Laboratory evaluation of antifeedant compounds for inhibiting settling by cereal aphids

Semiochemicals offer several potential strategies for reducing crop losses caused by aphid pests (Pickett et al., 1994). One approach is the application of antifeedant compounds to crops, thereby manipulating aphid host selection behaviour to reduce both direct feeding damage and virus transmission (Pickett et al., 1987). Numerous compounds have been tested for aphid antifeedant properties. ‘Half leaf’ choice tests, allowing the polyphagous pest aphid Myzus persicae (Sulzer) access to treated and control leaf areas, led to the identification of a number of active compounds, largely of plant origin (Griffiths et al., 1989). Polygodial was particularly active (Asakawa et al., 1988), and M. persicae discriminated between treated and control leaf areas within 2 min of access to plants (Powell et al., 1993). Quassin and other quassinoids also showed promising activity (Polonsky et al., 1989). The addition of the indolizidine alkaloid castanospermine to artificial diet solutions inhibited settling and survival by the pea aphid, Acyrthosiphon pisum (Harris) (Dreyer et al., 1985). Topical applications of the limonoid tetranortriterpenoid azadirachtin were only weakly active against M. persicae (Griffiths et al., 1989), and although strawberry aphids, Chaetosiphon fragaefolii (Cockerell), were deterred by a neem seed oil formulation, activity was not related to azadirachtin levels (Lowery & Isman, 1993). The hop resin-derived -acids lupulone and colupulone were tested against M. persicae, and were not active (Griffiths et al., 1989), although these compounds were effective deterrents to the two-spotted spider mite, Tetranychus urticae Koch (Jones et al., 1996). In the present study, observations were made of the settling behaviour of two cereal aphid species, Sitobion avenae (F.) and Rhopalosiphum padi (L.). In addition to the compounds mentioned above, hop -acids and iso-acids (Verzele & De Keukeleire, 1991) were tested.