Hoppers

The world is home to a wide variety of leafhoppers, both in terms of number of species and range of morphological disparity. One of the more diverse leafhopper families is the Delphacidae, including over two thousand species from around the globe. Delphacids are relatively small leafhoppers that are easily distinguished from other families by the possession of a large movable spur at the end of the tibia of the hind leg. I can't say as I know what the function of this spur is, but similar structures in other insect groups may be used for grooming.

Brown leafhoppers Nilaparvata lugens, from ICAR. The individual on the right is a long-winged disperser, the one on the left is a flightless brachypter.

Delphacids feed on the phloem of their host plants; the greater number of species are associated with monocots such as grasses. A number of species are significant economic pests; perhaps the most infamous are the brown leafhopper Nilaparvata lugens and white-backed leafhopper Sogatella furcifera which attack rice. They feed at the base of rice plants, causing the formation of round, yellow patches that soon dry up and turn brown, a condition known as 'hopper burn'. Death of the entire plant will often follow. As well as the direct damage from feeding, these leafhopper species also transmit viruses that further impact yields. Historically, numerous famines have been blamed on leafhopper outbreaks, such as the Kyoho famine of 1732 that saw rice production reduced to only 10% of its previous level. Estimates of the number of people affected by the famine seem to vary widely—according to Wikipedia, the official death toll was a bit more than twelve thousand people, but estimates of the actual number of fatalities range well in excess of 150,000. In more recent years, leafhopper outbreaks may be exacerbated by indiscriminate fertiliser and pesticide use, with the latter reducing competition for the hoppers from other insects or predators.

Delphacids (and many other leafhoppers) commonly exhibit polymorphism in wing development with both flying macropterous and flightless brachypterous forms occuring in a single population. The question of macroptery vs brachyptery is an environmental one. If a developing delphacid receives sufficient nitrogen then it will develop into a flightless adult, remaining in the place of its birth to continue to benefit from the good feeding conditions there. But if feeding conditions become degraded and the developing nymph is deprived of nitrogen then it will develop into a fully-winged adult that can leave its home in search of more favourable conditions elsewhere. Because of their small size, migrating delphacids may be carried long distances by the winds. In the case of pest species, this phenomenon of migration further exacerbates the problem of control as hopper populations from different countries are regularly mixed, increasing genetic diversity and resistance to varying control methods.

REFERENCE

Urban, J. M., C. R. Bartlett & J. R. Cryan. 2010. Evolution of Delphacidae (Hemiptera: Fulgoroidea): combined-evidence phylogenetics reveals importance of grass host shifts. Systematic Entomology 35: 678–691.