AERIAL HOW OF BARLEY YELLOW DWARF VIRUSES AND OF THEIR VECTORS IN WESTERN FRANCE

During the years 1989-1992 cereal aphids were caught alive in a low le vel (1.5 m high) suction trap operated in Le Rheu (Brittany, France) a nd tested for BYDV transmission. In most cases comparisons with data c ollected simultaneously by a 12.2 m suction trap operating in the same site resulted in good relationships between weekly catches at both he ights. Results from transmission tests showed that: (i) the two main B YDV vectors were Rhopalosiphum padi and Metopolophium dirhodum during the years of experiment; (ii) PAV and MAV were the commonest viruses a nd RPV was relatively scarce; (iii) during spring M. dirhodum appeared to be the most important MAV vector and nearly as good a PAV vector a s R. padi; (iv) during autumn R. padi was the only vector of the three viruses with mixed transmission allowing it to transmit also MAV prob ably by heteroencapsidation. To give an indication of the risk of infe ction, infectivity indices were calculated by multiplying the numbers of aphids caught by the 12.2 m suction trap by the proportion that wer e infective. These infectivity indices agreed with field records of pr imary infections.