Introduction to the currant-lettuce aphid
The Currant-lettuce aphid, Nasonovia ribisnigri, is an economically significant pest of lettuce crops where its presence leads to financial loss for growers as a result of unmarketable lettuce heads.
It is a small, soft bodied insect often orange in colour. It spends the majority of it time using its specialised piercing mouthparts (stylet) to suck the sap from the phloem of plants, reducing quality and yield through direct feeding damage, and in some cases transmitting plant viruses.
N. ribisnigri has a complex life cycle which contributes to its success as a pest. Throughout, the summer females undergo asexual reproduction to produce clones of themselves where their populations increases rapidly on lettuce crops. However, as temperature and day lengths decrease as winter approaches males are produced which migrate to the winter host of Ribes species (Currants). It is on this host where sexual reproduction takes place with females who produce cold resistant overwintering eggs. When temperatures increase again in the Spring the eggs hatch and the nymphs exploit the nutrient rich buds of the winter host before returning to lettuce again in the late spring/ early summer.
It has also been reported that in some temperate regions with mild winters, including the South of England, N. ribisngiri has become completely asexual having lost its sexual phase to survive as live insects all year round on alternative host to Currants which are thought to include Chichorium (Chicory), Veronica (Speedwell) and Hieracium (Hawkweed) species.
Aphids are such sucessful pests due to their high reproductive rates. This is achieved through:
- Telescoping of generations where the daughters of the mother are already pregnant before being born themselves
- Short generation times (nymph to adult) birth to adult in approximatley 10 days (at 20 degrees). On reaching adulthood asexual reproduction begins almost immediatley.
- Asexual reproduction- avoiding the need and cost of producing males
- Vivaparity- offspring are born as live young meaning they are independent from birth and do not require further energy input from their mothers