Submitted to: Virus Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/27/2013
Publication Date: 7/8/2013
Citation: Spear, A., Yokomi, R.K., French, R.C., Stenger, D.C. 2013. Occurrence, sequence polymorphism and population structure of Circulifer tenellus virus 1 in a field population of the beet leafhopper. Virus Research. 176:307-311. Interpretive Summary: The beet leafhopper (Circulifer tenellus) is an insect pest of economic concern primarily due to its ability to transmit plant pathogens, including viruses causing curly top disease of sugar beet and vegetable crops, and the spiroplasma causing citrus stubborn disease. The beet leafhopper is a migratory insect that moves seasonally from overwintering refuges to summer breeding grounds. However, information concerning relationships among overwintering and summer breeding populations, verification of long distance migration routes, and the degree of interaction among regional populations is mostly anecdotal. A virus (Circulifer tenellus virus 1) infecting the beet leafhopper was evaluated as a surrogate genetic marker to define population structure of the beet leafhopper. Incidence, prevalence and nucleotide sequence variation of the virus within a population of the beet leafhopper in the San Joaquin Valley of California was assessed. Results indicate that the virus is common in the field and exhibits sufficient genetic diversity to serve as a surrogate marker for the beet leafhopper. Use of virus population genetics data for defining beet leafhopper populations at high resolution will allow for improved understanding of the ecology of this migratory insect pest. Such knowledge may then be applied to regional pest control programs aimed at reducing crop losses resulting from infection by disease agents transmitted by the beet leafhopper.
Technical Abstract: The potential of Circulifer tenellus virus 1 (CiTV1) as a surrogate marker to determine population structure of the beet leafhopper (BLH; Circulifer tenellus [Baker]) was assessed. Prevalence, incidence, and nucleotide sequence polymorphism of CiTV1 present in BLH adults collected from the southern San Joaquin Valley (SJV) of California in spring and summer of 2010 was determined. Prevalence of CiTV1 was 100%; at least one CiTV1 positive BLH was collected from each of 35 locations sampled. Among 365 BLH adults sampled, 119 (32.6%) were positive for CiTV1. Incidence of CiTV1 ranged from 10% to 80% among locations. Chi-square tests indicated that observed CiTV1 incidence values differed from expected values based on collection season (greater in summer than in spring) but not based on geography (east versus west or north versus south) within the region sampled. Sequence polymorphism revealed the presence of three CiTV1 strains, designated A, B, and C. Strain A was most common (82.4%), strain B was less common (16.8%), and only one isolate representing strain C (0.8%) was encountered. Chi-square tests indicated that observed frequencies of strains A and B did not differ from expected values in either space or time, indicating that season of collection or specific locations sampled did not influence deduced structure of the SJV population of CiTV1. The results validate CiTV1 as a suitable surrogate for evaluation of BLH population structure. Application of the surrogate data set infers that BLH in the southern SJV constitute a single population, with individual genotypes freely circulating in both space and time. Such a result is not unexpected for a highly mobile insect within a region that lacks physical barriers. Use of CiTV1 as a surrogate marker may have utility to evaluate gene flow among BLH populations occurring in widely separated regions of the Western U.S. and may have sufficient resolution to define relationships among overwintering populations with distant summer breeding populations throughout the established range of this migratory insect.