Seasonal emergence-time effects on adult longevity, fecundity, and egg viability of northern and western corn rootworms (Coleoptera: Chrysomelidae)

Seasonal emergence time was studied to determine its influence on adult vigor and reproductive fitness of field-collected Diabrotica barberi Smith and Lawrence and D. virgifera virgifera LeConte. Time of emergence was divided into six 2-wk intervals (lots; pooled from beetles collected every 2 d from onset to end of seasonal emergence cycle), which served as treatments. Beetles were maintained in single-insect oviposition chambers on a natural diet and were provided soil as an oviposition substrate. The experiment was arranged in a randomized complete block design with 10 replicates. Female D. barberi survived on natural diet for averages of up to 89 d within lots. Earliest emerging (lot 1) beetles of both species lived significantly longer than those from later lots, thus suggesting reduced fitness as the season advanced. Lot fecundity means ranged from 133 to 312 eggs (maximum 1,036) and 357 to 736 (maximum 1,864) eggs per female for D. barberi and D. virgifera, respectively. Corresponding with greater longevity, increased fecundity was also observed with early-emerging females of both species. Beetles emerging during the first part of the growing season appeared to be generally healthier and more reproductively fit than their latter-emerging counterparts. These findings may warrant further evaluations to determine possible effects on late-season management efforts in adult corn rootworm suppression programs. Methodologies associated with insect maintenance and assessment of reproductive biology proved suitable for both species. Additionally, these findings may offer valuable insight needed to refine procedures for laboratory rearing and egg production from D. barberi