The insertion of specific lectin genes into crops is showing value in IPM programs for controlling pestilent organisms. Lectins belong to a broad group of bioactive peptides called defensins that elicit a variety of responses that can defend plants from a range of factors including environmental stress, predation by insects, and infestations by bacteria, fungi, and nematodes. Many agricultural plants lack lectin defenses, however, making them susceptible to yield losses from pest infestations.

John and Angharad Gatehouse of Durham University, UK, and their research team report successfully inserting lectin genes into potatoes to facilitate the biological control of lepidopteran larvae.(1) Their goal was to facilitate biological control of the plant-feeding larval form of Lacanobia oleracea, tomato moth, using both the lectin-expressing transgenic potato and a parasitoid wasp, Eulophus pennicornis. In effect, they succeeded in producing a pesticidal potato that specifically harms the phytophagus moth larvae without impairing the beneficial wasps that prey on the pest.

GNA (Galanthus nivalis agglutinin) is a naturally-occurring lectin found in snowdrop plants (Galanthus nivalis). The amaryllis, iris, and lily families are noted for strong plant defense mechanisms that include defensin production. Lectins are favored over other pesticidal plant compounds because of their low toxicity to humans and domesticated animals at levels that are effective against insect larvae, and GNA does not appear to damage other organisms once the pest ingests it.

In this study, the Gatehouse team used potato plants expressing GNA at levels equaling 1% of the total soluble proteins of the plant. These levels had been shown to effectively reduce Lacanobia oleracea damage in previous research trials.(2) The transgenic plants were compared to control plants without the GNA gene. Greenhouse trials were conducted on 18 transformed and 18 non-transformed potatoes plants. Each plant was manually infested with 15 third-instar caterpillars. Ten days later, a first wave of parasitoid wasps were released into one of the greenhouses. Another set of wasps was introduced two days later just as the caterpillars were reaching the fifth instar stage. Data was collected seven days after the initial introduction of wasps.

Tomato moth caterpillars damaged significantly more leaves per plant on the control potatoes in both greenhouse trials. This result supports previous studies indicating the effectiveness of GNA on reducing Lacanobia oleracea predation. Non-transgenic plants infested with the larvae that were exposed to the parasitic wasps showed less leaf damage than those not exposed to wasps; however, leaf damage was most reduced in lectin-expressing transgenic plants subject to larvae predation by wasps.

GNA-expressing plants did not significantly decrease the population of Lacanobia oleracea larvae. However, the GNA did affect a significant decrease in caterpillar growth, thereby causing the reduction in plant feeding damage. The parasitoid wasps caused significant decreases in caterpillar number and weight on both the control and GNA-expressing plants. GNA did not enhance the susceptibility of the caterpillars to wasp predation.

The study evaluated whether GNA exposure harmed the parasitoid wasps. Analyses indicated no significant impact on wasp development. A slight reduction in wasp number for the GNA trials was not statistically significant and did not reduce the ability of the wasps to parasitize the caterpillars.

This study demonstrated that GNA plants, used in conjunction with biological control, significantly reduced crop damage to a greater extent than either strategy used alone. The advantages of using this system are that it is less likely than traditional pesticide treatment to produce resistant pests, is less toxic to the beneficial parasitic Eulophus pennicornis, and thus would likely reduce the need for environmentally harmful and costly pesticides.

Sources

1. Bell HA, et al. 2001. Transgenic GNA expressing potato plants augment the beneficial biocontrol of Lacanobia oleracea (Lepidoptera; Noctuidae) by the parasitoid Eulophus pennicornis (Hymenoptera; Eulohidae). Transgenic Research 10: 35-42.

2. Gatehouse AMR, et al. 1997. Transgenic potato plants with enhanced resistance to the tomato moth (Lacanobia oleracea): growth room trials. Molecular Breeding 3: 49-63.