High-Tech Trap Crop
Trap crops - plants that an insect pest prefers over the desired crop - have
been tested in a number of agricultural settings, but in most cases have not achieved control levels high enough to completely replace chemical pesticides. Insects are attracted to the trap plant, but they multiply there and can spread to the adjacent crop. A variant on this concept is to incorporate expression of the Bacillus thuringiensis (B.t.) insecticidal protein into the trap plant. When the insect feeds on the transgenic trap plant, it dies and the insect population is reduced, thereby protecting the nearby commercial crop.
Dry Creek Laboratories of Hughson, CA, demonstrated this concept with codling moth (Cydia pomonella), a major pest of apples, pears, walnuts and other fruit. The female moth lays eggs on the leaves or fruit, which then hatch into larvae that burrow into the fruit, making them unmarketable. Pesticide sprays and pheromone disruption are generally used to control this pest. However, the female moth prefers to lay its eggs on apple trees. Under license from Monsanto, Dry Creek Laboratories developed apple trees capable of expressing a B.t. protein that was toxic to the codling moth larvae, with the intention of using these plants as trap crops in and adjacent to walnut orchards. A 90-acre field trial was established in 1997, and in the four subsequent years, worm damage to the walnuts was almost completely controlled without pesticide applications, equivalent to that in the plots sprayed three times per season with pesticides. While walnuts have also been transformed to express the B.t. protein directly, an attractive feature of this scheme is that the walnuts themselves are not transgenic and the method could be used to protect existing orchards by interplanting the B.t.-expressing apple or crabapple trees. Broader application of this approach could result in more effective trap crops for a number of annual and perennial crops. Unfortunately, Dry Creek Laboratories is unable to move forward at this time with commercialization of the B.t. apple plants due to the costs associated with the regulatory process required for biotech crops. (http://www.checkbiotech.org/root/index.cfm via Agnet, 5/6/04).
