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Colopha compressaElm cockscomb gall aphidOn this page: Identification & Distribution Biology & Ecology Are the galls aposematic? Life cycle Natural enemies Other aphids on the same hostIdentification & DistributionColopha compressa live in laterally compressed cockscomb-shaped galls along the midrib on the upper surface of elm leaves (see first picture below). These galls are yellowish, often tinged with red or entirely red. The fundatrices that induce these galls (see second picture below) are yellow or yellowish-green and are lightly covered with waxy powder.
First image above copyright Maria Fremlin, all rights reserved. The yellowish offspring of the fundatrices (see first picture below) develop to green alatae (see second picture below) which can be identified to species. For alatae of Colopha compressa with 6-segmented antennae, antennal segment IV is similar in length to antennal segment V (cf. Tetraneura spp. which have segment IV much shorter than segment V). For alatae with 5-segmented antennae, antennal segment III is more than 3 times the length of antennal segment IV (cf. Tetraneura species, which have antennal segment III less than 2 times antennal segment IV). The fused apical rostral segment (RIV+V) is 0.8-0.9 times the length of the second hind tarsal segment (HTII) (cf. Colopha graminis & cf. Colopha ulmicola, which both have RIV+V 0.6-0.75 times the length of HTII). The media of the forewing is once-branched (cf. Colopha graminis which has the media of the forewing unbranched).
First image above copyright Maria Fremlin, all rights reserved. The alatae produce dark yellow apterae (not pictured) on the secondary host which have a body length of 0.9-1.5 mm, and secrete flocculent wax. Alatae of Colopha compressa emerge from their galls on elm (Ulmus) in July, from an opening on the underside of the leaf, and colonise the roots of sedges (Carex) and cottongrass (Eriophorum). Alate sexuparae return to elm in September-October, although some populations may persist on the roots of sedges throughout the winter months. Colopha compressa is found throughout Europe, east to Turkey, Ukraine and Kazakhstan, and has been introduced to Siberia. Biology & EcologyAre the galls aposematic?Inbar (2014) et al. suggested that chemically protected galls which are also conspicuous are aposematic. Aposematic (warning) coloration is a biological phenomenon in which poisonous, dangerous or otherwise unpalatable organisms visually or chemically advertise these qualities to other animals. The evolution of aposematic coloration is based on the ability of potential enemies to associate the visual or olfactory signal with the risk, and to avoid such organisms as prey. Typical colours of aposematic animals are yellow, orange, red, purple, black and white and combinations of these. Aposematic coloration in plants has in the past received much less attention than in animals, but recent studies suggest that the conspicuous coloration of thorns and leaves may advertise unpalatably to herbivores. Similarly aphid galls that combine high levels of defensive compounds with conspicuousness, size, shape, bright coloration and possibly odour, may well be aposematic. Galls of Colopha compressa (see picture below) are certainly very conspicuous on the leaves of elm.
Image above copyright Maria Fremlin, all rights reserved. It is proposed that the galls, which are made of host plant tissues, are manipulated by the inducing parasites to form all the components of aposematism (chemical defences and warning coloration or odours). Many galls of other aphid species are bright red, for example the banana-like galls of Baizongia pistaciae (up to 25 cm long), the crescent galls of Forda formicaria (up to 3 cm long), and the spherical galls of Geoica wertheimae (volume 4 cm3) (for pictures of all three see Fig 1.). Birds with tetrachromatic vision that can access galls across the canopy, such as the black-capped chickadee (Poecile atricapillus), are probably among the most important natural enemies involved in the evolution of gall visual signalling. The interesting thing about Colopha galls is that their colour is quite variable. Some of this variation is accounted for by the age of the gall - older galls are redder - but there also seems to be variation between sites, as can be seen in the galls shown below.
Image above copyright Beentree under a Creative Commons Attribution-Share Alike license.
Image above copyright Maria Fremlin, all rights reserved.
Image above copyright Dr László Érsek, all rights reserved. Perhaps the degree of reddening is related to the amount of toxin/repellent present in the gall. Life cycleKot & Kmieć (2013) report that the fundatrix of Colopha compressa forms pocket galls on the upper surfaces of leaves, near the midrib and mostly on the basal part of the leaf lamina. Visible discoloration of leaf blades below the gall was observed, after gall opening. Discoloration ranged about 50% of leaf blade, on average. Samsone (2012) et al. (2012) observed decreased levels of photosynthetic parameters associated with direct damage to photosystem II in Ulmus laevis leaves affected by Colopha compressa. The fundatrices that induce the galls are yellow or yellowish green and are lightly covered with waxy powder (the picture below shows athe fundatrix & several early instar nymphs). Their antennae are short, only about 0.12 times as long as the body. The body is oval or elongate, with wax plates on each of the thoracic and abdominal segments, and small siphuncular pores - which may be present or absent.
Image above copyright Dr László Érsek, all rights reserved. The fundatrix produces large numbers of light-yellow nymphs, all of which mature to alatae. The images below show young alatoid nymphs inside a gall.
Images above copyright Dr László Érsek, all rights reserved. The alatae produced in the galls on elm colonise the roots of sedges (Carex) and cottongrass (Eriophorum), where they reproduce parthenogenetically through the summer. In autumn sexuparae return to the elm, where the sexuales mate and the oviparae lay overwintering eggs. Natural enemiesAs well as providing many of the images of Colopha compressa, Dr László Érsek has also provided a picture of syrphid larva found in the gall. Rotheray (1984) has noted that the larvae of Pipiza syrphids tend to specialize on aphids in galls, so it seems likely that the larva below is a Pipiza species.
Image above copyright Dr László Érsek, all rights reserved. Pipiza larvae are either green or dark brown and they differ from most other syrphid larvae in having the body coated in pubescence - as is the case for the larva pictured above. The most likely species of Pipiza is Pipiza luteitarsis which has been reared from pseudogalls of Eriosoma ulmi on elm (Rotheray, 1984). Predators from other insect groups have been recorded from Colopha galls. For example Megaselia chainensis (Diptera, Phoridae) larvae prey on Colopha ulmicola in its cockscomb galls on American elm (Ulmus americana) and pupate in the galls (in Disney, 1994). Other aphids on same hostPrimary hostsBlackman & Eastop list 22 species of aphid as feeding on English elm (Ulmus procera) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 14 as occurring in Britain (Show British list).
Secondary hosts
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