part of a broad investigation into the processes operating in the dynamics of arthropod populations under grants toC. B. Huffaker from the U. S. Public Health Service, National Institutes of Health and the U. S. Department of Agriculture.     

X-ray microdensitometry applied to subfossil tree-rings: growth characteristics of ancient pines from the southern boreal forest zone in Finland at intra-annual to centennial time-scales

A collection of subfossil wood of Pinus sylvestris (Scots pine) was exposed to X-ray densitometry. The collection of 64 samples from the southern boreal forest zone was dendrochronologically cross-dated to a.d. 673-1788. Growth characteristics were determined by performing density profiles including the following parameters: minimum density, earlywood and latewood boundary density, maximum density, earlywood width, earlywood density, latewood width, latewood density, annual ring width and annual ring density. Seven out of the nine parameters were found to contain non-climatic growth trends and six were found to be heteroscedastic in their variance. Tree-specific records were indexed, to remove the non-climatic growth trends and stabilize the variance, and combined into nine parameter-specific tree-ring chronologies. Growth characteristics of the pines changed in parallel with the generally agreed climatic cooling from the Medieval Warm Period to the Little Ice Age: pine tree-rings showed decreasing maximum densities from the period a.d. 975-1150 to a.d. 1450–1625. A concomitant change in the intra-annual growth characteristics was detected between these periods. The findings indicate that not only the trees growing near the species’ distributional limits are sensitive to large-scale climatic variations but also the trees growing in habitats remote from the timberline have noticeably responded to past climate changes.     

Sampling strategies for assessing the overall density of the cassava green mite (Mononychellus tanajoa)

Six different sampling methods to estimate the density of the cassava green mite, Mononychellus tanajoa, are categorized according to whether leaves or leaflets are used as secondary sampling units and whether the number of leaves on the sampled plants are enumerated, estimated from an independent plant sample, or not censused at all. In the last case, sampling can provide information only on the average number of mites per leaf and its variance, while information on stratum sizes is necessary to estimate the mean number of mites per plant as well. It is shown that leaflet-sampling is as reliable as leaf-sampling for the same number of sampling units. When stratum sizes are estimated from a separate plant sample, sampling time may also be reduced, but the estimated mean density and its variance may be biased if mite density and plant size are correlated. Sampling data show that the within-plant variance contributes relatively little to the overall variance of the population density estimates. It points at a sampling strategy in which the number of primary units (plants) is as large as possible at the expense of secondary units (leaflets) per plant. Mean-variance relationships may be applied to estimate sample variances and can be used even when only one leaflet is taken per plant per stratum. An unequal allocation of primary units among strata can increase precision, but the gain is small compared with an equal allocation. Leaf area can be predicted from the length of the longest leaflet and the number of leaflets.     

Effectiveness of larvae ofSyrphus ribesii andS. Corollae [Diptera: Syrphidae] as predators onMyzus persicae [Homoptera: Aphididae]

Capture efficiency, handling time and functonal response to prey density were studied in larvae ofSyrphus ribesii (L.) andS. corrollae (Fabr.) eatingMyzus persicae Sulz. at 20°C, 16 hrs light. First instar larvae ofS. ribesii had distinctly higher capture efficiency than 1st instar larvae ofS. corollae, both versus 1st instar and adult aphids. Second and 3rd instar larvae of both species seemed to prefer adult rather than 1st instar aphids, but no distinct difference in capture efficiency between the species was found. On comparable stages,S. ribesii always had shorter handling time thanS. corollae and it appeared in both species to be correlated with size of prey and predator. Handling time was thus shortest when 3rd instar larvae consumed 1st instar aphids. During one hour, 3rd instar larvae ofS. ribesii consumed aphids in quantities almost linearly dependent on aphid density (5, 10, 20 and 40 adult aphids/100 cm²), although the response also could roughly be described byHolling's “basic functional response curve”. On the contrary, 3rd instar larvae ofS. corollae soon reached a maximum consumption during one hour, being almost constant (5–7 aphids) at prey densities ≥10 aphids/100 cm².

