Question & AnswerQ&A (DA MEMORANDUM CIRCULAR NO. 17, SERIES OF 2003)
The main objective of the IRM strategy is to reduce the risk of the target insect, Asian Corn Borer (ACB), developing resistance to Bt corn plants through a combination of strategies.
The 'high dose and refuge' strategy refers to planting Bt corn at a high enough dose to guarantee over 99% protection from ACB, with a refuge area serving as a source of Bt susceptible insects to mate with resistant ones, maintaining population susceptibility.
The refuge can be either structured or unstructured. An unstructured refuge is represented by diverse scattered production systems, whereas a structured refuge involves a specific planting pattern, such as an 80% Bt to 20% non-Bt planted area.
The structured refuge must be implemented when either the adoption rate reaches 80% Bt corn in a cluster/production area of contiguous 200 hectares or more, or two years after the implementation of the IRM strategy for Bt corn technology.
Regulated sales means that the industry must implement a market cap limiting the volume of Bt corn sales to 95% in a given production area to maintain an unstructured refuge.
The DA is responsible for monitoring industry compliance, supporting related research studies, educating stakeholders, and capability building of its agencies to effectively implement the IRM strategy.
Studies required include baseline population susceptibility, biology and alternate host preference of ACB, integrated pest management, and insect biodiversity/management of agro-ecosystems.
They plan to pilot test the 80% Bt : 20% non-Bt seed combination in a 'bag-in-a-bag' format to assess its practicality and feasibility before broader implementation.
The DA will conduct a periodic review after every major cropping season, which is twice yearly in February and September.
Revalidation occurs when new information from completed studies or other Bt crop approvals for environmental release emerge to ensure the IRM system adequately mitigates resistance development.