Relationship of Soybean Pod Development to Bollworm and Tobacco Budworm Damage1

Abstract

Feeding damage by the bollworm, Heliothis zea (Boddie), and tobacco budworm, H. virescens (F.), to pods of the ‘Davis’ and ‘Pickett-71’ soybean cultivars did not differ significantly between insect speies. The cultivars ranged in developmental stage from early pod elongation to late pod fill. Damage was a negative function of the degree of pod development, when expressed as the number of seeds destroyed per larva, and when soybean development was expressed as the average thickness of pods in mm. Bollworm larvae each destroyed ca. 50 seeds on plants with pods in early developmental stages, but only ca. 5 seeds each on plants with pods in late developmental stages. The 6th instar was responsible for more damage than the 4th and 5th instars combined. These data provide necessary information to formulate better action levels (economic thresholds) for bollworm and tobacco budworm infestations during the R-4 through R-6 stages of soybean development.