Engineering Resistance to Insect Pests

Abstract

With a projected increase in world population to 10 billion over the next four decades, an immediate priority for agriculture is to achieve maximum production of food and other products in a manner which is environmentally sustainable and cost effective. Despite the synthesis of improved pesticides, and integrated pest management strategies, yield losses due to insects have actually increased slightly for most crops over the last two decades. The concept of utilising a transgenic approach to host plant resistance was realised in the mid 1990s with the commercial introduction of genetically modified crops expressing genes encoding the entomocidal d‐endotoxin from Bacillus thuringiensis ( Bt ). More recently this strategy has been extended to include the pyramiding (stacking) of genes encoding different Bt toxins for greater levels of pest control. Although not as yet a commercial reality, other strategies based on the use of plant derived genes (enzyme inhibitors, lectins) and those from animal sources, including insects (biotin‐binding proteins, neurohormones, enzyme inhibitors), are being developed. The use of fusion proteins to increase the spectrum and durability of resistance is also actively being pursued. However, if transgenic insect‐resistant crops are to play a useful role in crop protection, it is apparent that they must be compatible with the other components of integrated pest management (IPM). The current chapter addresses the role of insect‐resistant transgenic crops in agriculture and discusses both their current status and future developments. Given the importance of natural enemies in controlling pest populations, the potential impact of such crops on predators and parasitoids is also addressed.

Identification, Mapping and Pyramiding of Genes/Quantitative Trait Loci (QTLs) for Durable Resistance of Crops to Biotic Stresses

“…To increase pest control efficacy and delay resistance evolution, a gene pyramiding strategy has been employed in transgenic plants to produce two or more Bt toxins of dissimilar mode of action effective against the same target pest species [81][82][83]. Thus, crops pyramided with Bt genes express the insecticidal toxin in all of their tissues.…”

“…Thirdly, the pathogen avirulence (Avr) gene undergoes strong diversifying selection pressure or mutation to avoid recognition by host (R) genes [81]. The low levels of pathogenic resistance by some transgenic crops coupled with the negative perception of genetically modified plants have resulted in a relatively small number of transgenic lines being brought to late stage field testing and even fewer that have been successfully brought to market.…”

Environmental Impact of Genetically Modified Crops

“…Studies on adults and larvae of the two ladybird beetles Adalia bipunctata (Walker et al, 1998) and H. axyridis (Ferry et al, 2003;both Coleoptera: Coccinellidae) and the stinkbug Perillus bioculatus (Hemiptera: Pentatomidae) revealed that their major digestive proteolytic activity is cysteine-based (Ashouri et al, 1998;Overney et al, 1998). In contrast, carabid beetles have been found to rely upon serine proteases (both trypsin-like and chymotrypsin-like) for protein digestion (Gooding and Huang, 1969;Terra and Cristofoletti, 1996;Ferry et al, 2005) and N. brevicollis adults exhibited both serine and cysteine digestive protease activity .…”

“…Examples include: the ladybird H. axyridis (Ferry et al, 2003), different carabid beetles Ferry et al, 2005;Mulligan, 2006) and the predatory stinkbug P. bioculatus (Bouchard et al, 2003a,b). Indirect evidence for such an adaptation is also reported for larvae of C. carnea.…”

“…Most studies to date have demonstrated that crops transformed for enhanced pest resistance have no deleterious effects on beneficial insects (reviewed in Ferry et al, 2003;.…”