Abstract. Winged morphs of aphids were investigated from 2002 to 2004 in 4 Tunisian regions of potato seeds production in order to know the aphid diversity and the potential vectors of Potato Virus Y. This is a very important contribution to the knowledge of aphid fauna in Maghreb. A total of 50,030 aphids were caught using yellow water traps and one suction trap. 130 taxa were identifi ed including 103 species. Ten species are well represented in all regions prospected and typical species were also observed in every region. Some differences in species diversity appeared between regions which are discussed considering weather condition and vegetation.Résumé. La diversité d'Aphides (Hemiptera : Aphidoidea) en Tunisie en relation avec la production de plants de pomme de terre. Afi n de connaître les pucerons ailés potentiellement vecteurs de maladies de la pomme de terre (virus Y de la pomme de terre), des pièges ont été installés de 2002 à 2004, dans 4 régions de production de plants de pomme de terre en Tunisie. Cette étude est une importante contribution à la connaissance de la faune aphidienne dans le Maghreb. A partir des pièges jaunes et d'un piège à succion nous avons pu capturer 50.030 pucerons composés de 130 taxons dont 103 espèces ont été déterminées. Dix espèces sont abondantes dans toutes les régions, des différences entre les 4 régions ont cependant été révélées. Celles-ci sont discutées en relation avec les conditions de température et de végétation.

Potato leafroll virus (PLRV) is transmitted by aphids in a persistent manner. Although virus circulation within the aphid leading to transmission has been well characterized, the mechanisms involved in virus recognition at aphid membranes are still poorly understood. One isolate in our collection (PLRV-14.2) has been shown to be non-or only poorly transmitted by some clones of aphids belonging to the Myzus persicae complex. To determine where the transmission process was blocked within the aphid, three virus transmission procedures were used. PLRV-14.2 could not be transmitted, or was only very poorly transmitted, after acquisition from infected plants or from purified preparations. In contrast, it could be transmitted with more than 70 % efficiency when microinjected. Therefore, it is concluded that the gut membrane was a barrier regulating passage of PLRV particles from the gut lumen into the haemocoel of M. persicae. Comparison of coat protein (CP) and readthrough protein (RTP) sequences between poorly and readily transmissible isolates showed that PLRV-14.2 differed from other PLRV isolates by amino acid changes in both of these proteins. It is hypothesized that at least some of the changes found in CP and/or RTP reduced virus recognition by aphid gut receptors, resulting in reduced acquisition and subsequent transmission of PLRV-14.2.

In the context of an epidemiological study on Potato virus Y (PVY) in potato crops, Solanum elaeagnifolium Cav. was included in the weeds prospected. Surveys were carried out in four seed potato areas: Cap Bon, Manouba, Jendouba and Kairouan. S. elaeagnifolium was found in all areas, except Cap Bon. Virus‐like symptoms were observed on some S. elaeagnifolium plants in the field, i.e. leaf mottling and curling. Aphids were collected on these plants and were identified as Myzus persicae and Aphis fabae, both known to colonize potatoes and to transmit the standard PVYN isolate with transmission efficiencies of 95% and 43%, respectively. Forty‐seven plant samples were tested with ELISA for the presence of PVY. Positive reactions were obtained from 2/6, 5/18, 8/23 samples collected in Manouba, Jendouba and Kairouan, respectively. Virus transmission was carried out using M. persicae as vector from two samples of each region onto plantlets of Nicotiana tabacum cv Xanthi. All inoculated plantlets displayed typical symptoms of the PVYN strain group, confirmed by serological testing using specific antibodies. This is the first report of a PVY natural infection on S. elaeagnifolium in Tunisia. The abundance of this weed, its over‐wintering status and the high rate of PVY‐infected plants (31.9%) allow us to deduce that S. elaeagnifolium must be considered a reservoir species of PVY under natural conditions in Tunisia and probably in other Mediterranean countries. The presence of efficient aphid vectors of PVY on this weed in crops is additional evidence that S. elaeagnifolium may become a problem by acting as a source plant for PVY spread in potato crops.

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