Passive Pitfall Research Articles

Relative Efficiency of Pitfall Trapping vs. Nocturnal Hand Collecting in Assessing Soil-Dwelling Spider Diversity along A Structural Gradient of Neotropical Habitats

Assessing spider diversity remains a great challenge, especially in tropical habitats where dozens of species can locally co-occur. Pitfall trapping is one of the most widely used techniques to collect spiders, but it suffers from several biases, and its accuracy likely varies with habitat complexity. In this study, we compared the efficiency of passive pitfall trapping versus active nocturnal hand collecting (NHC) to capture low understory-dwelling spider taxonomical (morpho-species) and functional (hunting guilds) diversity along a structural gradient of habitats in French Guiana. We focused on four habitats describing a structural gradient: garden to the orchard to the forest edge to the undisturbed forest. Overall, estimated morpho-species richness and composition did not vary consistently between habitats, but abundances of ground-hunting spiders decreased significantly with increasing habitat complexity. We found habitat-dependence differences in taxonomic diversity between sampling strategies: NHC revealed higher diversity in the orchard, whereas pitfalls resulted in higher diversity in the forest. Species turnover resulted in high dissimilarity in species composition between habitats using either method. This study shows how pitfall trapping is influenced by habitat structure, rendering this sampling method incomplete for complex, tropical environments. However, pitfall traps remain a valuable component of inventories because they sample distinct assemblage of spiders.

Decomposition and insect colonization patterns of pig cadavers lying on forest soil and suspended above ground.

Hanging is one of the most common methods of suicide, and, although it is known that decomposition and patterns of insect fauna colonization of hanging cadavers differ from those of cadavers decomposing on the ground, these differences have only been sparsely studied in Europe so far. We studied the decomposition and insect colonization patterns of ten pig (Sus scrofa domestica) carcasses in a spruce forest near Neuchâtel, Switzerland, over a 32-day period in summer 2013 (July 1st - August 2nd). Five pig carcasses were suspended horizontally in metal cages one meter above the ground and five carcasses were placed directly on the ground. The species occurrence and abundance of Coleoptera and Diptera recovered from passive pitfall traps and collected manually on the carcasses were recorded. Indicator species of decomposition stages and suspended vs. ground cadavers were identified by Indicator Value (IndVal) analysis. The ground carcasses decomposed significantly faster than the suspended carcasses. Coleoptera and Diptera communities differed significantly over time, between treatment, and the treatment effect varied over time. Diptera were evenly distributed among the two treatments. Coleoptera were more abundant and less differentiated on the ground carcasses and represent better indicators of cadavers decomposing on the soil as well as decomposition stages. Our results suggest possible applications such as evaluating if a hanged cadaver has been dropped to the ground, or inversely if a cadaver first lying on the soil has later been hung to fake a suicide. However differences among studies suggest possible effects of meso-climate determined by habitat which should be explored further.

Eficiencia de trampas pitlight con led para el muestreo de coleoptera nocturnos (insecta) en selvas tropicales

RESUMEN. Se evaluó el uso de trampas de caída con luz portables (pitlight) con diodos emisores de luz (LED) para la captura de Coleoptera nocturnos en una selva tropical, con la finalidad de proveer herramientas eficientes para el monitoreo de insectos. Se comparó la diversidad de familias y morfoespecies recolectada con trampas de caída pasivas (pitfall) y con trampas de caída con luz (pitlight) de tresdistintas longitudes de onda (azul, blanca y amarilla), bajo la hipótesis de que las trampas pitlight son más eficientes, y que los insectos serán más atraídos por las longitudes de onda más cortas y de alta frecuencia. Además, el muestreo se dividió en dos períodos nocturnos de cinco horas, con el objetivo de analizar el tiempo necesario para obtener una colecta significativa. Las recolectas con trampas pitlight fueron notablemente superiores a las pitfall pasivas, y aunque no se encontraron diferencias significativas entre los valores de riqueza, abundancia y diversidad de coleópteros obtenidos con tres colores de LED (azul, blanco, amarillo), ni entre los horarios nocturnos de recolecta, sí se observó una alta disimilitud en la composición de morfoespecies entre los distintos tratamientos. Las trampas pitlight con LED son un método sencillo, portátil y económico que es capaz de obtener una captura eficiente y representativa en periodos de tiempo muy cortos, por lo quese recomienda su uso para el inventario de comunidades de insectos.

A newly innovated UV-Pit-Light trap efficacy for sampling beetles within oil palm plantations of various age stand types

