Assessment of density-dependent feeding damage by the cotton dusky bug, Oxycarenus laetus Kirby ( Hemiptera: Lygaeidae), in cotton

The dusky cotton bug, Oxycarenus laetus Kirby (Hemiptera: Lygaeidae), is a serious threat to cotton due to early cultivation of Bt cotton. These studies were carried out under laboratory and field conditions to estimate the feeding damage caused by O. laetus to seed weight, seed germination, and lint quality of cotton cultivar Bt-121 at 6 bug densities (0, 5, 10, 15, 20, and 25 adult pairs). The results revealed that seed germination and seed weight decreased, whereas percent reduction in seed germination and seed weight over control increased with increasing bug density. Bug density in the range of 5-25 pairs caused approximately 9.3%-40.7% reduction in seed germination and 7.5%-29.5% reduction in 100-seed weight over control in both laboratory and field trails. The color of lint changed from pure-white to white when bolls were exposed to 10 and 15 pairs of bugs, while it changed to light-yellow and slightly yellow when bolls were exposed to 20 and 25 pairs of bugs, respectively. Bug density had a high negative correlation with percent seed germination and 100-seed weight, while it had a high positive correlation with reduction in seed germination, reduction in 100-seed weight, and lint quality, under both laboratory and field conditions. Bug density explained more than 95% of total variability in seed germination, reduction in seed germination, 100-seed weight, and reduction in 100-seed weight under both laboratory and field conditions; it explained less than 95% (93.2%) of total variability in lint staining under field conditions. These results indicate that reductions in seed weight, seed germination, and lint quality depend upon bug density. Hence, appropriate control measures should be adopted to check consistent increases in the dusky cotton bug population to avoid seed germination and lint quality losses.