Entomology, Department of


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A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Entomology, Under the Supervision of Professor John E. Foster.
Lincoln, Nebraska: May, 2011

Copyright 2011 Difabachew B. Kondidie


The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is an economically important pest of maize, sorghum, cotton, and rice in the Western Hemisphere. Previous studies on genetic diversity of FAW focused on identification of the corn and rice host strains; there is limited information about geographic genetic variation. To bridge this gap, I investigated the genetic diversity of FAW using representative samples from the United States, Argentina, Panama, and Puerto Rico with amplified fragment length polymorphism (AFLP). This study also investigated the susceptibility of the Puerto Rico FAW population to ten different insecticides used by Dow AgroSciences (DAS) Research Station, Puerto Rico.

Analysis of molecular variance (AMOVA) using AFLP revealed that the majority (71.2%) of the total variation is within FAW populations; only 28% of the variation was among populations. This indicates significant gene flow for FAW throughout the Western Hemisphere. Also, cluster analysis showed the lack of regional genetic structuring. Moreover, there was no significant correlation between genetic dissimilarity and geographic distance, except for the Argentina samples, suggesting the presence of gene flow.

The FAW population in Puerto Rico remains susceptible to the insecticides used for its control. The insecticides Radiant, Orthene, and Larvin caused ˃ 60% FAW mortality 16 h after application. Generally larval mortality increased with time after insecticide application; 96 h after application the majority of the insecticides gave ˃ 80% control. Moreover, the dose rate study on selected insecticides showed that the current dosage used by DAS is sufficient to control the FAW.

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