Trap Diameter Research Articles

Pitfall trap design affects the capture efficiency of harvestmen (Opiliones) and millipedes (Diplopoda).

Pitfall trapping is one of the standard methods used for the capture of ground‐active arthropod groups. Despite being frequently used, the standardization of this method is problematic due to the large range of combinations of the individual parameters of pitfall traps with varying efficacy under different environmental conditions. We evaluated the effects of the trap diameter, the fixing fluid, and their combination on the capture efficacy for harvestmen (Opiliones) and millipedes (Diplopoda). We used pitfall traps with three different diameters: 3 cm, 5 cm, and 12 cm, filled with three types of fixing fluids (saturated fluid of NaCl, 10:1 mixture of 70% ethanol and glycerol and 4% formaldehyde). Altogether, 90 traps representing nine combinations of trap diameters and fixing fluid were placed on a mown meadow in spring and autumn intervals for a total of 45 days. We sampled 1,488 individuals representing 11 harvestmen species and 881 individuals representing 11 millipede species. Large (d = 12 cm) and medium (5 cm) traps captured significantly more millipede species and individuals than the small‐sized traps (3 cm). The same effect was observed for harvestmen species richness, whereas the medium traps (d = 5 cm) captured the highest mean activity of harvestmen. By analyzing the differences in the body sizes of the studied arthropods in relation to the trap diameter and fluid, we found that larger traps, as well as traps filled with NaCl solution, captured larger harvestmen more frequently than the other trap types. Our results revealed that the combination of larger traps (d = 5 and 12 cm) and formaldehyde was most effective in the capture of both studied groups. However, the disadvantage of formaldehyde is its toxicity.

Past thermal conditions affect hunting behaviour in larval antlions.

Some sit-and-wait predators, such as antlion larvae, construct traps to capture passing prey. The location of these traps depends on many abiotic and biotic factors, including temperature and the presence of conspecifics, which probably stimulate behaviours that minimize the costs and maximize the benefits of trap building. Here, we exposed second instar antlion larvae to elevated temperatures of 25°C (mild treatment) or 31°C (harsh treatment) for one month and then transferred them to common conditions (20°C) to examine the effects of previous thermal treatment on aggregation tendency and trap size. We predicted that antlions that experienced harsh conditions would subsequently increase the neighbouring distance and trap diameter to reduce competition with conspecifics and improve prey capture success, compensating for past conditions. In contrast with these predictions, antlions exposed to harsh conditions displayed a trend in the opposite direction, towards the decreased neighbouring distance. Furthermore, some of these antlions also built smaller traps. We discuss possible reasons for our results. The effects of previous thermal exposure have rarely been considered in terms of trap construction in antlions. Described effects may possibly apply to other sit-and-wait predators and are significant considering that many of these predators are long-lived.

To what extent can the tiny parasitoid wasps, Eretmocerus mundus, fly upwind?

AbstractBody miniaturization in insects is predicted to result in decreased flight speed and therefore limited ability of these insects to fly upwind. Therefore, tiny insects are often regarded as relying on passive dispersal by winds. We tested this assumption in a wind tunnel by measuring the burst speed of Eretmocerus mundus (Mercet), a beneficial parasitoid wasp with body length <1 mm. Insects were filmed flying upwind towards a UV light source in a range of wind speed 0–0.5 m/s. The Insects flew towards the UV light in the absence and presence of wind but increased their flight speed in the presence of wind. They also changed flight direction to be directly upwind and maintained this body orientation even while drifted backwards relative to the ground by stronger winds. Field measurements showed that the average flight speed observed in the wind tunnel (0.3 m/s) is sufficient to allow flying between plants even when the wind speed above the vegetation was 3–5 folds higher. A simulation of the ability of the insects to control their flight trajectory towards a visual target (sticky traps) in winds show that the insects can manipulate their progress relative to the ground even when the wind speed exceeds their flight speed. The main factors determining the ability of the insects to reach the trap were trap diameter and the difference between insect flight speed and wind speed. The simulation also predicts the direction of arrival to the sticky target showing that many of the insects reach the target from the leeward side (i.e. by flight upwind). In light of these results, the notion that miniature insects passively disperse by winds is misleading because it disregards the ability of the insects to control their drift relative to the ground in winds that are faster than their flight speed.

