Author
|
Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/21/2003 Publication Date: 5/1/2003 Citation: Nagoshi, R.N., Meagher Jr, R.L. 2003. FR tandem-repeat sequence in fall armywork (Lepidoptera: Noctuidae) host strains. Annals of the Entomological Society of America. 96(3):329-335. Interpretive Summary: The fall armyworm, Spodoptera frugiperda, is a major agricultural pest of corn, forage grasses, rice, cotton, and peanuts. Two strains of fall armyworm exist that have significant physiological and behavioral differences but are morphologically identical. Remarkably little is known about whether and to what degree interstrain matings occur in the wild, how the resulting hybrids differ from the parental strains, and whether there are strain-specific differences in migration and overwintering behaviors, information that is essential for the effective control of this pest. To facilitate strain identification, we developed a polymerase chain reaction (PCR)-based method to detect FR, a strain-specific element found in the nuclear genome in large tandem-repeat clusters. The improved sensitivity of our methodology over existing techniques was demonstrated by the detection of FR homologous sequences in corn strain individuals even though it was previously thought that FR sequences were exclusive to the rice strain. Even in these cases the PCR method detected strain-specific amplification patterns, indicating that the distinction between rice and corn strains is due to differences in copy number and organization in the genome rather than simply the presence or absence of FR. The availability of PCR-based methods for detecting strain- and population-specific molecular markers makes possible the rapid analysis of large numbers of field-collected samples. When used in combination with other PCR-detectable polymorphisms both nuclear and mitochondrial strain-specific molecular markers can be identified and compared. These methods are the basis of an ongoing study examining the distribution and behavior of the FAW strains in the wild. Technical Abstract: The fall armyworm, Spodoptera frugiperda, consists of two sympatric strains (rice and corn) that are morphologically identical. To facilitate strain identification, a polymerase chain reaction (PCR)-based method was developed to detect FR, a reportedly strain-specific element found in the nuclear genome in large tandem-repeat clusters. The efficacy and accuracy of the PCR method were tested on inbred laboratory lines of both rice and corn strains. Although it was previously thought that FR sequences were exclusive to the rice strain, we were able to isolate homologous sequences in a subset of the corn strain population. Even in these cases the PCR method detected strain-specific amplification patterns, indicating that the distinction between rice and corn strains is due to differences in copy number and organization in the genome rather than simply the presence or absence of FR. A second polymorphism detectable by PCR was also found that distinguishes between rice and corn strain laboratory colonies. The availability of PCR-based methods for detecting strain- and population-specific molecular markers will facilitate studies on strain distribution in the field and the examination of strain-specific behavior. |
