A COMPARATIVE STUDY OF HOST RECOGNITION AND THE SENSE OF TASTE IN LEPTINOTARSA

Summary Three species of Leptinotarsa beetles (L. decemlineata, L. texana and L. haldemani) with different host plant specificity were studied using behavioural and sensory physiological measures in an attempt to determine whether responses from chemosensory cells in the galeal sensilla of adult beetles vary with host plant preference in an understandable manner. Saps from leaves of Solarium tuberosum, S. elaeagnifolium, S. dulcamara and Lycopersicon esculentum were used as sensory stimuli. Behavioural observations were made on newly emerged adults and approach time, exploration time and number of bites in the first minute of the first meal were recorded. Number of bites in the first minute of the first meal differed across the four plant species for the three beetle species. For L. decemlineata and L. texana, sensory responses from cells in the galeal sensilla showed differences across plant species that could be related to host preference. It is suggested that at least two general types of sensory coding may be involved in host recognition by beetles in this genus. First, a 'coarse-grained' code based on degree of variability of input may operate to help the insect distinguish nonsolanaceous plants from solanaceous ones. Second, a 'fine-grained' code may help distinguish host from non-host within the family Solanaceae or perhaps within the genus Solarium. This fine-grained code may have elements of both the labelled line and across-fibre pattern codes discussed in the literature.