Box 2-8.Biological control

Biological control refers to the use of natural enemies of pests (i.e., their predators, parasitoids and pathogens) as pest control agents. Globally, the annual economic contribution of natural enemies has been estimated in the hundreds of billions of dollars worldwide, much of this due to indigenous species (Costanza et al., 1997; Naylor and Ehrlich, 1997; Pimentel, 1997; Pimentel et al., 1997; Gurr and Wratten, 2000; Alene et al., 2005; Losey and Vaughan, 2006). Conservation biocontrol supports the activity of indigenous natural enemies by providing them with suitable habitats and resources (Doutt and Nakata, 1973; Jervis et al., 1993; Kalkoven, 1993; Idris and Grafius, 1995; Murphy et al., 1998; Ricketts, 2001; Gurr et al., 2006) and by limiting the use of disruptive pesticides. Since conservation approaches are locally adapted, they rarely produce products that can be widely marketed and have attracted little interest from the private sector. Yet they constitute one of the most economically important types of biocontrol and form the cornerstone of much ecological pest management (Altieri and Nicholls, 2004). Farmers and public sector scientists have demonstrated practical applications in, e.g., the Biologically Integrated Orchard Systems (BIOS) of California (Thrupp, 1996), vineyard habitat management (Murphy et al., 1998), and rice ecosystem conservation (Settle et al., 1996).

     The importance of natural enemies is highlighted by the often explosive outbreaks of pests introduced into regions where they lack specific natural enemies. Classical biological control restores natural pest management by the identification and introduction of specific and effective natural enemies from the pest's home region (DeBach, 1964, 1974). Dramatic early successes in the late 19th century (cottony cushion scale in citrus, Caltagirone and Doutt, 1989) spurred classical biocontrol efforts around the world, but these methods were later displaced by the widespread adoption of cheaper and fast-acting synthetic pesticides. Under pressure to deliver fast results, entomologists economized on ecological studies and began releasing potential biocontrol agents prematurely with less success (Greathead, 2003). Confidence in biocontrol declined, until problems arising from pesticide use rekindled interest (Perkins, 1982). With better institutional support and funding, the success rate improved (Greathead, 2003). Initially, work in developing countries focused on large scale commercial, industrial and export tree crops with less direct impact on smallscale farmers (Altieri, et al., 1997). Subsequent programs focused on staple food crops and on building indigenous capacity in biocontrol (Thrupp, 1996).

     Institutional arrangements fostering collaboration enabled the scientific and technological processes associated with classical biocontrol in subsistence crops in Africa to provide a range of social, environmental, economic and cultural benefits (Norgaard, 1988; Zeddies et al., 2001; Bokonon-Ganta et al., 2002; de Groote et al., 2003; Neuenschwander et al., 2003; Moore, 2004; Macharia et al., 2005; Maredia and Raitzer, 2006; Omwega et al., 2006; ICIPE, 2006; Kipkoech et al., 2006; Macharia et al., 2007; Löhr et al., 2007). A noteworthy example is the control of cassava mealybug (Herren and Neuenschwander, 1991; Gutierrez et al., 1988; Neuenschwander, 2001, 2004). Follow-on effects included exten-

sive training of African scientists in biocontrol and the establishment of national programmes targeting invasive insect and weed pests across the region (Herren and Neuenschwander, 1991; Neuenschwander et al., 2003). Technical and administrative staff played a key role in designing and maintaining complex networks of collaboration (Wodageneh, 1989; Herren, 1990; Neuenschwander, 1993; Neuenschwander et al., 2003).

     Ecologists have raised concerns regarding potential impacts on non-target organisms of introduced biocontrol agents (Howarth, 1990; Simberloff and Stiling, 1996; Strong, 1997). However, after several early failures due to vertebrate and mollusc predator introductions in the late 19th-early 20th century (Greathead, 1971), the safety record of invertebrate biocontrol has become well established (Samways, 1997; McFadyen, 1998; Wilson and Mc- Fadyen, 2000; Wajnberg et al., 2001; Hokkanen and Hajek, 2003; van Lenteren et al., 2003). A substantial body of research has investigated nontarget effects of classical biological control (Boettner et al., 2000; Follett and Duan, 2000) and rigorous screening protocols and methodologies for environmental risk assessment of biocontrol agents now exist (Hopper, 2001; Strong and Pemberton, 2001; Bigler et al., 2006). FAO, CABI BioScience and the International Organization of Biological Control have developed a Code of Conduct for the Import and Release of Biological Control Agents to facilitate their safe import and release (Waage, 1996; IPPC, 2005).

     In contrast to conservation and classical biocontrol, augmentation involves mass production of naturally-occurring biocontrol agents to reduce pest pressure (DeBach, 1974; Bellows and Fisher, 1999). The decentralized artisanal biocontrol centers of Cuba offer one model of low-cost production for local use (Rosset and Benjamin, 1994; Altieri et al., 1997; Pretty, 2002). Augmentative control in Latin American field crops (van Lenteren and Bueno, 2003) and throughout the European glasshouse system (Enkegaard and Brodsgaard, 2006) offer others. Growing consumer interest in pesticide-free produce has helped establish a small but thriving biocontrol industry (van Lenteren, 2006), mostly in industrialized countries (Dent, 2005), with some uses in developing countries where pesticide use is difficult or prone to trigger pest outbreaks (i.e., sugarcane, cotton and fruit trees). The costs of production, storage and distribution of living organisms have made these products less attractive to the private sector than chemical pesticides; currently they comprise only 1-2% of global chemical sales (Gelertner, 2005). Their relatively limited use also reflects chronic underinvestment in public sector research and development of biological products and a regulatory system that disadvantages biological alternatives to chemicals (Waage, 1997). Biological pesticides, on the other hand, have been more successful because they fit into existing systems for pesticide development and delivery. Nevertheless, the growth of the global market for biocontrol products, recently at 10-20% per annum, is expected to continue (Guillon, 2004), and is most likely to play a key role in crop systems where pesticide alternatives are required.