Assessing Lepidopteran Abundance and Crop Injury in Soybean Lines Exhibiting a Synthetic Bacillus thuringiensis cry1 A Gene

Abstract

Transgenic lines of soybean, Glycine max (L.) Merrill, expressing a synthetic cry 1A gene from Bacillus thuringiensis Berliner (Bt), were evaluated in replicated field trials in 1999–2002 for suppression of lepidopteran pests and the resultant crop injury. Velvetbean caterpillar, Anticarsia gemmatalis Hübner, soybean looper, Pseudoplusia includens (Walker), and green cloverworm, Hypena scabra (F.), population densities were essentially absent throughout the growing season in each year of the study in each of the Bt lines evaluated compared with moderate (5–10 larvae per row-m) to heavy (15–20 larvae per row-m) populations in the isogenic and parental lines serving as soybean controls. Significant A. gemmatalis larval population reductions were observed in the Bt entries compared with the nonBt entries in each year of this study. The P. includens larval densities were significantly lower in Bt entries in the 3 yrs of this study when population densities were abundant, whereas H. scabra were lower in the Bt lines in the 2 yrs of this study when this species was present. Cumulative defoliation in nonBt soybean entries exceeded 95% in some years compared with 0.0–1.6% in the transgenic lines containing Bt. Yields of the transgenic soybean lines were equal to or higher than the non Bt lines examined in each year of this study. It appears that these Bt transgenic soybeans provide superior season-long control of the common lepidopteran pests on soybeans in the southern U.S., resulting in reduced defoliation levels and potentially higher yields compared with equivalent cultivars that lack the Bt trait.