Infectivity in natural populations of Delphacodes kuscheli vector of "Mal Rio Cuarto" virus

"Mal de Rio Cuarto" (MRCV) is the most important maize (Zea mays L.) virus disease in Argentina. MRCV epidemics occur when large populations of the in sect vector Delphacodes kuscheli migrated from winter cereals to emerging m aize crops. The objective of this study was to determine the probability of finding viruliferous and transmitter insects in natural macropterous D. ku scheli populations. Five experiments were performed. Groups of seven males or females were placed on susceptible maize hybrid plants (Cargill semident 4) at the coleoptile stage. Plant and insect samples were tested by DAS-EL ISA. The probability of viruliferous and transmitter insects was determined according to p=1-(1-1)(1/k) and the "t" test was used to compare the trans mission efficiency of males and females and of viruliferous and transmitter insects. The probability of transmitter insects varied between 1 to 5.2% a nd the probability of viruliferous insects ranged from 4.8 to 7.4%. There w ere no significant differences (P less than or equal to .05) between insect sexes in transmission efficiencies; on the contrary the probability of a s ingle viruliferous insect was significantly greater (P less than or equal t o .05) than that of a single transmitter insect. Information on the density and MRCV transmission of D. kuscheli will allow us to link vector populati on dynamics in analytical models to describe disease epidemics and design o f preventative control measures.