A newly innovated UV-Pit-Light trap specific for trapping beetle species within oil palm plantations is described and the results of experiments on its efficacies that were carried out within different oil palm age stands are presented. The UV-Pit-Light trap is made of two parts: a lower located 1-L plastic collection container inserted into the ground, 6V fast recharging lead-acid battery and 4-W miniature UV-bulb attached to electronic device with wire clips, with the upper located plastic stool for the basic stand and the wide plastic basin for rain and light shield. The UV-Pit-Light trap caught significantly higher beetle specimens, which also included several morphospecies from the common beetle families found in oil palm plantations with 1.5 to 2 times higher in abundances including Nitidulidae, Curculionidae, Scarabaeidae, and Tenebrionidae. Rare beetle families of Aderidae, Cerambycidae, Histeridae, and Lagriidae, which not to be found in passive pitfall trap, were caught in considerable abundances in the UV-Pit-Light trap. The short electro-magnetic wavelengths of UV-light source included many closely packed epigeal related micro-habitats, which makes the UV-Pit-Light trap specific for sampling beetles specifically related within micro-habitats of various oil palm age stand types. The use of only four units of UV-Pit-Light trap compared with 100 units of passive pitfall trap is adequate for sampling beetle species community which includes both the common and uncommon families, and include two times higher for the most abundant and common species than the passive pitfall trap. Thus, the UV-Pit-Light trap allows accurate and unbiased diversity and ecological evaluations of beetle species and proposed to be the specific trapping system for insect species dwelling within the epigeal related micro-habitats oil palm plantations.Â

Responses of the woodland salamander Ensatina eschscholtzii to commercial thinning by helicopter in late-seral Douglas-fir forest in northwest California

We examined responses of the woodland salamander Ensatina (Ensatina eschscholtzii) to commercial thinning by helicopter in late-seral Douglas-fir forest in northwestern California, USA, using a before-after control-impact (BACI) design. We employed passive pitfall traps on eight (four each treatment and control) 100 trap grids over eight years (1996–2003), three years pre- and five years post-treatment. We conducted 3–11 weekly site visits within each of 10 trap periods depending upon weather over two spring and eight fall periods for a total of 50 visits to test for differences in surface counts and body condition. We standardized data to captures/1000 trap nights. Surface counts over the eight years were highly variable with less surface activity in spring compared to fall. Although the BACI design allows for initial differences among pre-treatment grids there were none. However, in the three years post-treatment (1999–2001) mean counts on treatment grids were significantly lower than on control grids. By 2002 and 2003, post-treatment counts on control and treatment grids both declined substantially, such that despite 47% more salamanders on control grids, variability was sufficient to preclude statistical significance. Recapture rates averaged 23.3% for three years pre-treatment, but increased to 51.4% for the five years post-treatment. Pre-treatment population estimates increased on control grids post-treatment, however, surface density estimates declined. On treatment grids both population and density estimates declined following treatment. Body condition analyses indicated no significant differences between controls and treatments for either sex prior to or post-treatment. The three years of significant differences in surface counts between controls and treatments post-treatment, followed by no differences in the last two years of the study, combined with no differences in BCIs, lead us to conclude that the surface activity of Ensatina on treatments grids was only temporarily impacted by the thinning. Declining population estimates on treatment grids also indicated at least a temporary reduction in those populations. We unexpectedly found declines in counts and density estimates on both sets of grids over the eight years, suggesting a wider effect may be causing reductions in the surface activity of these salamanders, and possibly in their populations.

Structure and Development of the Attractive and Digestive Glands in the Carnivorous Pitcher Plant Nepenthes alata

Carnivorous plants have evolved diverse structures to attract, capture and digest insects to permit plant growth in nutrient deficient substrates. Members of the genus Nepenthes utilize a passive pitfall mechanism to trap prey. Insects are attracted to the pitcher by sugary secretions from the nectary glands in the peristome region lining the trap opening. This type of trapping method is accomplished through three integral features. First, after entering the pitcher, the arthropod’s ability to escape is obstructed by the inner protruding lip of the peristome (Fig. 1). Second, the surface of the peristome is covered by overlapping epidermal cells, directed towards the inner lumen of the pitcher (Fig. 2). When wet, the patterning of the peristome epidermal cells creates a slippery surface that interferes with the adherence of insect feet [1]. Third, below the peristome is an internal, slippery wax layer that also reduces the insect’s ability to climb out of the pitcher. SEM observations found substantial variation of the peristome (Fig. 3) and wax deposits among the seven species examined: N. truncata, N. maxima, N. ventricosa, N. rafflesiana, N. hirsuta, N. ephippiata, and N. albomarginata.

An efficient pit-light trap to study beetle diversity.

A new, highly efficient pit-light trap is described and results of experiments on its efficacy that were carried out in various types of forests are presented. The Luminoc® insect trap is made of two parts: a 1-L collection container inserted into the ground and an upper container which houses a 6-V lantern battery and a circuit for electronic control of a 1.8-W miniature fluorescent tube. A cover is fixed under the upper container to prevent rainwater from entering the collection container. The pit-light trap caught significantly more specimens, species and families of Coleoptera than passive pitfall traps. Many species of common families, such as Carabidae, Cantharidae, Curculionidae, Elateridae, Pyrochroidae, Scarabaeidae, Silphidae and Tenebrionidae were mainly caught in pit-light traps. Several species of uncommon families such as Byrrhidae, Melandryidae, Scraptiidae, Stenotrachelidae and Throscidae were caught only in pit-light traps. The light source increases the sampling area of a trap to include many micro-habitats, which makes pit-light traps more efficient tools that provide less variable results than the passive pitfall traps. The use of only three pit-light traps allows the capture of three times more 'abundant and common' species than any number of passive pitfall traps could provide. Thus, the pit-light trap allows an easier and more accurate characterization of Coleoptera communities than the passive pitfall trap. Because of its high efficacy, the pit-light trap should be considered as a standard tool to study, monitor and inventory beetle diversity.