The cotton line COT102 was engineered to resist attack from Lepidopteran insect pests such as the cotton bollworm (Helicoverpa zea), tobacco budworm (Heliothis virescens), pink bollworm (Pectinophora gossypiella), fall armyworm (Spodoptera frugiperd), beet armyworm (Spodoptera exigua), soybean looper (Pseudoplusia includens), cabbage looper (Trichoplusia ni), and cotton leaf perforator (Bucculatrix thurberiella).

This insect resistance is conferred by the vip3Aa gene, originally isolated from the common soil bacterium Bacillus thuringiensis strain AB88. The vip3Aa gene produces the insect control protein VIP3A in the plant tissues. VIP3A is a member of a class of recently discovered insecticidal proteins: VIP (vegetative insecticidal proteins) proteins are expressed by the bacterium during the vegetative stage, as well as during sporulation, the stage at which the delta-endotoxins (i.e., Cry proteins) are expressed. 

VIP proteins have an insecticidal mode of action similar to that of the delta-endotoxins: the ingestion by targeted insects leads to feeding cessation, loss of gut peristalsis, insect paralysis, and death. As with Cry proteins, VIP proteins also possess an active proteolytic core, which is activated by insect gut proteases, and binds to specific sites localized on the midgut lining of susceptible insect species. However, the VIP3A protein targets different molecules (i.e., receptors) in the mid-gut lining, and the binding results in the formation of ion channels distinct from those formed by delta endotoxins, such as Cry1Ab. 

VIP proteins are not expected to affect other invertebrate and vertebrate organisms, including beneficial arthropods, birds and mammals. Only lepidopteran insect species possess VIP binding sites on the surface of their gut epithelia, therefore, livestock animals and humans are not susceptible to these proteins. Also, since only lepidopteran insect species are targeted by the VIP proteins, species of other insect orders, including beneficial and pest species, are not expected to be affected by this insecticidal protein.