I. Definitions

Definition #1. Putative Resistance Event--A Cautionary Alert

A putative resistance event consists of any field of Bt cotton in which collections of 100 bolls yield 3% or more large larvae (3rd instar or later), pupae or PBW exit holes in bolls and a test indicates that bolls from which large larvae were recovered were expressing Bt. This is a cautionary alert and must not be construed to be a verified resistance event until: 1) the plants from which collections were made are confirmed to produce Bt toxin and, 2) bioassays are completed that confirm the reduced susceptibility of the pink bollworm surviving on Bt cotton.

Definition #2. A Verified Resistance Event.

A putative resistance event becomes verified if three conditions are met:

• A sample of 1000 bolls yields 3% or more containing large larvae (3rd instar or later), pupae, or PBW exit holes.
• A test yields a positive response for Bt toxin in a sample of 10 bolls from which PBW larvae were recovered.
• Standardized laboratory bioassays demonstrate that the PBW population of interest is significantly less susceptible to Cry1A(c) toxin than were baseline populations in 1997 (Simmons et al. 1998 and unpublished).

II. Remedial Action

A. Putative Resistance Event: Year of First Detection.

Once a putative resistance event occurs, alternative PBW controls should be implemented in that field. Measures should include one or more of the following:

• Adulticide treatments if crop is in active growing state, followed by additional insecticide applications (2) on a 3-day schedule, or based on adult emergence as predicted by phenological models.
• If crop is senescent, consider chemical termination to reduce squares and bolls less than 10 days old, accelerate harvest, and destroy crop residue by shredding of stalks followed by discing, and deep plowing (6" burial).
• If crop is defoliated, accelerate harvest and destruction of crop residue to further limit survival of resistant pink bollworm. Destroy crop residue as indicated above.
• Encourage producer to employ cultural practices intended to reduce pink bollworm overwintering, survival and reproduction in the field.

1. If resistance is verified in time to permit it, we strongly recommend that measures be taken to reduce the numbers of resistant pink bollworm that survive to the next season. These could include: adulticide treatments, early termination, and early plowdown, consisting of shredding of stalks followed by discing, and deep plowing (6" burial). Winter irrigation is also recommended to reduce survivorship of overwintering larvae.
2. Bt fields in the immediate vicinity of a verified resistance event should be examined to detect unusual survivorship of PBW. Results should be used to delimit the size of the affected area and to define the ‘Bt remedial action zone.’ We suggest sampling 300 bolls from Bt fields located within each of the 8 sections of land (designated by © in the adjacent figure) that surround the section of land on which the verified event (VE) occurred. Bt cotton fields in addition to the original VE field, containing 3% or more bolls infested with PBW should be considered affected by resistance for the purpose of delimiting the remedial action zone.
   
3. The ‘Bt remedial action zone’ should be delineated using GPS mapping technology currently in use at the ACRPC. This will ensure accurate records of locations of verified resistance. The remedial action zone should include all sections of land falling within 6 miles of the perimeter of the section(s) of land in which verified resistance events occurred (see figure below).
4. At such time as fields with verified resistance are detected in >3 different townships within a particular cotton growing region, the entire region may be designated as a Bt resistance remedial action zone.

1. Only non-Bt cotton or GM cotton that kills resistant individuals should be planted in the remedial action zone in the year(s) immediately following verification of resistance. This measure should be maintained until such time as bioassays of PBW from the remedial action zone demonstrate that the frequency of resistant individuals has declined to acceptable levels. What will constitute levels of resistance acceptable for allowing resumption of use of Bt cotton will be determined on an ad hoc basis by our Working Group, based on research experience that members have obtained from studies of pink bollworm resistance to Cry1Ac.
2. It is assumed that published University recommendations for monitoring and chemical control of pink bollworm will be followed within remedial action zones in order to limit survival of resistant pink bollworm. Additionally, timely crop termination (no production of bolls after Sept. 15) and early and thorough crop destruction, as detailed above, is strongly encouraged. The feasibility of releases of sterile pink bollworm should be investigated.
3. The recommendations of our working group regarding 1) Bt refuge management and 2) remedial action for responding to PBW resistance in Arizona should be re-evaluated annually and modified to account for new findings. Educational programs and regulatory measures should be devised to promote a high level of producer compliance with recommendations.

III. Recommended Organizational Roles

1. The Arizona Department of Agriculture within its organizational framework should serve a central role in implementing this plan, compiling statistics on use of Bt cotton, and promoting compliance with remedial action.
2. A sampling team comprising personnel from relevant organizations (ACRPC, UA, USDA) will be formed. This team will be ready in August of every year to conduct the sampling required to delineate resistance problems (as detailed above). Similarly, facilities and personnel at EARML will be prepared to conduct bioassays of up to 20 different populations of PBW per season. Funding for these efforts must be sustained.
3. Registrants should agree to suspend Bt cotton sales in remedial action zones until such time as either the frequency of resistant individuals is shown to have declined to levels deemed acceptable by our Working Group, or new Bt products free of cross-resistance are introduced, and the Arizona Bt Cotton Working Group has concluded that a modified resistance management strategy has been adopted that will adequately reduce the rate of development of further resistance to Bt cotton products.

IV. Select Resistance References from the AZ Bt Cotton Working Group