HOST LISTS AND KEYS |
Below there are links to plant
genera arranged in alphabetical order, with lists of the aphids recorded from
the plant species within each genus, followed where necessary with identification
keys to the aphids. Before clicking on these links and using these lists and
keys please read the introductory information about the Host Lists and Keys
section provided below. Please keep in mind that the keys are for
guidance only. They are not intended to provide definitive identifications on
their own, but to indicate a possible name for an aphid that has been found
colonising a particular plant. This name should be regarded as a hypothesis
requiring further confirmation, initially by consulting the Aphids
section of this website to check the appearance in life, recorded hosts and
geographical distribution. If your aphid does not conform to all the
information given, or if doubt remains for any reason, then a specialist in
aphid taxonomy should be consulted, and the identification checked against
Museum specimens and published descriptions. In view of certain recent
publications it seems necessary to stress that it is unwise and
scientifically unsound to publish records of species new to a country
or geographical
region solely on the basis of the information provided on this website. Any person using a dichotomous identification key should also be fully
aware that the features presented as the alternatives in each couplet are
those specifically chosen by the author of the key in order to allow the user
to follow one of two separate pathways, taking into account the ultimate
goals of each of these two pathways, which usually will have additional
branches. The features used early in a key therefore become less and less
appropriate as more and more target species are eliminated. It follows that
the information presented in any of the keys on this website should never be
used or cited out of the context of the key as a whole, except where this
information refers to a single target species. Here are links to names of plant
genera beginning:
N.B. The pages in the Host Lists and Keys section are best viewed at
a magnification of 125% or 150%. NOTES ON THE USE OF THE HOST LISTS AND KEYS
SECTION The host-aphid lists and keys in this
section demonstrate, and in fact owe their feasibility to, the fact that most
aphids are relatively host specific, and that this specificity is most
evident at the level of the host genus.
The number of aphid species recorded from any one plant genus varies
greatly, from one to more than 260 (on Artemisia),
and the proportion of these that are monophagous, oligophagous or polyphagous
also shows considerable variation. The reasons for these differences are
presumably part physiological and part phylogeographic. We hope that the
lists will serve the supplementary purpose of providing a useful database for
anyone studying the origins and evolution of the present-day associations
between aphids and their host plants. For those who prefer to work with hard copy,
all text files can be printed in their entirety, or individual host lists and
keys can be copied and pasted into Word or an equivalent word-processing
programme. Aphid/host
plant records are extracted from a wide variety of literature sources and
will inevitably include a percentage of misidentifications, both of aphid and
host plant. Many of the new host records for palaearctic aphids added since
our 1994 and 2006 books are from the major work by
Holman (2009), which includes all sources and is therefore a very valuable
source of additional information. Many new host records for aphids in the
western USA have been added in 2016, thanks to Andy Jensen and his website http://aphidtrek.org. As the aim is to list only true host plants
we have omitted any records that are clearly spurious, e.g. tree-dwelling
aphids such as Drepanosiphum
platanoides and Eucallipterus
tiliae that will often be found on vegetation below their respective host
trees, and other aphids that were obviously vagrant individuals. When an
aphid-host plant association is unusual or doubtful, the aphid species is
placed in square brackets. We have used square-brackets in all cases where an
aphid is listed but not included in the key, not only for records that we
consider doubtful, but also for unseen and little-known species where the
description does not provide sufficient information to discriminate it from
other related ones occurring on the same plant genus. Further information on
most of these species can be found in the Aphids
section, referring to the index to aphid species names if necessary. In general we have tended to
adopt a liberal approach, including species in a key even when we think that
their normal hosts are in other genera. Plant nomenclature has been extensively
revised, and to a large extent now follows The Plant List. Authorities for plant species names are
omitted except where there is ambiguity. Plant names that were misspelt in
the original records have been corrected where we could be reasonably certain
of the intended species. Plant names that could not be identified by
reference to any available database, or where the application of the name is
uncertain, have been included, but are followed by “(?)”. A key is provided to the aphid species on
each plant genus in all cases except where only one species is recorded from
that genus, or where all the species are polyphagous. Sometimes the aphids on
related plant genera are combined in a single key. In particular, we found it
