Host recognition in a pollen-specialist bee: evidence for a genetic basis

To investigate the effect of larval pollen diet on floral choice in a specialized bee species, we compared the floral preferences of individuals of Heriades truncorum (Megachilidae) reared on host pollen with those of individuals reared on two different types of non-host pollen. Females were allowed to nest in cages where both host and non-host flowers were available. All females, regardless of larval diet, restricted pollen collection to their host, although they visited the flowers of both host and non-host plants for nectar. When offered only the non-host pollen source, females ceased nesting activities. Males reared on non-host pollen exclusively restricted their patrolling flights to flowers of their normal host. This study provides the first empirical investigation of the imprinting theory in oligolectic bees, and unambiguously suggests that host recognition has a genetic basis in H. truncorum. We discuss the implication of this finding for the understanding of bee-flower relationship

Nesting in bark – the peculiar life history of the rare boreoalpine osmiine bee Osmia (Melanosmia) nigriventris (Hymenoptera, Megachilidae)

Osmia (Melanosmia) nigriventris (Zetterstedt) is a predominantly boreoalpine megachilid bee species, whose biology is poorly known due to its pronounced rarity all over Central Europe. The discovery of 19 nests in the Grisons and Valais (Switzerland) allowed for the investigation of its nesting biology and prompted the assessment of the species’ host-plant spectrum, phenology and distribution. All nests were in thick bark pieces of Larixdecidua, which lay in grassy vegetation on sun-exposed ground of open subalpine forests dominated by larch. The nests contained 1–26 brood cells constructed within one to several burrows tunneled out by the female bees with their specialized mandibles, which are distinctly stronger than those of related O. (Melanosmia) species known to nest in preexisting cavities or loose soil. The linearly arranged brood cells were separated from each other by three-layered partitions consisting of an interlayer of densely packed small bark particles sandwiched between two thin layers of chewed green leaves (“leaf pulp”). DNA metabarcoding of several nest plugs revealed that Potentilla (Rosaceae) and Helianthemum (Cistaceae) served as source of the leaf pulp. Anthraxanthrax (Bombyliidae) and Sapygasimilis (Sapygidae) parasitized the brood cells of O.nigriventris as shown by DNA barcoding of prepupae overwintering in the host’s nests. O.nigriventris is mesolectic and harvests pollen almost exclusively on Fabaceae (e.g. Lotus, Hippocrepis), Ericaceae (Rhododendron, Vaccinium) and Cistaceae (Helianthemum). Depending on the altitude, O.nigriventris emerges from the beginning of May to the first decade of June and thus qualifies as an early flying bee active in spring and early summer similar to the other European O. (Melanosmia) species. It likely needs two years for its development in the subalpine zone of the Alps and overwinters as prepupa in the first and probably as imago in the second winter. O.nigriventris has a Holarctic distribution, its disjunct Palaearctic range encompasses the boreal zone from Scandinavia eastwards to the Russian Far East, the Caucausus, the Alps as well as scattered locations at lower altitudes throughout Central Europe, where it is regarded as a glacial relict and has probably suffered strong declines during the last decades

Recruitment dynamics of the grove-dominant tree Microberlinia bisulcata in African rain forest: extending the light response versus adult longevity trade-off concept

In groves of ectomycorrhizal caesalpiniaceous species in the Atlantic coastal forest of Central Africa the dominant tree Microberlinia bisulcata, which is shade-intolerant as a seedling but highly light-responding as a sapling, shows very limited regeneration. M. bisulcata saplings were mapped in an 82.5-ha plot at Korup and found to be located significantly far (>40m) away from adults, a result confirmed by direct testing in a second 56-ha plot. Sapling growth over 6years, the distribution of newly emerging seedlings around adults, recruitment of saplings in a large opening and the outward extent of seedlings at the grove edge were also investigated. Two processes appear to have been operating: (1) a very strong and consistent restriction of the very numerous seedlings establishing after masting close to adults, and (2) a strong but highly spatially variable promotion of distant survivors by increased light from the deaths of large trees of species other than M. bisulcata (which itself has very low mortality rate). This leads to an apparent escape-from-adults effect. To maintain saplings in the shade between multiple short periods of release ectomycorrhizal connections to other co-occurring caesalp species may enable a rachet-type mechanism. The recorded sapling dynamics currently contribute an essential part of the long-term cycling of the groves. M. bisulcata is an interesting example of an important group of tropical trees, particularly in Africa, which are both highly light-demanding when young yet capable also of forming very large forest emergents. To more comprehensively explain tropical tree responses, the case is made for adding a new dimension to the trade-off concept of early tree light-response versus adult longevit