Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2005
Publication Date: 6/1/2006
Citation: Nagoshi, R.N., Meagher Jr, R.L., Nuessley, G., Hall, D.G. 2006. Effects of fall armyworm (Lepidoptera: Noctuidae) interstrain mating in wild populations. Environmental Entomology. 35:561-568. Interpretive Summary: Fall armyworm (FAW), is a significant pest of maize and turf grasses. Two strains exist that display significant differences in such important traits as plant host choice and pesticide susceptibility, but because they are morphologically identical relatively little is known about their behavior and distribution in the wild. In this study scientists at the USDA-ARS Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, FL, used a combination of molecular genetic techniques and field studies to examine strain-specific population behavior in agricultural and grass habitats in south Florida. A strain-specific and sex chromosome linked genetic marker was characterized and used to demonstrate that interstrain mating between R-strain females and C-strain males occurs and that the resulting hybrid represents a substantial proportion of trap captures in the corn and turf habitats in the overwintering areas of Florida. Differences in distribution between hybrids and their parents suggest that interstrain crosses have significant effects on such strain behaviors as plant host choice, with potentially important ramifications on biological control and other management strategies.
Technical Abstract: Fall armyworm is a significant agricultural pest in the United States, affecting most notably sweet corn and turf grass. Two genetically distinct but morphologically identical strains (R-strain and C-strain) exist that differ physiologically and behaviorally. Recent studies of overwintering populations in Florida indicate that the R-strain itself consists of two genetically distinct subgroups, with one having molecular markers consistent with interstrain hybridization between R-strain females and C-strain males. To test this possibility and examine the ramifications of interstrain mating on population behavior and strain fidelity, larvae and adult males were tested for genetic marker combinations representative of the host strains and potential hybrids. These studies demonstrated a sexually dimorphic distribution pattern for an R-strain-specific, sex-linked marker that is a predicted result of interstrain mating. Despite evidence of substantial interbreeding in the overwintering sites, both FR and the strain-diagnostic mitochondrial markers still showed the plant host and habitat biases associated with the host strains, indicating that strain integrity was largely maintained. However, there is evidence that the two R-strain subpopulations differ in habitat distribution in a manner suggestive of the ’hybrid‘ genotype being less specific in its plant host preference. The existence of a genetically distinct hybrid subpopulation must be taken into account when evaluating fall armyworm population dynamics and infestation patterns in overwintering areas.