Population dynamics of Melanaphis sacchari (Zehntner), the aphid vector of sugarcane yellow leaf virus under tropical conditions in India

Sugarcane yellow leaf disease (YLD) has emerged as a serious threat to sugarcane cultivation worldwide, particularly in India. The aphid, Melanaphis sacchari, has been proved to be the vector for the causative agent sugarcane yellow leaf virus (ScYLV) across the world. However, the population dynamics of the aphid are not established under field conditions. Hence, this study was conducted with the aim of studying the population dynamics of M. sacchari for four consecutive years (2015–2019) under the typical tropical conditions. The sugarcane aphid starts colonizing the crop in April, reaches its maximum in June–July, starts declining in August, and almost vanishes in September. Thus, the 5–7-month-old crop supports higher aphid population irrespective of the varieties, provided the climatic conditions are near-normal. A significant variation in the climatic conditions observed in 2016–2017 significantly altered the population dynamics of the aphid on sugarcane varieties. In 2016–2017, the aphid appeared late in May and extended till December. It was interesting to note that the aphid population was recorded to be higher in the diseased plants as compared with the healthy ones of the same variety. Further, the YLD-susceptible cvs CoC 671, Co 86032, Co 86010, CoPant 84211, and B38192 were recorded with comparatively higher numbers of aphid during the peak season in all the 4 years. The colonization of aphid was observed to be aggregate in nature and not uniform in all the plants of a variety and leaves of an infested plant. Increased levels of aphid infestation was found between + 5 and + 7 leaves in sugarcane plants, across the seasons and varieties, and rainfall was negatively associated with the build-up of aphid colonization. The study provides new findings on the dynamics of M. sacchari under tropical climate in India for the first time and contributes to the understanding of the disease epidemiology.