Aphid (Aphididae: Homoptera) vectors of Papaya ringspot virus (PRSV), bionomics, transmission efficiency and factors contributing to epidemiology.
Studies on identifying the predominant aphid vector species of Papaya ringspot virus (PRSV), their influence on epidemiology, efficiency of PRSV transmission and few aspects of management were undertaken from March 2003 to June 2006 at the Indian Institute of Horticultural Research (IIHR), Bangalore. Monitoring of transitory aphids using yellow funnel water traps in papaya orchards over two years revealed that three species of aphids such as melon or cotton aphid, Aphis gossypii Glover (64.22%), the green peach aphid, Myzus persicae (Sulzer) (9.88%) and cowpea aphid, A. craccivora Koch (9.66%) were dominant. Since transplanting, PRSV infection was recorded at weekly intervals based on symptoms. Fresh incidence of PRSV (%) coincided with number of aphids trapped four weeks prior to infection suggesting a strong link between the aphid vectors and PRSV incidence. Multiple regression models point to A. gossypii population in influencing fresh PRSV incidence. The transmission efficiency of three major species was studied. Single-aphid inoculation studies indicated that M. persicae (56%) and A. gossypii (53%) were significantly more efficient in transmitting PRSV than A. craccivora (38%). Following a single AAP on an infected leaf, M. persicae was more efficient than the other two species with 52.5% transmission after the first inoculation access period (IAP). However, its inoculation efficiency significantly decreased with the second and subsequent IAPs. Since A. gossypii is numerically dominant vector in south India in addition to being a more efficient vector capable of inoculating PRSV to multiple plants, it should be the target vector for control strategies. All the individual A. gossipii or A. craccivora were potentially capable of PRSV transmission, though efficiency varied between individuals. Studies carried out at Bhubaneshwar indicated that neither raising papaya in net house covered on all sides nor frequent application of insecticides or plant nutrients significantly decreased PRSV incidence.