Introduction

Efforts to manage weeds using biological control have been gaining momentum throughout the world, especially in the recent past (Delfosse, 2004). Developed countries, which are principally distributed in the temperate regions, have been practicing classical biological control efficiently, whereas developing countries, most of which are distributed in the tropical regions and have more limited resources, have not adopted deliberate measures for biological control of invasive plants to the same extent as developed nations. The first documented case of biological control of weeds in the tropics was in 1795 and involved the invasive plant Opuntia monacantha (Wildenow) Haworth (Cactaceae), which was controlled serendipitously in India due to the inadvertent introduction of Dactylopius ceylonicus (Green) (Hemiptera: Dactylopiidae) from Brazil in mistaken identity for Dactylopius coccus Costa (Hemiptera: Dactylopidae) (Rabindra and Bhumannavar, this volume; Zimmerman et al., this volume). Thereafter, it took more than a century for biological control of weeds to be rigorously adopted (e.g. biological control of lantana in Hawaii in 1902; biological control of cactus in Australia in 1912; Julien et al., 2007) and for invasive weed species to be recognized as an international problem (Harris, 1979).

Since the early 1900s, work has been predominantly carried out on weeds of the temperate regions in countries such as Canada, New Zealand, Australia, South Africa, and the USA. The USA, Australia, and South Africa, which include tropical segments (e.g. states of Florida, Hawaii, Queensland, Northern Territory, KwaZulu-Natal, Mpuma Langa, Limpopo) have developed programs on biological control of tropical weeds.