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IntraceLlular responses to olfactory signals (three components and the combination of mixtures which they can provide) of 90 morphological identified local and output interneurones of the bee antennal lobe (the so-called Homo LIN, Hetero LIN, Pluri ON and Uni ON) were analysed and classified into eight main categories of response profiles. The different morphological types exhibit differences m (i) background activity; (ii) response patterns; and (iii) selectivity and responsiveness to pure odours and mixtures. The results demonstrate that the responses to mixtures are unpredictable from the responses to the single components. Olfactory integration includes inhibitory processes. Results of the present work considered together with those related to the morphological and spatial aspects demonstrate that the antennal lobe layer of the bee olfactory neuronal network is characterized by a complex architecture and connectivity underlying highly complex and somewhat unpredictable intracellular responses.

Wholemount analysis with optic and confocal microscopy of iontophoretic ally stained (cobalt or Lucifer Yellow) bee antennal lobe interneurones led us to identify and classify four main types of olfactory responsive neurones, differing in their morphology and spatial distribution within the glomerular space and amongst the glomeruli in the whole antennal lobe. Two types of local interneurones (LIN), restricted to the antennal lobe were: (i) Homo LIN presenting an apparently similar density of arbors among all the glomeruli where they branch, the fine neurites being limited to the core of the glomeruli; (ii) Hetero LIN, also pluriglomerular, differ from the Homo LIN by a high dense neurite arborization in one particular glomerulus with fine branches invading the core and reaching the outermost part of this glomerulus. Two types of output interneurones (ON) having dendrites in the antennal lobe and axons projecting in other brain parts were: (i) Uni ON with dendrites invading the core and periphery of only one glomerulus; (ii) Pluri ON, pluriglomerular, with dendrites limited to the glomerular cores. The Uni ON axons follow the median tract and project to the mushroom bodies and lateral lobe of the protocerebrum. On the contrary, axons of Pluri ON follow several subtracts of the antenno-glomerular tract and project to various protocerebal structures or to the contralateral antennal lobe. Local interneurones and output interneurones both invade many glomeruli (1/3 to 2/3 and >50% of the total number, respectively), most being distributed in the different glomerular populations. The high complexity demonstrated in the architecture of the bee antennal lobe neurones might support the high functional complexity described elsewhere (Fonta a al., 1991; Sun et al., submitted).

Volatile chemicals are known to be essential factors that trigger or release different kinds of bumble- bees (Bombus sp.) behaviour, in intraspecific and interspecific relationships. Chemical analyses of the in- volved semio-chemicals are now in progress, and in parallel we have studied the nervous bases of identified odour recognition, for both males and females (queens and workers) of B. hypnorum and B. terrestns. The insects' antennae are provided with the sensory equipment for the detection of volatile compounds; the distribu- tion of placodea-type olfactory sensilla was studied by scanning electron microscopy. Responses of antennal sensory cells to floral and pheromonal components were recorded (EAG). Queens present the most numerous sensillar population and the highest amplitudes in EAG responses. These results might be linked to the polymor- phism of the body size and therefore to the antennal size of the three kinds of insects, the queens being the biggest in this insect population. Odour sensitivity depends on the molecular weight and the chemical func- tion of the tested molecules and appears to be higher for some floral compounds such as vanillin and pheromonal derivatives such as farnesol.