The objective of this study was to determine the feeding sites and behavior of the tobacco budworm Heliothis virescens F. and the effect of gland density and distribution as a potential mechanism of resistance in certain breeding lines of cotton.

In 1983, we planted forty breeding lines of cotton with varying degrees of resistance to tobacco budworm to study behavior and feeding sites of newly hatched larvae. During 1984, we restricted our study to 8 lines and conducted a more detailed study. We determined the plant parts on which the larvae feed and counted the gossypol glands present on these parts.

We found significant differences between 'Stoneville 213' and resistant lines in the number of gossypol glands on bracts of small squares (2 mm on side), calyx lobe, bract mid rib and total calyx. Correlation coefficients of gland densities on small square bract, calyx lobe, bract mid rib, and total calyx were each significant. The highest correlation coefficient was between gland densities on calyx lobe and total calyx. When first instar larvae were placed on squares and weighed at 7 and 12 days, the cotton lines containing glands in excess of 120 per small square bract or 80 in the calyx lobes produced worms significantly smaller than lines with gland densities below this number.

In past years, high gossypol content of cotton cultivars has been considered a primary resistance mechanism to the Heliothis complex. Research on gland densities and distribution as they influence feeding behavior of larvae has been limited. From this study gland density and distribution on the sites where larvae feed may serve as a stronger mechanism for resistance than previously considered.