Soluble low-molecular-mass protein isoforms were purified from chemosensory organs (antennae, tarsi and labrum) of the desert locust Schistocerca gregaria. Five genes encoding proteins of this group were amplified by PCR from cDNAs of tarsi and sequenced. Their expression products are polypeptide chains of 109 amino acids showing 40±50% sequence identity with putative olfactory proteins from Drosophila melanogaster and Cactoblastis cactorum. Direct structural investigation on isoforms purified from chemosensory organs revealed the presence in the expression products of two of the genes cloned. Two additional protein isoforms were detected and their molecular structure exhaustively characterized. MS analysis of all isoforms demonstrated that the four cysteine residues conserved in the polypeptide chain were involved in disulfide bridges (Cys29±Cys38 and Cys57±Cys60) and indicated the absence of any additional post-translational modifications. Immunocytochemistry experiments, performed with rabbit antiserum raised against the protein isoform mixture, showed selective labelling of the outer lymph in contact sensilla of tarsi, maxillary palps and antennae. Other types of sensilla were not labelled, nor were the cuticle and dendrites of the sensory cells. No binding of radioactively labelled glucose or bicarbonate was detected, in disagreement with the hypothesis that this class of proteins is involved in the CO 2 -sensing cascade. Our experimental data suggest that the proteins described here could be involved in contact chemoreception in Orthoptera.Keywords: chemosensory proteins; contact sensilla; disulfide bridges; Schistocerca gregaria; sequence analysis.Locusts and grasshoppers are major pests in agriculture. They have a solitary and a gregarious phase, characterized by different behaviour and morphological features [1]. All crop damage is caused by individuals in the gregarious phase.In the species Schistocerca gregaria, the shift from the solitary to the gregarious phase is preceded by an associating phase, triggered by volatile aromatic compounds, such as guaiacol, veratrol and phenylacetonitrile [2]. In the gregarious phase, the same chemicals, and perhaps related structures, induce aggregation of great numbers of individuals. Under these conditions this species becomes a plague and can destroy entire crops. Therefore, it is evident that these insects rely on chemical communication and that their populations could be controlled by the use of the appropriate chemical stimuli.Despite such pressing objectives, biochemical study of the olfactory system had been limited until recently to Lepidopteran species with large antennae. In the last few years, however, molecular biology techniques have made such research feasible in small insects of wider interest, such as Drosophila melanogaster. In this paper we report the isolation of soluble low-molecularmass proteins in antennae, tarsi and labrum of S. gregaria, their complete structural characterization by combined Edman degradation/MS procedures and the cloning of...

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We studied the parasitoid complex of\ud Bactrocera oleae Rossi (Diptera: Tephritidae) in\ud order to analyse the parasitism response to landscape\ud structure at different spatial extents. Olive fruits were\ud sampled and incubated in the laboratory for insect\ud emergence, thus allowing the calculation of parasitoid\ud emergence rates. A landscape analysis was performed\ud in five concentric buffers, ranging from 0.5 to 2 km\ud diameter around the sampling points. Woodland was\ud chosen as focal class. The percentage of landscape and\ud the splitting index, a measure of fragmentation, were\ud used to quantify landscape composition and configuration,\ud respectively. Significant effects of landscape\ud on parasitism rates were detected. In particular, the\ud percent parasitoid emergence was negatively affected\ud by the splitting index of woodland at a spatial extent\ud ranging from 1 to 2 km. These findings suggest that\ud landscape characteristics are likely to affect parasitoids\ud in well-structured agroecosystems as well. In\ud particular, connectivity at a large scale may favour\ud B. oleae parasitoids more than the abundance of\ud woodland. Potential implication

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