Lantana is one of the worst weeds in the world, a category 1b species in South Africa in terms of the Alien and Invasive Species Regulations (AIS), National Environmental Management: Biodiversity Act (Act No 10 of 2004). Land occupiers are legally obliged to control it, or to remove and destroy it if possible. No trade or planting is allowed. It comprises a complex of vigorous, prolific, man-made hybrids, bred in Europe from unrecorded parents from Central and South America, and spread all over the world as a hardy, ornamental shrub, with multi-coloured flowers. Dispersed by fruit-eating birds, it establishes along fence lines and under trees, where it out-competes indigenous plants and forms impenetrable, prickly thickets that reduce natural pasturage, productivity of cattle farming, access to water supplies and tree plantations, biodiversity and land values.
A total of 9 lantana biocontrol agents and 3 associated insects were established on lantana in South Africa before 1997 (listed below). The damage is caused by the developing larva or nymph. Some of these agents undergo sporadic, localized outbreaks that defoliate whole stands of lantana, but the plant recovers completely, and continues to densify and spread.
Current South African research into biological control of lantana focuses on developing new, host-specific, biocontrol agents (listed below), to supplement the activity of the agents established earlier. With financial support from the Department of Water Affairs and Forestry's Working for Water Programme during the period 1997-2010, the lantana biocontrol research team obtained 30 promising-looking candidate agents from the Central American Region, and evaluated them in quarantine in South Africa. Of these, 13 were rejected internally because they were found to be inadequately host-specific or non-pathogenic ('x' in the list below, below), 9 were shelved ('~') for various reasons (such as breeding difficulties or giving preference to another species in the same genus), and 7 were found to be acceptably host-specific for release ('*'), whilst 1 is undergoing host-specificity testing ('?').
The lantana biocontrol agents established in South Africa are generally widespread but very sparse, reaching only about 10% of maximum abundance (Table 1). The introduction of the lantana herringbone leafminer, Ophiomyia camarae has significantly improved biocontrol of lantana along the hot and humid coast of KwaZulu-Natal, but it is sparse inland, and cannot overwinter on the highveld.
EC: Easten Cape; GP: Gauteng; KZ: KwaZulu-Natal; LP: Limpopo; MP: Mpumalanga; NW: North West; WC: Western Cape. Data ex Heystek (2006)
The shocking truth is that the 'generally very healthy' state of lantana in South Africa is 'with' or 'after' biocontrol. The lantana biocontrol agents currently established are simply unable to stop the weed densifying and spreading. To control lantana, one has to resort to very thorough and persistent mechanical plus chemical treatment. . Lantana biocontrol is nevertheless of value, because it reduces the rate of growth and reproduction of the weed, which reduces the frequency and cost of applying other control measures.
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