Fecundity and juvenile survival of shape Bembidion lampros and Tachyporus hypnorum

Fecundity and development from first instar larvae to adult beetles were studied for Bembidion lampros Herbst (Coleoptera; Carabidae) and Tachyporus hypnorum F. (Coleoptera; Staphylinidae). Both species reproduce in arable fields, where they are known to contribute to the natural control of cereal aphids. They are univoltine and have similar life cycles and development times. T. hypnorum females laid approximately 3 times more eggs than B. lampros females. Relative lifetime fecundity of B. lampros was very low with an average of 10 eggs per female. Based on the time where half of the populations had dispersed from the overwintering sites into an arable field B. lampros started egg-lay 100°D (°C>9) and T. hypnorum 200°D (°C>3) after dispersal. Mortality in the juvenile stages was found to be an important factor in the population dynamics of both B. lampros and T. hypnorum. The survival from first instar larvae to adults was on average 34% for B. lampros independent of soil type, 21% for T. hypnorum developed in sandy soil and 49% when developed in clayey soil under semi-field conditions. Enlargement of B. lampros and T. hypnorum populations to increase the natural control of aphids during their establishment in cereal fields may be possible if the conditions for juvenile development are improved.     

The abundance and reproductive activity of common Carabidae in a winter wheat crop

Abstract. 1. The number of common carabid beetles trapped-irr a wheat field on a clay with flint soil from May to October in.1971–77 differed greatly: Harpalus rufipes and Pterostichus melanarius were numerous every year; but the appearance of H.aeneus, P.madidus, Agonum dorsale, Nebria brevicollis, Notiophilus biguttatus, Bembidion lampros and Trechus quadristriatus was much more variable.
2. The numbers caught were not correlated with rainfall. Catches of the large species were positively correlated with accumulated temperature above an assumed activity threshold of 5°C, whereas the smaller beetles were negatively correlated with accumulated temperature, suggesting that the danger of desiccation at high temperatures limits their activity.
3. The egg-laying periods of the commonest species were: B.lampros and A.dorsale from late April to June; overwintered P.melanarius, H.rufipes and H.aeneus in May and June, with the summer generation of these species and of P.madidus from July to September; T.quadristriatus during August and September; N.brevicollis from September to November; N.biguttatus and C.fossor laid in the early summer and again in the autumn.
4. A few male and female H.rufipes and H.aeneus , and one female P.melanarius and N.brevicollis were each parasitized by a single tachinid larva; one P.melanarius was infested with a mermithid parasite.     

The influence of different age classes on the seasonal activity and reproduction of four medium-sized carabid species inhabiting cereal fields

Reproduction and survival of four carabid species commonly occurring in cereal fields in central Sweden were investigated. The adult-overwintering Pterostichus cupreus L. bred in early summer (June), and the largest proportion of sexually active beetles were found to be in their first breeding year; only a minority were 2 (or more) years old. In contrast, the larval-overwintering P. melanarius Illiger, P. niger Schaller and Harpalus rufipes De Geer had a biennal life cycle, and mainly old beetles (2 years or older) contributed to the population's reproductive effort each year. The long prereproductive adult phase in the larval-overwintering species and the relatively short summer in central Sweden prevented many new-generation adults from breeding in their first year. Several overlapping breeding cohorts are therefore present each year, and overwintered beetles bred throughout summer and during part of the autumn. Mandible wear (combined with other characters) was used to determine the age of beetles. However, the rate of mandible wear also was found to vary, depending upon the extent to which each species burrowed in the ground. The ecological significance of (a) a long adult life and (b) the existence of several overlapping breeding cohorts for reproduction and survival of populations in cereal fields is discussed.     

