Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
Californian woolly oak aphidOn this page: Identification & Distribution Other aphids on the same host
Identification & Distribution
Feeding by fundatrices of Stegophylla essigi in spring causes the edges of young leaves of its host, coast live oak (Quercus agrifolia), to curl upward (see first picture below of young galls). Over time the resultant pseudogalls become thickened and red. Fundatrices inside the gall (see second picture below) are dark green, covered in curly white wool. They are very much like apterae of later generations, but their antennae nearly always have just 5 segments.
Both images above copyright C.A. Clark under a Creative Commons licence.
Subsequent apterous viviparae of Stegophylla essigi (see two pictures below) are broadly oval, pale grey-green to olive, covered in white wax wool. Their antennae have 5 or 6 segments. Antennal segment II is at most 2.5 times as long as the width of the mid-portion of that segment (cf. Stegophylla quercifoliae, where antennal segment II is 3.0-3.5 times as long as its midlength width) The vertex has wax glands like those on the dorsal sclerites (see below). The rostrum, when extended, reaches past the middle coxae, and the apical rostral segment (RIV+V) is 1.0-1.1 times the length of the second hind tarsal segment (HTII) (cf. Stegophylla quercicola, which has RIV+V 0.8-0.9 times as long as HTII).
There are 6 rows of dusky sclerites down the abdominal dorsum (see clarified mount below), each sclerite bearing 1 hair, and a variable number (3-14) of roundish, evenly stippled wax-glands. These sclerites are often absent or rudimentary on the anterior tergites. On tergite VII the sclerites are partially fused to give 4 sclerites, on tergite VIII they are fused to fused to an uninterrupted band. The dorsal hairs are thin and rather long. The legs are pale, with very thick femora and stout tibiae. The siphunculi are pore-like, each set in the center of a convex sclerite of about 0.11 mm diameter with 5-7 hairs. The body length of adult Stegophylla essigi apterae is 1.2-1.8 mm.
Alate viviparae of this species do not appear to have been described.
Stegophylla essigi feeds on various native oak species in California, including California live oak (Quercus agrifolia), blue oak (Quercus douglasii), coastal sage scrub oak (Quercus dumosa), and interior live oak (Quercus wislizeni). The species is not rare, but in an area where it occurs, often only a very few trees out of many have colonies. Colonies may be found on both the upper and undersides of the leaves in summer. It is holocyclic, with oviparae and both apterous and alate males produced in November. Hille Ris Lambers (1966) found that populations may also overwinter parthenogenetically on evergreen oaks, especially between leaves spun together by caterpillars. It is so far recorded from California and Oregon in the USA.
Other aphids on the same host
Stegophylla essigi has been found on 7 species of oak (Quercus agrifolia, Quercus douglasii, Quercus dumosa, Quercus garryana, Quercus kelloggii, Quercus lobata, Quercus wislizeni).