Effect of different host substrates on hemipteran salivary protein profiles ∗

The chemical composition of the watery saliva of hemipteran (both homopteran and heteropteran) insects is crucial for effective feeding, because these insects rely heavily on saliva for extra-oral digestion (Cohen, 1995, 1996, 1998) or detoxification of defensive chemicals (Miles & Oertli, 1993). For phytophagous hemipterans, saliva can also be involved in plant injury. Yet, salivary composition has been studied in relatively few species, primarily aphids (Miles, 1999) and predaceous heteropterans (Cohen, 1995, 1998), and infrequently in direct relation to plant injury. Also, most studies have used homogenates or extracts of salivary glands coupled with colorimetric assays. Only a few studies have used electrophoretic methods to examine secreted saliva of hemipterans, e.g., aphids (Baumann & Baumann, 1995; Madhusudhan & Miles, 1998), a phytophagous heteropteran (Taylor & Miles, 1994), and some predaceous heteropterans (Cohen, 1990). Our goal was to determine whether changes in host substrates caused modification in the protein content within the secreted saliva of several hemipteran species. In particular, we were interested in comparing related species that cause different plant injuries, and to compare phytophagous and entomophagous