Landscape level processes driving carabid crop assemblage in dynamic farmlands

Landscape heterogeneity has been shown to be a major factor in the maintenance of biodiversity and associated services in agricultural landscapes. Farmlands are mosaics of fields with various crop types and farming practices. Crop phenology creates asynchrony between fields sown and harvested in different periods (winter vs. spring crops). The present study was conducted to examine the influence of such spatio-temporal heterogeneity on biodiversity, with the hypothesis that it would lead to spatio-temporal redistribution (shifting) of species. Species richness and activity-density of carabid beetles in winter cereal (winter) and maize (spring) crops were compared across 20 landscapes distributed along a double gradient of relative area and spatial configuration of winter and spring crops. Maize fields were sampled in spring and late summer for comparison over time. The response of carabid species richness to landscape heterogeneity was weak in spring, but maize field richness benefited from adjacencies with woody habitat, in late summer. In spring, increased length of interfaces between winter and spring crops lowered carabid activity-density in winter cereal fields, suggesting that maize fields acted as sinks. Interfaces between woody habitats and crops increased activity-density in both crop types. We found no evidence of spatio-temporal complementation, but different species benefited from winter cereals and maize in spring and late summer, increasing overall diversity. These findings confirm the role of adjacencies between woody and cultivated habitats in the conservation of abundant carabid assemblage in winter cereals and maize. We conclude that between-field population movement occurs, and advocate for better consideration of farmland heterogeneity in future research.     

Organic mulches vs. black plastic in organic strawberry: does it make a difference for ground beetles (Col., Carabidae)?

Abstract:  Carabid beetles were sampled by pitfall traps in May–September 2002 and 2003 in an experimental organic strawberry field in seven different mulching row treatments and in fescue-growing row spaces to determine the effect of mulches on carabid activity–density and species composition. There were no differences between treatments or row spaces in total numbers of all carabid species in either season. Of the 67 identified species and 4374 individuals, the most trapped ones were Clivina fossor (11.7% of total catch), Dyschirius globosus (10.2%), Patrobus atrorufus (9.3%), Pterostichus niger (8.8%), Bembidion properans (7.4%), Pterostichus melanarius (6.0%), Bembidion lampros (5.7%), Pterostichus crenatus (5.7%), Amara communis (4.1%), Trechus secalis (3.9%), Pterostichus strenuus (3.9%), Loricera pilicornis (3.1%), Harpalus rufipes (2.8%) and Carabus nemoralis (2.6%). Large carabid species P. niger and P. melanarius were trapped more in all mulched rows than in row spaces, and C. nemoralis was trapped more in the mixture of pine woodchip/buckwheat husk mulch than in row spaces, barley straw and birch woodchip mulch. The small but abundant species P. atrorufus was trapped more in buckwheat husk mulch than in row spaces and B. properans in row spaces than in buckwheat husk mulch. H. rufipes , being also a pest in strawberry, was trapped more in cut grass mulch than in row spaces. The Shannon H' diversity index was significantly higher in the mixture of pine woodchip/buckwheat husk mulch than in black plastic, buckwheat husk mulch or in row spaces, and in birch woodchip and cut grass mulches than in row spaces. The results of trapping studies show the species preference to the specific mulches, and reflect positive or negative effect of mulches on carabid diversity with consequences to plant protection.     

Habitat choice of some field-inhabiting carabid beetles (Coleoptera: Carabidae) studied by recapture of marked individuals

ABSTRACT.

• 1 Habitat choice of some field-inhabiting carabid beetles was studied in the field, and included the adult-overwintering Bembidion lampros Herbst, Pterostichus cupreus L. and Agonum dorsale Pontoppidan, and the larval-overwintering Trechus secalis Paykull, Pterostichus melanarius Illiger, P.niger Schaller and Harpalus rufipes De Geer. These were compared to the forest-inhabiting and adult-overwintering species, Carabus nemoralis Müller.
• 2 Marked beetles were released in the centre of a circular enclosure which was placed on the edge between a cereal field and a wood. The direction of movement in this circle was compared with that in a control circle placed entirely in the cereal field.
• 3 In the field/wood circle, adult-overwinterers and the larval-overwin-terer H.rufipes choose to move into the cereal field. The majority of T.secalis. P.melanarius and C.nemoralis, however, moved into the wood, while P.niger exhibited no preference.
• 4 In the field circle, adult-overwinterers moved towards the more sun-exposed parts of the circle, whereas the movements of larval-overwin-terers were random.
• 5 Some species-specific characteristics considered important for habitat choice by these carabid beetles, and the relevance of these characteristics for their dispersal behaviour are discussed.

