High Viral Load in the Planthopper Vector Delphacodes kuscheli (Hemiptera: Delphacidae) is Associated With Successful Transmission of Mal de Río Cuarto Virus

Abstract

Delphacodes kuscheli Fennah (Hemiptera: Delphacidae) is the main natural vector of Mal de Rõ ´o Cuarto virus (family Reoviridae, genus Fijivirus, MRCV), which infects different gramineae and causes the most important maize (Zea mays L.) disease in Argentina. MRCVÐvector interactions usually are studied using different winter cereals as hosts. Under experimental conditions, Ͻ50% of D. kuscheli planthoppers fed on a MRCV-infected plant can transmit the virus to wheat (Triticum aestivum L.). This fact is inßuenced by insect development stage at acquisition and the latency period. This work describes the relation between transmission efÞciency and MRCV accumulation in its planthopper vector. First-and third-instar D. kuscheli nymphs were allowed to feed on MRCV-infected plants, and 9 or 17 d after the acquisition access period (AAP), viral load of transmitting and nontransmitting planthoppers was quantiÞed by quantitative polymerase chain reaction. The transmitting planthoppers showed signiÞcantly higher viral titers than nontransmitting ones, suggesting that successful transmission is positively associated to viral accumulation in the insect. However, planthoppers of the third-instars group did not transmit the virus 9 d after AAP, even when 46% had similar titers to the transmitting insects of the other treatments. These results indicate that additional factors inßuence MRCV transmission efÞciency when acquisition occurs in older planthoppers. This is the Þrst precise quantitative analysis of MRCV in its main vector species and will deÞnitely contribute to better understand planthopperÐFijivirus interactions and its epidemiological implications.