SYSTEMIC ANTIFEEDANT EFFECTS OF AZADIRACHTIN ON THE PEACH-POTATO APHID MYZUS-PERSICAE

The electrical penetration graph (EPG) method was used to analyse the feeding behaviour of apterous, adult Myzus persicae (Sulzer) (Homopter a: Aphididae) on Nicotiana clevelandii (Gray) seedlings, treated syste mically with azadirachtin. A preliminary experiment showed that the ef fects of tethering aphids for EPG recording were minimal. The percenta ge of the 9 h recording period devoted to non-penetration activities, and to stylet pathway patterns increased as the azadirachtin concentra tion in the root treatment increased. The number of probes initiated, and the numbers of sieve tube penetrations also increased with increas ed azadirachtin concentration. The mean time elapsing between the init iation of the first probe to reach a sieve element and contact with th is tissue was not significantly altered by azadirachtin treatment. How ever, azadirachtin treatment significantly reduced the percentage of p robes that reached sieve elements and increased non-penetration activi ty before and after the first period of ingestion from the sieve eleme nts. The percentage of the recording period spent in the EPG pattern a ssociated with sieve tube penetration was significantly reduced by an azadirachtin concentration of 300 ppm, and the duration of each indivi dual penetration was significantly reduced by an azadirachtin concentr ation of 100 ppm. When the total EPG was split into 3 h periods, signi ficant interactions were seen between time period and azadirachtin con centration for the duration of non-penetration, pathway, and sieve tub e penetration patterns.