Comparative Behavioral and Protein Study of Salivary Secretions in Homalodisca spp. Sharpshooters (Hemiptera: Cicadellidae: Cicadellinae)
A novel brush-induced method to physically stimulate salivation was applied to the glassy-winged and smoke tree sharpshooters (Hemiptera: Cicadellidae: Cicadellinae). This technique enabled the direct observation of salivary secretion processes, solidification of saliva, and collection of salivary secretions. For both species, brush-induced saliva was first secreted in liquid form, a portion of which gradually solidified to form the salivary sheath for both sharpshooter species. Proteins of similar molecular weight were obtained from brush-induced saliva extracts from both sharpshooters. Extracts from dried sheaths collected from Parafilm membranes over artificial diet had a different protein profile from brush-induced saliva extracts. The latter contained fewer proteins than extracts of the liquid content of salivary glands. Two proteins appeared in all three of the extracts from hemolymph, salivary glands, and brush-induced saliva, one of which also appeared in dried sheath extracts. Our findings support previous research by others that there is a limited flow of protein from hemolymph to salivary glands and brush-induced saliva. There is also some protein modification associated with saliva solidification. The quantity and composition of proteins suggest the brush-induced saliva collection method has merit for future biochemical analyses of saliva. The implications of this work could potentially include illuminating the mechanism of inoculation by the Pierce's disease bacterium, Xylella fastidiosa.