Sampling of insect communities is very challenging and for reliable interpretation of results the effects of different sampling protocols and data processing on the results need to be fully understood. We compared three different commonly used methods for sampling forest beetles, freely hanging flight-intercept (window) traps (FWT), flight-intercept traps attached to trunks (TWT) and pitfall traps placed in the ground (PFT), in Scots pine dominated boreal forests in eastern Finland. Using altogether 960 traps, forming 576 sub-samples, at 24 study sites, 59760 beetles belonging to 814 species were collected over a period of a month. All of the material was identified to species, with the exception of a few species pairs, to obtain representative data for analyses. Four partly overlapping groups were used in the analyses: (1) all, (2) saproxylic, (3) rare and (4) red-listed species. In terms of the number of species collected TWTs were the most effective for all species groups and the rarer species the species group composed of (groups 1-2-3-4) the larger were the differences between the trap types. In particular, the TWTs caught most red-listed species. However, when sample sizes were standardized FWTs and TWTs caught similar number of species of all species groups. PFTs caught fewer species of all species groups, whether the sample sizes were standardized or not. In boreal forests they seem to be unsuitable for sampling saproxylic, rare and red-listed species. However, the PFTs clearly sampled different parts of species assemblages than the window traps and can be considered as a supplementary method. The abundance distribution of saproxylic species was truncated lognormal in TWT and pooled material, whereas unclassified material failed to reveal lognormal distribution in all the trap types and pooled material. The results show that even in boreal forests sample sizes of at least thousands, preferably tens of thousands of individuals, collected by a high number of traps are needed for community level studies. Relevant ecological classification of material is also very important for reliable comparisons. Differences in the performance of trap types should be considered when designing a study, and in particular when evaluating the results.
Estimating the spatial dispersion of pest arthropods is crucial for the development of reliable sampling programs and one of the main components of integrated pest management. The natural spatial distribution of a population of a species may be random, uniform, or aggregated and can be so classified based on calculation of variance to mean relations and related dispersion indices. In this work some classical density-invariant dispersion indices and related regression models are used for the first time to quantify the spatial dispersion of an important peach pest Anarsia lineatella Zeller (Lepidoptera: Gelechiidae) and construct fixed precision sequential sampling schemes. Taylor's power law, Iwao's patchiness regression and Nachman's model were used to analyse the damage to peaches caused by A. lineatella. All three regression models fit the data well, although the results indicate that Iwao's patchiness model provides a better description of the relationship between variance and mean density. Taylor's b and Iwao's b regression indices were both significantly smaller than 1, indicating that the distribution of individuals was uniform rather than random or aggregated. According to Green's and Kuno's models, the minimum sample size at the precision level of 0.2 varies from 3 samples, when total population density is more than 3 larvae/sample, to 10 samples, when population density is between 1 and 2 larvae/sample. Kuno's fixed sampling plan indicates that a small number of samples (i.e., 3-10 branches with fruit) is sufficient to estimate the mean population density of A. lineatella larvae with a precision of 0.2. The Resampling for validation of sampling plans (RVSP) method confirmed that the average level of precision of the fixed sequential plans matched the desired precision in most cases. The sampling plan presented here provides a level understanding of A. lineatella spatial ecology suitable for pest manage, Petros Damos., and Obsahuje bibliografii
A tobacco field in Greece was sampled during the 2001 and 2002 growing seasons to assess the seasonal trends in densities and spatial distributions of the aphid Myzus persicae (Sulzer) and its predatory mirid Macrolophus costalis (Fieber). On repeated occasions between June (just after the transplantation) and September (just before harvest), 20 tobacco leaves (10 from the upper and 10 from the lower plant part) were taken from randomly chosen plants. These leaves were sampled for aphids and mirids. In both years, the highest aphid densities were recorded during July and August, while aphid numbers were low in September. In contrast, the majority of M. costalis individuals were found during September when aphid numbers were low. Significantly more M. persicae individuals were found in the upper part of the plants, whereas significantly more M. costalis individuals were found in the lower part of the plants. As indicated by Taylor's Power Law estimates, both species were aggregated in their spatial distributions among sampling units (leaves). Wilson and Room's model, based on the Taylor's estimates, was used to calculate the mean number of aphids and mirids, from the proportion of sampling units (leaves) that had > 0 individuals of each species. This model provided a satisfactory fit of the data for both the aphid and the mirid. In addition, Wilson and Room's model was successfully used to predict the mean number of aphids and mirids in a series of samples that were carried out in the same area between June and September 2003 for model validation. Finally, equations are given for the calculation of precision in estimating the mean number of aphids or mirids per sampling unit, and the required sample size for a given level of precision.
Pollinating insects are important and therefore, it is important to be able to assess and monitor changes in their abundance. Consequently, it is essential that the methods used to collect data have some level of precision and are accurate. In the present study, two commonly used methods: colour pan-traps and sweep netting along transects, were compared. A total of 1775 specimens of 120 species of four insect families were caught in twelve clear-cuts in southern Sweden. Overall, Lepturinae (Cerambycidae; 5 species) and Cetoniidae (Scarabaeidae; 2) were trapped in larger numbers by pan-traps and Syrphidae (62) and Apoidea, both social (10) and solitary (41), by sweep netting. The catches of none of the above groups of insects by the two methods were correlated. These results show that the composition of catches of the two methods are very different, which has implications when choosing a method for sampling or monitoring and comparing and analysing published data.
This article presents a critical evaluation of the growing popularity of online social surveys for the exploration of attitudes and behaviours within higher educational institutions. More specifically this article addresses a number of key issues: the construction of representative online samples, and the presentation of the results from an institutional census constructed from an online survey with a low response rate. The improper use of statistical significance tests, and the reporting of systematic errors when quota sampling is employed in surveys is also discussed. This study compares and evaluates four recent academic surveys: (a) the Czech wave of the EUROSTUDENT IV survey fielded by SC&C, (b) A Research Survey on Academic Staff at Czech Colleges and Universities undertaken by SC&C in 2009, (c) surveys of students and (d) employees at Palacky University Olomouc undertaken by the newly established Laboratory of Social Research. This article shows that an improper interpretation of online surveys resulted in a missrepresention of the views of university students and academic staff on the state of Czech higher education and opinions concerning different tertiary education reform measures., Dan Ryšavý., and Obsahuje bibliografii a bibliografické odkazy
This article presents a critical evaluation of the growing popularity of online social surveys for the exploration of attitudes and behaviours within higher educational institutions. More specifically this article addresses a number of key issues: the construction of representative online samples, and the presentation of the results from an institutional census constructed from an online survey with a low response rate. The improper use of statistical significance tests, and the reporting of systematic errors when quota sampling is employed in surveys is also discussed. This study compares and evaluates four recent academic surveys: (a) the Czech wave of the EUROSTUDENT IV survey fielded by SC&C, (b) A Research Survey on Academic Staff at Czech Colleges and Universities undertaken by SC&C in 2009, (c) surveys of students and (d) employees at Palacky University Olomouc undertaken by the newly established Laboratory of Social Research. This article shows that an improper interpretation of online surveys resulted in a missrepresention of the views of university students and academic staff on the state of Czech higher education and opinions concerning different tertiary education reform measures.