Plasticity in extended phenotypes: how the antlion Myrmeleon crudelis adjusts the pit traps depending on biotic and abiotic conditions

Abstract The physical structures built by animals are considered extended phenotypes that reflect how organisms make decisions and deal with changes in their biotic and abiotic environment. We summarize the results of several studies on Myrmeleon crudelis, a neuropteran larva that digs pit-traps in the soil to capture small arthropods (mostly ants) in the tropical dry forests of Costa Rica. Specifically, we showed how this species responds to varying biotic and abiotic conditions with changes in the design and/or location of its pit traps. Several experiments and field comparisons indicate that: 1) antlions adjust the pit design according to the abundance and type of prey. When prey is scarce, antlions increased trap diameter, an architectural adjustment that enhances the probability of prey encounter. Antlions that experienced high prey abundance, but the prey easily escaped, then increased pit depth, an adjustment that increases the chance of prey retention; 2) soil compaction strongly reduced pit-trap size and abundance; 3) antlions preferred soils with high proportion of fine-particle size to build pits. In fine-grained soil, pit-traps are larger and more efficient to capture prey than traps in coarse-grained soils; and 4) pit-traps may also be affected through indirect effects of soil structure and vegetation cover. Areas with fine-soil presented less plant cover, and plant cover could be beneficial for antlions because it acts as a shelter against direct sunlight and rainfall, or it may represent a cost because it is a source of leaflitter falling in the pits. The works summarized here how trap-building predators can exhibit considerable flexibility in trap construction in response to various biotic and abiotic factors, emphasizing how the study of extended phenotypes can be a useful approach to better understand the flexibility of foraging behaviors.

Effects of soil substrate on the ecological features of the sand pit-building Antlions Myrmeleon formicarius Linnaeus, 1767 (Neuroptera: Myrmeleontidae) larvae in the Amanos Mountains of Turkey

The hunting behavior of antlion larvae is unique in the insect world and soil characteristics may strongly affect their microhabitat selection. Therefore, the substrate type of sand pit construction is expected to have an important role in their traps. Different types of soil substrates can be inhabited by Myrmeleon formicarius Linnaeus, 1767 larvae. This study was conducted during 2018-2019 June-August in the Amanos Mountains of Turkey to examine assess the relationship between the microhabitat preference of larvae of M. formicarius. In this study, five substrate types were determined as particularly according to their habitat preference. In this study, the preference of fine-grained soils is found more adaptive because of the pits are constructed in these substrates are more functional for longer periods and they are much more successful in trapping their preys than the coarse-grained soil pits. Furthermore, it was found that there is a direct relationship between the pit size and substrate particle structure. Therefore, the detection and selection of microhabitats under more convenient ecological conditions, which increase capture success and elucidate the hunting strategy, may be carried out during strong soil substrate selection for Myrmeleon Linnaeus species. It was concluded that there is no strong relationship between the soil substrate type, pH, and trap diameter.

Effect of pan trap size on the diversity of sampled bees and abundance of bycatch

Monitoring pollinator health and pollination is among the top priorities to safeguard pollinators and secure pollinator services. Assessments of sampling methods are therefore essential for developing a standardized protocol for long-term pollinator monitoring. Pan trapping is a popular technique to survey pollinators, but limited information is available on the effect of pan trap diameter on the abundance, richness, and body size of sampled bees, as well as on the abundance of bycatch (non-targeted arthropods). We conducted experiments using four diameters of yellow pan traps in three habitats (a semi-natural phrygana habitat, a roadside, and a salt flat) on the Greek island of Lesvos during a 10-day period in late June/early July of 2017 and 2018. We found that pan traps of 4, 7, 10, and 12 cm captured a similar richness of bees and have little or no effect on the abundance estimates of bees and flies. Pan trap diameter did not affect body size of collected bees. Bycatch accounted for 62.8% of the arthropods collected and increased with the diameter of the pan traps in the phrygana and roadside habitats. According to literature, many researchers, especially outside Europe, use pan traps of various diameters (7–34 cm), volumes (96.1–2000 ml), and shapes (round, square, rectangular, or hexagonal). To reduce potential negative effects on populations of other beneficial arthropods, as well as to minimize processing effort and costs, we recommend using small pan traps (7 cm), unless standardized pan trapping protocols have already been adopted.

Influence of Hoop-Net Trap Diameter on Capture Success and Size Distribution of Comparatively Large and Small Freshwater Turtles

We investigated the influence of hoop-net trap size on number and size of captures for comparatively large (Chelydra serpentina [Snapping Turtle]) and small (Chrysemys picta [Painted Turtle]) freshwater turtle species. We trapped turtles at 32 ponds throughout West Virginia in the summers of 2016 and 2017, with each pond sampled for 5 consecutive days using five 0.91-m–diameter and five 0.76-m–diameter baited hoop-net traps. We captured a total of 98 and 283 unique Snapping Turtles and Painted Turtles, respectively. Larger-diameter traps captured more Snapping Turtles and smallerdiameter traps captured more Painted Turtles. Mean carapace length was greater for both species in larger-diameter traps, but this result was possibly influenced by the ability of the smallest Painted Turtles to escape through the mesh of the larger traps. Our results indicate that hoop-net–trap diameter can substantially influence both number and size distribution of captures, and thus, trap size is an important sampling design consideration for freshwater turtle research and monitoring using hoop-net traps.

