Daniel Cherix

Occurrences of flesh flies (Diptera: Sarcophagidae) on human cadavers in Switzerland, and their importance as forensic indicators

From 1993 to 2008, criminal investigations were conducted in the western part of Switzerland with special attention to blowfly and flesh fly species in order to estimate the post-mortem interval when requested by the police authorities. Flesh flies were found in only 33 cases out of 160. Five species of the genus Sarcophaga were identified (S. africa, S. argyrostoma, S. caerulescens, S. similis and S. sp.). The main species found on corpses (larval stage) was S. argyrostoma. The thermal constant (K) calculated for this species in Switzerland is 380.6 ± 16.3 (mean ± S.D.) degree-days. With the exception of S. caerulescens, found three times in the larval stage on corpses, the three other species are of minor forensic importance. S. argyrostoma is found during summer and indoors. This species colonises dead bodies, usually the same day as blowfly species, and it could be used to estimate the post-mortem interval. Other species are discussed in the light of current knowledge on their biology and ecology. It is recommended that voucher material be deposited in a museum, allowing further studies by relevant specialists, thereby helping investigators and avoiding misidentifications.

A stratified approach for modeling the distribution of a threatened ant species in the Swiss National Park

We present models predicting the potential distribution of a threatened ant species, Formica exsecta Nyl., in the Swiss National Park (SNP). Data to fit the models have been collected according to a random-stratified design with an equal number of replicates per stratum. The basic aim of such a sampling strategy is to allow the formal testing of biological hypotheses about those factors most likely to account for the distribution of the modeled species. The stratifying factors used in this study were: vegetation, slope angle and slope aspect, the latter two being used as surrogates of solar radiation, considered one of the basic requirements of F. exsecta. Results show that, although the basic stratifying predictors account for more than 50% of the deviance, the incorporation of additional non-spatially explicit predictors into the model, as measured in the field, allows for an increased model performance (up to nearly 75%). However, this was not corroborated by permutation tests. Implementation on a national scale was made for one model only, due to the difficulty of obtaining similar predictors on this scale. The resulting map on the national scale suggests that the species might once have had a broader distribution in Switzerland. Reasons for its particular abundance within the SNP might possibly be related to habitat fragmentation and vegetation transformation outside the SNP boundaries.

Codeine accumulation and elimination in larvae, pupae, and imago of the blowfly Lucilia sericata and effects on its development

The aim of this study was to evaluate the reliability of insect larvae as samples for toxicological investigations. For this purpose, larvae of Lucilia sericata were reared on samples of minced pig liver treated with different concentrations of codeine: therapeutic, toxic, and potentially lethal doses. Codeine was detected in all tested larvae, confirming the reliability of these specimens for qualitative toxicology analysis. Furthermore, concentrations measured in larvae were correlated with levels in liver tissue. These observations bring new elements regarding the potential use of opiates concentrations in larvae for estimation of drug levels in human tissues. Morphine and norcodeine, two codeine metabolites, have been also detected at different concentrations depending on the concentration of codeine in pig liver and depending on the substance itself. The effects of codeine on the development of L. sericata were also investigated. Results showed that a 29-h interval bias on the evaluation of the larval stage duration calculated from the larvae weight has to be considered if codeine was present in the larvae substrate. Similarly, a 21-h interval bias on the total duration of development, from egg to imago, has to be considered if codeine was present in the larvae substrate.

Monitoring Butterfly Abundance: Beyond Pollard Walks

Most butterfly monitoring protocols rely on counts along transects (Pollard walks) to generate species abundance indices and track population trends. It is still too often ignored that a population count results from two processes: the biological process (true abundance) and the statistical process (our ability to properly quantify abundance). Because individual detectability tends to vary in space (e.g., among sites) and time (e.g., among years), it remains unclear whether index counts truly reflect population sizes and trends. This study compares capture-mark-recapture (absolute abundance) and count-index (relative abundance) monitoring methods in three species (Maculinea nausithous and Iolana iolas: Lycaenidae; Minois dryas: Satyridae) in contrasted habitat types. We demonstrate that intraspecific variability in individual detectability under standard monitoring conditions is probably the rule rather than the exception, which questions the reliability of count-based indices to estimate and compare specific population abundance. Our results suggest that the accuracy of count-based methods depends heavily on the ecology and behavior of the target species, as well as on the type of habitat in which surveys take place. Monitoring programs designed to assess the abundance and trends in butterfly populations should incorporate a measure of detectability. We discuss the relative advantages and inconveniences of current monitoring methods and analytical approaches with respect to the characteristics of the species under scrutiny and resources availability.