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Résumé L'efficacité prédatrice (proportion de toutes les rencontres entre larves de syrphes et pucerons se terminant par la capture et la succion de pucerons), la durée d'activité et la relation entre l'absorption de nourriture et la densité des proies (5, 10, 20 et 40Myzus persicae Sulz. aptères au 5^e stade larvaire/100 cm²) ont été étudiées chez des larves deSyrphus ribesii (L.) etS. corollae (Fabr.) à 20°C et 16 h de photopériode. Les L₁ deS. ribesii présentent une efficacité prédatrice des pucerons des premier et dernier stades nettement plus élevée que les L₁ deS. corollae (S. ribesii: 71 et 38%;S. corollae: 42 et 0%). Chez les larves des 2^e et 3^e stades, on n'a observé aucune différence d'efficacité prédatrice entre les 2 espèces, mais une préférence pour les pucerons adultes. La durée d'activité deS. ribesii est dans tous les cas plus courte que celle deS. corollae pour un même stade de larves et de pucerons. Une corrélation positive semble exister entre la taille des proies et celle des prédateurs. La durée d'activité est la plus courte pour des prédateurs en L₃ s'alimentant de pucerons au premier stade (1,3 mn chezS. ribesii et 2,3 mn chezS. corollae). L'absorption de nourriture enregistrée en une heure chezS. ribesii varie presque linéairement avec la densité des pucerons; elle correspond d'autre part assez bien à la formule deHolling. L'absorption de nourriture parS. corollae atteint un maximum de 7 pucerons à l'heure et demeure pratiquement constante à partir d'une densité≥10 pucerons/100 cm².

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The author wishes to thank techn. ass.Bodil Horgen for assistance during the experiments     

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.     

The line transect method for estimating densities of large mammals in a tropical deciduous forest: An evaluation of models and field experiments

We have evaluated techniques of estimating animal density through direct counts using line transects during 1988–92 in the tropical deciduous forests of Mudumalui Sanctuary in southern India for four species of large herbivorous mammals, namely, chital (Axis axis). sambar (Cervus unicolor). Asian elephant (Elephas maximus) and gaur (Bos gaurus) Density estimates derived from the Fourier Series and the Half-Normal models consistently had the lowest coefficient of variation. These two models also generated similar mean density estimates. For the Fourier Series estimator, appropriate cut-off widths for analyzing line transect data for the four species are suggested. Grouping data into various distance classes did not produce any appreciable differences in estimates of mean density or their variances, although model fit is generally better when data arc placed in fewer groups. The sampling effort needed to achieve a desired precision (coefficient of variation) in the density estimate is derived. A sampling effort of 800 km of transects returned a 10% coefficient of variation on estimate for ehital; for the other species a higher effort was needed to achieve this level of precision. There was no statistically significant relationship between detectability of a group and the size of the group for any species. Density estimates along roads were generally significantly different from those in the interior of the forest, indicating that road-side counts many not be appropriate for most species.     

The life history of the diving beetle, Lancetes angusticollis (Curtis) (Coleoptera: Dytiscidae), on sub-Antarctic South Georgia

Two populations of the world's most southerly diving beetle (Lancetes angusticollis) were studied on sub-Antarctic South Georgia between November 1995 and April 1996. Parallel observations were made on laboratory cultures of each life stage. All juvenile stages of L. angusticollis are voracious predators, preying mainly on the herbivorous copepod Boeckella poppei. Adult beetles additionally predate benthic ostracods. Laboratory predation rates and field population densities found in this study suggest that L. angusticollis has a more significant impact on its prey than recognised in recent studies of South Georgian lakes. Spring field samples contained only a few individuals of larval instar IV and adults. Young larvae were present from December onwards, with a rapid progression through juvenile instars during the summer months. Fourth instar larvae left the water for pupation between mid-December and at least mid-February. Combining these observations with known developmental threshold temperatures for each life stage implies that L. angusticollis has a complex biennial (minimum) life-cycle, with overwintering possible in three life stages [aquatic larvae, terrestrial pupae (not proven) and aquatic adults]. L. angusticollis may be a suitable indicator species in the context of climate warming studies: a small (1°C) rise in mean environmental temperatures, comparable to that already observed at several sub-Antarctic and maritime Antarctic localities, would allow completion of an annual (univoltine) life-cycle, with concomitant rapid population increase, and serious implications for trophic interactions in these simple lake ecosystems. Received: 24 November 1997 / Accepted: 12 April 1998     

Variations in the Microcystin Production of Planktothrix rubescens (Cyanobacteria) Assessed from a Four-Year Survey of Lac du Bourget (France) and from Laboratory Experiments

Between 1999 and 2002, a routine survey of water quality in the Lac du Bourget was performed to study the dynamics and microcystin (MC) production of Planktothrix rubescens. Using liquid chromatography coupled to diode array detection and mass spectrometry, we found that two main variants ([d-Asp³] and [d-Asp³, Dhb⁷] microcystin-RR) were produced. The proportion of these two variants was not influenced by the depth or season of sampling. Expressed in microcystin-LR equivalents, high microcystin concentrations were recorded from August to December each year, reaching values of up to 6.7 μg L⁻¹. A significant correlation was found between the microcystin cell content and the cell densities of P. rubescens. Cellular quotas of microcystins ranged from 0.1 to 0.3 pg cell⁻¹. Simultaneously, laboratory experiments were performed on a strain of P. rubescens isolated from the lake to assess the potential impact of various P–PO₄³⁻ concentrations on intra- and extracellular microcystin production. Unlike natural populations, this strain only produced [d-Asp³] MC-RR. The intracellular microcystin content was similarly correlated to the cell density, but the cellular quota was slightly higher (0.3–0.7 pg cell⁻¹) than in the natural population. Again, as in the natural population, a linear relationship was found between growth rate and microcystin production rate. These findings support the hypothesis that environmental factors, such as phosphate concentrations, have no direct impact on microcystin production by P. rubescens, but act indirectly by affecting growth rate.     