     

Offspring performance in dynamic habitats: key factors for a riparian carabid beetle

Abstract.  1. Knowledge of the ecology of carabid species is largely restricted to adults, although larval mortality is assumed to be the key factor in overall mortality. As low-mobility larvae are unable to avoid unfavourable conditions, habitat selection of reproducing adults should be clearly affected by the habitat factors which determine offspring performance.
2. The present study examines the key habitat factors governing the distribution patterns of Bembidion velox larvae and adults on the river banks of the River Elbe by means of habitat suitability models. The validity of the determined habitat factors for offspring performance and survival was tested in laboratory experiments.
3. In the field, B. velox adults as well as larvae show a strong association with semi-terrestrial, sandy, open soil habitats.
4. In the laboratory, overall mortality of larvae reared in different substrates was lowest in sand of medium grain size mixed with fine and coarse sand. The first larval instars in particular reacted sensitively to variations in grain size. Furthermore, flood resistance of eggs was demonstrated, as 90% of larvae hatched under permanently flooded conditions.
5. Short development times were recorded, with 4–7 days for hatching of young larvae from eggs after oviposition and approximately 28 days for the development of adults from newly hatched larvae. This probably increases the survival probability for the pre-imaginal stages in dynamic habitats.
6. In conclusion, it can be said that reproductive success is strongly dependent on oviposition site selection by adults as this reflects the ecological demands of the immature stages.     

The spatial dynamics of crop and ground active predatory arthropods and their aphid prey in winter wheat

The distribution of aphid predators within arable fields has been previously examined using pitfall traps. With this technique predominantly larger invertebrate species are captured, especially Carabidae, but the technique provides no estimate of density unless mark-recapture is used. However, many other numerically important aphid predators occur in arable fields and relatively little is known about their distribution patterns nor whether they exhibit a density-dependent response to patches of cereal aphids. Identification of the most effective predators can allow management practices to be developed accordingly. In this study, the distribution of cereal aphids and their predators was examined by suction sampling within a field of winter wheat in Devon, UK, along with visual estimates of weed patchiness. Sampling was conducted on four occasions in 1999 across a grid of 128 sample locations. The distribution of 11 predatory taxa from the Carabidae, Staphylinidae and Linyphiidae was examined. Additionally, the total number of aphid predators and a predation index were used in these analyses. Carabid adults and larvae, along with staphylinid larvae showed the strongest aggregation into patches and the most temporal stability in their distribution. Other taxa had more ephemeral distributions as did the cereal aphids. The distribution of carabid larvae was disassociated from the distribution of cereal aphids for the first two sampling occasions indicating biocontrol was occurring. Other predatory groups showed both association and disassociation. Carabid larvae, Bathyphantes and total numbers of Linyphiidae showed a strong correlation with weed cover for two of the sample dates. Cereal aphids were disassociated from weed cover on three sampling occasions.     

