Amara similata

Abstract: Several studies have shown that the mainly granivorous carabid beetles, e.g. Amara spp., include animal food in their diet to a considerable extent. We therefore hypothesized that the performance of these beetles would be enhanced by dietary mixing including both seeds and animal food. In order to test this, we conducted laboratory feeding experiments with adults and larvae of Amara similata. Both adults and larvae were subjected to different diet treatments including: seeds, houseflies, grasshoppers, earthworms, slugs and snails in pure and mixed diets. Larval survival, development time, pupal and teneral weights were used as indicators of food quality for the larvae. For the adult beetles, mass change was used as an indicator of food quality. We found seeds to be high-quality food, while all pure animal diets were of low quality for both adults and larvae. Animal foods added to the seed diet had both positive and negative effects. A mixed diet of all foods enhanced the mass gain of adults compared with the seed diet, but reduced larval performance dramatically. Earthworms and grasshoppers added to seeds increased the pupal and teneral weights, while reduced larval survival. Thus, A. similata is omnivorous with a mainly granivorous feeding habit. It may gain benefits on some fitness parameters and incur costs on others from preying or scavenging on animal food. Therefore, the overall fitness consequences of a mixed seed-animal diet are uncertain.

Abstract: Many carabid beetles (Coleoptera: Carabidae) are known to feed on plant seeds, but the level of specialization on this food differs. This is the first study in which seed consumption is assessed for all larval instars and adults of ground beetles. Three species of Amara with syntopic occurrence, Amara aenea (DeGeer), Amara familiaris (Duftschmid) and Amara similata (Gyllenhal), were examined. Larvae of all three instars and adults were fed seeds of Stellaria media (L.) Vill., Capsella bursa-pastoris (L.) Med. and Taraxacum officinale Wick. ex Wigg. in a laboratory no-choice experiment. In general, larvae, particularly the first instar, showed greater differences in seed consumption than the adults, although the latter showed similar but less marked pattern. Amara aenea consumed all offered seed diets in all life stages. All three larval instars of granivorous A. familiaris almost exclusively fed on seeds of S. media and the adults also ate significantly more of this than other seeds. Amara similata consumed mostly seeds of C. bursa-pastoris in the first instar and adult stages, whereas the larvae of the later instars seemed to be unspecialized on particular seed diet. Differences in seed-specific consumption between larval instars in granivorous carabids are reported for the first time. The results provide further support for the parallel evolution of various degrees of granivory in the genus Amara, which may ultimately facilitate species coexistence. The daily seed consumption by the larvae was comparable or (in case of the third instar) even higher than that by the adults. Hence, we suggest that larvae may be the important consumers of seed in the field and should not be forgotten when seed predation is assessed.

Abstract: In the present study, the importance of diet in terms of fecundity is compared for three species of the carabid genus Amara (Coleoptera: Carabidae), using an insect diet, two types of seed diet (Capsella bursa-pastoris, Stellaria media) and a mixed diet. It is expected that the species of carabid studied have different food requirements for reproduction. Diet affects reproduction performance and egg production significantly. A mixed diet and both single-seed diets are suitable for reproduction in Amara aenea (DeGeer) because a higher proportion of the females reproduce and lay significantly more eggs than on a purely insect diet. Females of Amara familiaris (Duftschmid) do not reproduce unless provided with seeds of S. media. Seeds of C. bursa-pastoris or a mixed diet are equally suitable diets for reproduction of Amara similata (Gyllenhal); a diet of insects or seeds of S. media is unsuitable. The results support the hypothesis that the species under investigation have specific food requirements, suggesting that seed feeding has evolved to different degrees in particular species: A. aenea is omnivorous, whereas A. familiaris and A. similata specialize on the seed of a particular plant species or family. This resource partitioning facilitates co-occurrence of carabid species.

Abstract: The carabid beetles Amara similata and Poecilus cupreus are abundant in Central European winter oilseed rape (OSR) fields and potential antagonists of OSR pests. Therefore, they were investigated in 29 OSR fields relative to the influence of field and landscape parameters on their nutritional condition, reproductive potential and activity density. Nutritional condition was measured by a condition factor (CF). Fecundity of female beetles was expressed by the number of ripe oocytes in the ovaries. Activity density comprised the number of individuals caught with pitfall traps during their peak of reproductive period. Soil productivity and pest abundance (as a proxy of local prey availability) were considered as field parameters. Landscape parameters comprised the distance to the next fallow and the percentage of crop area around each study field. In eight of ten cases, pest abundance proved to be the most important factor explaining carabid characteristics, indicating that P. cupreus and A. similata consume insect pests in OSR fields. Pest abundance influenced the CF of both species and sexes positively. Oocyte numbers of A. similata were negatively related to the distance to the next fallow. Oocyte numbers of P. cupreus tended to increase with increasing pest abundance. Activity density of female A. similata was negatively influenced by soil productivity. Activity density of male A. similata and of female and male P. cupreus was negatively influenced by pest abundance. When analysing exclusively the influence of severe OSR pests (Meligethes aeneus, Ceutorhynchus napi and Dasineura brassicae), abundance of larval M. aeneus and C. napi was most important in explaining the CF and activity density of male A. similata, and male and female P. cupreus. M. aeneus and C. napi could be an essential prey for the carabids studied which may reduce the pests, thereby contributing to the protection of OSR from pest herbivory.