Can Generalist Predators be Effective Biocontrol Agents?

Abstract

Theoretical developments are helping us to comprehend the basic parameters governing the dynamics of the interactions between generalist predators and their many pest and nonpest prey. In practice, however, inter- and intraspecific interactions between generalist predators, and between the predators and their prey, within multispecies systems under the influence of rapidly changing biotic and abiotic variables are difficult to predict. We discuss trade-offs between the relative merits of specialists and generalists that allow both to be effective, and often complementary, under different circumstances. A review of manipulative field studies showed that in approximately 75% of cases, generalist predators, whether single species or species assemblages, reduced pest numbers significantly. Techniques for manipulating predator numbers to enhance pest control at different scales are discussed. We now need to find ways of disentangling the factors influencing positive and negative interactions within natural enemy communities in order to optimize beneficial synergies leading to pest control.

Larval Life History Responses to Food Deprivation in Three Species of Predatory Lady Beetles (Coleoptera: Coccinellidae)

“…In addition to many attempts to use them in classical biological control, some being highly successful, ladybeetles are also being translocated or mass produced and released for the control of various pests (Pu 1976;Singh 2004). Lately, the role of generalist predators such as ladybeetles is being recognized in conservation biological control through conservation and enhancement techniques (Symondson et al 2002;Obrycki et al 2009). …”

Managing biotic interactions for ecological intensification of agroecosystems

“…A time-lag is, therefore, to be expected when manipulating biotic interactions through ecological intensification and its duration is likely to depend on a multitude of factors such as species dynamics, the strength of the biotic interaction (generalist vs. specialist) and the landscape context. For instance, a specialist predator will provide efficient control of a prey in the medium term whereas a generalist predator would provide more rapid but less efficient control (Hanski and Woiwod, 1991;Symondson et al, 2002). The question arises of whether the timing of the response of biological control is compatible with agricultural objectives (e.g., crop yield and farm income) or whether there would be too great an offset in the timing of the control by ecological processes and the change in management system hence limiting potential benefits.…”

Assessing non-target effects and host feeding of the exotic parasitoid Apanteles taragamae, a potential biological control agent of the cowpea pod borer Maruca vitrata

“…The effects of a biological agent on non-target herbivore species depend on its degree of specialization (Henneman and Memmott 2001;Symondson et al 2002;Louda et al 2003). A strictly specialist parasitoid may not affect non-target herbivore species.…”

“…A strictly specialist parasitoid may not affect non-target herbivore species. A relative specialist parasitoid that has a narrow host range is expected to have a limited environmental risk, while a generalist is expected to affect non-target hosts (Henneman and Memmott 2001;Symondson et al 2002;Louda et al 2003;van Lenteren et al 2003). The host range of a parasitoid can be viewed physiologically or ecologically (Louda et al 2003;Babendreier et al 2003Babendreier et al , 2005Haye et al 2005).…”