Landscape- and time-dependent benefits of wildflower areas to ground-dwelling arthropods

Wildflower areas are a popular agri-environment scheme to counteract agro-biodiversity loss. Yet, their benefits are controversially discussed. Since inconsistent benefits may be owed to landscape context and temporal dynamics, we applied a multi-year study to unravel effects of permanent and transient habitats on ground-dwelling arthropods in wildflower areas and cereal fields.Across three consecutive years, we studied activity density, species richness and community composition of rove beetles, carabid beetles and spiders in ten pairs of wildflower areas and cereal fields along independent gradients of proportions of permanent semi-natural habitats or transient wildflower areas.Arthropod responses to the proportions of permanent semi-natural habitats often followed a hump-shaped pattern, whereas transient wildflower areas seemed to drive linear responses. An interactive effect on rove beetle richness in wildflower areas implies that benefits were highest either at intermediate proportions of permanent semi-natural habitats or at lower proportions, but with additional availability of transient wildflower areas or in landscapes with low proportions of permanent semi-natural habitats, but high proportions of wildflower areas. However, ground-dwelling arthropod activity density or species richness did not systematically increase over the three study years.Our results suggest that both permanent and transient habitats differ in how they affect biodiversity, possibly due to different temporal continuity and resource diversity. Benefits of permanent semi-natural habitats seemed highest at an equilibrium between an increasing resource-related species pool and an increasing diversity dilution, whereas benefits of transient wildflower areas seemed to increase with resource complementarity and connectivity at the landscape scale. Nevertheless, both habitats seem to complement each other and considered in concert, seem to be most effective in promoting benefits of wildflower areas to ground-dwelling arthropods at intermediate landscape complexity. The substantial variation in diversity patterns among years with weather extremes, suggests that optimizing benefits of wildflower areas requires further multi-year studies.     

Capacity of Bembidion lampros and Tachyporus hypnorum to survive periods of starvation in early spring

The capacity of the polyphagous predators Bembidion lampros Herbst (Coleoptera; Carabidae) and Tachyporus hypnorum F. (Coleoptera; Staphylinidae) to survive starvation in early spring was investigated. The two species are of similar size and live in the same habitat. They have similar life cycles; where adults emerge in autumn, hibernate during winter and disperse during spring into arable fields where they reproduce and then die. Both species showed an ability to survive long periods of starvation after hibernation. However, B. lampros could live without food several weeks longer than T. hypnorum.Fat content was measured to estimate the energy reserves of beetles in the field. The fat content of B. lampros was at a constant level of 23% both when fed ad libitum in the laboratory and when collected in the field during spring. The fat content of B. lampros was reduced to a level of 7% when they died by starvation. Fat content of T. hypnorum was more variable both when fed ad libitum in the laboratory (17–33%), when collected in the field during the spring (20—26%) and when they died by starvation (10–20%).Neither the mean longevity of starved beetles nor the fat content of specimens collected in the field indicated that the beetles suffered high mortality due to a food shortage in early spring before movement into arable fields.     

Commuting,shifting or remaining?: Different spatial utilisation patterns of wild boar Sus scrofa L. in forest and field crops during summer

In a radiotelemetry study in North-East Germany, we analysed spatial utilisation of 22 female wild boar (Sus scrofa) out of 21 wild boar groups during summer (2003–2006). We compared summer season home ranges (16 May–15 August) with “field home ranges”, i.e. periods between first and last appearance within cereal fields. Wild boar appeared inside fields with beginning of grain and rapeseed flowering and vanished usually with harvest. Three types of spatial utilisation patterns were defined: “field sows”, who shifted their home range entirely into fields; “commuters”, who roamed between forest and fields; and “forest sows”, who remained in the forest. Yearlings were predominantly commuters, whilst family groups did not roam but either shifted to fields or stayed in forest.Field sows had smaller mean field home ranges than total summer home ranges, whereas commuters and forest sows showed no differences. All three groups did not differ significantly in home range size measures but, however, showed different mean shifts from spring to summer home range. The home range sizes of sows of the different spatial patterns were similar, as all resources were permanently available all-over the study area. However, dislocations into outstanding profitable nutritional habitats (e.g. agricultural fields in summer) may enlarge annual home ranges of commuters and field sows.     

