A new host specific insect for the control of Pereskia aculeata (Cactaceae)

A new host specific insect for the control of Pereskia aculeata (Cactaceae)
Iain Paterson and Martin Hill
Department of Zoology and Entomology, Rhodes University, PO Box 94, Grahamstown 6140

Pereskia aculeata Miller (Cactaceae) is still a problematic invasive in South Africa. The plant outcompetes native vegetation and leads to a reduction in native plant biodiversity. Many protected areas, including national parks and world heritage sites, are threatened by P. aculeata infestations resulting in  a  large  amount of  resources being  used  to  try  control the  weed.  Mechanical and chemical control is ineffective, expensive and unsustainable because of the plants ability to grow from small cutting and because herbicides are not translocated within the plant tissue. Biological control  is  considered  the  only  possible  method  that  could  reduce  the  negative  impacts  of  P. aculeata.

One biological control agent, Phenrica guerini Bechyne (Chrysomelidae) has been released on P. aculeata, and although the insect has established at many sites around the country, the damage inflicted by the insect appears to be minimal. New biological control agents are required to reduce the density of P. aculeata to appropriate levels.

In this study, a new potential biological control agent for P. aculeata, Catorhintha schaffneri (Coreidae) was subjected to host specificity testing. Newly hatched nymphs were allowed to feed on six plant species in the Cactaceae, ten species in the closely related plant families, the Basselaceae and Portulaceae, and eight species in more distantly related plant families that have similar mucilaginous or succulent leaves to plants in the Cactaceae. Development to the adult stage was only possible on P. aculeata and the closely related congener, Pereskia grandifolia. Pereskia grandifolia is an exotic species that is a declared weed in South Africa so any damage inflicted to P. grandifolia in South Africa is of little concern. No survival to the adult stage was reported on any other species.

Catorhintha schaffneri is safe for release in South Africa. An application for release will be submitted pending the results of an impact study to ensure that the agent is destructive enough to warrant release.  The  impact  of  C.  schaffneri  on  P.  aculeata  is  expected  to  be  significant  based  on observations in quarantine and in the native range where it is very damaging.