Performance of sugar beet hybrids with sugar beet root maggot-resistant pollinators

Sugar beet root maggot (SBRM; Tetanops myopaeformis ) is a major insect pest of sugar beet throughout much of North America. Two insecticides with the same mode of action are used almost exclusively for SBRM control. Alternative control strategies would be required if insecticide-resistant SBRM developed or the insecticides were no longer available due to regulatory actions. Germplasm lines with SBRM resistance are available, but information on the SBRM resistance of hybrid cultivars created by crossing these lines with a SBRM-susceptible cms parental line is lacking. This study compared the performance of four hybrids with SBRM-resistant pollinators to two susceptible hybrids, with and without insecticide, in four environments. In all environments, the hybrids with the SBRM-resistant pollinators and no insecticide had root yields equal to the SBRM-susceptible commercial hybrid with insecticide. In two environments, the root yields of the SBRM-susceptible hybrids were low and the difference between the root yields with and without insecticide was relatively small, indicating the insecticide was ineffective. In contrast, the root yields of the SBRM-resistant hybrids, with or without insecticide, in these trials were substantially higher than the susceptible hybrids and similar to corresponding root yields at the other sites. Based upon these trials, it appears that hybrids produced with the currently available resistance sources would have sufficient SBRM resistance to prevent catastrophic yield reductions due to SBRM feeding, could reduce uncertainty caused by fluctuations in insecticide effectiveness, would provide protection against the development of insecticide-resistant SBRM strains, and also provide a useful level of SBRM protection, if the current insecticides were no longer available.