Grasshopper
Grasshoppers eat large quantities of foliage both as adults and during their development, and can be serious pests of arid land and prairies. Pasture, grain, forage, vegetable and other crops can be affected. Grasshoppers often bask in the sun, and thrive in warm sunny conditions, so drought stimulates an increase in grasshopper populations. A single season of drought is not normally sufficient to stimulate a major population increase, but several successive dry seasons can do so, especially if the intervening winters are mild so that large numbers of nymphs survive. Although sunny weather stimulates growth, there needs to be an adequate food supply for the increasing grasshopper population. This means that although precipitation is needed to stimulate plant growth, prolonged periods of cloudy weather will slow nymphal development.
Hemiptera
Hemipterans can dramatically cut the mass of affected plants, especially in major outbreaks. They sometimes also change the mix of plants by predation on seeds or feeding on roots of certain species. Some sap-suckers move from one host to another at different times of year. Many aphids spend the winter as eggs on a woody host plant and the summer as parthogenetically reproducing females on a herbaceous plant.
Phloem sap, which has a higher concentration of sugars and nitrogen, is under positive pressure unlike the more dilute xylem sap. Most of the Sternorrhyncha and a number of Auchenorrhynchan groups feed on phloem. Phloem feeding is common in the Fulgoromorpha, most Cicadellidae and in the Heteroptera. The Typhlocybine Cicadellids specialize in feeding on non-vascular mesophyll tissue of leaves, which is more nutritious than the leaf epidermis. Most Heteroptera also feed on mesophyll tissue where they are more likely to encounter defensive secondary plant metabolites which often leads to the evolution of host specificity. Obligate xylem feeding is a special habit that is found in the Auchenorrhyncha among Cicadoidea, Cercopoidea and in Cicadelline Cicadellids. Some phloem feeders may take to xylem sap facultatively, especially when facing dehydration. Xylem feeders tend to be polyphagous; to overcome the negative pressure of xylem requires a special cibarial pump. Phloem feeding hemiptera typically have symbiotic micro-organisms in their gut that help to convert amino acids. Phloem feeders produce honeydew from their anus. A variety of organisms that feed on honeydew form symbiotic associations with phloem-feeders. Phloem sap is a sugary liquid low in amino acids, so insects have to process large quantities to meet their nutritional requirements. Xylem sap is even lower in amino acids and contains monosaccharides rather than sucrose, as well as organic acids and minerals. No digestion is required (except for the hydrolysis of sucrose) and 90% of the nutrients in the xylem sap can be utilised. Some phloem sap feeders selectively mix phloem and xylem sap to control the osmotic potential of the liquid consumed. A striking adaptation to a very dilute diet is found in many hemipterans: a filter chamber, a part of the gut looped back on itself as a countercurrent exchanger, which permits nutrients to be separated from excess water. The residue, mostly water with sugars and amino acids, is quickly excreted as sticky "honey dew", notably from aphids but also from other Auchenorrhycha and Sternorrhyncha.