Development of a bioassay method for larval western corn rootworm (Coleoptera: Chrysomelidae)

Western corn rootworm, Diabrotica virgifera virgifera LeConte, is a serious pest of maize (Zea mays L.) in the United States. Because western corn rootworm larvae live in the soil, conducting an on-plant bioassay to screen novel management tools can be challenging. This study aimed to identify growth media for a greenhouse bioassay system suitable for studying interactions between western corn rootworm larvae and maize plants. We assessed the effects of growth medium on the growth of maize plants and on the survival and development of western corn rootworm larvae. Additionally, we characterized how larval density affected rootworm survival in the bioassay system. Plants grew well in soil collected from an agricultural field; however, this bioassay environment also resulted in poor survival of western corn rootworm larvae. By contrast, larval survival was greatest when plants grew in vermiculite, but this medium tended to produce the lowest values for metrics of plant growth. In general, a potting medium was conducive to both higher levels of larval survival and plant growth metrics. These results suggest that use of a potting medium or a mixture of soil collected from the field with other amendments, such as potting medium, could provide an environment conducive to both the growth of maize plants and the survival of rootworm larvae. This bioassay approach offers a novel bioassay system, which may potentially be applied to screen insecticides, microbial biopesticides, and plant-incorporated protectants.