Effect of pitfall trap type and diameter on vertebrate by‐catches and ground beetle (Coleoptera: Carabidae) and spider (Araneae) sampling

Summary1. To determine the diversity of epigaeic arthropods, pitfall traps are a suitable and widely accepted sampling method. Unfortunately small mammals such as shrews, voles and mice are accidentally caught by these traps, sometimes very frequently depending on trap type and size.2. Here we present an experiment examining the influence of trap types, conventional cup traps vs. funnel traps, and of trap diameter on catches of carabid beetles, spiders and unwanted by‐catches of small mammals.3. The number of sampled carabid beetles increased significantly with diameter of the traps and presence of a funnel. The number of species was not affected by trap type or trap size.4. For spiders, significantly more individuals and more species were found in larger traps. After correcting for difference in sample size by rarefaction, spider species number was still higher in larger traps. The use of a funnel had no effect on spider assemblages.5. Funnel traps and a smaller trap diameter strongly reduced catches of small mammals, on average by at least 2/3. While catches of arthropods increased with increasing trap size independent of trap type, the number of small mammals caught in the traps was not greater in larger traps when a funnel was used.6. Based on our results and other studies on the efficiency of different pitfall trap types, we recommend to use funnel traps of larger diameter (approximately 9 cm) to more efficiently sample epigaeic arthropod assemblages and to minimize unwanted catches of small mammals.

Formation of power-law electron spectra in collapsing magnetic traps

The energy distribution of the fast electrons captured into a collapsing magnetic trap in the solar corona is calculated as a function of the trap length and diameter. It is shown that if the electrons injected into the trap have a power-law spectrum, then their spectrum remains a power-law one with the same slope throughout the acceleration process for both the Fermi and betatron acceleration mechanisms. For electrons with a thermal injection spectrum, the model predicts two types of hard X-ray sources, thermal and nonthermal. Thermal sources are formed in traps dominated by the betatron mechanism. Nonthermal sources with a power-law spectrum are formed when electrons are accelerated by the Fermi mechanism.

Evaluation of mass-trapping for control of tea tussock moth Euproctis pseudoconspersa (Strand) (Lepidoptera: Lymantriidae) with synthetic sex pheromone in south China

Field experiments were conducted to evaluate the effect of dosage, trap placement, trap diameter and trap colour on the trap captures of tea tussock moth, Euproctis pseudoconspersa, in a tea plantation located in Guizhou province in southern China during the 2001 field season. The optimum dosage of synthetic sex pheromone was 1.5 mg/septum in a trap. Trap captures of males were maximized with traps paced 90 cm above the ground. Traps of 32 cm in diameter caught significantly more males than those of 20 cm, and white traps caught significantly more males than traps of other colors. The control effect by mass-trapping technique on tea tussock moth was investigated in the same tea plantation in 2002 and 2003. Twenty-five traps/ha were used in the 2-year, large-scale mass-trapping experiment, and a total of 146,767 males were captured. In the pheromone-treated field, mating rates were significantly reduced on nine of 12 sample dates. Larval and egg densities were reduced by 27.87–50.85 and 38.89–51.11%, respectively, compared with the untreated field. Our results suggest that mass-trapping is promising as a control agent for use against the tea tussock moth.

Using Malaise traps to sample ground beetles (Coleoptera: Carabidae)

Pitfall traps provide an easy and inexpensive way to sample ground-dwelling arthropods (Spence and Niemela 1994; Spence et al. 1997; Abildsnes and Tommeras 2000) and have been used exclusively in many studies of the abundance and diversity of ground beetles (Coleoptera: Carabidae). Despite the popularity of this trapping technique, pitfall traps have many disadvantages. For example, they often fail to collect both small (Spence and Niemela 1994) and “trap-shy” species (Benest 1989), eventually deplete the local carabid population (Digweed et al. 1995), require a species to be ground-dwelling in order to be captured (Liebherr and Mahar 1979), and produce different results depending on trap diameter and material, type of preservative used, and trap placement (Greenslade 1964; Luff 1975; Work et al. 2002).

