Sweet taste cells play critical roles in food selection and feeding behaviors. Drosophila sweet neurons express eight gustatory receptors (Grs) belonging to a highly conserved clade in insects. Despite ongoing efforts, little is known about the fundamental principles that underlie how sweet tastants are detected by these receptors. Here, we provide a systematic functional analysis of Drosophila sweet receptors using the ab1C CO2-sensing olfactory neuron as a unique in vivo decoder. We find that each of the eight receptors of this group confers sensitivity to one or more sweet tastants, indicating direct roles in ligand recognition for all sweet receptors. Receptor response profiles are validated by analysis of taste responses in corresponding Gr mutants. The response matrix shows extensive overlap in Gr–ligand interactions and loosely separates sweet receptors into two groups matching their relationships by sequence. We then show that expression of a bitter taste receptor confers sensitivity to selected aversive tastants that match the responses of the neuron that the Gr is derived from. Finally, we characterize an internal fructose-sensing receptor, Gr43a, and its ortholog in the malaria mosquito, AgGr25, in the ab1C expression system. We find that both receptors show robust responses to fructose along with a number of other sweet tastants.Like hormone receptors and neuroreceptors, ORs recognize biologically meaningful chemical ligands, and shape responses of olfactory sensory neurons (OSNs), thus regulating many behaviors. Reading errors on the part of ORs may have deleterious consequences for species propagation; therefore, we should expect odorant-selectivity to be a key feature of olfactory systems. Early electrophysiological studies proposed that OSNs could be classified as “specialists” which responded to pheromone components or “generalists” which responded to host or plant odors Insect olfactory receptor (OR) genes belong to a distinct gene family encoding heteromeric (Neuhaus et al., 2005; Lundin et al., 2007; Smart et al., 2008) ligand-gated ion channels comprised of a variable sensing component and an obligatory co-receptor, named Orco .....Insect olfactory receptors (ORs) detect chemicals, shape neuronal physiology, and regulate behavior. Although ORs have been categorized as “generalists” and “specialists” based on their ligand spectrum, both electrophysiological studies and recent pharmacological investigations show that ORs specifically recognize non-pheromonal compounds, and that our understanding of odorant-selectivity mirrors our knowledge of insect chemical ecology. As we are progressively becoming aware that ORs are activated through a variety of mechanisms, the molecular basis of odorant-selectivity and the corollary notion of broad-tuning need to be re-examined from a pharmacological and evolutionary perspective.PLANTAS GASTAM ENERGIA EM METABOLITOS SECUNDÁRIOS QUE NÃO PARECEM NENHUMA FUNÇÃO ANTI-HERBIVORIA ....67% DOS INSECTOS CONHECIDOS E DOS DESCONHECIDOS TAMBÉM SÃO FITÓFAGOS DESENVOLVENDO POR ISSO UMA SÉRIE DE RECEPTORES ALTAMENTE EFICIENTES NA DETECÇÃO DE PLANTAS ...COMO A Pieris brassicae e as couves QUIMIORECEPTORES ALTAMENTE ESPECIALIZADOS PLANTAS ACUMULAM ENERGIA PARA A REPRODUÇÃO NÃO TÊM ESTRATÉGIAS DE FUGA NUNCA SAEM NOS FINS DE SEMANA E RARAMENTE VÃO A ALGUM LADO DE LIVRE VONTADE ...LOGO DESENVOLVEU DEFESAS QUÍMICAS CONTRA OS ASSALTANTES DAS SUAS RESERVAS ...RESERVE RAIDERS ? NO...Odor Detection in Insects: Volatile Codes M. de Bruyne & T. C. Baker Received: 27 March 2008 /Revised: 23 April 2008 /Accepted: 28 April 2008 / Published online: 6 June 2008 # Springer Science + Business Media, LLC 2008 Abstract Insect olfactory systems present models to study interactions between animal genomes and the environment. They have evolved for fast processing of specific odorant blends and for general chemical monitoring. Here, we review molecular and physiological mechanisms in the context of the ecology of chemical signals. Different classes of olfactory receptor neurons (ORNs) detect volatile chemicals with various degrees of specialization. Their sensitivities are determined by an insect-specific family of receptor genes along with other accessory proteins. Whereas moth pheromones are detected by highly specialized neurons, many insects share sensitivities to chemical signals from microbial processes and plant secondary metabolism. We promote a more integrated research approach that links molecular physiology of receptor neurons to the ecology of odorants..

Although it is the brain that transforms a set of chemical
stimuli comprised of individual odorants (chemicals) into
distinct odors (sensations) and associates them with a
behavioral response, the ORNs are the sensors that limit
what can be detected. The scope and accuracy with which
odors can be identified is determined by how many
different sensors there are and how they are tuned to
different chemicals. Insect ORNs are bipolar neurons that
develop from epithelial cells (Keil 1997). In early development,
a pre-sensillum cluster of cells is formed (Ray and
Rodrigues 1995; Endo et al. 2007). Some of these will
move basally and become neurons, but three remain apical
and form the accessory cells that will wrap themselves
around the neurons. While it is the neurons that process
odor information, accessory cells provide the extracellular
milieu that supports their function (Park et al. 2002). These
cells form sensilla, small cuticular structures where the
neuronal dendrites are bathed in a lumen filled with mucuslike
sensillum lymph (Zacharuk 1985). Pores in the cuticle
allow odorants to pass and dissolve in the lymph
(Steinbrecht 1997).
The majority of olfactory sensilla can be found on the
antennae, but smaller sets are also located on other head
appendages such as maxillary (de Bruyne et al. 1999) or
labial palps (Stange 1992; Kwon et al. 2006). Irrespective
of their location, all ORNs project to the antennal lobe of
the brain. Olfactory sensilla fall into two ultrastructural
categories, double walled (dw) and single walled (sw;

Antennation is a behaviour frequently described before mating or egg laying. The precise
role of contact chemoreceptors in this kind of behaviours is however, unknown. For a
conclusive interpretation of our data on the neuronal coding and central representation of taste 
information from the antennae, the involvement of antennal gustatory receptors in mating
behaviour, host-plant detection and oviposition and their possible interactions with olfactory
receptor neurons remains to be investigated.
A scanning electron microscopic study showed no sexual dimorphism in the distribution
of taste sensilla on the antennae. Mass fills of antennal afferents and backfills of individual
contact chemoreceptive sensilla using Neurobiotin revealed 4 distinct projection areas of
antennal gustatory sensilla. Two areas are within the deutocerebrum: the antennal motor and
mechanosensory centre (AMMC) and a region situated posteriorly to the antennal lobes. The
two other areas are in the tritocerebrum/suboesophageal ganglion complex. As our
electrophysiological investigations showed that different neurons in the same sensillum
respond to different stimuli, including mechanical stimuli for one of the neurons, it can be

hypothesized that the projection areas are functionally distinct