Dieter Wittmann

Robber bees (Lestrimelitta limao) and their host chemical and visual cues in nest defense byTrigona (Tetragonisca) angustula (Apidae: Meliponinae)

The nest of the stingless bee,Trigona (Tetragonisca) angustula, is guarded by bees positioned in the nest entrance and others hovering in front of it. Hovering guard bees track returning foragers sideways along the last 10 cm in front of the nest, but intercept and incapacitate nest intruders by clinging with mandibles to wings and legs. When attacked by the cleptobiotic stingless beeLestrimelitta limao, the colony strengthens its aerial defense with hundreds of additional hoverers. To test our hypothesis that this reaction is due to interspecific chemical communication based on kairomone effects, we presented synthetic cephalic volatiles of both species at the nest entrance and counted the number of bees leaving the nest and taking up hovering positions. We conclude that guard bees recognizeL. limao by the major terpenoids of their volatile cephalic secretions, geranial, neral (=citral) and 6-methyl-5-hepten-2-one; other components may fine-tune this recognition. The effect of chemical stimuli is not significantly enhanced by combination with a dummy ofL. limao. Guard bees, we hypothesize, respond to this kairomone by secreting a species specific alarm pheromone; a major component of this pheromone, benzaldehyde, recruits additional bees to defend the nest.

Nest architecture and distribution of the primitive stingless bee, Mourella caerulea (hymenoptera, apidae, meliponinae): Evidence for the origin of plebeia (s. lat.) on the gondwana continent∗

The stingless bee Mourella caerulea is distributed in the subtropical parts of Brazil, Argentina and Paraguai. In the Serra do Sudeste of Rio Grande do Sul, on the southern part of the Brazilian shield, this species is one of the most abundant meliponine bees. Nests of M. caerulea are built in the soil and exhibit architectural characters typical to all other genera of obligatory ground nesting species, like Schwarziana, and the African genera Meliple‐beia, Plebeiella and Plebeina. The possibility that the similar solutions for the construction of subterranean nests in these genera did not evolve by convergence or parallelism is discussed. The occurence of Mourella together with other more primitive representatives of the Plebeia group on the southern parts of the Brazilian Shield cannot be explained by biogeographic models proposed by some authors. Adopting an alternative model we suggest that, during the lower Cretaceous, ancestor populations of the Pleibeia‐ line inhabiting the meridional shields of We...

Nectar dehydration by male carpenter bees as preparation for mating flights

SummaryFemales of all social and many solitary bees dehydrate nectar before storing it or adding it to larval provisions. Nectar dehydration by males has rarely been documented. We report on the neotropical facultatively social carpenter bee Xylocopa nigrocincta, in which the nest constant males are fed nectar by their female nestmates. Males dehydrate the nectar at the nest entrance before leaving the nest for mating territories. We show that males thereby minimize their water load, resulting in an improvement of their energy budget during hovering flights in their territories. Males can prolong the duration of territorial flights if they cany highly concentrated nectar. We assume that nectar dehydration as a pre-mating behavior is not correlated with the social organization in Xylocopa species. However, the behavior is particularly weil-developed in X. nigrocincta, where during the mating period males remain integrated in the nest society and are fed by their mothers and sisters.

Visually controlled station-keeping by hovering guard bees ofTrigona (Tetragonisca) angustula (Apidae, Meliponinae)

Summary1.Guard bees of the stingless beeTrigona (Tetragonisca) angustula typically hover in very stable positions on both sides of and close to the nest entrance; for most of the time they face the flight corridor or the nest entrance (Fig. 2). Individual bees occupy a distinct airspace which they can leave for short excursions but return to afterwards (Fig. 3). When they change their position, they adjust their body-axis orientation to keep the nest entrance within their frontal visual field (Fig. 4). The accuracy of station-keeping decreases with the distance from the nest (Fig. 5).2.Guard bees stay tightly coupled to the nest when the whole nestbox is oscillated through 20 cm forward and sideways with respect to the direction in which the nest entrance is pointing. They hold their position and distance relative to the nest entrance by flying forward, backward and sideways while keeping the angular orientation of their body long axis constant for most of the time (Figs. 6, 7). They temporarily lag behind the nest movement when they actively change their angular orientation or when the nest moves away from them. After the movement of the nest stops, bees which have lagged behind regain hovering stations close to the nest (Fig. 8).

Nest Architecture, Nest Site Preferences and Distribution of Plebeia wittmanni (Moure & Camargo, 1989) in Rio Grande do Sul, Brazil (Apidae: Meliponinae)

The new species of stingless bees, Plebeia wittmanni, was found during a four years survey of the bees of Rio Grande do Sul, Southern Brazil. Bees of this species construct their nests in cavities of rocks. As the brood nest is not surrounded by an involucrum, the nest architecture can easily be disintegrated and parts of the nest can be built wherever space is available in a crack. Apparently cracks and crevices in granite rocks provide preferable nesting sites. The distribution of P. wittmanni in Rio Grande do Sul suggests that its dispersal is closely related to the occurrence of appropriate rocks, especially granite. In other areas this species was observed as culture follower, nesting in cracks in walls.

Progressão da floração e antese de Allium cepa L. (Alliaceae) em Candiota, RS, Brasil

The necessity for pollination by insects depends on the morphology of the flower, the degree of self-fertility and the arrangement of the flowers. We studied the progression of the flowering of Allium cepa L., by measuring the frequency of visits by Apis mellifera L., the anthesis phase and pollen viability. The flowering period in the cultivar Crioula (56 days) was longer than in Bola Precoce (50 days). The duration of the peak of flowering was similar in both cultivars, 15 and 17 days respectively. The correlation between the frequency of visits by A. mellifera and the number of umbels with open flowers was high in Crioula and average in Bola Precoce. The anthesis occured at 7 and 8 days respectively in the two cultivars. Contrary to other observations, we have verified incomplete protandry in both cultivars. Stigmas were receptive when the styles had reached a length of 4-5.5 mm. The average percentage of pollen viability was 90.46 (Crioula) and 80.25 (Bola Precoce).