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Common dogwood-grass aphidOn this page: Identification & Distribution Biology & Ecology On spring host On summer host On autumn host Other aphids on the same host Damage & Control
Identification & Distribution:
In spring on dogwood (Cornus) the apterous fundatrices of Anoecia corni are dark brown or blackish (see first picture below). They have reduced eyes and 5-segmented antennae, whereas subsequent generations have large compound eyes and 6-segmented antennae. The siphunculi of all Anoecia corni forms are reduced to inconspicuous pores. Winged forms, both spring migrants and the sexuparae returning to Cornus in autumn (see second picture below), have a large black pterostigmal spot on the forewing, and a white band bordering the dark patch on abdominal tergites III-VI (cf. Anoecia vagans which has no dark dorsal abdominal patch).
It is difficult to separate the apterae of Anoecia corni from two other Anoecia species that (may) occur on dogwood, but the alates may be distinguished by examining their antennae (see micrographs below showing the alate Anoecia corni and a close-up of the antenna). The 5th and 6th antennal segments of Anoecia corni alates both have secondary rhinaria (c.f. Anoecia vagans which has none on those segments). The third antennal segment of Anoecia corni has 9-17 secondary rhinaria (c.f. Anoecia major which has 13-22 secondary rhinaria on that segment). The body length of winged forms is quite variable, ranging from 1.9-3.0 mm. The third picture above shows a colony of Anoecia corni on its secondary host - roots of grasses, attended by the common black ant Lasius niger.
In Europe Anoecia corni host alternates between dogwood (Cornus spp.) and roots of grasses (Poaceae). In eastern Asia and in areas where introduced (South Africa and North America), the dogwood-grass aphid remains all year round on grasses and some cereals. The species is found throughout Europe, and in Asia, Africa, and North and South America.
Biology & Ecology:
On primary host (spring)
These spring generations are often attended by ants.
The pictures above and below show common black ants (Lasius niger) attending the fundatrices and their developing alatiform (future winged) nymphs.
On secondary host (summer)
The four pictures below all show Anoecia cf. corni on its secondary host. Again they are attended by ants, most commonly by Lasius niger, but sometimes by Lasius flavus (Depa & Wojciechowski, 2008).
The second picture above shows a mixed species group of root aphids including both Anoecia corni (with the dark sclerotized dorsum) and Tetraneura ulmi with which Anoecia species are often associated.
The apterae with the rather shiny black dorsal cuticle are typical Anoecia corni. We are unsure whether the very lightly marked alate shown in the picture below is an unusually early sexupara or is a different Anoecia species.
In late summer they produce winged migrant sexuparae (females whose offspring develop to sexual forms) which return to the primary host, dogwood.
On primary host (autumn)
Having returned to dogwood, they produce large numbers of pale young nymphs as shown in the picture below.
This results in a rapid build-up in numbers.
Such high numbers may attract large numbers of predators as reported by Jaskiewicz (2003) who recorded both syrphid (hoverfly) and coccinellid (ladybird) larval predators. They apparently had little effect on the aphid population as they only built up towards the end of the season.
Some colonies are attended by ants which also reduces predation levels. The colony above was attended by the ant Lasius fuliginosus, also recorded attending Anoecia corni by Quinet et al. (1997) .
These nymphs develop into oviparae and winged males. After mating, the oviparae lay their overwintering eggs on dogwood.
Other aphids on same host:
Anoecia corni has been recorded from 20 Cornus species. Most Anoecia species are restricted to North America.
Blackman & Eastop list about 30 species of aphids as feeding on dogwoods worldwide, and provides formal identification keys for aphids on Cornus.
Damage and control
Dogwood aphid is said to lower the ornamental value of Cornus alba shrubs, especially in autumn, causing deformations, discoloration and early leaf fall. Neem oil has been suggested as an effective means of control on dogwood.
It is unclear whether Anoecia corni cause any damage to the summer host - grasses and cereals. A'Brook (1980) has shown that the dogwood aphid can transmit barley yellow dwarf virus (BYDV) to cereals. However, levels of infestation are largely unknown. It is reported to be a minor pest of rice. Given the uncertainty of its effect on yield, it is seldom if ever controlled on cereals.