Toxicity

Most of the insects feeding on fronds or cones of Cycads are aposematic. The toxicity of the plant, of the cones and the seeds is very high, and, though many reptiles, birds, and mammals seem to eat with impunity their cones and their contents, livestock in New-Guinea, Australia, South Africa is gravely and definitely poisoned when feeding on the cones. PJ has seen very often, in New Guinea, the cows sick after having eaten young cones. They turn and turn over themselves like mad cows before dying. In Cycads, toxins are numerous, cycasine, neocycasin, mac-rozamine and methylamino-L-alanine and are probably sequestred in some specialized cells of the cones and leaf tissue, the idioblasts (Schneider et al, 2002; Norstog et al, 1992).

Many lycaenids (Lepidoptera) are specialized for feeding on cycad fronds, as Catochrysops pandava Horsfield in Indonesia and Chilades cleotas kaiphas Fruhstorfer in New Guinea, various species of Eumaeus in Florida, Central America, etc. Those butterflies borrow their toxicity from their host-plant. Miriam Rothschild (Rothschild, 1992; Rothschild et al, 1986) has specially studied Eumaeus atala and its gregarious caterpillars, brightly coloured, and containing cycasin, a violent poison. The lycaeanid, despite its toxicity, seemed once endangered in Florida, but PJ saw plenty of them on cycads in Miami botanical gardens.

Some seeds from coastal species of cycads contain a spongy tissue and they float. The sarcotesta or external envelop of Maro%amia seeds contains a high concentration of macrozamine, a very efficient toxin. These seeds are often brightly coloured to attract local animals, naturally immune to the poison. The seeds are often red, scarlet, orange or yellow and most of the time bright. Some cones are often orange, red or yellow (Encephalartos^), sometimes even green, contrasting then with the seed colour.

It may be noted that some Cycas seeds, after cooking, are eaten by Australian aborigines. The stem of other species is a minor source of sago in the Philippines, the fronds and even the fruits are sometimes eaten in Malaysia. As for the cassava, precautions should be taken by those who want to get a taste of it for the first time because the toxicity of the plant. Zamia extracts are sometimes also used as a poison, though they are edible only after a special treatment of the roots. It is the same in Africa with Encephalartos. Aulacoscelis when offered to chickens kill them instantaneously. The chamorro aborigines in Guam eat flying foxes (Pterotus marianus), and the bats eat the seeds of cycas trees (Cycas mironesia). That causes a degenerative brain disease among humans. Toxicity of the cycads could be due to cyanobacteria associated with the roots.

The toxicity of the leaves and of the fruits is so strong that the beetles, which feed on them are very toxic themselves, and are thus protected from predators. Weevils, which feed on the parenchymatic tissue, avoid partially the toxins by keeping clear of the epidermic trichomes. Brain dementia in Guam has been attributed to the consumption of bats feeding on cycads, as has been mentioned above.

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