Pavel Saska

Forty years of carabid beetle research in Europe – from taxonomy, biology, ecology and population studies to bioindication, habitat assessment and conservation

Abstract ‘Carabidologists do it all’ (Niemelä 1996a) is a phrase with which most European carabidologists are familiar. Indeed, during the last half a century, professional and amateur entomologists have contributed enormously to our understanding of the basic biology of carabid beetles. The success of the field is in no small part due to regular European Carabidologists’ Meetings, which started in 1969 in Wijster, the Netherlands, with the 14th meeting again held in the Netherlands in 2009, celebrating the 40th anniversary of the first meeting and 50 years of long-term research in the Dwingelderveld. This paper offers a subjective summary of some of the major developments in carabidology since the 1960s. Taxonomy of the family Carabidae is now reasonably established, and the application of modern taxonomic tools has brought up several surprises like elsewhere in the animal kingdom. Progress has been made on the ultimate and proximate factors of seasonality and timing of reproduction, which only exceptionally show non-seasonality. Triggers can be linked to evolutionary events and plausibly explained by the “taxon cycle” theory. Fairly little is still known about certain feeding preferences, including granivory and ants, as well as unique life history strategies, such as ectoparasitism and predation on higher taxa. The study of carabids has been instrumental in developing metapopulation theory (even if it was termed differently). Dispersal is one of the areas intensively studied, and results show an intricate interaction between walking and flying as the major mechanisms. The ecological study of carabids is still hampered by some unresolved questions about sampling and data evaluation. It is recognised that knowledge is uneven, especially concerning larvae and species in tropical areas. By their abundance and wide distribution, carabid beetles can be useful in population studies, bioindication, conservation biology and landscape ecology. Indeed, 40 years of carabidological research have provided so much data and insights, that among insects - and arguably most other terrestrial organisms - carabid beetles are one of the most worthwhile model groups for biological studies.

Temperature effects on pitfall catches of epigeal arthropods: a model and method for bias correction

Summary Carabids and other epigeal arthropods make important contributions to biodiversity, food webs and biocontrol of invertebrate pests and weeds. Pitfall trapping is widely used for sampling carabid populations, but this technique yields biased estimates of abundance (‘activity‐density’) because individual activity – which is affected by climatic factors – affects the rate of catch. To date, the impact of temperature on pitfall catches, while suspected to be large, has not been quantified, and no method is available to account for it. This lack of knowledge and the unavailability of a method for bias correction affect the confidence that can be placed on results of ecological field studies based on pitfall data. Here, we develop a simple model for the effect of temperature, assuming a constant proportional change in the rate of catch per °C change in temperature, r, consistent with an exponential Q10 response to temperature. We fit this model to 38 time series of pitfall catches and accompanying temperature records from the literature, using first differences and other detrending methods to account for seasonality. We use meta‐analysis to assess consistency of the estimated parameter r among studies. The mean rate of increase in total catch across data sets was 0·0863 ± 0·0058 per °C of maximum temperature and 0·0497 ± 0·0107 per °C of minimum temperature. Multiple regression analyses of 19 data sets showed that temperature is the key climatic variable affecting total catch. Relationships between temperature and catch were also identified at species level. Correction for temperature bias had substantial effects on seasonal trends of carabid catches. Synthesis and Applications. The effect of temperature on pitfall catches is shown here to be substantial and worthy of consideration when interpreting results of pitfall trapping. The exponential model can be used both for effect estimation and for bias correction of observed data. Correcting for temperature‐related trapping bias is straightforward and enables population estimates to be more comparable. It may thus improve data interpretation in ecological, conservation and monitoring studies, and assist in better management and conservation of habitats and ecosystem services. Nevertheless, field ecologists should remain vigilant for other sources of bias.

Granivory in terrestrial isopods

Abstract Granivory (seed feeding) evolved in many animal groups. Field observations hint at the existence of granivory in terrestrial isopods (Crustacea: Isopoda: Oniscidea), for which it was previously unknown. In this paper granivory in terrestrial isopods is addressed for the first time, focusing on (i) seed acceptance in the presence of plant litter and (ii) size as a constraint for acceptance and consumption. In a laboratory choice experiment, Armadillidium vulgare consumed seeds of Capsella bursa‐pastoris and Poa annua when plant litter was present. In a no‐choice experiment, seeds of seven plant species were offered to four isopod species giving 13 combinations in total [A. vulgare (seven species of seeds), Oniscus asellus (two), Porcellio scaber (two), and Porcellionides pruinosus (two)]. The tested isopods differed in their acceptance (proportion of individuals consuming seeds) and consumption (both number and amount of seeds eaten) of seed species. Size as a constraint was demonstrated in A. vulgare offered Cirsium arvense seed, since the probability that this large seed was eaten increased with body size of the isopod. In the other 10 seed–isopod pairs, seed consumption increased linearly with isopod body size. Granivory is thus widespread in terrestrial isopods, although the tendency to eat seeds differs between species.

