Biological control against parthenium weed in Australia.

Abstract Parthenium hysterophorus is an annual herbaceous plant native to the tropical Americas, which is widely adventitious and now occurs in East Africa, parts of Asia and Australia. It is a major crop and pasture weed in India and Australia in particular, where it is also a human health hazard, causing allergic dermatitis and respiratory problems. A biological control programme involving the introduction of insects from the Americas started in Australia in 1975 and is still in progress. Six species of insects have been released, of which four are established but only one, the moth Epiblema strenuana , is exerting significant control on the weed. The moth larvae form galls in the parthenium stems and shoots; damage by several larvae stunts plants and reduces seed production. Unfortunately, the erratic climate interferes with the control: long dry periods reduce the moth population to very low levels so that when the parthenium germinates after rain there is inadequate control. Efforts to establish other biocontrol agents are continuing in Australia. India rejected E. strenuana because of attack on Guizotia abysinnica in tests, but has successfully established the leaf-feeding chrysomelid Zygogramma bicolorata with promising results. Other insects evaluated in Australia are available and should be tested for use in India and other countries with a parthenium problem.