What are the factors that influence successful biological control of Cereus jamacaru De Candolle (Cactaceae) in South Africa?

What are the factors that influence successful biological control of Cereus jamacaru De Candolle (Cactaceae) in South Africa?
Guy F. SUTTON, Iain D. Paterson
Biological Control Research Group, Department of Zoology and Entomology, Rhodes University, P.O. Box 94, Grahamstown, 6140, South Africa

The success of biological control agents can be highly variable among target weed populations. The mechanisms that determine such variability are poorly understood, and an understanding of these factors would allow biological control practitioners to improve existing management programs. Field observations of an environment-transforming weed, Cereus jamacaru (Queen of the night cactus), indicate that biological control efforts employing the mealybug Hypogeococcus pungens (Hemiptera: Pseudococcidae) may be more effective against certain weed populations than others, suggesting that distinct genetic types may be present in South Africa. This study will investigate several factors which may explain the variable nature of the control of C. jamacaru. The factors investigated will include the suitability of the control agent H. pungens, incompatibility between H. pungens and C. jamacaru populations and the impact of top-down regulation on H. pungens by predators and parasitoids. The methods employed will include field surveys of C. jamacaru populations and their interaction with H. pungens, climatic matching, molecular and morphological taxonomic evaluation of the weed populations, herbivore performance bioassays on different weed populations and combined field and laboratory-based assessments of the impact of predation and parasitism on H. pungens. This research will indicate whether H. pungens is a suitable biological control agent of all forms of C. jamacaru and determine factors that must be taken into account when implementing biological control using this agent.