Abstract
The desert locust Schistocerca gregaria recognizes multiple chemical cues, which are received by olfactory sensory neurons housed in morphologically identifiable sensilla. The different sensillum types contain olfactory sensory neurons with different physiological specificities, i.e., they respond to different categories of chemical signals. The molecular basis for the sensilla-specific responsiveness of these cells is unknown, but probably based on the endogenous receptor repertoire. To explore this issue, attempts were made to elucidate whether distinct odorant receptors (ORs) may be expressed in a sensilla-specific manner. Analyzing more than 80 OR types concerning for a sensilla-specific expression revealed that the vast majority was found to be expressed in sensilla basiconica; whereas only three OR types were expressed in sensilla trichodea. Within a sensillum unit, even in the multicellular assembly of sensilla basiconica, many of the OR types were expressed in only a single cell, however, a few OR types were found to be expressed in a consortium of cells typically arranged in a cluster of 2–4 cells. The notion that the OR-specific cell clusters are successively formed in the course of development was confirmed by comparing the expression patterns in different nymph stages. The results of this study uncover some novel and unique features of locust olfactory system, which will contribute to unravel the complexity of locust olfaction.
Highlights
Locusts, like the desert locust Schistocerca gregaria, are characterized by a remarkable phase polyphenism and can switch between a solitarious and a gregarious phase (Van Huis et al, 2007; Pener and Simpson, 2009)
Riboprobes labeled by Biotin for the olfactory receptor co-receptor (Orco), a marker for insect olfactory sensory neurons (OSNs), were employed to visualize the ensemble of all sensory neurons in s. basiconica or s. trichodea, an example is depicted in Figure 1B indicating a large cluster of Orcopositive below a s. basiconica and a small cluster of Orcopositive cells below a s. trichodea
The results of the present study may contribute toward an understanding of the observation that morphologically identifiable sensilla on the antennae of the desert locust Schistocerca gregaria comprise OSNs, which respond to different categories of chemical signals (Ochieng’ and Hansson, 1999)
Summary
Like the desert locust Schistocerca gregaria, are characterized by a remarkable phase polyphenism and can switch between a solitarious and a gregarious phase (Van Huis et al, 2007; Pener and Simpson, 2009). In the gregarious phase, migrating locust swarms can cause severe agricultural and economic damages in the habituated areas like Africa and Asia (Roffey and Popov, 1968; Skaf et al, 2006; Simpson and Sword, 2008; Pener and Simpson, 2009). Besides tactile and visual stimuli, the sense of smell plays an important role in the life cycle and phase change of locusts (Ould Ely et al, 2006; Cullen et al, 2010; Maeno et al, 2011; Wang et al, 2015, 2019; Pregitzer et al, 2017).
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