Vip3A is a group of vegetative insecticidal proteins (i.e., produced during the vegetative stage of bacterial growth) from Bacillus thuringiensis, a gram-positive bacterium commonly found in soil. The Vip3A proteins are highly toxic to some lepidopteran insects.

Vip3Aa20 is a mutated form of the vip3Aa19 gene from the Bacillus thuringiensis strain AB88. The mutation occurred by two codon changes within the vip3Aa19 coding sequence when this gene was introduced in the maize event MIR162. One of these was a silent mutation and the other codon change resulted in an amino acid substitution. Therefore, the vip3Aa gene variant present in MIR162 maize has been designated vip3Aa20.