Field studies were conducted in Louisiana during 1962 and 1963 to determine the seasonal abundance of flying aphid populations in sugarcane fields and to relate this to the seasonal spread of sugarcane mosaic virus (SCMV). Winged aphids were caught on sticky traps and also collected from sugarcane plants. The incidence of SCMV symptoms was determined periodically in experimental plots.
Of the 9 known vectors of SCMV, only Acyrthosiphon piston (Harris), Hysteroneura selariae (Thomas), Myzus persicae (Sulzer), Rhopalosiphum maidis (Fitch), and Schizaphis grammum (Rondani) occurred during periods of virus spread in sufficient numbers to be considered of probable importance in the spread of SCMV. These five species plus Aphis gossypii Glover, A. maidiradicis Forbes, A. craccivora Koch, Rhopalosiphum paid (L.) complex, R. Pseudobrassicae (Davis). R. rufiabdominalis (Sasaki), Tetrancura hirsula (Baker) and Therioaphis maculata (Buckton) constituted 90% of 5231 aphids representing 69 species which were caught on sticky traps during these studies.
Populations of alatae of all species mentioned above, except T. maculata , were found to be significantly correlated with periodic increases of SCMV symptoms. There was also a significant correlation between periodic increases in Disease symptoms and the total numbers of aphids trapped 4 weeks earlier.
Except for R. pseudobrassicae , alatae of all aphids mentioned above, plus Sipha flava (Forbes), Dactynotus ambrosiae (Thomas), Chailophorus vimnalis Monel, and Aphis sp., were caught on plants. Only H. setariae and R. maidis were found colonizing on sugarcane.
Probably more than three-fourths of the total virus spread during one crop year occurred during late winter and spring. Aphids were trapped in greatest abundance during March, April, and May of 1962 and 1963. Approximately 80% of the total aphids which migrated over sugarcane fields during a month period (while some tying portions of sugarcane plants were exposed above the soil surface) did so between March 1 and May 31, 1963, Flying aphid populations were much lower during (all than in spring, hut higher than in summer.
There appeared to be no significant difference in the rate of spread of SCMV among sugarcane plants of different ages.