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Cocksfoot aphidOn this page: Identification & Distribution Biology & Ecology Life cycle Natural enemies Other aphids on the same host
Identification & Distribution:
The yellowish-brown feeding damage along the midline of the cocksfoot grass leaf, visible on both sides of the leaf (see first picture below), is characteristic. The adult aptera of Hyalopteroides humilis (see second picture below) 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 third picture above) 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. 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.
We have since found black mummies (?Ephedrus plagiator) or ?Aphelinus sp.
Other aphids on the same host
Hyalopteroides humilis has been recorded from 4 Poaceae species (Arrhenatherum elatius, Bromus sterilis, Holcus lanatus, Dactylis glomerata) but is usually found on Dactylis glomerata - the other 3 may be overflow or accidental hosts (depending on how the samples were obtained).
Blackman & Eastop list 42 species of aphid as feeding on cocksfoot grass (Dactylis glomerata) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 34 as occurring in Britain (Show British list).
Damage and control
Hyalopteroides 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.