Indigenous plants and weeds on the Makhathini Flats as refuge hosts to maintain bollworm population susceptibility to transgenic cotton (Bollgard)

The Makhathini Flats is mainly a small-scale farming area, with many farmers planting cotton varieties that have been modified to contain the Bt gene derived from Bacillus thuringiensis var. kurstaki (Bollgard™). This gene produces an endotoxin that provides resistance to attack from the bollworm complex. Cotton growers who plant transgenic cotton are required to plant a refuge area of non-transgenic cotton, as stated in the license agreement for Bollgard™. In addition to this requirement, indigenous plants and weeds were investigated as an additional refuge for bollworms. Scouting was used to monitor the number of bollworms (American or 'African' bollworm, Helicoverpa armigera (Hubner), spiny bollworms Earias biplaga Walker and Earias insulana Boisduval and the red bollworm Diparopsis castanea Hampson). Bollworm larvae were found to be present in high numbers on nine plant species that may serve as refuges. Abutilon austro-africanum Hochr. and A. sonneratianum (Cav.) Sweet, appeared to be the preferred alternative host plants of spiny bollworm.