The absolute population density of adult Pardosa agrestis (Westring, 1862), the dominant epigeic spider species in many arable lands in Central Europe, was quantified in two alfalfa fields using a multiple mark-recapture method. The resulting density estimates are presented together with catch data from simultaneously performed suction sampling and pitfall trapping. Two week long mark-recapture surveys were conducted in August 1995 and 1996 using grids of 11 × 11 live-catching pitfall traps covering a square area of 400 m2 in the first, and 900 m2 in the second survey. The trap checking and marking procedure, using individual codes, was done daily. Over 5,000 spiders were marked in the two surveys. The number of spiders caught varied greatly between days. The recapture rate was also variable, ranging between 5-19%. Recaptured animals moved considerable daily distances, marked animals left the area of the trapping grid within a few days. Population sizes were estimated for 3 day time windows during which period the population could be considered closed. Spider densities were calculated from the estimated abundances and the capture area, which consisted of the grid area plus a boundary strip calculated from the estimated movement ranges of spiders. The resulting densities were close to 2 males and 1 female per m2 in the first, and 4.5 males and 4.5 females per m2 in the second experimental site. Suction sampling caught very few adult individuals and gave unsatisfactory data for statistical comparison. Live catching pitfall trap catches did not correlate with the derived mark-recapture density estimates across the short time windows, but for the entire trapping sessions the catches were consistent with the density estimates.
Dispersal of the sevenspotted lady beetle, Coccinella septempunctata, was measured in a series of mark-release-recapture experiments in Utah alfalfa. In three experiments, samples were taken in a radial pattern around the release point. Released beetles for the most part left the 0.36 ha (68 m diameter) sample area within 24 hours, and their average residence time in the sample area was calculated as 12, 6 and 1.6 h in the three experiments, respectively. The spatial distribution of beetles around the point of release could be described with normal distributions whose variance increased linearly in time with 3.8, 1.1 and 0.34 m2 per hour. In three additional field experiments the departure of marked beetles was compared between sugar-sprayed plots and control plots. Residence time was 20-30% longer in sugar-sprayed plots than in control plots, with mean residences of 5.3, 3.6, and 2.9 h in the sugar-sprayed plots in the three experiments, respectively, and means of 4.4, 2.7, and 2.4 h in the control plots. The density of unmarked beetles rose by a factor of 10-20 in the sugar sprayed plots during the first 4 to 6 hours following early morning spraying of sugar. This rapid and substantial increase in density cannot be explained by the slightly longer residence time in sugar-sprayed plots. We hypothesize that the aggregation in sugar-sprayed plots is mostly due to greatly increased immigration into those plots, in response to volatiles produced by the plant-pest-predator assembly.
The adult sex ratio among the genus Parnassius is usually strongly male biased and close to 2 : 1. This paper presents the results of comparative studies, on the basis of data from wild and captive reared populations of apollo butterfly in the Pieniny National Park (Western Carpathians, Poland). Sex ratio among the wild population is strongly male biased and close to 2 : 1, whereas there was no sex ratio bias among the captive population. However, among the captive individuals caught after releasing into the wild, males significantly outnumbered females. There was a significant, sex-related, difference in activity pattern recorded in the field studies: while the majority of females were observed sitting, males were usually flying. This result suggests that the observed sex ratio shifting is at least partially an artifact caused by the more cryptic behaviour of females. The sex ratio bias was more pronounced in the wild population than in captive individuals caught after releasing into wild, which suggests that difference in detectability between the sexes is not the only reason for males outnumbering females.
To conserve the predators and parasitoids of agricultural pests it is necessary to understand their population structure in a mixed landscape, and to consider the spatial and temporal changes in their distribution and movement of adults and larvae. We studied the distribution and movement of the ground beetle Carabus yaconinus (Coleoptera: Carabidae), which inhabits farmland-woodland landscapes. We placed a large number of pitfall traps along the border between a wood and an orchard and counted the number of C. yaconinus adults and larvae caught in the traps from 13 April to 28 June 2005. Some of the adults were marked before they were released. Adults were most abundant at the edge of the wood and the number caught gradually decreased when entering into the wood. In contrast, larvae were only found in the interior of the wood, although they moved closer to the edge of the wood as they matured. Adult females were collected within the wood and neighbouring orchards more frequently than adult males. It is likely that females enter woodlands in search of oviposition sites and leave woodlands in search of high-protein food sources to support reproduction. For sustaining populations of C. yaconinus it is necessary to have woodlands of at least 60 m in width adjacent to farmland. It is possible to design an appropriate landscape if the habitat requirements of the predatory arthropods are well understood.