Oviposition preference,larval performance and adaptation of Trichoplusia ni on cabbage and cotton

Most female herbivores ensure to lay eggs where their offspring can develop successfully. The oviposition preferences of females affect strategies in pest management. In this study, the performance of two cohorts of Trichoplusia ni larvae on cabbage and cotton (after they had been transferred from their original host plants) were investigated. The preferences of female moth ovipositing and larval feeding on these two host plants were observed. The results indicated that plants significantly affected oviposition preference of the female adults and development and survival of larvae of T. ni. All females preferred to lay eggs on cabbage than cotton regardless from which host they originated. The detrimental effects of cotton on the development and survival of T. ni larvae originated from cabbage (CaTn) increased with the increase of the larval age when they were transferred. In addition, the host plant change did not significantly affect the development and survival of larvae of T. ni originating from cotton (CoTn). Larvae of CaTn preferred cabbage plants as compared to cotton plants, whereas larvae of CoTn did not show a significant choice. Although the adult females preferred laying eggs on cabbage, they did not show preferences between cotton and cabbage in a Y‐tube olfactometer test. The hypothesis of oviposition preference and performance of larvae was supported by the results of CaTn, whereas they not supported by those from CoTn. Based on these results, the strategy to manage this serious pest was discussed.     

Bimodal life cycle of the burying beetle Nicrophorus quadripunctatus in relation to its summer reproductive diapause

Abstract 1. Under natural conditions in Kyoto, Japan, the reproductive activities of Nicrophorus quadripunctatus Kraatz (Coleoptera: Silphidae) decreased in summer and the species showed a bimodal life cycle.
2. In the laboratory, most adult pairs raised at 20 °C under a LD 12:12 h regime reproduced when provided with a piece of chicken. In adults raised at 20 °C under a LD 16:8 h regime, however, both reproductive behaviour and ovarian development were reduced. It is concluded that these adults entered a reproductive summer diapause.
3. High temperature (25 °C) also suppressed the reproductive behaviour even under a favourable LD 12:12 h regime. In the field, therefore, adults reduce their reproductive activity in summer because of diapause induced by long-day photoperiods and direct inhibition of reproduction by high temperatures.
4. When the temperature was changed from 20 °C to 25 °C immediately after hatching of larvae, they reached the wandering stage in 95% of adult pairs. When the temperature was changed from 20 °C to 25 °C immediately after oviposition, however, no larvae hatched in 85% of pairs. Egg mortality was significantly higher at 25 °C than at 20 and 22.5 °C; no eggs hatched at 27.5 °C. The physiological mechanisms for reducing reproduction probably prevent the beetles from inefficient oviposition in summer.     

Oviposition substrate selection by Florida mosquitoes in response to pathogen‐infected conspecific larvae

The impact of the presence of larval mosquito pathogens with potential for biological control on oviposition choice was evaluated for three mosquito species/pathogen pairs present in Florida. These included Aedes aegypti infected with Edhazardia aedis, Aedes albopictus infected with Vavraia culicis, and Culex quinquefasciatus infected with Culex nigripalpus nucleopolyhedrovirus (CuniNPV). Two‐choice oviposition bioassays were performed on each host and pathogen species with one oviposition cup containing infected larvae and the other cup containing uninfected larvae (control). Both uninfected and E. aedis‐infected female Ae. aegypti laid significantly fewer eggs in oviposition cups containing infected larvae. Uninfected gravid female Ae. albopictus and Cx. quinquefasciatus oviposited equally in cups containing uninfected larvae or containing larvae infected with V. culicis or CuniNPV, respectively. Gravid female Ae. albopictus infected with V. culicis did not display ovarian development and did not lay eggs. The decreased oviposition by gravid Ae. aegypti in containers containing E. aedis‐infected larvae may indicate that the infected larvae produce chemicals deterring oviposition.     

