Feeding preference and performance of Helicoverpa zea (Lepidoptera: Noctuidae) larvae on various soybean tissue types

Helicoverpa zea Boddie (Lepidoptera: Noctuidae) feeding preference and performance on soybean tissue types is poorly understood. We assessed preference by looking at feeding behavior and resulting performance of 2nd and 4th instar H. zea larvae on leaves, flowers, and pods in no-choice and choice assays. Consumption indices were calculated and observed feeding behaviors were used to indicate preference; survival, growth rate, and larval body mass were recorded as measures of performance. Second instars performed better when fed leaf tissue than when fed other tissue types. In no-choice assays, 32% of 2nd instars that fed exclusively on newly emerging trifoliates reached the pupal stage, and 50% of those that fed exclusively on fully emerged leaf trifoliates survived to pupation. Early instar survival was poor (ranging from 0 to 3%) on all other tissue types, including flowers, stems, and pods. However, when given a choice of tissue types throughout their larval lifetime, 2nd instars preferred to feed on newly emerging trifoliates and early developing pods, consuming on average 51 and 38%, respectively, of each tissue type. In no-choice assays, 4th instars performed best on pods with fully developed seeds; however, when presented with a choice throughout their lifetime, late instars did not feed at a higher rate on any single tissue type. If H. zea exhibits similar behavior under field conditions, information on preference can be used to inform management practices and may aid in the development of conventionally bred and transgenic varieties.