Exceptional biological control of two varieties of Cylindropuntia fulgida (Cactaceae) in South Africa using a recently-identified different biotype of the cochineal insect, Dactylopius tomentosus (Dactylopiidae)

Abstract

The cactus Cylindropuntia fulgida (Engelm.) F.M. Knuth., from Mexico and southwestern USA, invades conservation and pasture land in the arid regions of South Africa. Mechanical and chemical control, and attempts at biological control, have been ongoing since the early 1970 s but, until recently, with little success. Two distinct morphological varieties of C. fulgida are recognized in South Africa, viz. Cylindropuntia fulgida var. fulgida Engelm. (‘chain-fruit cholla’) and Cylindropuntia fulgida var. mamillata (Schott ex Engelm.) Backeb. forma monstrosa Coult (‘boxing-glove cactus’). In 2008, a specific biotype - the ‘cholla’ biotype - of the cochineal insect, Dactylopius tomentosus (Lamark), that was obtained from Cylindropuntia cholla (F.A.C. Weber) F.M.Knuth in Baja California Sur in Mexico, was released on C. fulgida var. fulgida, and later, in 2011, on C. fulgida var. mamillata in South Africa. It has brought these cactus weeds under remarkably effective biological control. We assess the efficacy of biological control for the two morphological varieties of C. fulgida in South Africa. In the Northern Cape province, D. tomentosus ‘cholla’ effectively controls detached cladodes and small, rooted plants of chain-fruit cholla, but, following rain, old plants repeatedly coppice and regrow from their woody trunks. Hand-felling and stacking of cochineal-weakened C. fulgida var. fulgida plants killed them within 1–2 years. Cylindropuntia fulgida var. mamillata is under exceptionally effective biological control wherever D. tomentosus ‘cholla’ has been released. At two sites in the Northern Cape province that were monitored, approximately 90% of the plants died during the first ten months after release, while practically all were dead another 7 months later. The ‘cholla’ biotype of D. tomentosus has been supplied to Australia for use against various invasive Cylindropuntia species in that country.