Biology and Control of the Currant-Lettuce Aphid (Nasonovia ribisnigri) Gemma Hough ([email protected]) Supervisor: Dr Rosemary Collier School of Life Sciences, The University of Warwick, Wellesbourne, Warwick CV35 9EF Life cycle Introduction Winter Spring • During summer N. ribisnigri reproduces asexually on lettuce and • N. ribisnigri prefers to feed in lettuce hearts where it is related species. protected from certain insecticide sprays and natural enemies. Males and females • In autumn, males are produced and both sexes migrate to the winter host (Ribes species). Males mate with females who lay overwintering • Insecticide resistance has been detected in some produce eggs cold-resistant eggs. populations and whilst several new insecticides are available to growers, they may still not provide a complete • In the spring the eggs hatch and nymphs colonise shoots of the solution. winter host before migrating to lettuce once again. • Some N. ribisnigri have overcome the resistance provided • Some clones have lost their sexual phase and overwinter as live by resistant lettuce cultivars. We call them resistance- insects on other herbaceous hosts (see below). breaking (Rb) clones. Autumn Summer Results What’s next? Development time from nymph to adult for resistance-breaking Percentage survival of resistance-breaking (Rb) and wild- Percentage survival of resistance-breaking (Rb) and (Rb) and wild-type (WT) N. ribisnigri on susceptible and type (WT) N. ribisnigri on alternative hosts to lettuce wild-type (WT) N. ribisnigri on Butterhead cultivars resistant (Nr) lettuce cultivars 120 from different plant breeding companies 1.Determine how well N. 20.00 100 ribisnigri can overwinter on 100 18.00 alternative hosts. 16.00 80 80 14.00 10 °C 60 60 12.00 2.Determine whether 15 °C 40 predators and fungi play a 10.00 40 20 °C 8.00 20 role in the mid-summer 6.00 25 °C 0 20 crash Percentage of aphids survivingonof aphids Percentage 4.00 (%) nymph from 7 of development day of development from nymph (%) nymph from of development 0 Development time to adult (days) adult to time Development 2.00 3.Quantify the effects of day 0.00 9 day survivingat of aphids percentage Mean length on development of Rb Saladin Rb Eluarde Rb Rotary WT Saladin WT Eluarde WT Rotary (Sus) (Nr) (Nr) (Sus) (Nr) (Nr) both WT and Rb N. ribisnigri on lettuce. Aphid type and lettuce cultivar Aphid type and host plant Aphid type and lettuce cultivar All alternative host plant species screened supported Rb N. ribisnigri can survive equally well on 1. N. ribisnigri develops faster at higher temperatures. 4.Quantify temperature and development and reproduction of WT and Rb N. different resistant and susceptible Butterhead day length requirements for 2. Rb aphids develop at the same rate as WT aphids at ribisnigri, except for Prickly Sowthistle. cultivars. each temperature. key overwintering stages on 3. Some WT aphids survived to adulthood on resistant Ribes species. lettuce but had longer development times and earlier Orange Prickly Chicory Smooth Spiked Wall mortality. Hawkweed Sowthistle (Chichorium Hawksbeard Speedwell speedwell (Hieracium (Sonchus intybus) (Crepis capillaris) (Veronica (Veronica aurantiacum) asper) spicata) arvensis).