Increased activity of a hybrid Bt toxin against Spodoptera frugiperda larvae from a maize field in Cuba.

Spodoptera frugiperda is the most important maize pest in Cuba. The activity of seven Bacillus thuringiensis Cry1 toxins (five wild-type and two domain-swapped) was investigated in bioassays against newly hatched larvae from adults collected in a Cuban maize field. The CryAAC (1Ac/1Ac/1Ca) hybrid showed the lowest effective dose (50% lethal dose, LD50) of 288 ng/cm² contrasting with parental Cry1Ca and Cry1Ac, which were not lethal (LD50 > 3000). The wild type Cry1Fa was the second most active toxin (LD50 565 ng/cm²). Hybrid H04 (1Ab/1Ab/1Ca) was only weakly toxic (LD50 1750 ng/cm²). To our knowledge, this is the first report where the CryAAC hybrid toxin is tested against this insect pest. [ABSTRACT FROM AUTHOR]