Influence of dung volatiles on the process of resource selection by coprophagous beetles

Summary. Most dung beetles colonize the faeces of several vertebrate species without much discrimination, and are thus often considered as polyphagous. Recent studies have provided evidence for clear feeding preferences in scarab beetles colonizing dung of herbivore species, but little is known about these insects’ abilities to discriminate among odours from faeces of various herbivores. In this study, trophic preferences were examined using blocks of pitfall traps baited with dung from four different herbivore species, i.e., sheep, cattle, horse, and red deer, in a mountainous area of south-central France. 4941 coprophagous scarabs, belonging to 27 species, were captured. Beetles were more attracted to dung of sheep (2257 individuals) than that of cattle (1294 individuals), followed by deer dung (768 individuals) and horse dung (622 individuals). Eleven of the 27 beetle species collected had significant feeding preferences for one of the four dung types. For each insect species, trophic habits did not vary between the two different sites of trapping, an open pasture and a wooded habitat. In laboratory olfactometer bioassays, scarab beetles orientated preferentially towards the dung volatiles from the dung type they preferred in the field. Trypocopris pyrenaeus, Anoplotrupes stercorosus, and Aphodius rufipes were more attracted to volatile compounds from sheep dung, Onthophagus fracticornis significantly preferred horse dung volatiles, and Aphodius haemorrhoidalis responded positively to deer dung odours. The role of dung olfactory cues in the process of resource selection by dung beetles is discussed.     

Semiochemicals mediating host-finding behaviour in the phoretic association between Macrocheles saceri (Acari: Mesostigmata) and Scarabaeus species (Coleoptera: Scarabaeidae)

Summary. Phoresy is an interspecific association where mobile organisms ensure small and/or wingless organisms to colonize patchy distributed environment. Macrocheles saceri (Acari: Mesostigmata) is a phoretic mite which specialized on Scarabaeus dung beetles (Coleoptera: Scarabaeidae). Variation for phoretic load and sites for mite fixation on beetle body has been tested according to Scarabaeus species. The number of setae on beetle body cannot explain the observed patterns in mite fixation. Evidence was provided that the semiochemicals of the host cuticle play a kairomonal role in the host finding behaviour of phoretic mites. In addition semiochemicals ensure host discrimination.     

Environmental risk assessment of veterinary pharmaceuticals: development of a standard laboratory test with the dung beetle Aphodius constans

The environmental risk assessment of veterinary pharmaceuticals for dung beetles is required if the substance is an anti-parasiticide for the treatment of pasture animals. However, the demonstration of the environmental safety of those substances for dung fauna is hampered by the fact that no standardized laboratory test system is currently available. Here a test system using the temperate dung beetle species Aphodius (Agrilinus) constans (Scarabaeidae: Aphodiinae) Duftschmidt is described. The survival of first instar larvae of A. constans exposed to a model substance, dimethoate, spiked into formulated (i.e. dried, formulated and re-wetted) or fresh dung was measured over a period of three weeks. Larvae performed better in formulated dung which also proved to be more suitable for mixing-in test substances homogenously. Dimethoate caused significant larval mortality with LC50 values within a range of 1.3-2.8 mg a.s./kg dung (d.w.), depending on the dung type. Based on the data presented here, it is recommended to incorporate this new test system in the risk assessment process for veterinary pharmaceuticals. However, an international ringtest should to be performed beforehand to ensure adequate validation of the method.     

Entwicklung und Einsatz eines standardisierten Labortests für Dungkäfer (Aphodius constans) zur Prüfung der Ökotoxizität von Veterinärpharmaka

Goal, Scope, and Background

According to European legislation, an environmental risk assessment of veterinary pharmaceuticals for dung beetles is required if the substance is a parasiticide for the treatment of pasture animals. However, the demonstration of the environmental safety of those substances for dung beetles is strongly hampered by the fact that no standardized test system is available so far. Therefore, starting with recommendations from the SETAC advisory group DOTTS (Dung Organism Toxicity Test Standardization), a test system using the widespread temperate dung beetle species Aphodius constans was developed.

Methods

Using experiences gained at the University of Montpellier (e.g. in field studies) and in other terrestrial tests, details of culturing and testing of A. constans were investigated in a project sponsored by the German Environment Protection Agency (UBA). Basically, the survival of young larvae of A. constans exposed to the test substance spiked into formulated (i.e. dried, grounded and re-wetted) or fresh dung is measured over a period of three weeks. Using the model substance dimethoate (an insecticide required as positive control in tests with the predatory mite Hypoaspis aculeifer) the suitability of the new test was checked. Afterwards, the new test method was used to determine the toxicity of four common veterinary pharmaceuticals (ivermectin, dicyclanil, moxidectin, praziquantel) in formulated and fresh dung. Finally, the effects of ivermectin on the dung beetles were determined in a test using fresh dung from treated cattle.

Results and Conclusions

For Dmethoate LC₅₀-values were found in a range of 1–3 mg a.s./kg dung (dew.), depending on the dung type. Praziquantel did not show eirecis in the tested concentration range (i.e. up to 1000 mg a.s./kg Dung (DW). The LC₅₀-values of the other three pharmaceuticals were very low (<6 mg a.s./kg dung (DW)). With the exception of Dicyclanil no differences between formulated and fresh dung were identified. In the case of ivermectin the LC₅₀-value were even lower: about 0.5 mg a.s./kg dung (DW). No differences between the results of test in which the substance was spiked into dung and those tests which were performed with dung from treated cattle were found. These results prove the sensitivity as well as the robustness of this test method.

Recommendations and Perspectives

Based on the experiences reported here, it is recommended to standardize this test in an international ring test so that it can be incorporated in the risk assessment process for veterinary pharmaceuticals as described in the currently developed international registration guidelines.