Western bean cutworm egg and larval survival

Western bean cutworm (WBC) Striacosta albicosta is a native pest of dry beans and corn. An understanding of WBC egg and larval survival is critical to developing appropriate management practices. The objectives of these studies were to assess the survival of WBC eggs and larvae in the laboratory and field. Field studies were conducted in 2008 and 2009 across three Nebraska Ecoregions: Scottsbluff, Clay Center; and Concord. WBC egg survival and development were evaluated in the lab at three temperatures (16°C: 87.96% and 12.4 days; 25°C: 93.36% and 6.19 days; 30°C: 51.31% and 5.04 days). Larval survival in the lab, held 13 days at 25°C and fed silk and pollen diets, was approx. 63% (58-72%). Under field conditions at Concord and Clay Center, corn was artificially infested by cutting leaf squares containing single egg masses and covering with a square of screen forming a “sandwich”. The percentages of eggs hatched were 76.39% and 89.04%, respectively. Larval survival was determined in the field at three locations. The number of the eggs, infested 20 days before, was correlated with the number of the larvae. In Scottsbluff (2008) the relationship was significant (p-value=0.0002; r2=0.58) and the mean number of the larvae was 0.73/plant. At Concord and Clay Center (2008 and 2009) the relationships between egg and larval densities were not significant and were 0.11 larvae/plant and 0.08 larvae/plant, respectively. The results indicate that early instar survival is critical to WBC establishment, and environmental conditions and plant stage may have important effects.