Stephen Micinski and William "Bill" F. Waltman Jr.

The commercial release of Bollgard cotton in 1996 gave cotton growers a new pest management tool. Bollgard cotton, a transgenic product, includes a gene from a bacterium, Bacillus thuringiensis. This transferred gene enables the plant to produce a toxin that provides significant control of the tobacco budworm, Heliothis virescens, and the pink bollworm, Pectinophora gossypiella, while being safe for humans, other animals and the environment.

Despite its usefulness as an insect pest management tool, Bollgard cotton has several weaknesses. With a toxin produced by a single type of gene (cryIA), Bollgard cotton is extremely effective against some caterpillar pests, like the tobacco budworm, but less effective against others including the bollworm (Helicoverpa zea), soybean looper (Pseudoplusia includens) and armyworms. Another concern with Bollgard cotton is the development of resistance in the pests it is meant to control. This is because Bollgard cotton has a single, highly toxic protein present season-long in all its plant parts.

To address these concerns, scientists at Monsanto, the company that produces Bollgard cotton, have introduced a second gene (cry2Ab) with insecticidal properties into the product. The result is a transgenic cotton, Bollgard II, which has increased insecticidal activity against pests that Bollgard was weakest on and makes resistance development less likely.

Bollgard II Trials
Bollgard II cotton was evaluated during 1999 and 2000 at the LSU AgCenter Red River Research Station in Bossier City. Both years cotton was planted in late May on a Caplis very fine sandy loam. Bollgard II was compared with Bollgard and a non-transgenic cotton, DP 50. The experimental design involved both sprayed and nonsprayed plots. The sprayed plots received weekly applications (early July through mid-August) of an insecticide (Karate Z or Tracer 4SC) for worm control, and the other plots received no insecticide applications for worm control. All other insect pests were controlled on an as-needed basis, and applications were made to the entire trial. Insect damage was assessed weekly from early July through mid-August.

Both years, Bollgard and Bollgard II cottons had significantly fewer insect-damaged squares than the DP 50 cotton in both the sprayed and nonsprayed plots. In 2000, bollworm/tobacco budworm season-long mean square damage exceeded 15 percent in the DP 50 nonsprayed plots; the damage was only 6.2 percent in the DP 50 sprayed plots. The Bollgard II nonsprayed plots averaged 0.7 percent square damage compared with 1.7 percent damage in the Bollgard plots in 2000 (Figure 1).

In 1999, bollworm/tobacco budworm boll damage was not observed in the Bollgard and Bollgard II plots, regardless of whether the plots were sprayed. Boll damage in the DP 50 was 11.9 percent for the sprayed plots and 20 percent for the nonsprayed plots. In nonsprayed plots in 2000, season-long mean boll damage was 4.2 percent in the Bollgard plots and 0.2 percent in the Bollgard II plots, and DP 50 had 15.8 percent boll damage (Figure 2).

In general during 2000, soybean looper numbers were too low to observe differences between varieties. On August 9, however, a significant number of soybean loopers were picked up. Bollgard II was more effective in controlling loopers than spraying with Karate Z, which was applied August 3 (Figure 3).

Yields from 1999 and 2000 are shown in Table 1. In 1999, yields in the sprayed plots were not significantly different among varieties. In 2000, the sprayed Bollgard and Bollgard II plots yielded significantly more seedcotton per acre compared to the DP 50 variety. Both years in the nonsprayed plots, the Bollgard varieties yielded significantly more seedcotton per acre than the DP50 variety. In the nonsprayed plots in 1999, the Bollgard II plots outyielded the Bollgard plots by 311 pounds seedcotton per acre. Although the differences were not statistically different, the trend was reversed in 2000 with the Bollgard plots yielding 201 pounds seedcotton per acre more than the Bollgard II plots.

Bollgard II Advantages
Bollgard II has several advantages over Bollgard. First, the addition of the new cry2Ab gene may reduce the likelihood of insect resistance in the insects the original Bollgard controlled. Second, some increased spectrum of insecticidal activity was observed. Soybean loopers, which were at best only suppressed by Bollgard cotton, appear to be controlled by Bollgard II. Bollworm/tobacco budworm damage was less in the Bollgard II plots than the Bollgard plots, although differences were small. No differences were observed in armyworm numbers, but populations of armyworms were extremely light during the course of these trials.

Pending approval from the U.S. Environmental Protection Agency, Monsanto will conduct trials in 2001 under an Experimental Use Permit. Full registration is anticipated by the end of 2001 with limited quantities available in 2002.

Stephen Micinski, Associate Professor, and William "Bill" F. Waltman Jr., Research Associate, Red River Research Station, Bossier City, La.

(This article appeared in the winter 2001 issue of Louisiana Agriculture.)