Molecular markers allow sibling species identification in red wood ants (Formica rufa group)

Red wood ants (Formica rufa group) constitute a group of species that are considered to be among the most promising bioindicators in forest ecosystems. However, because of their morphological similarity and intraspecific variability, morphological species identification can be difficult. Considerable expertise is necessary to discriminate between the sibling species F. lugubris and F. paralugubris, two species that often live in sympatry in the same Alpine forests. New taxonomic tools providing rapid and reliable species identification are needed. We present a simple and reliable molecular technique based on mtDNA (COI gene) and a restriction enzyme for discriminating between F. lugubris and F. paralugubris. We confirm the validity of this method with a Bayesian analysis based on microsatellites. This new molecular tool represents a clear breakthrough for discriminating between F. lugubris and F. paralugubris and is likely to be helpful in large‐scale biomonitoring.

Functional diversity decreases with temperature in high elevation ant fauna

Severe environmental conditions filter community species compositions, forming clines of functional diversity along environmental gradients. Here, the changes in functional diversity in ant assemblages with severe environmental conditions in the Swiss Alps were investigated. Eight sites were sampled along an elevation gradient (1800–2550 m). The variation in functional diversity was analysed along an elevation gradient considering four traits: social structure (monogynous vs. polygynous), worker size, pupal development, and nest structure. Ant species richness and functional diversity decreased with decreasing temperature. Species found in colder habitats tended to live in subterranean nests rather than in mounds and exhibit a polymorphism in queen number, either within or across populations. The phylogenetic diversity did not decrease at colder temperature: Formicinae and Myrmicinae occupied the full range of elevations investigated. An insulation experiment indicated that mounds are more thermally insulated against the cold compared with soil. The absence of a mound‐building ant from high elevations probably results from a reduction in the amount of vegetal materials provided by coniferous trees. More severe abiotic conditions at higher elevations act as a filter on ant assemblages, directly through physiological tolerances to the abiotic conditions and indirectly as the vegetation necessary for nest building shifts with elevation.

A scientific note on the ant pitfall for quantitative diagnosis of Varroa destructor

The mite Varroa destructor is a global challenge for apiculture and accurate quantification crucial for adequate and timely pest management. However, foraging ants are regularly found in hives and may interfere with mite diagnosis. Here, we quantify for the first time the impact of ants. We expect lower mite numbers on bottom boards with foraging ants and that estimates of phoretic mites are ant independent. From July to August 2007–2009, the experiments were conducted with 64 queenright honey bee colonies (predominantly Apis mellifera carnica, Table I). One apiary was used for 3 years, but each time, new colonies were monitored. All colonies (~11 frames of bees, 6–10 brood frames) were housed in Dadant hives (12 frames) with bottom board inserts for mite quantification (Imdorf et al. 2003) and placed in groups of four or five each on hive stands with four steel polders (50 cm aboveground). All colonies were treated in summer and fall using formic and oxalic acid (Imdorf et al. 2003). To quantify the impact of ants, we added traps (water-filled buckets [∅=20 cm]) to each of the four steel polders of the hive stands. At least once a month, water was refilled, and the surrounding vegetation was cut. The controls remained without traps. Quantifications were conducted weekly by removing the bottom board inserts and counting all mites and ants. In 2009, we also collected weekly 200 bee workers from the brood nests of 18 colonies for 8 weeks to evaluate the number of phoretic mites following Ritter and Ruttner (1980). For that purpose, nine colonies received traps (= treatments), and nine remained without (= controls) for 4 weeks; then, the groups were exchanged by relocating traps. Thus, we obtained from the same colonies mite infestation loads from both bottom board counts and phoretic mite estimates with or without ant traps. We also monitored all stands to investigate whether they were exposed to ant foraging. Ants were collected for taxonomic identification using morphometrics (Seifert 2007). We performed Kruskal–Wallis and Mann–Whitney U post hoc tests to compare ant and mite numbers. To test whether there is a regression between ant and mite numbers, we constructed a Linear Mixed Model (LMM), with log-transformed V. destructor numbers as the dependent variable, log-transformed ant numbers as fixed effect and colony as random effect, resulting in normally distributed residuals:

