The biology and control of the currant lettuce aphid Nasonovia ribisnigri
Abstract: Nasonovia ribisnigri is the most economically important pest aphid of lettuce. Unlike other lettuce aphids, its preference to feed in the centre of lettuce heads, where it is protected from the effects of certain insecticides and natural enemies, makes it challenging to control. In lettuce IPM programmes, insecticides and resistant lettuce cultivars are recommended to manage this pest. While some systemic insecticides are particularly effective, N. ribisnigri can express resistance to certain insecticides. Lettuce cultivars with resistance to N. ribisnigri (Nr gene) are widely cultivated, but new strains of N. ribisnigri, which can overcome this host-plant resistance, threaten their future.The aim of this study was to determine whether varying Nr gene introgression backgrounds used by different plant breeding companies have an impact on the level of resistance in their cultivars to UK wild-type and resistance-breaking aphid biotypes. The study screened six Butterheard cultivars including two susceptible cultivars (Clarion and Charles) and four resistant cultivars (Aljeva, Malfalda, Skyphos, Rotary).The mean percentage of aphids surviving nine days after infestation of the plants with new-born nymphs was determined. Rb N. ribisnigri had relatively high survival on all the Butterhead cultivars, indicating that Rb N. ribisnigri can survive on both resistant and susceptible lettuce cultivars. When comparing the effectiveness of the resistant cultivars in controlling WT N. ribisnigri, there were no significant differences between the cultivars with all aphids suffering almost 100% mortality by day nine. Therefore, these results suggest that the varying Nr gene introgression backgrounds used by different plant breeding companies have no impact on the level of resistance in the cultivar.