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Crimson-tipped monkshood aphidOn this page: Identification & Distribution Colour Other aphids on the same host
Identification & Distribution
Adult apterae of Brachycaudus napelli have an extensive black sclerotic shield over most of the dorsum, but the posterior, and much of the underside, are dark crimson (cf. Delphiniobium junackianum, which has no dark sclerotic shield and is coloured uniformly dark blue-green). Their antennae are 0.6-0.7 times as long as the body, and the terminal process is 2.7-4.3 times the length of the base of antennal segment VI. All the apterae are alatiform, and antennal segment III bears 10-25 secondary rhinaria (cf. Brachycaudus aconiti, which has 0-8 secondary rhinaria in the aptera). The apical rostral segment (RIV+V) is 0.9-1.2 times the length of second hind tarsal segment (HTII) (cf. Brachycaudus aconiti, which has RIV+V 1.2-1.6 times the length of HTII). The first hind tarsal segment (HTI) has only 2 hairs (cf. Brachycaudus aconiti in southern Europe, and Brachycaudus rociadae in the USA, which both have 3 hairs on HTI). The siphunculi have a very well developed flange, and are 1.7-2.4 times the caudal length. The siphunculi are 0.31-0.55 times the length of antennal segment III (cf. Brachycaudus aconiti, which has siphunculi 0.57-1.0 times the length of antennal segment III). The cauda is helmet-shaped, shorter than its basal width and with about 10 hairs. The body length of adult Brachycaudus napelli apterae is 2.0-2.9 mm.
Note: Brachycaudus napelli is in subgenus Acaudus along with Brachycaudus aconiti, to which it is closely related. Brachycaudus aconiti occurs in central and southern Europe, and parts of Asia.
Images above copyright Renze Borkent, all rights reserved.
Alatae of Brachycaudus napelli (not pictured) have similar characteristics to the apterae except their antennae are about 0.8 times the body length, and the antennal terminal process is about 5 times the base of antennal segment VI. Alatae bear 17-37 secondary rhinaria on antennal segment III and 0-4 on segment IV.
Brachycaudus napelli mainly feeds on monkshood (Aconitum spp.), forming colonies on the stems, flowers and fruits, and sometimes on the leaves. It is also found on delphinium (Delphinium spp.). Both Aconitum and Delphinium species are normally toxic to animals. The aphid does not host alternate, and sexuales (oviparae and apterous males) develop in the autumn. The crimson-tipped monkshood aphid is found in west and north-west Europe, south to Spain, and has also been recorded from Austria and the Czech Republic.
Biology & Ecology
Crimson red and black is a widely used combination of colours for warning intentional predators (such as birds) and unintentional predators (such as herbivores) that the prey is distasteful or otherwise nasty. The picture below shows the threatened neotropical frog, Oophaga granulifera, otherwise known as the granular poison frog.
Granular poison frog (Oophaga granulifera), copyright Patrick Gijsbers 21/01/08, under a Creative Commons by-sa 4.0 licence.
The aphid Brachycaudus napelli has adopted a similar 'colour scheme'. An aphid can either be using Batesian mimicry (where the insect is not distasteful, but is mimicking one that is) or Mullerian mimicry (where it is distasteful and using a commonly-used warning colour or pattern).
Image above copyright Renze Borkent, all rights reserved.
Given the highly toxic alkaloids present in the foodplant of Brachycaudus napelli, this seems most likely to be Mullerian mimicry. The aphids sequester toxins from their food plant, and redeploy them against predators. Other examples of this are given by Uroleucon tanaceti, which eat tansy (Tanacetum) which contains thujone, camphor and myrtenol, and Uroleucon solidaginis, which eat golden rod (Solidago) which contains pyrrolizidine alkaloids. Read more about aposematic coloration in aphids.
Other aphids on the same host