Odor perception in three Coleoptera: molecule, receptor & neuron

Sammanfattning: In this thesis, the sense of olfaction and its links to behavior was studied in the cetoniid chafers Pachnoda interrupta and P. marginata, and the bark beetle Ips typographus. P. interrupta is a pest on sorghum in Ethiopia, and I. typographus is a spruce pest in the palearctic, and an aim was to uncover new control methods. In I. typographus, the olfactory receptors (ORs) that determine response specificity in olfactory receptor neurons (ORNs) were investigated. Phylogenetic analysis showed that I. typographus and Tribolium castaneum ORs form a Coleoptera-specific subgroup. At the next level of the olfactory system, ORN response to food odorants was compared between P. interrupta and P. marginata. Both are opportunistic polyphages on fruits and flowers, but are present in disparate habitats. P. interrupta is found in savannah, and P. marginata in tropical Africa. The two species showed a high degree of overlap in their ORN arrays, indicating that a similar sensory strategy for food search is viable in both habitats. Field trapping with compounds eliciting strong ORN response identified a powerful attractant for P. interrupta, 2,3-butane diol. In a P. interrupta study, coupled gas chromatographic-electroantennographic detection identified antennally active compounds from sorghum, Sorghum bicolor, and another food host, Abutilon figarianum. Field tests indicated that single compounds (e.g. methyl salicylate) were more important than mixtures in attraction to these two hosts. Field studies of mating and aggregation in P. interrupta showed that unmated females were attractive to males, and to both sexes when combined with food. Female-specific compounds were identified by mass spectrometric comparison of male and female extracts. Field tests of these established that phenylacetaldehyde was highly attractive to both sexes, implying that it is part of the P. interrupta pheromone. These findings create novel possibilities for control. Phenylacetaldehyde and attractive food compounds could be used for mass trapping of P. interrupta. The identified I. typographus ORs make a search for pheromone and repellent receptors possible. Compounds that hyper-excite these receptors could be used for mass trapping or disruption of host search.