Potential impact of Spodoptera exigua and Helicoverpa zea on glandless cotton in New Mexico

Cotton glands produce gossypol, a natural defense against insect pests. Glandless cotton varieties are available, but losses from pests have prevented commercial development.  Some areas of New Mexico have somewhat lower insect pressure, with high predation and desiccation, suppressing pest populations.  With appropriate management and monitoring of insect pests, growers could potentially produce glandless varieties as a niche crop with greatly added seed value. In 2011-2013, field and field to lab trials were conducted on a New Mexico State University farm to determine susceptibility to lepidopterous pests. 

In field to lab trials, bollworm and beet armyworm survival was 2-6 times higher at pupation on glandless cotton in 2013. Survival was not affected by nitrogen although there were some impacts on development.  Glandless cotton had twice as many damaged squares in the field in 2012 and 2013 but, there were no difference in 2011. The number of damaged squares were not affected by nitrogen levels. Monitoring of each instar indicated that beet armyworm was significantly more likely to molt into a sixth instar when feeding on conventional rather than glandless cotton. This delay in development allowed beet armyworm to compensate for slower weight gain and pupate at weights similar to those fed on glanded cotton despite being significantly smaller at 14 days.  Glandless cotton is more susceptible to insect injury, but will likely be manageable as a valuable niche crop.