<Tr> <Td> Sternorrhyncha </Td> <Td> 12,500 </Td> <Td> Upper Permian </Td> <Td> aphids, whiteflies, scale insects </Td> <Td> plant - sucking bugs, some major horticultural pests; most are sedentary or fully sessile; </Td> </Tr> <P> The defining feature of hemipterans is their "beak" in which the modified mandibles and maxillae form a "stylet" which is sheathed within a modified labium . The stylet is capable of piercing tissues and sucking liquids, while the labium supports it . The stylet contains a channel for the outward movement of saliva and another for the inward movement of liquid food . A salivary pump drives saliva into the prey; a cibarial pump extracts liquid from the prey . Both pumps are powered by substantial dilator muscles in the head . The beak is usually folded under the body when not in use . The diet is typically plant sap, but some hemipterans such as assassin bugs are blood - suckers, and a few are predators . </P> <P> Both herbivorous and predatory hemipterans inject enzymes to begin digestion extraorally (before the food is taken into the body). These enzymes include amylase to hydrolyse starch, polygalacturonase to weaken the tough cell walls of plants, and proteinases to break down proteins . </P> <P> Although the Hemiptera vary widely in their overall form, their mouthparts form a distinctive "rostrum". Other insect orders with mouthparts modified into anything like the rostrum and stylets of the Hemiptera include some Phthiraptera, but for other reasons they generally are easy to recognize as non-hemipteran . Similarly, the mouthparts of Siphonaptera, some Diptera and Thysanoptera superficially resemble the rostrum of the Hemiptera, but on closer inspection the differences are considerable . Aside from the mouthparts, various other insects can be confused with Hemiptera, but they all have biting mandibles and maxillae instead of the rostrum . Examples include cockroaches and psocids, both of which have longer, many - segmented antennae, and some beetles, but these have fully hardened forewings which do not overlap . </P>

What is a unique characteristics of insects in the order hemiptera check all that apply