Orco¹ homozygous adults exhibit a significantly decreased preference for apple juice in olfactory trap assays, as compared to controls.

The adult olfactory receptor neurons of Orco¹ homozygotes are electrophysiologically silent; neurons additionally expressing Orco^UAS.mCherry, Orco^{CBSΔ.UAS.mCherry}, Orco^{W341Δ.UAS.mCherry} or Orco^{RH344EE.UAS.mCherry} under the control of Scer\GAL4^{Orco.2.642.Hsim\VP22} show an apparently normal dendritic morphology, as compared to controls.

In olfactory preference assays for polyamines, Orco¹/Orco¹ flies do not show any significant difference in their attraction to putrescine or cadaverine, as compared to wild type, and females do not show any significant difference in their aversion to oviposit on polyamine-rich substrate (plain, sugar-free 1% agarose supplemented with either putrescine or cadaverine) versus non-supplemented substrate, as compared to wild type.

Orco¹/Orco² mutants are anosmic and do not display 'weathervaning' (modulation of direction in response to chemotaxis).

Expression of Orco^{Scer\UAS.T:Avic\GFP} in one olfactory sensory neuron, under the control of Scer\GAL4^Or42b.PF and in an Orco¹/Orco², reduces the strength of 'weathervaning' in chemotaxis, compared to wild-type larvae with bilateral function. These larvae exhibit the reorientation bais observed in wild-type.

Homozygous Orco¹ mutant larvae do not have altered preference for larval-treated substrate, compared to controls.

As in wild type, Orco¹/Orco² mutant males exhibit inhibition of the female contact-induced male-male aggression seen in wild type males that have previously been exposed to females.

Orco¹/Orco¹ Or22-expressing olfactory neurons show a lack of response following odorant stimulation with ethyl butyrate.

In contrast to wild type, homozygous and Orco¹/Orco² flies do not show a preference for ethanol-containing food odors (over food odors without ethanol) in an olfactory choice assay. Homozygous flies prefer food odors over water, and ethanol over water. They show a reduced preference for food vs water compared to wild-type controls.

The social space index of mutant flies is not significantly different from wild-type controls.

Larvae with olfactory input restricted to the Or42a-expressing olfactory receptor neurons (expressing Orco^Scer\UAS.cLa under the control of Scer\GAL4^Or42a.PF in a Orco¹/Orco¹ background) follow a concentration path distant from the odour source in an assay to study the response to a stable gradient of the odour ethyl butyrate (30mM odour source). To orbit around the source in this way, the mutant larvae implement small-amplitude turns, which maintain their bearing close to 90[o]. Turns are triggered in the mutant larvae at odour concentrations three times lower than those that trigger turns in the wild type. The targeted concentration does not coincide with the region where the amplitude of the concentration gradient is maximal. In contrast to wild type, turns in the mutant larvae are preceded by episodes where the bearing remains constant. For a low-concentration odour source (7.8mM), the mutant larvae show attraction throughout the odour gradient's range and accumulate near the source. For a high-concentration odour source (125mM), the mutant larvae navigate up-gradient, before they bifurcate to avoid regions of high odour intensities. In contrast, wild-type larvae display invariant attraction to low and high concentrations. The mutant larvae turn towards the gradient for concentrations lower than 0.5μM, but turn away from the gradient at higher concentrations.

Larvae with olfactory input restricted to a single unilateral Or42a-expressing olfactory receptor neuron (expressing Orco^{Scer\UAS.T:Avic\GFP} under the control of Scer\GAL4^Or42a.PF in a single olfactory receptor neuron in a Orco¹/Orco² background) navigate poorly and show tortuous paths in an assay to study the response to a stable gradient of the odour ethyl butyrate, failing to robustly orient towards the gradient.

Orco¹ mutants do not respond to either 2-methylpyrazine or 2-ethylpyrazine.

Homozygous flies show a stronger avoidance response to a number of carboxylic acids (acetic acid, propionic acid and butyric acid) than do control flies in a T-maze choice assay.

Homozygous flies show a stronger avoidance response to pyridine and to 2-3-butanediol than do control flies in a T-maze choice assay.

Homozygous flies show a weaker avoidance response to butyraldehyde than do control flies in a T-maze choice assay.

Homozygous flies show a significant attraction response to ammonia in a T-maze choice assay.

Homozygous flies show a significant attraction response to pentyl acetate in a T-maze choice assay, in contrast to wild-type flies which show an avoidance response to this odour.

Orco¹ mutant flies do not exhibit a difference in beer preference compared to wild-type flies. Orco¹ flies, with the antennae surgically removed (so removing other ionotropic receptors) still display a preference for beer, although at a reduced level.

Or83b¹ mutants cannot detect attractive odorants.

Or83b¹ flies exhibit a normal ethanol-induced olfactory startle response.

Or83b¹ flies exhibit reduced ethanol-induced hyperactivity during the first ethanol exposure, but an increase in locomotor activity upon repeated ethanol exposure compared to controls. Ethanol sedation sensitivity or sedation tolerance is not affected.

Homozygous and Orco¹/Df(3R)ED5156 flies significantly reduced avoidance of citronellal in a direct airborne repellent test (DART) assay.

Mutant flies show a significantly reduced avoidance of benzaldehyde in a DART assay.

ab11 olfactory receptor neurons do not respond to10% citronellal in mutant flies, in contrast to wild type.

Mutants are not able to discriminate between 1-octen-3-ol and 3-octanol, and neither odour is learnable by the mutants in a one-odour training, one-odour test task. The mutant larvae do not show any preference towards either odour after either one-odour or two-odour training.

Male flies show a reduction in male-male aggression (a significant reduction in lunging behaviour) compared to controls.

Orco¹/Orco² mutant larvae direct turns towards and away from the peak of the gradient with equal probability in an assay to study the response to an exponential gradient of the odorant isoamyl acetate, in contrast to wild-type larvae, which direct more than 63% of turns towards the gradient.

Larvae with olfactory input restricted to the Or42a-expressing olfactory sensory neurons (expressing Orco^Scer\UAS.cLa under the control of Scer\GAL4^Or42a.PF in a Orco¹/Orco² background) are more sensitive to isoamyl acetate than wild-type animals in an assay to study the response to a radially symmetrical odour gradient, showing significant responses to the odour at source concentrations as low as 0.12M. Mutant and wild-type larvae navigate efficiently along the odorant line (from low to high odorant concentration) in an assay to study the response to an exponential odorant gradient, in response to either isoamyl acetate, isopropyl acetate, 2-hexenal or anisole.

Or83b¹/Or83b² Or67d-expressing olfactory sensory neurons show severely decreased spontaneous activity compared to control neurons.

The frequency of close-proximity encounters at night and in the early morning between male-female pairs (isolated from other flies and entrained to a 12:12 LD cycle) is significantly reduced in Or83b¹ homozygous animals.

Olfactory sensory neuron morphology and membrane organization appear normal in Or83b¹/Or83b² mutants.

Or83b¹ larvae do not respond to odours to which wild-type larvae respond with strong chemotaxis.

Or83b¹ larvae fail to respond to 34 odours and weakly respond to a further 2 odours that wild-type larvae chemotax towards. Or83b¹ adults show severely impaired responses to acetoin and are anosmic to 2-phenylethanol.