Sampling and monitoring wood ants

Wood ants ( Formica rufa group) are the ecological centre of many temperate and boreal forest ecosystems, with influence over ecosystem processes and other organisms. Owing to their dominance and keystone role, there are many reasons why it may be desirable or necessary to sample or monitor wood ants. Most field-based studies are based on exploring the relationships between red wood ants and their environment, be it the effects wood ants have on their surroundings via their nesting or foraging activities, or the effect a changing environment has on the ants. Given their keystone roles with the ecosystem, red wood ants can be useful indicators of ecosystem health, environmental degradation or restoration, or climate change (Torossian 1977b; Sorvari and Hakkarainen 2007b). With many species in Eurasia threatened and those in North America little understood, there is often simply a requirement to assess whether a species is present or not, or whether introductions or translocations have been successful. Unlike most other invertebrates, and indeed even other ant species, most red wood ants build conspicuous and long-lasting mound nests that facilitate their census. However, as for other ant species, this social living presents particular challenges for sampling and monitoring. Careful planning and the application of considered methods are needed to overcome these difficulties. This chapter provides an overview of the sampling methods and approaches that have been directly applied to wood ants, and the theory underpinning them. Where methods or approaches are ineffective or warrant further development, these are highlighted. The goal is to recommend a set of reliable and easy to use methods that can provide accurate and repeatable data, which are comparable between studies. The challenges of studying red wood ants Consideration of life cycle and seasonality Effective sampling or monitoring of wood ants presents considerable theoretical and practical problems. Wood ants are social insects which are patchily distributed and territorial. Moreover, there are seasonal patterns to the abundance and presence of certain castes. The queen (or queens) and some workers are present throughout the year, though not always visibly so. Males and particular stages of brood are present only for part of the year and this can depend on factors such as colony size and age, food availability and local environmental variables.

Wood ant reproductive biology and social systems

Transmitting genes from one generation to the next is the fundamental basis of natural selection and evolution. Understanding the reproductive biology of a species is, therefore, fundamental to understanding how the species evolved and how it is adapted to its environment. In eusocial insects such as the wood ants ( Formica rufa group), reproduction is invested in a specialised reproductive caste, which produces both the workers and the next generation of sexual individuals. This chapter introduces the reproductive biology of wood ants, and also gives a general view of the life cycle of a wood ant colony to put the reproductive biology in context. Wood ant life cycle The wood ant life cycle is strongly linked to seasonal changes in the environment. Wood ant colonies generally first become active, after winter quiescence, in early spring when the sun begins to heat the nest and, in some locations, melt the snow (Figure 2.1). The timing of the beginning of activity is strongly influenced by the local climate, altitude and nest location. In Switzerland, for example, significant colony activity usually begins in March or April (Cherix 1981; Chauternes 1988). On warm and sunny days, early in spring, worker activity begins and the internal temperature of the nest begins to rise to between 25°C and 30°C. Nest temperature remains at this level for the entire active season, even when, during early spring, the outside temperature is close to freezing (discussed in detail in Chapter 4) (Rosengren et al . 1987). Workers gather in the warm nest core and their nutrient-producing glands become more active, converting lipids and protein into food ready to be fed to queens and future larvae (Bausenwein 1960). The queen(s) remain(s) in the warm nest core for several days and lay ‘winter eggs’. The larvae hatching from these eggs are fed by the overwintering workers, usually developing into sexuals in about 6 weeks (Otto 2005). The queen(s) then retire(s) to the lower nest chambers to start to produce ‘summer eggs’, which usually develop into workers (Otto 2005). Reproduction generally takes place in early summer, with thousands of sexual individuals flying away from their nests and participating in nuptial flights (e.g. Cherix et al . 1991).