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Common dogwood-grass aphidIdentification & Distribution Biology & Ecology Damage & Control
Identification & Distribution:Anoecia corni apterous fundatrices in spring on dogwood (Cornus) are dark brown or blackish. 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, have a large black pterostigmal spot on the forewing, a white band around the top of the abdomen and a dark patch on the abdomen covering tergites 3-6. The body length of winged forms is quite variable ranging from 1.9-3.0 mm.
The first picture above shows two mature apterous Anoecia corni fundatrices (wingless stem mothers) with several developing nymphs. The siphunculi are reduced to pores and the antennae have only 5-segments (not visible in the picture). The winged form (shown in the second picture) above has two clear distinguishing features - a large black pterostigmal spot on the forewing, and a dark patch on the abdomen covering the posterior tergites 3-6 bordered by a white band. Both can be seen in the second picture.
It can be difficult to separate Anoecia corni from two other Anoecia species that (may) occur on dogwood. The 5th and 6th antennal segments of Anoecia corni 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 Anoecia corni antenna (see picture above) has secondary rhinaria on both the 5th and 6th segments, and has 14 secondary rhinaria on the third antennal segment.
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.
Biology & Ecology:
On primary host (spring)Overwintering eggs of Anoecia corni hatch in spring and give rise to a spring generation of fundatrices. The picture below shows developing alatiform nymphs.
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)
Here 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.
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.