Journal or Publishing Institution: Genetics, Evolution and Biological Control
Author(s): Obrycki, J.J., Ruberson, J.R. and Losey, J.E.
Article Type: Report
Record ID: 1801
Conclusions: 1. The current high-dose strategy will reduce densities of natural enemies that tend to be more host specific, perhaps to a greater extent than the use of insecticides. The elimination of target species may cause local extinctions of host-specific natural enemies, creating metapopulation dynamics. As discussed previously (Bernal et al., 2002), the widespread use of transgenic Bt crops will probably have greater negative effects on parasitoid species that tend to be more host specific, than on predatory species. However, to understand the full extent of these effects, several key questions must be addressed. What is the role of specialist natural enemies in population suppression of insect herbivores in annual cropping systems? How will elimination of specialized natural enemies affect levels of biological control? Will the long-term use of transgenic insecticidal crops simplify agroecosystems, reducing the connections within existing food webs?
2. In contrast to effects on specialist natural enemies, agroecosystems where transgenic crops reduce insecticide use will probably experience higher levels of generalist predators compared with systems receiving insecticides. However, significant reductions in the density of prey targeted by the transgenic crop may cause increased competition and intraguild predation. The net result for pest suppression will need to be quantified.
3. Owing to reduced insecticide usage and/or differential effects on non-target species and their natural enemies, densities of secondary pest populations may increase. These increased densities may benefit natural enemies, or alternatively, may require additional use of insecticides.
4. Levels of toxins in non-target herbivores, which will be influenced by the type of feeding behaviours and mode of action of the transgenic toxin, e.g. acute versus chronic effects, will influence natural enemy populations. Altered behaviours of insect herbivores exposed to transgenic toxins will affect natural enemies (Winterer and Bergelson, 2001; Gore et al., 2002).
5. Long-term monitoring of population dynamics of natural enemy and host species in transgenic fields is required. For example, the absence of lepidopteran larvae from transgenic Bt rice fields may cause predator dispersal or switching behaviours, which may alter levels of biological control of the brown leafhopper, N. lugens (Bernal et al., 2002).
6. Transgenic insecticidal crops provide a valuable experimental tool for determining the relative importance of individual pest species (Baute et al. 2002), and can provide a basis for a better understanding of multitrophic-level interactions in agroecosystems. Large-scale studies of the interactions between transgenic insecticidal crops, herbivores and natural enemies are needed to provide an understanding of the population dynamics of these interactions (Schuler et al., 2001).
7. The high selection pressure resulting from the high-dosage strategy may enhance the development of tolerant pest populations, particularly for species with limited mobility and discrete generations, and may even lead to speciation, based upon developmental asynchrony between resistant and susceptible populations (see the discussion in Cerda and Wright, 2002).
Keywords: Transgenic Crops, Insecticidal Crops, Pest Management, Transgenic Cotton, Transgenic Maize, Bacillus thuringiensis kurstaki, Lepidoptera, European Corn Borer (Ostrinia nubilalis), Bt Cotton, Colorado Potato Beetle (Leptinotarsa decemlineata), Gene Flow, Ecological Disruption, Food Web, Integrated Pest Management, Conservation, Ecological Principles, Biological Control
Citation: Obrycki, J.J., Ruberson, J.R. and Losey, J.E., 2004. Interactions between natural enemies and transgenic insecticidal crops. Genetics, Evolution and Biological Control, pp.183-206.
