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Ovatomyzus boraginacearum (= Ovatomyzus calaminthae)
Alkanet aphidOn this page: Identification & Distribution Biology & Ecology
Identification & Distribution:Apterae of Ovatomyzus boraginacearum are usually whitish to pale greenish yellow, but may be brownish yellow to orange in overwintering populations. Their antennal tubercles are smooth and well developed. The pale antennae are longer than the body, and the terminal process of antennal segment 6 is 1.5-2.3 times the length of antennal segment 3. The pale siphunculi do not have any distinct subapical polygonal reticulation, and are slightly swollen subapically, narrowing to a slight constriction before the flange. Ovatomyzus boraginacearum is a very small aphid, with a body length of only 0.9-1.6 mm.
The alkanet aphid lives scattered on the undersides of leaves of its host plants, which are mainly in the family Boraginaceae, especially alkanet (Pentaglottis), lungwort (Pulmonaria officinalis) and comfrey (Symphytum officinale), and less commonly in the family Dipsacaceae. Ovatomyzus boraginacearum does not have sexual forms, but is reported to have a specialized hibernating apterous morph. It has been found in several European countries including England, Germany and Netherlands, as well as in Iran.
Biology & Ecology
Life cycleOvatomyzus boraginacearum is mainly found on members of the Boraginaceae, especially alkanet (Pentaglottis sempervirens) (see picture below).
Reproduction through the year is entirely parthenogenetic, and there is no host alternation, although the species can sometimes be found on reserve hosts such as herb Bennet (Geum urbanum) (see Ripka, 2001 )
Ovatomyzus boraginacearum does not generally form large dense colonies. Instead the adults scatter their larvae about over the leaves (see picture below of adults with immatures).
As with Ovatomyzus stachyos in Denmark, Ovatomyzus boraginacearum can be found outdoors in Britain in the middle of winter - and at any other time of year.
ColourFor most of the year, apterae of Ovatomyzus boraginacearum are whitish to pale greenish yellow (see picture below taken in September).
Some forms are instead brownish yellow, often with a faint orange patch on the dorsum (see first picture below taken in March 2017). Darker forms (brownish yellow or orange) are thought to be overwintering forms.
However, the second picture above was taken in mid-summer 2017 and shows the same reddish-range patch. Perhaps this reddish colour is a reaction to a developing endoparasitoid, rather than the brownish overwintering form.??
Natural enemiesThe leaves and stems of Boraginaceae are densely covered in trichomes, one purpose of which is presumably to discourage herbivores. Selvi & Bigazzi (2001) describe the leaf surface and anatomy of the Boraginaceae, including seven types of trichomes. Ovatomyzus boraginacearum appears to be the only aphid species specific to Pentaglottis, although five polyphagous species can occasionally be found on it.
The plant's defences appear to have been successful in reducing the number of aphid species that feed on Ovatomyzus, but they also seem to have reduced the number of predators that can move around on its leaves and stems. Larvae of Syrphidae and Coccinellidae are conspicuous by their absence, and the only predators we have found (so far) feeding on Ovatomyzus are cecidomyiid larvae (see yellowish predatory larva in picture below).
The scattered dispersal of this aphid may be adaptation to predation by these predators (although we have found cecidomyiid larvae to be major predators of some more typical 'colony-forming' aphids). There are of course several species of cecidomyiids that predate aphids, which at present we cannot differentiate at the larval stage.