Vegetative and reproductive biomass accumulation in field corn: response to root injury by western corn rootworm (Coleoptera: Chrysomelidae)

A 2-yr field study was conducted to evaluate the effects of larval injury by western corn rootworm, Diabrotica virgifera virgifera LeConte, on vegetative and reproductive biomass accumulation of field corn, Zea mays L. Studies in 1989 were conducted in irrigated, silty clay loam soil, whereas in 1990, the possible interacting effects of soil texture (silty clay loam, loam, and sandy loam) and soil moisture (furrow-irrigated and dryland) were examined. In both years, during the early phases of injury (feeding by first and second instars), the vegetative biomass was detrimentally affected. Larval infestations reduced leaf area and leaf wet weight by up to 17.4%. However, during the period of peak injury by third instars and during the postinjury period, the plant biomass accumulation response differed slightly between the 2 yr. Overcompensatory and exact compensatory responses were noted in 1989 and 1990, respectively. In 1989, dry weights of injured plants were greater than the uninjured plants at approximately 2 wk following pupation and in 1990, plants from the two treatments had similar biomass. The reason for the differing response was probably related to the plant development stage at the time of peak injury. In 1989, plants were in the V15 stage, averaging 8,350 cm2 leaf area, whereas in 1990, plants were in the V8-V10 stage with 4,761.3 cm2 leaf area. The greater amount of photosynthetically active tissue in 1989 compared with 1990 may have allowed the plants to respond better to the injury. In addition, rootworm-injured plants were unable to utilize, for the production of vegetative biomass, the supplemental soil moisture through irrigation compared with uninjured plants. The root injury apparently inhibited the plants from utilizing the soil moisture. Plant response to stress was generally similar in all three soil textures. The compensation and maintenance of unaltered levels of vegetative tissue biomass appeared to be at the sacrifice of reproductive tissue biomass. Western corn rootworm larval injury consistently reduced corn grain yield by up to 15.0% in 1989 and by 40.7% in 1990.