Oviposition Choice of Two Fall Armyworm (Lepidoptera: Noctuidae) Host Strains

Fall armyworm, Spodoptera frugiperda (J. E. Smith), is a noctuid species that is composed of two morphologically identical sympatric host strains (corn and rice) that differ in their distribution among plant hosts. In an effort to explain observations of host fidelity in the field, ovipositional preference of the two strains on corn (Zea mays L.) or pasture grass (Cynodon nlemfuensis Vanderyst var. nlemfuensis) was determined using two greenhouse bioassays. In the first bioassay, corn strain females placed more eggmasses on the screen enclosure than on corn plants while grass plants contained an intermediate number of eggmasses. Rice strain females placed most of their eggmasses on grass plants. In the second bioassay, corn strain females placed an equal number of eggmasses on corn and grass plants in comparison to rice strain females which placed >3.5× more eggmasses on grass plants than on corn plants. Individual eggs as part of the eggmasses were also counted on plants and on the screen enclosure. Corn strain females equally placed eggs on the two host plants and on the screen enclosures, however rice strain females placed more eggs on grass plants compared to corn plants or the screen enclosure. This is the first report of consistent differential oviposition between corn and rice strain fall armyworm females.