The availability and use of wood resources at the multi-period settlement site of Pyeonggeo-dong, Jinju, South Korea

Analysis of wood charcoal that was conducted as a part of an interdisciplinary project at Pyeonggeo-dong, a multi-period agricultural complex located in Jinju, South Korea, reveals oak (Quercus sp.) to be the most commonly encountered wood over the period of 4000–1500 cal. b.p. The charcoal data indicate that Quercus was one of the most abundant woody plants in the surrounding vegetation, although its dominance in the charcoal assemblage may partly represent preferential human selection in the past. The data suggest that Quercus-dominant forest declined with the growth of a secondary forest of Platycarya strobilacea around the site from about a.d. 300. This change postdates by more than a thousand years the earliest evidence of large-scale agriculture, which is visible in the form of carbonized crops and large tracts of prehistoric agricultural fields. A relatively large number of pit dwellings for the Three-Kingdoms period (ca. a.d. 300–500) at Pyeonggeo-dong suggests that this late sign of human impact on vegetation is related to the extension of agricultural fields to previously uncultivated hilly areas and/or increased needs for fuel and timber caused by high population density of the site.     

Effect of Coleus Size and Variegation on Attack Rates, Searching Strategy, and Selected Life History Characteristics of Cryptolaemus montrouzieri (Coleoptera: Coccinellidae)

Twenty-four-hour attack rates and the search strategy of third instar Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae) attacking 1 to 16 third instar Planococcus citri Risso (Homoptera: Pseudococcidae) were measured on green and yellow-variegated Solenostemon scutellarioides (L.) Codd (= Coleus blumei (Bentham)) (Labiatae) plants of different sizes. Selected life history characteristics of C. montrouzieri fed different amounts of P. citri as prey from third instar to adults were also examined. On average, predators attacked 1 to 4 mealybugs, depending on the number of mealybugs and plant size. There was no effect of plant color on attack rates. Attack rates were positively related to prey density, whereas the estimated area searched by predators was inversely related to prey density. Analyses suggest that leaf area was the plant characteristic that most affected attack rates. Predators fed few prey had a decrease in body weight and survival. The implications for the use of C. montrouzieri in biological control are discussed.     

Relationship between indoor and outdoor airborne fungal spores, pollen, and (1→3)-β-D-glucan in homes without visible mold growth

In this exploratory study, indoor and outdoor airborne fungal spores, pollen, and (1→3)-β-D-glucan levels were determined through long-term sampling (24-h) using a Button Personal Inhalable Aerosol Sampler. The air samples were collected in five Cincinnati area homes that had no visible mold growth. The total count of fungal spores and pollen in the collected samples was conducted under the microscope and Limulus Amebocyte Lysate (LAL) chromogenic assay method was utilized for the determination of the (1→3)-β-D-glucan concentration. For the combined number concentration of fungal spores and pollen, the indoor and outdoor geometric mean values were 573 and 6,435 m⁻³, respectively, with a geometric mean of the Indoor/Outdoor (I/O) ratio of .09. The geometric means of indoor and outdoor (1→3)-β-D-glucan concentrations were .92 and 6.44 ng m⁻³, respectively, with a geometric mean of the I/O ratio equal to .14. The I/O ratio of (1→3)-β-D-glucan concentration was found to be marginally greater than that calculated based on the combined number concentration of fungal spores and pollen. This suggests that (1→3)-β-D-glucan data are affected not only by intact spores and pollen grains but also by the airborne fragments of fungi, pollen, and plant material, which are ignored by traditional enumeration methodologies. Since the (1→3)-β-D-glucan level may elucidate the total exposure to fungal spores, pollen, and fungal fragments, its I/O ratio may be used as a risk marker for mold and pollen exposure in indoor environments.     

Notes on the biology of a spider parasiteColpomeria kincaidii Ashmead [Hymenoptera: Ichneumonidae]

C. kincaidii, an ectoparasite ofTetragnatha laboriosa Hentz, was found most commonly in spring and fall. Peak parasitism was 18%. They appeared to oviposit only on middle instar spiderlings, and winter as larvae attached to spiders.

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Résumé C. kincaidii, un ectoparasite deTetragnatha laboriosa Hentz, a été trouvé très communément au printemps et en automne avec un taux de parasitisme maximum de 18%. Il semble pondre seulement sur les stades juvéniles moyens de l’araignée et hiverner à l’état de larves fixées aux araignées adultes.