Abstract

Parthenium hysterophorus, of Neotropical origin, is the most predominant weed of vacant plots, waste lands and pastures in most parts of India. It has been established that growth inhibitors released from this plant to the soil through leaching, exudation of roots and during decay of residues suppress local vegetation and threatens natural diversity. P.hysterophorus is also reported to affect agriculture, human health and livestock production in India. As manual, chemical and competitive displacement methods are not practicable, biological control trials were initiated by importation and releases of the chrysomelid beetle Zygogramma bicolorata. The insect established readily, after releases were initiated in 1984, and started building up damaging population levels from 1988. Since then it has spread over more than 200,000 sq km area in and around Bangalore, causing large scale defoliation of parthenium and encouraging the growth of vegetation formerly suppressed by this weed. But the insect was noticed to feed on sunflower in a few isolated fields in Karnataka, raising fears of a host shift. However, detailed laboratory and field studies clearly indicated that Z.bicolorata is unlikely to become a pest of sunflower. The results of the studies carried out to date indicate that Zbicolorata has the potential to bring about permanent reduction in the density of P.hysterophorus in Bangalore and surrounding areas. However, it may be desirable to import additional natural enemies such as the leaf mining moth Bucculatrix parthenica and the seed feeding weevil Smicromyx lutulentus. Similarly, importation of host- specific plant pathogens such as Puccinia abrupta var. partheniicola, may also contribute to the successful biological control of this noxious weed throughout India.

Keywords: Biological Control, Weeds, Parthenium hysterophorus, Helianthus annuus, Zygogramma bicolorata