Environmental Protection Agency WHITE PAPER ON RESISTANCE IN LEPIDOPTERAN PESTS OF BACILLUS THURINGIENSIS (Bt) PLANT-INCORPORATED PROTECTANTS IN THE UNITED STATES April 11, 2018 TABLE OF CONTENTS ABSTRACT ............................................................................................................................................................................ 5 DOCUMENT ORGANIZATION ......................................................................................................................................... 8 I. BACKGROUND ...................................................................................................................................................... 8 A. PEST OF BT CORN AND BT COTTON ............................................................................................................................. 8 B. CURRENT IRM STRATEGIES AND REQUIREMENTS FOR BT CORN AND COTTON ........................................................ 10 C. CURRENTLY REGISTERED BT CORN PLANT-INCORPORATED PROTECTANTS FOR LEPIDOPTERAN PESTS .................. 12 D. CURRENTLY REGISTERED BT COTTON PIPS FOR LEPIDOPTERAN PESTS ................................................................... 13 E. CURRENT RESISTANCE MONITORING AND MITIGATION STRATEGIES FOR BT CORN AND COTTON ........................... 14 1. Bt Corn – Resistance Monitoring and Mitigation ................................................................................................. 14 a. Bt Corn – Annual Population Sampling and Bioassays .......................................................................................................15 b. Bt Corn – Investigation of Reports of Unexpected Damage ................................................................................................17 c. Bt Corn – Resistance Mitigation ..........................................................................................................................................17 2. Bt Cotton – Resistance Monitoring and Mitigation .............................................................................................. 19 a. Bt Cotton – Annual Population Sampling and Bioassays ....................................................................................................19 b. Bt Cotton – Investigation of Reports of Unexpected Damage .............................................................................................19 c. Bt Cotton – Resistance Determination Criteria ....................................................................................................................20 d. Bt Cotton - Mitigation ..........................................................................................................................................................20 II. PROBLEM FORMULATION .............................................................................................................................. 20 A. CASES OF LEPIDOPTERAN RESISTANCE IN THE US .................................................................................................... 21 B. CAUSAL FACTORS OF RESISTANCE ........................................................................................................................... 21 1. All Bt toxins are non-high dose for H. zea and expedite resistance development ................................................. 21 2. Bt toxins expressed in both corn and cotton exert continuous selection pressure on some pests ......................... 21 3. Mosaic of single and pyramided traits undercuts pyramid durability .................................................................. 22 4. Use of seed blends in the southern US expedite resistance in ear-feeding pests of corn ...................................... 22 5. Refuge non-compliance undercuts durability of pyramids ................................................................................... 22 6. Methodology for sampling insects and diet bioassays delays resistance detection .............................................. 22 7. Lack of regulatory triggers for unexpected injury delays reporting of putative resistance .................................. 23 8. Current definition of resistance delays mitigation actions ................................................................................... 23 9. Cross-resistance between Bt toxins reduces durability of pyramids ..................................................................... 23 10. Non-functional pyramids lead to faster resistance development ...................................................................... 23 11. Mitigation of resistance occurs too late ........................................................................................................... 23 12. S. albicosta resistance to Bt corn ..................................................................................................................... 24 a. Limited availability of Cry-toxins reduce longevity of Vip3A technology ..........................................................................24 b. Low amount of refuge for single Bt trait reduces its durability ............................................................................................24 c. Seed blends and risk resistance ............................................................................................................................................24 III. SCIENTIFIC UNCERTAINTIES WITH IRM FOR LEPIDOPTERA PESTS AND POTENTIAL IMPROVEMENTS TO IRM STRATEGIES FOR BT CROPS ........................................................................ 24 A. LEPIDOPTERAN RESISTANCE REPORTS IN THE CONTINENTAL US ............................................................................. 24 1. H. zea resistance and field failure reports ............................................................................................................ 25 2. D. grandiosella resistance reports ........................................................................................................................ 27 3. S. frugiperda resistance reports ............................................................................................................................ 28 4. S. albicosta resistance reports .............................................................................................................................. 29 B. CAUSAL FACTORS OF RESISTANCE ........................................................................................................................... 31 1. Non-high dose traits and risk of faster resistance development ........................................................................... 31 2. Toxins expressed in corn and cotton exert continuous selection pressure ............................................................ 32 2 3. Mosaic of single and pyramided products undercuts durability of pyramids ....................................................... 33 4. Seed blends in the southern US and faster resistance development in ear-feeding pests of corn ......................... 34 a. Mosaic of variable toxin expressions in kernels ...................................................................................................................34 b. Pollination pathways, survival, and development: ...............................................................................................................35 c. Maternal Bt plants: ...............................................................................................................................................................35 i. Mosaic of kernels with variable Bt expression for a three-gene pyramid planted to pure stands ....................................36 ii. Mosaic of kernels with variable Bt expression for single trait products planted to pure stand ........................................37 d. Cross-pollination of refuge ears in RIBs: .............................................................................................................................37 5. Refuge non-compliance in the southern US undercuts durability of pyramids ..................................................... 39 6. Methodology for insect collections and diet bioassays delays resistance detection ............................................. 41 a. Current Resistance Monitoring and Mitigation Strategies for Bt Corn and Cotton ..............................................................41 b. Summary of H. zea Bioassay Results ...................................................................................................................................41 7. Lack of thresholds for unexpected injury delays reporting of putative resistance ................................................ 47 a. Lack of regulatory UXI thresholds .......................................................................................................................................47 b. Criteria for UXI thresholds ..................................................................................................................................................47 8. Current regulatory definition of resistance delays mitigation actions .................................................................. 49 9. Cross-resistance between Bt toxins reduces durability of pyramids ..................................................................... 50 10. Non-functional pyramids lead to faster resistance development .....................................................................