Particle accumulation in a cylindrical sediment trap under laminar and turbulent steady flow: An experimental approach

The hydrodynamical, fluid and particle parameters which control flushing rates, flow cells, and accumulation rates of particulate matter in cylindrical (MultiPIT) sediment traps were quantified in a flume simulation using a seeding technique for 25–45 µm particles. Particle collection was found to be a trap- and particle-specific filtering process encompassing advective and gravitational entry of particles over a reduced trap aperture area, and gravitational-turbulent removal of particles at the bottom of the internal flow cell. Trapping efficiency increased up to 10-fold with increasing horizontal flow velocity (1–30 cm · s−1). For given flow velocity, the trap over-and undercollected particles relative to their weight, i.e. (theoretical) Stokes settling velocity. The trapping efficiency increased with increasing trap Reynolds number ReT, changed by the approaching velocity in our experiments. Opposite findings from earlier experiments using the flume seeding technique and changing ReT by altering the trap diameter (Butman, 1986) are discussed. Semi-empirical equations are derived for the accumulation process of light, heavy and intermediate particles. From these, measured trap fluxes can be converted into in-situ verticle particle flux except for light particles.

The effects of pitfall trap diameter on ant species richness (Hymenoptera: Formicidae) and species composition of the catch in a semi‐arid eucalypt woodland

AbstractAnts play an important role in Australian biodiversity and environmental impact assessments, with pitfall‐trapping being the principal sampling method. However, the relationship between trap diameter and ant species catch has not been investigated in the context of survey design. Using four different trap diameters, each at a density of one trap per 100 m2, the present study asks three questions: (i) given an equal number of traps, do traps with larger diameters catch more species than smaller‐diameter traps?; (ii) do traps with small diameters bias against large or rare species?; (iii) for equal area of the trap mouth, do small but more numerous traps catch more species than fewer but large traps? A total of 84 species were sampled within the 1600 m2 study site, with numbers of species for trap diameters of: 18mm (46 species), 42mm (56 species), 86mm (62 species) and 135mm (64 species). At equal trap density, 18 mm traps caught significantly fewer species than larger traps. Traps of 86 mm and 135mm were no more efficient than 42mm traps. Only 86mm and 135mm traps caught all species > 10mm in length (6 species). For equal area of the trap mouth, small traps were more efficient than large traps. Differences in the catch of the different‐sized traps were due primarily to different capture rates of the rare species (40 species): 18mm traps caught 25% of rare species, 42 mm caught 41%, 86 mm caught 44% and 135 mm caught 52%. The role of rare ant species in environmental impact studies is discussed.

Frequency shifts and modulation effects due to solenoidal magnetic field inhomogeneities in ion cyclotron mass spectrometry

Solenoidal (i.e. axially symmetric) magnetic field inhomogeneities, which in addition have symmetry under the operation z → − z are the most important to Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry since they introduce frequency shifts at first-order in perturbation theory. Frequency shifts for all three fundamental modes are derived for the leading second-order and fourth-order solenoidal inhomogeneities without any restrictions on the initial conditions. The analytical frequency shifts agree very well with frequency shifts obtained from numerical trajectory calculations using the exact classical equations of motion. The effect of the inhomogeneity on the ion trajectory is solved analytically. For a strong magnetic bottle field, the cyclotron motion is frequency modulated at twice the z-oscillation frequency resulting in sidebands. However, the amplitude of these sidebands is negligibly small for typical inhomogeneity strengths. The effect of a magnetized ICR trap on the homogeneity of the magnetic field is studied by analytical methods. We find that the leading magnetic bottle field decreases as d −3, where d is the cylindrical ion trap diameter.

Influence of trap colours and placement on captures of the hairy rose beetle, Tropinota squalida Scop. (Coleoptera: Scarabaeidae)

Plastic dishes 30 cm dia. and 15 cm depth filled with water as traps for Tropinota squalida Scop, adults and painted blue, green, red, white and yellow were exposed in infested peach areas at Abo-Sultan during 1987–1988. Traps painted blue showed high degrees of attractancy to the pest. White, yellow and green attracted the least number of beetles while red was found to have no attraction. Trapping is considerably influenced by microecological conditions, trap placement and trap diameter. Blue traps (25) were sufficient to suppress the pest population in an infested peach area. Blue trap could be considered as a new forecasting method and for studying the swarming dynamics of T. squalida adults.

