ESTABLISHMENT OF NELTUMIUS-ARIZONENSIS (COLEOPTERA, BRUCHIDAE) ON MESQUITE (PROSOPIS SPECIES, MIMOSACEAE) IN SOUTH-AFRICA

Species of Prosopis (Mimosaceae), or mesquites, are invasive rangeland weeds in South Africa's Western Cape and Northern Cape Provinces. Two bruchid seed-weevil species, Algarobius prosopis (Le Conte) and A. bo ttimeri Kingsolver, were released for biological control in 1987 and 1 990, respectively. Seed-feeding biocontrol agents were selected becaus e mesquite pods are valued as livestock fodder. Livestock grazing of b ruchid larvae developing in mesquite seeds, however, limits the effect iveness of these agents. Livestock grazing also exacerbates mesquite i nfestations because scarified seeds are dispersed widely in vertebrate dung. In response to the livestock grazing problem, Neltumius arizone nsis (Schaeffer), a bruchid reputed to be capable of ovipositing on im mature, tree-borne pods, was released at three sites in Western Cape P rovince in 1993 and 1994. Small populations of N. arizonensis have bec ome established at the release sites. Overall, N. arizonensis was 18 t imes less abundant than A. prosopis. In some months N. arizonensis egg s were heavily parasitized by Uscana sp. (Trichogrammatidae), but the effect of this on N. arizonensis population dynamics is uncertain. Wes tern Cape N. arizonensis populations need more time to increase in siz e. The introduction of other, more injurious biocontrol agents such as the cecidomyiid bud feeder Asphondylia prosopidis Cockerell should be considered. (C) 1997 Academic Press.