Serological Detection of Corn Stunt Spiroplasma and Maize Rayado Fino Virus in Field-CollectedDalbulusspp. from Mexico

Abstract

Corn stunt spiroplasma (CSS) experimentally acquired from maize (Zea mays) was detected by enzyme-linked immunosorbent assay (ELISA) in extracts from individual as well as groups of 5 D. maidis and in extracts from individual D. elimatus, D. gelbus, D. guevarai and D. quinquenotatus. CSS was detected by ELISA in all exposed but none of the unexposed individuals of all species. Infective assays gave the following transmission rates: D. maidis 100%, D. elimatus 83%, D. gelbus 0%, D. guevarai 25% and D. quinquenotatus 50%. CSS infection of these species was detected more reliably by ELISA than by infectivity assay. Purified CSS antigen was detected by ELISA at 25 but not at 10 ng/ml. CSS was detected by ELISA in about 10% of 436 individual Dalbulus leafhoppers field-collected in Mexico in 1982, and maize rayado fino virus (MRFV) was detected in 5.5% of 828 leafhoppers collected in 1981 and 1982. Incidence of MRFV in maize plants in the field where the leaf hoppers were collected in 1981 was 35-40%. As demonstrated by Wilk''s statistic (W), the absorbance (A405nm) values of the unexposed leafhoppers in ELISA were generally normally distributed. On the basis of this distribution, when the mean of A405nm values plus 3 times the population standard deviation for the unexposed controls was used to calculate the lower limit of acceptance for positive A405nm values, the type I error rate had an upper band of 7% for a sample size (N) of 8 and of 1.3% for N = 30.