Did you know?
In the last 10 years the introduction of transgenic cotton and IPM has resulted in a 80% reduction in pesticide use which has had a positive effect on biodiversity in and around cotton.
Complete Final Report
The adoption of Integrated Pest Management (IPM) principles plays a crucial role in the future sustainability of a cotton industry based on transgenic cultivars in the Northern Territory (NT). Certain pest insects, some of which are present in the NT, have a demonstrable ability to develop resistance to conventional, and possibly novel, control tactics, and IPM utilises strategies to minimise that risk. Tactics employed during trials in Katherine included avoidance of high summer insect pest densities via a winter cropping system, reliance on natural enemies for biological control, provision of unsprayed refuges like companion crops for natural enemy proliferation, trap crops to attract insect pests away from cotton, understanding the ability of cotton plants to compensate for pest insect damage, and utilisation of target selective insecticides at lowest effective concentration only when absolutely necessary. The idea was to maintain a balance of insects, both good and bad, so principal insect pests were maintained below thresholds that cotton plants could tolerate without loss of yield. Transgenic cotton currently requires few insecticidal treatments in Katherine, allowing natural enemies to do their work, and IPM research is needed to ensure this system improves and remains sustainable.
Transgenic cotton trialled in Katherine produces proteins from a common bacteria (Bt) in its tissues that are poisonous to a select group of insect pests. Refuge crops play a pivotal role in prolonging the control efficacy of transgenic cotton by permitting development of relatively large numbers of pest individuals not exposed to these Bt proteins. Should a resistant individual successfully develop on transgenic cotton, its genes are dissipated when it mates within the local population dominated by non-resistant individuals from neighbouring companion crops. Irrigated lablab produces large numbers of Helicoverpa armigera moths, which are potentially resistant to Bt cotton, in the NT during the winter growing season, and was tested as a possible companion crop for a local transgenic cotton production system.Although lablab effectively maintains relatively large numbers of H. armigera season long, insect pest and natural enemy densities and lint yield and quality from cotton crops grown with and without lablab companions were not different. Companion crops with more discernible advantage to cotton production should be trialled to improve IPM in the future.
Insecticide use was kept to a minimum during cotton IPM trials in Katherine. The number of applications and products utilised per season steadily decreased as the IPM system was refined. In the final year of the project, an average of 2.8 sprays of mainly fipronil to selectively control sucking insects were applied to cotton crops which achieved record yields.
The majority of insect pest suppression was achieved via Bt cotton’s inherent control
potential, which has not waned for the life of the project, and biological control with natural enemies. Many different insects make up the suite of effective natural enemies in Katherine cotton, most importantly ladybeetles, hover flies, spiders and parasitic wasps called Trichogramma. Ladybeetles and hover flies effectively control aphids and whitefly in Katherine cotton when not disrupted by insecticide application. Spiders are more robust and persist season long in Katherine cotton, but are less selective with prey, eating pests and natural enemies alike. Trichogramma parasitise a high percentage of H. armigera eggs early season in Katherine. They contribute to the management of possible resistance in H. armigera as parasitised eggs do not hatch so are never exposed to Bt proteins. Natural enemies are critical to the Katherine cotton IPM system, and their pest control efficacy governs the need, or lack there of, for judicious insecticide selection and application.
Managing potential resistance in moth pests requires a thorough understanding of their seasonal phenology. Four moth pests of cotton, including H. armigera, were monitored using pheromone traps in strategic locations throughout the Katherine region. Helicoverpa armigera persist year round with population peaks in both the wet and dry seasons in Katherine, hence their potential to develop resistance if continually exposed to repeated control measures. Closely related H. punctigera tend to migrate into crops early dry season so are less likely to develop resistance. Pectinophora gossypiella are a wet season phenomenon, so this potentially devastating cotton pest is effectively avoided by cropping through winter. Spodoptera litura are prevalent in the wet season but persist into cotton crops through the dry so, although they tend to be less damaging than the other three moths, their pest status and possible control measures require examination. To date, H. armigera resistance to Bt proteins has not caused problems in Katherine, although resistance to conventional insecticides is of concern and has been detected, often to products not utilised by the cotton project. Area wide management of H. armigera should be adopted to ensure potential resistance to insecticides does not become problematic in the Katherine region. Continued monitoring of H. armigera, H. punctigera and S. litura populations would be required should cotton production trials proceed.
The Katherine IPM project has laid the foundation for environmentally sound pest management in future local transgenic cotton production systems. Further development and refining of the IPM system is of course reliant on continued regionally specific research should cotton trials proceed. Rigorous adoption and application of the IPM principles outlined herein is critical to the future sustainability of transgenic cotton production in the NT.