Molecular approach to describing a seed‐based food web: the post‐dispersal granivore community of an invasive plant

Communities of post-dispersal granivores can shape the density and dispersion of exotic plants and invasive weeds, yet plant ecologists have a limited perception of the relative trophic linkages between a seed species and members of its granivore community. Dandelion seeds marked with Rabbit IgG were disseminated into replicated plots in the recipient habitat (South Dakota) and the native range (Czech Republic). Arthropods were collected in pitfall traps, and their guts were searched for the protein marker using enzyme-linked immunosorbent assay (ELISA). Seed dishes were placed in each plot, and dandelion seed removal rates were measured. The entire experiment was repeated five times over the dandelion flowering period. Gut analysis revealed that approximately 22% of specimens tested positive for the seed marker. A more diverse granivore community had trophic linkages to seeds than has been previously realized under field conditions. This community included taxa such as isopods, millipedes, weevils, rove beetles, and caterpillars, in addition to the traditionally recognized ants, crickets, and carabid beetles. Rarefaction and Chao analysis estimated approximately 16 and 27 species in the granivore communities of the Czech Republic and South Dakota, respectively. Synthesis: Generalist granivore communities are diverse and polyphagous, and are clearly important as a form of biotic resistance to invasive and weedy plants. These granivore communities can be managed to limit population growth of these pests.

Treatment by glyphosate-based herbicide alters life history parameters of the rose-grain aphid Metopolophium dirhodum.

Glyphosate is the number one herbicide in the world. We investigated the sub-lethal effects of this herbicide on the aphid Metopolophium dirhodum (Walker), using an age-stage, two-sex life table approach. Three concentrations of the herbicide (low - 33.5, medium - 66.9 and high - 133.8 mmol dm−3 of active ingredient) and distilled water as the control were used. The LC50 of the IPA salt of glyphosate on M. dirhodum was equivalent to 174.9 mmol dm−3 of the active ingredient (CI95: 153.0, 199.0). The population parameters were significantly negatively affected by herbicide application, and this negative effect was progressive with the increasing concentration of the herbicide. A difference of two orders of magnitude existed in the predicted population development of M. dirhodum between the high concentration of the herbicide and the control. This is the first study that comprehensively documents such a negative effect on the population of an herbivorous insect.

The effects of habitat, density, gender and duration on overwintering success in Bembidion lampros (Coleoptera: Carabidae)

In temperate climates, winter mortality is a key factor influencing insect survival. In Bembidion lampros (Coleoptera: Carabidae), an abundant polyphagous predator in arable farmland, we investigated how habitat, population density, gender and duration of overwintering affect the winter mortality and body condition of survivors. In a field experiment, we introduced beetles at two population densities into isolators placed either in the interior of the field or in the grassy boundary. Half of the isolators were collected in mid‐March, and the remaining half were collected in mid‐April. Across all treatments, 44–92% of the beetles survived until spring. Survival was significantly higher in the field interior than in the boundary. The longevity of individuals starved after overwintering was higher in females than in males and was positively related to the length of time spent at the overwintering site. Population density was positively related to percentage survival but did not affect body condition. Our results suggest that biotic factors such as population density and predation, though little studied, may have a similar significance as abiotic factors. Even ubiquitous carabid species inhabiting agroecosystems have specific requirements for overwintering. Understanding these requirements is useful for developing techniques to support their overwintering success.

Synchronization of a Coleopteran Parasitoid, Brachinus spp. (Coleoptera: Carabidae), and Its Host

Abstract Laboratory experiments have shown that larvae of ectoparasitoids Brachinus explodens Duftschmid and Brachinus crepitans (L.) (Coleoptera: Carabidae) develop on pupae of spring breeding species of the genus Amara (Coleoptera: Carabidae). In this study, we investigated the synchronization of the critical stages of host and parasitoid in the field. We simulated the development of both genera under field conditions in spring 2003, combining 1) field data (activity-density measured by pitfall traps and oviposition), 2) thermal constants for development (lower development threshold and sum of effective temperatures), and 3) meteorological data (average daily temperature at a depth of 2.5 cm). In early spring, adults of Amara oviposited in weedy areas, which provided plenty of seed with which to feed their larvae. Pupation was predicted to occur from June to early July. Brachinus adults arrived later than their hosts, and females started to oviposit when Amara larvae were just about to pupate, and Brachinus larvae hatched when Amara pupae became available. The synchronization of the critical stages of host and parasitoid observed in the field strongly supports the existence of a host-parasitoid relationship between Amara pupae and Brachinus larvae.