南非盲走螨实验种群的发育历期及生命表

在27℃条件下,以粗脚粉螨Acarus siro L.为饲料饲养观察南非盲走螨Typhlodromus(Anthoseius) transvaalensis(Nesbitt)的生长发育和繁殖情况,组建实验种群生命表。结果表明,南非盲走螨行孤雌生殖,卵、幼螨、前若螨、后若螨、成螨产卵前期各阶段发育历期分别为2.00,0.72,1.96,1.53,1.77d,完成1个世代发育需7.98d,雌成螨平均寿命14.82d、平均产卵量25.75粒,各种群生命参数分别为:净增殖率R0=25.01,世代平均周期T=13.71,内禀增长率rm=0.23,周限增长率λ=1.26,种群倍增所需日数t=2.95。采用小空间湿度控制法,测定不同湿度对南非盲走螨卵的孵化和成螨产卵的影响。结果表明,卵发育和孵化的最适湿度为75.0%~85.0%,96.0%的相对高湿度对成螨的产卵和存活均有不利影响。以橘全爪螨Panonychus citri McGregor不同螨态为猎物时,南非盲走螨对橘全爪螨幼螨的捕食量最大,日平均捕食量为5.40头,而对橘全爪螨雌成螨则几乎不取食。     

Mismatch between the timing of oviposition and the seasonal optimum. The stochastic phenology of Mediterranean acorn weevils

1. The timing of reproduction is predicted to match the period of maximum food availability. In this sense, the case of many phytophagous insects in temperate regions is very illustrative, as their larvae usually depend on a resource only available for a limited period of time each year. 2. For 3 years the interactions between the weevil Curculio elephas and the Mediterranean Holm oak Quercus ilex were studied. Weevil larvae grow within the acorns, feeding on the cotyledons. The timing of oviposition will determine food availability for the larvae, as acorns stop growing once they are attacked. 3. Acorn temporal growing patterns did not change between years and food availability for larvae was at its highest in October, when temperature was still suitable for larval development. However, oviposition phenology did change between years. In 2002 females oviposited later, larvae grew within larger acorns, and their body mass was significantly higher than in 2003 or 2004, when females oviposited into early acorns. 4. Thus, weevils do not always adjust oviposition to the best possible feeding conditions for their offspring. Rather, they seem to maximise their own lifetime fitness, ovipositing as soon as they emerge in late summer. Emergence, in turn, depends strongly on stochastic events such as summer storms in the Mediterranean region. 5. Under a climate change perspective, the trend towards higher August rainfall recorded in our study area may alter oviposition phenology, with the subsequent cascade effects on weevil body size and fitness     

Farmland carabid beetle communities at multiple levels of spatial scale

Carabid beetle communities were studied at three levels of spatial scale, i.e. within fields (three sets of traps, mean distance 15 m), between fields (five fields within 1 km from each other) and between patches of farmland (four study areas 4-8 km from each other). We compared carabid assemblages sampled on five crop types in each study area, i.e. ley. set-aside, spring cereal, potato, and sugar beet. Because of small sample sizes, only the community composition was studied within fields with a DCA ordination, but the differences were small. Analyses of species richness, activity density, community composition as revealed by DCA ordinations, dominance structure, diversity, and evenness showed that carabid communities varied significantly among patches of farmland but not between fields with different crops within the patches. Only the communities of potato fields were found lo resemble each other. Only five carabid beetle species showed a preference for crops, and twelve species favoured some study areas. We conclude that the effect of spatial scale should be emphasised in further studies as it seems that carabid beetles may be very localised even in agricultural habitats.     

