Factors Affecting the Relative Abundance of Arthropods on Nectaried and Nectariless Cotton1

This study further confirms that nectariless cultivars of cotton are less attractive than the near-isogenic nectaried cultivars when grown in small plots. The results also indicate that pest and beneficial arthropods are not reduced to the same degree. Of the 15 pest categories, 7 were little reduced by the nectariless cultivar, whereas the remaining eight had reductions of 24 to 42% averaged for the 4-year study period. All 15 beneficial species categories showed a significant (P < 0.05) reduction on the nectariless cultivar (38 to 69% four year averaged reduction), these being affected to a greater degree than the pest. A disturbing question that remains is whether the utility of nectariless cultivars for reducing pest pressures is afforded at commercial levels of planting. As plot size increased from 0.11 to 4.05 ha, the reduction on the nectariless cultivar decreased from ca. 38 to 32%. The rate at which the differences between the nectaried and nectariless cultivars decreases implies that the advantage with the nectariless cultivar might disappear with commercial scale plantings. Further large-scale trials would however be required for confirmation of this trend