Non-Apis bees are relevant pollinators of crops like rape, alfalfa, tomatoes, fruits and others. Poorly known, they often are more efficient in pollination than honeybees. Various bee species are specialized to certain plant species, nesting habitates and other environmental factors like microclimatic conditions. No wonder that many bee species are endangered today.

Systropha & Biastes 

There are two, rather rare species of spiral-horned bees in central-Europe, Systropha planidens and Systropha curvicornis (Halictidae). Mating behavior, reproductive biology and chemical communication were the aims of my studies of Systropha.

The common name "spiral-horned bees" derives from the fact that the males of both species have "coiled" antennae. The five distal flagellomeres are reduced in size and usually folded up to a three-cornered spiral as the REM scans show below (left: idle position of the male antenna; right: detail; below: artificially expanded).

Spiral-horned bees are solitary and nest in the ground. Females of both European species forage pollen exclusively on the lesser bindweed Convolvulus arvensis (Convolvulaceae). They therefore are so-called oligolectous, i.e. pollen foraging is restricted to only a few host plant species. A second bindweed species, Convolvulus cantabrica, has been reported to serve as a pollen source for the mediterranean region. Nearly 30 Systropha species have been described. All of them occur in the Old World and are expected to feed on Convolvulus resp. Convolvulaceae only. Exceptional among bees is the manner how females carry the pollen to the nest. For a full load they also use the upper parts of the metasoma. The photo right below shows a pollen-loaded female perched on a bindweed flower.

Males (photo left below) patrol Convolvulus flowers where they establish territories and wait for receptive females. Copulations then take place in the flowers. The males also regularely sleep in the flowers where they get completely enclosed in the afternoon and are hidden for the rest of the day and during night.

Both Systropha species are parasited by the cuckoo bee Biastes brevicornis (Apidae, Nomadinae). Cuckoo bees are cleptoparasites which neither build nests by themselves nor forage pollen for the larvae. The cuckoo females rather intrude nests of a host species and lay their eggs in provided cells. The cuckoo larva feeds from the pollen supply instead of the host larva which does not survive.

Like many other cuckoo bees, Biastes brevicornis is highly specialized on its host species (only Systropha bees). It has lost all hair structures important for pollen transport. Males and females of cuckoo bees have no nests of their own and during night therefore sleep above the ground on plants, blades of grass etc. typically bitten with their mandibles only. The photo right below shows both sexes of Biastes brevicornis doing so with the black male on the right. The female has a red metasoma (photo left below).

Andrena & Nomada 

Another solitary bee which I investigate is the sand bee Andrena danuvia (Andrenidae). This vernal bee is very common in the city of Austria´s capital Vienna, where it was originally described from. The drawing below shows nest aggregations in Vienna as mapped in 2003 (purple: district borders, N=nest holes, +=encounters of individuals where no nests were found). 

 The taxon Andrena danuvia is not verified yet but unlike the closely related Andrena cineraria its metasoma is intensely metallic blue (male on the photo left below). Regarding pollen sources this species is a generalist but in town has become facultatively oligolectous on flowers of maples (genus Acer, Aceraceae), the most common trees along the historic avenues of the city´s center.

Andrena danuvia also has its cuckoos: Nomada bees (Apidae, Nomadinae). Their common name "wasp bees" reflects their wasp-like colored habitus. In fact, they hardly can be distinguished from true wasps. The photo right above shows a female of Nomada goodeniana at an aggregation site of Andrena danuvia. Such aggregations sometimes contain more than 3500 nest entrances.

Further investigations are planed to prove the species status of Andrena danuvia and the existence of (precopulatory) isolation from the (sibling?) species Andrena cineraria through visual and chemical cues. Additionally, I am interested in chemical communication between host and parasite species, especially in which semiochemicals are used in host (nest) recognition by Nomada cuckoos.

Publications:

Fraberger, R. & Ayasse, M. (1996): Male reproductive behaviour in two species of Systropha bees (Halictidae). Proc. XX. Int. Congr. Entomol., Firenze, p. 380

Fraberger, R. (1998): Paarungsverhalten, Brutbiologie und chemische Kommunikation der heimischen Spiralhornbienen-Arten Systropha planidens und S. curvicornis und ihres Brutparasiten Biastes brevicornis (Hymenoptera: Halictiade, Anthophoridae). Diplomarbeit, Univ. Wien, engl. Summary, pp. 1-119

Fraberger, R. (2005): Bionomie der Sandbiene Andrena danuvia Stöckhert 1950 (Hymenoptera, Andrenidae) und aktuelle Vorkommen in Wien (Bionomics of the vernal bee Andrena danuvia and nest aggregations in the city of Vienna). Linzer biol. Beitr. 37 (2): 1481-1499 

Fraberger, R. et al. (in prep.): Female odor bouquets in the European spiral-horned bees, Systropha planidens and S. curvicornis (Hymenoptera: Halictidae): chemical compounds, ontogenetic modulations and species-specific differences.

Fraberger, R. et al. (in prep.): Antennal response in the cuckoo bee Biastes brevicornis (Hymenoptera: Apidae, Nomadinae): evidence for chemical signals of female hosts and pollen in host nest recognition.

©All photos belong to Raphaelo Fraberger and are not authorized for private and any other use.

A-1090 Vienna, Austria