Aphidalia
General
The shallot aphid, Myzus ascalonicus, is extremely polyphagous. It feeds on crops such as onions, shallots, strawberries, lettuce, brassicas and potatoes and many ornamentals. The shallot aphid is cosmopolitan and widely spread in Europe.
Life cycle and appearance of The shallot aphid
Aphids have a complex life cycle, with both winged and wingless forms of adults and a great variety in colour. In greenhouses, reproduction takes place by parthenogenesis, with unfertilized viviparous females continuing to produce new generations of females. Aphids moult four times before reaching adulthood. With each moult they shed white skin, betraying their presence in the crop.
Wingless females of the shallot aphid are 1.1-2.2 mm long and shiny brownish green to dirty yellow. Their legs and antennae are pale, apart from the ends of the antennae and the tarsi. The siphunculi are short an swollen towards the apex.
The shallot aphid does not alternate to another host plant for overwintering and there is no sexual stage in the life cycle. No eggs are produced. Myzus ascalonicus is cold hardy and overwinters in sheltered places and greenhouses. Numbers of this aphid can build up even in winter and early spring when temperatures are still low. Winged forms are produced and migrate to other crops until June.
Damage symptoms
Feeding of shallot aphid on strawberries invokes a strong host plant reaction. Infested plants become severely stunted when growth starts in spring. Petioles are shortened and leaves curled and twisted. Blossom trusses are also affected, fruits remain small and yield is reduced.
On bulbs and shallot, the aphids often occur at the end of the storage period causing malformation of new plants.
