Effect of nitrogen rate on corn rootworm (Diabrotica spp.) beetle emergence and sex composition using Bt and non-Bt hybrids

Nitrogen is a necessary biological component of corn (Zea Mays L.) and corn rootworm (Diabrotica spp.) development. Recommended fertilization rates routinely reflect maximum economic yield, but nitrogen effects on beetle emergence, sex ratios and emergence timing from corn rootworm-active Bt (Bacillus thuringiensis Berliner) producing hybrids remain unknown. This study examines the effect of increased nitrogen rates on beetle emergence, sex ratio of emerged adults and timing of beetle emergence from transgenic corn and possible implications for Insect Resistance Management (IRM) plans. The experiment contained a factorial treatment arrangement in a split-plot randomized complete block design with six nitrogen rates as the main plots and three hybrids, differing in corn rootworm traits, as the sub-plots. Beetles were collected every two to three days during emergence using cut-plant emergence cages. Resulting beetle concentrations and sex composition were calculated. Beetle emergence was significantly affected by an interaction between hybrid and nitrogen rate. Male beetle emergence experienced an interactive effect between hybrid and applied nitrogen rates, while female beetle emergence was affected by hybrids only. Hybrids significantly affected timing of beetle emergence for both sexes, but nitrogen rates only had a significant impact on timing of male beetle emergence. Implications of nitrogen effects on beetle emergence, influence on sex ratios and timing of emergence in relation to IRM plans will be discussed.