Biology, images, analysis, design...
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Identification & Distribution:Apterae of Myzus hemerocallis are described by Blackman & Eastop (1984) as being pale yellowish green or yellowish white. We note that whilst immatures and freshly ecdysed adults are pale yellowish green, the mature wingless adults (see picture below) have an orange-brown hue anteriorly and posteriorly - which does not seem to have been noted in the literature. Myzus hemerocallis siphunculi are tapering or cylindrical on the distal half and are more than 2.5 times as long as the cauda.
The day lilly aphid attacks the basal (concealed) parts of young leaves of day lily (Hemerocallis) and lily of the Nile (Agapanthus). Myzus hemerocallis is a pest of East Asian origin, but is now also widely distributed on Hemerocallis. It has been found in Australia, New Zealand, N&S America, Kenya, France and the UK. Smith et al. (2007) give the year 2000 as the first record for the species in UK. Currently the UK Food and Environment Research Agency (FERA) has fourteen records of the species (ours is the 15th) - detected in England and Wales, mostly on Hemerocallis imported from the USA (pers. comm. Chris Malumphy). Rothamsted suction traps have picked up winged adult Myzus hemerocallis in July 2002 at Starcross in Devon, and at Writtle in Essex (pers. comm. Mark Taylor via Ed Baker).
Biology & Ecology:
We first came across Myzus hemerocallis on a potted day lily hybrid 'Black magic' on sale in a Sussex nursery glasshouse in early April 2015. No aphids were visible, but some of the leaves were covered in exuvia - a sure sign of a current (or past) aphid colony. Moreover some ants were clearly interested in this particular plant.
Separating the leaves revealed a large colony of the day lily aphid shown in the picture below.
Aphids feeding between the leaves produce large quantities of honeydew (see first picture below). This attracted ants (in our case Lasius species, see second picture below), although they mainly seemed to be collecting the honeydew from the leaves (termed gleaning) rather than collecting the honeydew from the aphids as it was exuded.
When we first found the colony, there were very few alates present, but as the colony grew (in strict confinement to prevent escapees) and density increased, nearly all the adults were winged (see first picture below).
Note that molecular data has confirmed that Myzus hemerocallis does not really belong in the Myzus genus, and is possibly closer to the genus Hyalomyzus (Blackman & Eastop (1984) )
Myzus hemerocallis was again present on potted Hemerocallis in the same Sussex nursery glasshouse in March 2016 (see picture below).
Either any attempts made to eliminate the infestation had been unsuccessful, or the source nursery was still supplying infested plants. Whichever is the case, it seems likely this aphid is now well established in Britain - albeit, thus far, only known from glasshouse plants.
Damage and control
Myzus hemerocallis may cause significant damage to an infested plant with growth being slowed, new foliage yellowed and, in the case of heavy infestations, flowering prevented. Control on the plant by spraying either water (to knock them off) or a contact insecticide is hampered by the aphids' feeding position which is deep within the base of the leaves. A systemic insecticide would presumably be effective, but natural enemies, if present, may keep numbers low enough to prevent any damage.