Flow in Cylindrical Sediment Traps

Flow behavior in cylindrical settling traps was observed in steady flow for trap Reynolds numbers (Re) between 1,600–30,500. The effects due to aspect ratio, wall thickness, a funnel at the bottom of the trap, and the presence of a mooring line were investigated. Although the data are semiquantitative, they show that upwelling frequency and intensity increased as Re increased and as the aspect ratio decreased. The relationships between the thickness of the bottom layer, the frequency of upwelling, and the settling velocity of a particle determines whether deposition occurs through the bottom tranquil layer or the viscous sublayer. Since the thickness of the bottom tranquil layer can be scaled by the trap diameter, the settling behavior of particles cannot be modeled simply by Re and the aspect ratio, as can flow behavior, but also depends on the ratio of flow velocity to settling speed. Flow behavior induced by wave action is similar in many ways to that generated by steady flow at the same Re. Depending upon flow conditions in the trap, either the measured flux or the size distribution of the material collected may differ substantially from that outside the trap. Traps that are designed so that upwelling does not occur during their deployment will give the best estimates of flux and particle distribution. This means that in most cases several small traps are preferable to a single large trap.

SEX RATIO VARIATIONS IN XYLOPHILOUS ACULEATE HYMENOPTERA.

Organisms which reproduce sexually may often provide differing relative investments in offspring of the two sexes, and factors influencing the proportions of these investments are poorly understood. Theoretical discussions (Trivers, 1972; Charnov, 1979) have rarely been supported by adequate field evidence (but see Cowan, 1978; Alcock, 1979). Fisher (1958) initially described how, in random mating populations of sexual species, a 1:1 investment ratio should evolve and be maintained (evolutionarily stable strategy sensu Maynard Smith and Price, 1973). This theory has been elaborated upon, incorporating such factors as parental condition, offspring mortality, and structure of mating populations (Hamilton, 1967; Trivers and Willard, 1973; Werren and Charnov, 1978). The results, as Werren and Charnov (1978) express it, is that for a population to be in evolutionary equilibrium, it should be devoting half of the parental reproductive resources to each sex. However, a 1:1 investment ratio may not always be the optimum. Under circumstances of local mate competition, differential benefits between sexes from a resource, greater mortality of offspring of one sex during periods of parental care, or unusual sex determining mechanisms (see Maynard Smith, 1978), biased investment ratios may evolve. Studies often assume a 1:1 sex ratio, basing such assumptions on whole population studies for a single year, or for several years. Such broad, long term data may obscure important variations in sex ratios and investment ratios in local populations over a single generation, as discussed below. Xylophilous aculeate Hymenoptera normally construct nests consisting of a linear series of provisioned cells in abandoned beetle burrows or other holes in wood. Many such wasps and bees will accept artificial nesting sites (trap-nests) and are well suited to an examination of investment ratios, particularly since sex determination based on haplodiploidy and facultative insemination of eggs allow female manipulation of brood sex ratios. Krombein (1967) discusses general biological data on many species. Eggs of a given sex are laid in series within a single nest, rather than at random; female-containing cells are larger than male-containing cells, and usually occur toward the blind end of a nest. Adult females searching for nest sites will accept holes of various diameters, within a certain range, each species apparently preferentially selecting holes of given diameters (Longair, unpubl.). Previous studies have used similar methods, offering bundled traps of different diameters. However, these studies have suffered from two major failings, if data are to be used in determination of population sex ratios. Traps of different diameters were usually offered in different relative numbers (e.g., twice as many 5 mm traps as 7 mm traps). As various authors (Medler and Fye, 1956; Koerber and Medler, 1958; Fye, 1965; Krombein, 1967) have pointed out, and as shown here, sex ratio tends to vary with nest diameter, such that whereas cells containing females are larger than cells containing males, a greater proportion of male eggs are laid in traps with a smaller diameter boring. Therefore, greater numbers of one hole diameter could have affected overall estimates of sex ratios. Similarly, hole sizes offered in previous studies have often been only of a limited range, failing to fully encompass those diameters accepted by searching females. This again could bias sex ratio estimates. The mode of presentation of traps in this study was specifically intended to provide an adequate range of hole diameters, with equal numbers of each trap diameter offered; resulting distribution of hole diameter use is thus unbiased with respect to those factors discussed above, and subsequent sex ratio estimates are based on natural nest size use distribution for the species studied.

A Simple Device for Retrieving Instruments or Traps Set Under Ice

Recovery of instruments or traps suspended under ice is often difficult because refreezing at the circumference of the hole decreases the hole diameter to less than trap diameter, and freezes around the attached line. Line freezing can be reduced by suspending the instrument from the center of the hole. A device consisting of two lengths of wood hinged together, with recurved nails at the lower end can then be used to catch and recover the instrument line through an adjacent hole. These procedures reduce retrieval time by two thirds, and eliminate the damage to instruments or trapped animals that often occurs during recovery. The device can be easily made or repaired on site. Key words: under-ice sampling, under-ice trapping, instrument recovery, arctic