Azadirachta indica metabolites interfere with the host-endosymbiont relationship and inhibit the transmission of potato leafroll virus by Myzus persicae

The effects of neem (Azadirachta indica A. Juss) seed kernel extracts (NSKE) and azadirachtin on the ability of Myzus persicae (Suit.) to transmit potato leafroll luteovirus (PLRV) was studied. Moreover, it was investigated whether treatments with these compounds would exert an effect on larval growth and mortality, and on the aphid intracellular symbionts. Endosymbiotic bacteria play an essential role in the performance of aphids, and in luteovirus transmission by aphids. NSKE and azadirachtin were offered to one-day-old M. persicae nymphs via a membrane feeding system. The neem metabolites displayed a 100% mortality at doses higher than 2560 ppm. At intermediate doses, ranging between 320 and 2560 ppm, larval growth and mortality were affected in a dose-dependent manner. The transmission of PLRV by M. persicae was inhibited by 55-90%. The endosymbiont population of the aphid was clearly affected by a treatment with neem metabolites as the release of their most abundant protein, Buchnera GroEL, into the haemocoel of the aphid was inhibited. Moreover, morphological aberrations on the bacterial endosymbionts were observed in aphids which fed on 2560 ppm of azadirachtin. At doses lower than 160 ppm of NSKE or azadirachtin, the endosymbiont population of M. persicae, and mortality, growth and feeding behaviour were similar to that of the untreated groups of aphids. However, PLRV transmission was still inhibited by 40-70%. The possible targets of the neem metabolites in the aphid are discussed.