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Agency Position Paper for June 2004 SAP (5/04/04)
The Agency has reviewed and evaluated the product characterization data, human health data, ecological toxicity data, and insect resistance management plan for the Cry1F/Cry1Ac proteins expressed in Widestrike cotton, and the data to support continuation of the 95:5 external, unsprayed structured refuge for cotton bollworm resistance management for Bollgard cotton and Bollgard II cotton. Following is a brief description of the Agency’s position based on the scientific findings.
The mammalian toxicity data submitted for WideStrike cotton includes toxicity testing on each individual Cry protein as well as studies with the combination of Cry1Ac and Cry1F. All the tests were done with purified protein at high doses approaching the limit dose values for acute oral toxicity. Based on the results of mammalian toxicity studies and product characterization data for the Cry1F and Cry1Ac proteins expressed in WideStrike cotton, the Agency’s risk assessment indicates that WideStrike cotton should not cause adverse effects to human health.
Based on the evaluation of the submitted limit dose testing data and information on the general biology of Bt Cry proteins, the Agency’s ecological risk assessment did not identify any adverse effects on the flora and fauna of the cotton agroecosystems that would be expected from the cultivation of WideStrike cotton. Specific data were reviewed relating to aquatic and terrestrial wildlife, Cry protein fate in soils, potential effects on soil biota and field census data examining the effects on non-target foliar insects, and endangered or threatened species hazard assessment, particularly Lepidoptera listed as threatened or endangered by the United States Fish and Wildlife Service. The submitted studies examined the effects of the Cry1F and Cry1Ac proteins separately and in combination to detect any possible synergistic effects. No synergistic effects or increase in non-target host range as a result of stacking were identified.
WideStrike cotton, expressing both the Cry1F and Cry1Ac insecticidal control proteins, is intended to protect cotton from feeding by three key lepidopteran pests of cotton in their respective geographies: tobacco budworm (Heliothis virescens, TBW, Lepidoptera: Noctuidae)), pink bollworm (Pectinophora gossypiella, PBW, Lepidoptera: Gelechiidae), and cotton bollworm (Helicoverpa zea, CBW, Lepidoptera: Noctuidae). Dow AgroSciences’ (Dow’s) proposed insect resistance management (IRM) plan for WideStrike proposes the following refuge options:
1. 5% external unsprayed refuge option. Five percent of the cotton fields must be planted to non- Bt cotton and not be treated with any lepidopteran-control technology. The refuge must be at least 150 ft. wide (preferably 300 ft.) and within ½ mile (preferably adjacent or within 1/4 mile or closer) of the Bt cotton.
2. 20% external sprayable refuge option. Twenty percent of the cotton fields must be planted to non- Bt cotton and may be treated with lepidopteran-active insecticides (or other control technology) except for microbial Bt formulations. The refuge must be within 1 mile (preferably within ½ mile or closer) of the Bt cotton fields.
3. 5% embedded refuge option (for TBW and CBW). Five percent of a cotton field (or fields) must be planted with non- Bt cotton as a block within a single field, at least 150 ft. wide (preferably 300 ft. wide) or single field blocks within a one mile squared field unit. The refuge may be treated with lepidopteran-active insecticides (or other control technology) only if the entire field or field unit is treated at the same time.
4. Embedded (in-field strip) refuge option for PBW. One single row of a non- Bt cotton variety must be planted for every 6 to 10 rows of Bt cotton. This can be treated with lepidopteran-active insecticides (or other control technology) only if the entire field is treated at the same time.
5. Community refuge option. Farmers can combine neighboring fields within a one-mile squared field unit that act as a 20% sprayable refuge or the 5% unsprayed refuge. Participants in the community refuge option must have a community refuge coordinator and appropriate documentation is required.
Based on the Agency’s analysis, the Dow IRM plan is appropriate for insect resistance management to the Cry1F and Cry1Ac proteins expressed in WideStrike cotton. The Dow CBW modeling efforts show that we can have high confidence that there will not be a significant change in population fitness of CBW on WideStrike cotton in a 15-year time horizon even without a high dose for either Cry1Ac or Cry1F and incomplete cross-resistance (20 to 60% maximum shared binding). For TBW, the addition of a second insecticidal control protein (ICP), makes the 20% refuge even more durable than for a single ICP expressed at a high dose and reduces the refuge size (as compared to a single, high dose ICP) needed for the same level of protection as predicted by past TBW resistance management models across the same time horizon. For PBW, WideStrike cotton expresses a high dose of Cry1Ac. Cry1F is not effective against PBW. A market mix of different Bt cottons, as well as other control technologies, further reduces the expected selection pressure for resistance against the Cry1F and Cry1Ac proteins expressed in WideStrike cotton.
As a condition of the Bollgard® cotton and Bollgard® II cotton registrations, EPA required the Monsanto Company conduct CBW alternate host research studies and pyrethroid overspray studies that would support the adequacy of the 5% external, unsprayed, structured refuge for CBW resistance management. Based on the Agency’s review of the pyrethroid overspray studies, pyrethroid oversprays in Bollgard cotton fields will increase the level of control of CBW and delay the evolution of resistance. The Agency’s review of the two-year alternate host studies conducted in five states indicates that both C3 and C4 alternative hosts serve as unstructured refugia. CBW moths are produced on alternative hosts in sufficient numbers throughout the cotton growing season (synchronous) to mate with any putative resistant CBW moths emerging in Bollgard or Bollgard II cotton fields and dilute resistance. That is, the susceptible CBW moths coming from alternative hosts will reduce the intensity of Cry1Ac and Cry2Ab2 resistance selection in CBW and lower the likelihood of resistance evolution. Despite the limitations EPA has identified associated with the Gustafson et al. (2001/2004) model, both the pyrethroid overspray data and alternate host data support the model’s predictions that it will take many times longer for CBW resistance evolution than without the inclusion of these parameters. Other data regarding CBW reverse migration indicated no significant impact on CBW adaptation to Bt corn and cotton. Based on the Agency’s analyses, the pyrethroid overspray studies and alternative host studies support the continuation of the 5% external, unsprayed structured non-Bt (Bacillus thuringiensis) cotton refuge for CBW resistance management.