Habitat and resource use by larval and juvenile fishes in an arid-land river (Rio Grande, New Mexico)

1. Studies of mesic temperate and tropical rivers suggest an important role for floodplain habitats as nursery areas for larval and juvenile fishes. In arid‐land rivers the extent and duration of flooding is diminished and habitats and resources used by larval fishes are poorly known. Our study documented habitat and resource use of larval fishes in the Rio Grande, New Mexico, an arid‐land river. 2. Spatial and temporal distribution of larval and juvenile fishes and their inferred microhabitat preferences were studied during spring, summer and autumn, 2003. Stable carbon (¹³C : ¹²C) and nitrogen (¹⁵N : ¹⁴N) isotope ratios were measured to identify nutrient sources and characterise trophic positions of young‐of‐year fishes in this system. 3. Some fishes recruited during high flows (in spring), whereas others recruited during low‐flow periods in late summer. Regardless of the timing of reproduction, microhabitats with lower current velocity and higher temperature appeared to serve as vital nursery grounds for Rio Grande fishes. Ephemeral backwaters and disconnected side channels held the highest abundance and diversity of larvae and juveniles. 4. Stable isotope analyses revealed that fish larvae obtained carbon predominately from algal production in early summer, but used organic carbon derived from emergent macrophytes as river discharge decreased in mid‐summer. This shift may have been facilitated by microinvertebrate prey that grazed down edible algae and then switched to macrophytes in mid‐summer. Nitrogen isotope ratios did not differ among species or early life stages, suggesting that larval and juvenile fishes use similar food resources, especially when restricted to isolated pools in summer.     

Observations on the biology and ecology of the chrysomelid beetle Gastrophysa polygoni in cereal fields

Abstract. 1. Observations were made on the biology of Gastrophysu polygoni (L.) (Coleoptera: Chrysomelidae) in cereal fields in southern England in 1977, 1978 and 1979. Adults of the overwintering generation emerged in late April/ May and there were usually two generations during the spring and summer months. In 1979 there was some evidence for at least a partial third generation.
2. In the field, the oviposition period was 44 days in the first generation and c . 25 days in the second. Fecundity varied from 586 to 1028 eggs per female and was higher in the first than in the second generation in both 1977 and 1979; in 1978 the reverse was true.
3. Every year there were Iarge losses in the numbers within a generation. However, only one parasite was bred from the developmental stages and a pathogen attacking the larvae was found only in 1977.
4. In some fields and in some years, harvesting and straw burning operations were carried out when eggs were present on the plants. Harvesting did not result in a significant reduction in the numbers of eggs. Burning reduced the numbers of egg batches. The effect was most severe when the straw was spread over the field prior to burning.
5. In the field, significantly more eggs were laid on plants of Polygonum aviculare than on P.convolvulus . In the laboratory, larval survival was higher and duration of development shorter on these two species than on other Polygonaceae found on the farm.     

Humidity responses and water balance of riparian species of Bembidiini (Col., Carabidae)

Abstract. 1. The humidity responses of Asaphidion pallipes (Duftschmid) and Bembidion spp. were studied at various temperatures in choice chambers.
2. Several species initially showed a hygropositive or indifferent response. Other species had a hygronegative reaction which later changed to a hygropositive one. The duration of the hygronegative reaction varied with species, age, temperature and relative humidity. B.litorale (Olivier) and B.semipunctatum (Donovan) change response when they have lost 8–9% of their initial body weight as water.
3. The survival time of species of Bembidion under dry conditions was short compared with that reported for many other carabid beetles. Newly emerged adults of B.argenteolum Ahrens that had been kept away from sand for 3 weeks had lower transpiration rates than any other species. Young adult Bembidion had lower transpiration rates than those in the breeding phase, larvae and dead adults. Transpiration rate appeared to be inversely proportional to the relative humidity whereas there was a non-linear increase in weight loss with increasing temperature.
4. The species gain most water by drinking and/or from food.
5. There was no correlation between humidity response and transpiration rate or ability to tolerate dry conditions of the species. There was, however, a correlation between behaviour/habitat affinity and humidity response. Diurnal species, living in sandy or silty, half shady-exposed habitats had an initial hygronegative response, whereas those which hide among gravel/stones, leaves or vegetation were indifferent or hygropositive.