W. Coetzer et Jh. Hoffmann, ESTABLISHMENT OF NELTUMIUS-ARIZONENSIS (COLEOPTERA, BRUCHIDAE) ON MESQUITE (PROSOPIS SPECIES, MIMOSACEAE) IN SOUTH-AFRICA, Biological control, 10(3), 1997, pp. 187-192
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.