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Oriental grass root aphid (see note below)On this page: Identification & Distribution Other aphids on the same host Damage & Control
Identification & Distribution
The galls of Tetraneura nigriabdominalis on elm are rose-red and whitish green when immature, but rose-red with a greenish stalk when mature (see pictures below). They are stalked, elongate, spindle-or pouch-shaped, pubescent (hairy), not shiny, and often with a pointed apex (cf. galls of Tetraneura ulmi, which are stalked, shiny, but not pubescent; or cf. galls of Tetraneura caerulescens, which are stalked, globular and matt; or cf. galls of Tetraneura fusiformis, which are stalked, spindle-shaped and pubescent, but with numerous granular protuberances).
Note: Tetraneura nigriabdominalis is sometimes described as 'rice root aphid', but that name is more commonly used for Rhopalosiphum rufiabdominale. For a long time Tetraneura nigriabdominalis was confused with another aphid, Tetraneura fusiformis, a major pest of rice in Africa, the Middle East, India and south-east Asia.
First two images above copyright Marko Šćiban, all rights reserved.
The Tetraneura nigriabdominalis fundatrix (see first two pictures below) which stimulates production of the gall is greenish with a variable amount of wax dusting. The offspring of the fundatrix which develop within the gall (see third picture below) are light green and covered with wax tendrils. These develop to emigrant alatae.
First image above copyright Marko Šćiban, all rights reserved.
The emigrant alatae (not pictured) have a shiny black head and thoracic lobes and a brown abdomen. Antennal segment V is 1.7-3.0 times longer than segment VI (including the terminal process), and bears 5-14 secondary rhinaria (cf. Tetraneura ulmi, whose antennal segment V is 1.2-1.7 times longer than segment VI, and bears 3-8 secondary rhinaria). The primary rhinarium on antennal segment VI is not enlarged (cf. Tetraneura ulmi, which has the primary rhinarium on VI enlarged.) The apical rostral segment (R IV+V) is 0.47-0.70 times longer than the second hind tarsal segment (HTII) (cf. Tetraneura ulmi, which has RIV+V 0.66-0.84 times longer than HTII).
The adult apterae of Tetraneura nigriabdominalis on the secondary host, grass roots, are rather small, greenish-white or brownish-white, plump and oval bodied, but not so globose as in most other Tetraneura species (cf. Tetraneura ulmi, which has the adult apterae orange yellow and globose; or cf. Tetraneura caerulescens, which has the adult apterae orange-brown to brown and secreting bluish flocculent wax). The body has long marginal hairs (cf. Tetraneura ulmi which has short fine marginal hairs). The apical rostral segment (R IV+V) is 1.20-1.73 times longer than second of hind tarsal segment (HTII) (cf. Tetraneura ulmi, which has RIV+V 1.83-2.71 times longer than HTII). Wax glands each usually comprise a group of rather large facets without any clear central area. The body length of adult Tetraneura nigriabdominalis apterae on the secondary host is 1.5-2.5 mm.
Tetraneura nigriabdominalis forms galls on various elm species (e.g. Ulmus canescens, Ulmus japonica, Ulmus minor, Ulmus parvifolia, Ulmus procera and Ulmus pumila). It host alternates to the roots of grasses and cereals (Cynodon, Digitaria, Oryza, Saccharum, Setaria). Feeding by apterae of Tetraneura nigriabdominalis on the roots of some grasses causes a reddish purple discoloration of the leaves. It is found in the Far East (China, Japan, Korea) where it is thought to have originated, and is now also found in Georgia, Kazakhstan, southern and south-east Europe and the USA. In Britain Tetraneura nigriabdominalis has only been found in southern England as galls on bonsai elms imported from Japan, but may well establish in Britain given the continuing expansion of its range into northern Europe - presumably due to climate warming (Walczak et al., 2017).
Other aphids on the same host
Tetraneura nigriabdominalis has been recorded from 10 species of elm (Ulmus canescens, Ulmus davidiana, Ulmus glabra, Ulmus japonica, Ulmus laevis, Ulmus macrocarpa, Ulmus minor, Ulmus parvifolia, Ulmus procera, & Ulmus pumila).
Blackman & Eastop list about 75 species of aphids as feeding on elms worldwide, and provides formal identification keys for aphids on Ulmus. Most of the aphids are in five genera: Colopha, Tinocallis, Eriosoma, Kaltenbachiella, and Tetraneura.
Tetraneura nigriabdominalis has only been found in Britain as galls on bonsai elms imported from Japan.
Damage and control
Tetraneura nigriabdominalis is an important pest of rice in the Far East. Walczak et al. (2017) have expressed concern that Tetraneura nigriabdominalis might also become a serious pest on the roots of maize, a crop being increasingly widely grown in Europe.