Encoding of plant odour information in insects: peripheral and central mechanisms

Abstract

Insects are suitable model organisms for studying mechanisms underlying olfactory coding and olfactory learning, by their unique adaptation to host plants in which the chemical senses are essential. Recent molecular biological studies have shown that a large number of genes in insects and other organisms are coding for olfactory receptor proteins. In general, one receptor type seems to be expressed in each neurone. The functional characterisations of olfactory receptor neurones have been extensive in certain insect species, demonstrating a fine-tuning of single neurones to biologically relevant odourants; both insect and plant produced volatiles. Stained neurones of the same functional type have been shown to project in one and the same glomerular unit in the primary olfactory centre, the antennal lobe. This corresponds to molecular biological studies, showing projections in one glomerulus by neurones expressing the same receptor type. Comparison of these findings with physiological and morphological characterisations of antennal lobe neurones has indicated correspondence between input and output of the glomerular units. Examples are presented from studies of heliothine moths. From the antennal lobe, the olfactory information is further conveyed to the mushroom bodies, particularly important for learning, and the lateral protocerebrum, a premotoric area. The three brain areas are regions of synaptic plasticity important in learning of odours, which is well studied in the honeybee but also in species of moths.

The Relevance of Background Odor in Resource Location by Insects: A Behavioral Approach

“…The question of how complex odor mixtures are perceived and further processed in the brain of insects and vertebrates has been addressed in several reviews in the last several decades (e.g., Stone 1966, Visser 1986, Masson and Mustaparta 1990, Smith and Getz 1994, Hildebrand and Shepherd 1997, Galizia and Menzel 2000, Mustaparta 2002, Wilson and Stevenson 2003, Ache and Young 2005, Wilson and Mainen 2006. The combination of RIO and habitat background odor may result in a new odor gestalt due to synergistic or antagonistic inter actions between components at different levels of odor perception and integration, which are attributable to the kinetics of the dose-response curves and the kinetics of ligand-receptor binding (Hildebrand and Shepherd 1997, Getz 1999, Duchamp-Viret et al 2003.…”

Coding and interaction of sex pheromone and plant volatile signals in the antennal lobe of the codling moth Cydia pomonella

“…In male moths, pheromone information is relayed to the macroglomerular complex (MGC), a group of large, sexually dimorphic glomeruli, whereas environmental odour, including plant volatile, information is relayed to a larger number of sexually isomorphic, ordinary glomeruli (OGs) (Anton and Hansson, 1995;Mustaparta, 2002). Despite the apparent morphological separation of the two pathways, processing of pheromones and other olfactory information is not qualitatively different.…”

Behavioral and neurophysiological responses of an insect to changing ratios of constituents in host plant-derived volatile mixtures

“…Adult females perceive these odors via specialized olfactory receptor neurons, and use the volatiles as chemical cues to identify suitable plants for feeding and/or oviposition (Anton et al, 2007;Cardé and Willis, 2008;Mustaparta, 2002). Volatile blends differ between plant species both qualitatively and quantitatively (Baldwin et al, 2006;Bruce et al, 2005;Dötterl et al, 2005).…”