Studies on cucurbit viruses in Madras State. IV. Some aspects of the relationships of Melon Mosaic Virus strain to its three aphid vectors

Abstract

Melon Mosaic Virus (MMV) was non-persistent in its three aphid vectors. The pre-acquisition fasting threshold, acquisition threshold and the inoculation feeding threshold were 5 minutes, 10 seconds and 60 seconds respectively for Myzus persicae, 15 minutes, 30 seconds and 3 minutes respectively for Aphis gossypii, 60 minutes, 60 seconds and 5 minutes respectively for A. nerii. The optimum number of viruliferous aphids per plant for maximum transmission was 30 in all the vectors. Increasing the number of aphids above this optimum decreased the percentage transmission of the virus. In the case of myzus persicae, the reduction in the percentage transmission was conspicuous when 240 aphids per plant were used whereas in A. nerii the decrease was noticed even when 100 aphids per plant were used. The percentage transmission by fasted aphids was more than by the non-fasted ones. Persistance of the virus during fasting was for 90, 45 and 30 minutes respectively in M. persicae, A. gossypii and A. nerii while during feeding it was 30, 15 and 10 minutes respectively. The aphid vectors were ranked in the following descending order of transmission efficiency: Myzus persicae, Aphis gossypii and A. nerii. The length of the pre-acquisition fasting period varied inversely as the efficiency. More efficient the vector, shorter was the fasting period. The acquisition threshold and incoulation feeding threshold also varied inversely as the efficiency of the vector. The fall in the efficiency of transmission when the number of aphid vector was increased above the optimum was considered to be due to a salivary inhibitor. Apterous forms of the aphid vectors were more efficient transmitters of the viruses than the alate forms. It was concluded that all aphids have a salivary inactivator, the quantity secreted varied from species to species, the efficiency of transmission being inversely correlated with the quantity of inhibitor secreted.