Biology and control of currant lettuce aphid nasonovia ribisnigri

Abstract

There is a consensus that the development of successful Integrated Pest Management strategies requires a detailed understanding of pest biology. In the case of the currant lettuce aphid (Nasonovia ribisnigri), an economically important pest aphid of lettuce, sources of such information are limited. This study considers key aspects of N. ribisnigri biology which influence its control. In particular, it makes comparisons between biotypes which succumb to (wild-type) or overcome (resistance-breaking), the host plant resistance (Nr-gene) in commercial lettuce cultivars. Experiments on the effects of temperature and photoperiod on the development of N. ribisnigri showed no differences between wild-type and resistance-breaking biotypes. At low temperatures (5, 10 and 15ºC), wild-type biotypes developed to adulthood on resistant cultivars, indicating that the Nr-gene is temperature sensitive. A linear regression between development rate and temperature estimated a lower developmental threshold of around 4.7ºC. Nasonovia ribisnigri usually overwinters as a diapausing egg but overwintering nymphs/adults have been observed. In the laboratory eggs were obtained at 12ºC 13L:11D. Sequential sampling of eggs from the field suggested that diapause ended between late January and early February. Post-diapause development was estimated to take <50 day-degrees using a LDT of 4.7°C. Nasonovia ribisnigri survived the winter as nymphs/adults on Veronica arvensis in the Midlands. Other weed species were suitable hosts in the labratory: Chichorium intybus, Crepis capillaris, Lapsana communis, Hieracium aurantiacum, Hieracium pilosella, Veronica spicata and Veronica officinalis. Field trials, using sequentially planted plots of lettuce, and applying 'exclusion' and pesticidal treatments indicated that natural enemies and emigration regulate aphid populations in the summer and contribute to the mid-summer crash. A large-scale screen of 96 cultivars and wild relatives of lettuce identified new sources of resistance against wild-type and resistance-breaking biotypes. Results from this study can be used to inform further development of an Integrated Pest Management strategy for this pest