Fast Population Growth in Physogastry Reproduction of Luciaphorus perniciosus (Acari: Pygmephoridae) at Different Temperatures

Abstract Luciaphorus perniciosus Rack is one of the most serious pests of several cultivated mushroom species including Ganoderma lucidum (Fr.), Flammulina velutipes Karst., Auricularia polytricha (Mont.) Saac., Lentinus polychrous Lev., and Lentinus squarrosulus (Mont.) Singer in Thailand. Adult female Lu. perniciosus produce offspring inside their physogastric hysterosomas, with all embryos developing through to the adult stage while remaining in the abdomen. Once the abdomen ruptures, the female parent dies and the offspring consisting of mostly fertilized female adults along with a few male adults continue to emerge from the cadaver of the mother for a period of several days. This peculiar type of reproduction after the death of the mother is a special case for life table analysis and has not been discussed previously in demographic analyses. In this study, the life table data of this mite fed on Le. squarrosulus were collected at 25, 30, and 35 °C and analyzed by using the age-stage, two-sex life table. The standard errors of population parameters were estimated by using the bootstrap technique (200,000 bootstraps). At 25, 30, and 35 °C, females started reproduction at ages 9, 5, and 3 d, respectively; the net reproductive rates (R 0) were 192.27, 253.81, and 234.11 offspring. Due to their rapid development and high fecundity, the r values were as high as 0.4189, 0.8653, and 1.0892 d–1 at 25, 30, and 35 °C, respectively. Computer projection indicated that the mushroom mites Lu. perniciosus is capable of a threefold daily increase at 35 °C.

Host plants mixture and fitness of Kolla paulula: with an evaluation of the application of Weibull function

The xylem‐feeding leafhopper Kolla paulula (Walker), a vector of Pierces disease, occurs primarily on weeds in and around fruit and ornamental crop orchards in Taiwan. Because our preliminary studies showed that K. paulula performed poorly when reared on pilose beggarticks (Bidens pilosa L. var. radiata) (PB) or trilobate wedelia (Wedelia triloba (L.)) (TW) alone, we collected the life table data of K. paulula reared on a mixture of both host plants to determine the effect at the population level. During their lifespan, 95.6% of feeding time was spent on the major host plant (PB) and only 4.4% on the minor host plant (TW). The intrinsic rate of increase (r), finite rate of increase (λ), net reproduction rate (R0) and mean generation time (T) of K. paulula were 0.0487, 1.0500 day−1, 35.86 offspring and 73.4 days, respectively. Because more than 95% of the insects have been observed feeding on both plants, this would indicate that the minor host plant may play an important role in the fitness of K. paulula regardless of the short feeding time. We calculated the percentage contribution to the population parameters made by females that had fed on both PB and TW and compared these with the values obtained for offspring of females that had fed solely on PB. We also evaluated the usefulness of applying the Weibull distribution in demographic studies. We demonstrated that when there is a higher mortality in specific life stages, the fitted Weibull distribution would be inaccurate in describing the survival curve and that application of the fitted curve to the calculation of life expectancy or other statistics would result in significant discrepancy to the actual curve.

Efficiency of host utilisation by coleopteran parasitoid

In insect larvae, optimising food utilisation with respect to available meals and time is essential for achieving maximum adult body size, which is a relevant proxy of fitness. We studied the efficiency of food conversion, body size, mortality, and development time in a solitary idiobiont ectoparasitoid, Brachinus explodens (Coleoptera: Carabidae), reared in the laboratory on the pupae of another carabid genus, Amara. The efficiency of conversion index (ECI - ratio of ingested to assimilated food) was, on average, 54.1±1.1% (n=76), with a minimum of 26.9% and a maximum of 81.6%. The rate of increase in biomass gained (W(gained)) with biomass of the host was constant in females, but it decreased in males over the range of host body mass. Females, therefore, grew heavier from hosts of the same mass compared to males. Body length increased with the host mass and was correlated with W(gained) identically for both sexes. Mortality was unaffected by the host mass, but it significantly increased below 20°C. In contrast, the development time of the feeding phase of the larva increased with the host mass at 20.3 and 23.7°C, but it remained unaffected at 26.9°C and in all three temperatures considering pupal development. W(gained) increased with development time up to ca. 8 days of larval feeding at 23.7°C. To our knowledge, our data are the first on food utilisation in solitary idiobiont coleopteran ectoparasitoids, and they present the highest values of ECI in insects.