Biotype Matching of Chromolaena for More Successful Biological Control

Many phytophagous insects and pathogens are highly specific in their host requirements, and will develop sub-optimally or not at all on biotypes of a plant species dissimilar from that on which they are collected. This clearly has major implications for the success of biological control. Chromolaena odorata has a native range stretching from the southern USA to northern Argentina. The species displays wide phenotypic variation, both across its range and within localised areas. Until 1997, the biotype of chromolaena invasive in southern Africa had not been found to match that of any plants from its native range. Such matching was considered a priority because of the low success of some agents in the biocontrol programme in South Africa. Since 1997, increasing evidence has accumulated indicating that the southern African chromolaena biotype originates from one or more of the islands of the Greater Antilles in the northern Caribbean. Taking into account findings in the field as well as colonial links, Jamaica seems the most likely origin. Recent surveys of both Jamaica and Cuba have revealed a relatively poor diversity of insects on chromolaena relative to the South American mainland. It is thus still considered necessary to target insect species from the latter area, if it can be shown that they are not biotype-specific.