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Cocksfoot aphidIdentification & Distribution Biology & Ecology Other species on the same host
Identification & Distribution:The adult aptera (see first picture below) of Hyalopteroides humilis is medium sized elongate-oval pale yellowish green. The dorsal cuticle is rugosely sculptured and is not mealy. The antennae are shorter than the body. Antennal tubercles are well developed but rather low and have a small pointed process on the inner side of each of them, projecting forwards, with a hair on top of it. The median frontal tubercle is flat. The siphunculi are very small and thin, about 0.3-0.4 times the length of the cauda, with a barely visible apical flange. The cauda is long, tongue-shaped and blunt.
The alate Hyalopteroides humilis (see second picture above on grass blade with adult aptera) is also pale yellowish green with no abdominal markings. The head, antennae, legs, siphunculi and cauda are darker than in the aptera, and the wing veins are weakly brown-bordered. The micrographs below show adult apterous Hyalopteroides humilis in alcohol.
The clarified slide mounts below are of adult viviparous female Hyalopteroides humilis : wingless, and winged.
The cocksfoot aphid (Hyalopteroides humilis) lives along the midline on the uppersides of leaves of cocksfoot grass (Dactylis glomerata). There is no host alternation and the aphid is not attended by ants. The yellowish-brown feeding damage along the midline shown in the picture is characteristic. Males have been recorded, but most populations have probably lost the sexual stage in the life cycle. Hyalopteroides humilis is found in Europe east to Russia and in North America.
Biology & Ecology
In Britain Hyalopteroides humilis appears to overwinter as viviparae. Hille Ris Lambers (1949) reported the finding of a fundatrix and assumed the species overwintered in the egg stage, but could find no oviparae. Shaw (1946) found apterae at the roots of Dactylisin early spring, indicating that they had overwintered as viviparae. Dransfield (1975) was able to find parthenogenetic viviparae right through the winter months in the Dactylis tussocks in Berkshire, UK. Oviparae have been found and described by Orlob (1961) in New Brunswick in Canada where the winter is more severe than in UK.
The leaf of Dactylis is V-shaped in cross section at the base. This provides a degree of protection and concealment for the aphids which are spaced out along the midrib (see picture below).
Dransfield (1975) described the population dynamics of Hyalopteroides humilis in an area of grassland in which Dactylis glomerata was the dominant species. After overwintering as viviparae, the aphid population increased in spring, to reach a peak in late May. Alatae were produced in May and June apparently in response to increasing densities.
Numbers then declined sharply in June, but showed a brief resurgence in September. Changes in food quality determined the basic population trends through the year. Prevailing temperatures governed the winter survival rate and the rate of increase in spring. The cumulative effects of declining food quality, alate production and natural enemies resulted in the population crash in June.
Dransfield (1975) found that the dominant primary parasite of Hyalopteroides humilis was Aphidius urticae (see pictures below of mummy and adult parasitoid), but Aphidius avenae was also recorded occasionally.
The micrograph below shows an adult Aphidius cf. urticae reared from Hyalopteroides humilis.
Levels of hyperparasitism varied considerably from year to year, with Asaphes vulgaris being the commonest species. Few predators were found until June when syrphid larvae and staphylinid larvae became active. Larvae of the syrphid Melanostoma mellinum were found predating Hyalopteroides humilis.
Other species on the same host
Blackman & Eastop list 43 species of aphid as feeding on cocksfoot grass (Dactylis glomerata) worldwide, and provide formal identification keys. Of those aphid species, Baker (2015) lists 35 as occurring in Britain: Anoecia corni, Anoecia vagans, Aphis_craccivora, , Aploneura lentisci, Atheroides serrulatus, Aulacorthum solani, Baizongia pistaceae, Diuraphis noxia, Forda formicaria, Forda marginata, Geoica setulosa, Geoica utricularia, Hyalopteroides humilis, Jacksonia papillata, Laingia psammae, Melanaphis pyraria, Metopolophium albidum Metopolophium dirhodum, Metopolophium festucae, Myzus ornatus, Myzus persicae, Paracletus cimiciformis, Rhopalomyzus lonicerae, Rhopalomyzus poae, Rhopalosiphum maidis, Rhopalosiphum oxyacanthae, Rhopalosiphum padi, Schizaphis graminum, Sipha elegans, Sipha glyceriae, Sipha maydis, Sitobion avenae, Sitobion fragariae, Tetraneura ulmi and Utamphorophora humboldti.
Damage and controlHyalopteroides humilis does cause some very characteristic damage to the cocksfoot grass upon which it feeds. Any leaf supporting a colony turns brown in a narrow band around the midvein (see picture below).
The brown discoloration is most likely caused by a toxin injected by the aphid when feeding.
Control is generally not considered economic.