Under attack, a lima bean plant calls in hungry mites as bodyguards
When spider mites chew a lima bean's leaves, the plant releases airborne chemicals that summon a carnivorous mite, which hunts the attackers. It also bribes the bodyguards with nectar produced outside its flowers and can release cyanide from damaged tissue. The humble butter bean runs a sophisticated chemical defence.
Wounding and substances in insect saliva trigger a signalling pathway, driven mainly by jasmonic acid, that makes the plant emit what researchers call herbivore-induced plant volatiles. Any organism able to detect them can respond, including neighbouring plants, but the key audience is Phytoseiulus persimilis, a predatory mite. In experiments, infested plants pumped out more volatiles, and the predators became better at finding prey and more drawn to the plant, even after the spider mites had been removed. Extra nectar gives the predators an alternative meal, keeping them around.
Phaseolus lunatus was domesticated twice. An Andean line, dated to about 2000 BC, produced the large-seeded lima type, while a Mesoamerican line around AD 800 gave the small-seeded Sieva type. Peru's Moche culture, which flourished from AD 1 to 800, grew the beans heavily and often depicted them in art. Cultivation reached north of the Rio Grande by about 1300 and the Old World in the 1500s. The name came from shipping crates stamped with their origin, Lima, Peru, during the Spanish colonial era.
Naming is tangled. Lima beans and butter beans belong to the same species, though cooks often use lima for small green seeds and butter bean for large yellowish ones. In the Carolinas butter bean means a big flat pale variety, while India calls them double beans and Valencians put them in paella as garrofo. Seeds can be white, black, red or mottled, and heirloom varieties such as the red-speckled Christmas lima take around 78 days to mature. The Carolina Sieva suffered seed crop failures in 2011 and 2012 that still limited supply a decade later.
Bush types mature earlier than climbing types, which can reach 5 metres, and pods grow up to 15 centimetres long. In the United States lima beans are grown mainly around Delaware and the mid-Atlantic for processing. Raw beans contain phytohaemagglutinin and are toxic unless boiled for at least ten minutes; canned ones are already cooked.
Source: Lima bean
