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Identification & Distribution

Adult apterae of Rhopalosiphum maidis are elongate-bodied olive green to bluish-black aphids, sometimes dusted with wax. The areas around the bases of the siphunculi and often other parts of the dorsum are a darker green or purplish black (cf. Rhopalosiphum padi which has a rusty red suffusion around the siphuncular bases). The antennae are dark except for segment III and part of IV, and the terminal process is 1.7-2.8 times the length of the base of antennal segment VI. The apical segment of the rostrum (RIV+V) is about 0.8 times the length of the second hind tarsal segment (HTII). The siphunculi are dark and rather short, not flared at the apex and only 1.1-1.4 times the length of the cauda. Immature Rhopalosiphum maidis are usually a somewhat lighter blue-green, with clearly marked darker areas around the bases of the siphunculi.

All images above copyright Mihajlo Tomić, all rights reserved.

The alate Rhopalosiphum maidis has a yellow-green to dark green abdomen with darker areas around the bases of the siphunculi, but no other dorsal dark markings anterior to the siphunculi.

Clarified mount images above copyright Brendan Wray, AphID, USDA APHIS PPQ, Bugwood.org under a Creative Commons Attribution-Noncommercial 3.0 License.

Image above copyright Mihajlo Tomić, all rights reserved.

Rhopalosiphum maidis populations are anholocyclic on grasses (Poaceae) in most parts of the world, but in parts of Asia (where Rhopalosiphum maidis originated) it host alternates with Prunus spp. as the primary host. It only occurs sporadically in cool temperate climates such as Britain and southern Scandinavia, but is cosmopolitan in warmer climates, where it can be an important pest of cereals. Rhopalosiphum maidis are commonly attended by ants (see picture above) which consume the abundant honeydew.

 

Damage and control

The corn leaf aphid is mainly found on maize and sorghum, occasionally on barley, and sometimes on other crops such as sugar cane and tobacco. The leaves, leaf sheath and inflorescence may be covered with colonies of dark green aphids and the resulting honeydew. Feeding results in mottling and distortion of the leaves, dwarfing of new growth, and sometimes plant sterility due to damage to the inflorescence. Rhopalosiphum maidis mainly attacks and damages young plants, although damage is often minimised by the activities of predators. The pictures below are from northern Nigeria and show (first) exuvia from a previous infestation on maize, and (second) a just-mated pair of coccinellid predators (a Cheilomene species, possibly Cheilomenes sulphurea).

Rhopalosiphum maidis is also a vector of many different virus diseases in cereals and other crops. These include barley yellow dwarf virus (BYDV) and cereal yellow dwarf virus (CYDV), the most widespread diseases of small grain cereals.

 

Other aphids on same host:

Acknowledgements

We are very grateful to Mihajlo Tomić for permitting us to use his images of live Rhopalosiphum maidis in Serbia.

We have made provisional identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994) and Blackman & Eastop (2006) supplemented with Blackman (1974), Stroyan (1977), Stroyan (1984), Blackman & Eastop (1984), Heie (1980-1995), Dixon & Thieme (2007) and Blackman (2010). We fully acknowledge these authors 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).

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