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Aphidinae : Macrosiphini : Macrosiphum californicum


Macrosiphum californicum

California willow aphid

On this page: Identification & Distribution Other aphids on the same host

Identification & Distribution

Adult apterae of Macrosiphum californicum (see two pictures below) are elongate spindle-shaped aphids coloured yellowish green, with darker green internal colour on the median line and on lateral portions. The antennae beyond the base of antennal segment III are pale brown, with the apices of segments III-VI black. The legs, siphunculi and rostrum are pale with dusky tips, and the cauda is pale. The antennal terminal process is 6.5-7.5 times the base of antennal segment VI (cf. Aphis farinosa, which has the terminal process 1.6-2.5 times the base of segment VI) . The antennal tubercles are well developed, with divergent inner faces (cf. Aphis farinosa, which has undeveloped antennal tubercles). The rostrum reaches past the second pair of coxae. The siphunculi are long, about 1.3 times the length of antennal segment III; they are darkened distally, with only the apical 9% with polygonal reticulation. The cauda is tapering, rather broad, and bearing 3-5 pairs of lateral hairs and 1-2 single dorsal preapical ones. The body length of adult Macrosiphum californicum apterae is 1.9-2.6 mm. Young immatures are pale yellow (see second picture below of immature with adult), whilst fourth instars have darker green markings like the adult.

Note: Jensen in Aphidtrek has suggested that there are at least two species of Macrosiphum being referred to as Macrosiphum californicum using Salix as host. The main distinction between them is the number of setae on the cauda, but the colour varies as well. Some specimens have bold dorsal internal stripes, as in the photo below, while other specimens are a simple plain green with mostly dark siphunculi.

Both pictures above copyright Jesse Rorabaugh under a public domain licence (CC0).

The alate Macrosiphum californicum (not pictured) has the head and prothorax pale green, the thoracic lobes yellow-brown, and the siphunculi dusky, occasionally lighter at the base. There are rather few secondary rhinaria (5-10), and these are confined to the basal half of antennal segment III. The ovipara has the head pale brownish yellow, and the body pale green mottled with light coral-red. The proximal thirds of the hind tibiae are swollen to twice the diameter of their narrowest portion, and thickly covered with sensoria. The male is alate, with the head and thorax blackish brown, and the abdomen pale green with black cross bands and lateral areas.

The images below show a clarified slide mount of Macrosiphum californicum, and a colony of the species along the midvein of a willow leaf.

First picture above copyright Jesse Rorabaugh under a public domain licence (CC0)
Second picture copyright Andrea Wuenschel under a Creative Commons Licence.

Macrosiphum californicum is monoecious on a variety of different Salix species, including weeping willow (Salix babylonica), shining willow (Salix lucida), yellow willow (Salix lutea) and almond-leaved willow (Salix triandra). It was first described by Clarke (1917) who reported it occurring as small colonies on the tips of new growth of willow. Judging from the second picture above, they favour feeding along the midvein of the willow leaf. The species is holocyclic with sexuales occurring in October. The California willow aphid is common and widely distributed in North America, and also recorded from Honduras.


Other aphids on the same host

Macrosiphum californicum has been recorded on 8 willow species (Salix amygdaloides, Salix babylonica, Salix laevigata, Salix lasiandra, Salix lasiolepis, Salix lutea, Salix scouleriana, Salix triandra).


We are grateful to Jesse Rorabaugh and Andrea Wuenschel for making their pictures available for use under public domain and creative commons licences respectively.

We have used the keys and species accounts of Clarke (1917) and Palmer (1952) along with information from Roger Blackman & Victor Eastop in Aphids on Worlds Plants. We fully acknowledge these authors and those listed in the reference sections as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure provided by Blackman & Eastop (2006).

Useful weblinks


  • Clarke, W.T. (1917). A list of California Aphididae. The Canadian Entomologist 35(9), 247-254. (p. 254) Full text

  • Palmer, M.A. (1952). Aphids of the Rocky Mountain Region: including primarily Colorado and Utah, but also bordering area composed of southern Wyoming, southeastern Idaho and northern New Mexico. Thomas Say Foundation, Denver. Full text