most convenient to key all grass-feeding aphids (even although some are
monophagous or genus-specific) together under Digitaria, and a similar procedure was adopted for aphids on
ferns (under Polypodium), mosses
(under Polytrichum) and orchids
(under Cymbidium). There are
cross-references to these keys under the host lists of all the relevant plant
genera. The very large aphid faunas of some genera – Artemisia, Quercus and Salix for example - are divided up in a
preliminary 'master' key, to avoid long and cumbersome keys with 100 or more
couplets. If numerous aphid species in one genus are involved - Cinara
on pines or Eriosoma on elms for example - then we have taken
advantage of any apparent specificity shown by the aphids to limit the number
of species that have to be discriminated in any one key. It is very important to note that the keys
are intended specifically for aphids found feeding on or colonising a named
plant species, and those for aphids on herbaceous plants are based almost
exclusively on the apterous viviparous morphs (apt.) found in mid- to late
spring and summer. The stem mother or fundatrix (fund.) developing from the
overwintering egg usually has a distinctive morphology, so samples collected early
in the season (particularly when consisting of adult apt. with a few progeny)
must be treated warily. There are inevitable exceptions, particularly in the
case of tree-dwelling aphids, where
there are no apt. to key, either because the viviparous females are all alate
(al.) or, in the case of some heteroecious aphids on their primary host
plants, because all the progeny of the fund. are al. spring migrants. In all
such cases the morph(s) to which the key can be applied are, we think,
clearly indicated. Polyphagous aphids occur on most common
plant genera, and to avoid a great deal of
repetition many keys at some point lead the user to a key to
polyphagous aphids, or to some part of it. Links in the keys to tree-dwelling
aphids take the user to a separate, shorter key to the polyphagous aphids
recorded from trees, although many of the species are the same as those in
the more comprehensive key that is provided to polyphagous aphids on
herbaceous plants and shrubs.. Many of the polyphagous aphid species on herbs
and shrubs are in any case likely to be found on any plant along with aphids
with more specific tastes, so it makes sense to transfer the user to the
polyphagous aphids key at an appropriate point, even when only rather few
polyphagous species have actually been recorded from the plant genus in
question. In fact the first question for anyone setting out to identify an
aphid from any herbaceous plant or shrub should be “Is it one of the common
polyphagous species?” (See also the introductory comments to the polyphagous
aphids keys.) Whereas the keys in Aphids on the World’s Crops (Blackman & Eastop 2000) are
relatively simple and can be used for unmounted specimens viewed under a
binocular microscope, the user of the keys on this website will need to make
microscope slide whole mounts of the aphids to be identified. We recommend
that Canada balsam mounts are prepared as these are of proven permanence, and
can withstand a range of temperatures and humidities. A simple procedure for
preparing balsam mounts is that of Martin (1983); for details of this and
other advice on mounting, labelling and storage of aphid specimens see the Techniques
section of this website. An important point to emphasise is that the exposure
to and removal of potassium hydroxide need to be carefully carried out, as over-potashing will cause bleaching, and
the extent and distribution of cuticular pigmentation is often used as a key
character. The degree of confidence one can have in any
identification made with a key in this book will depend on a range of
factors. We have tried to make the keys as comprehensive as possible. This
meant including species that we have not been able to examine ourselves on
the basis of their published descriptions. Unseen species are indicated by an
asterisk (*). Also included are little-known species of which only a few
specimens have been described or examined (in some cases only a single
specimen), and which potentially have a much greater range of character
variation. Where there are discriminants between two nominal species we have
used them, even when we suspect that further work may prove them to be
unreliable. If we suspect that two species are synonymous then this is
indicated in the text for one or other of them in the Aphids
section. So as a general rule, specimens that run in
a key to a common species are more likely to be reliably identified than
those that run to an asterisked name, or to a species that transpires to be
little-known or locally distributed when the name is looked up in the Aphids
Section. You need to proceed with caution, for example, if the name that you
arrive at is that of a species new to your region, and be extremely
sceptical if, for example, you are in
Patagonia and you have identified your aphid as a species that is only known
from a single sample collected many years ago in Mongolia! If in doubt, always consult an experienced
aphid taxonomist. Also
included in the lists and keys are a rather large number of undescribed
species from the BMNH collection, providing details of their host, country of
origin and collector. The formal naming of new species is, of course,
fundamentally important, but describing species properly is very
time-consuming. Descriptions should normally include both apterous and alate
morphs, and if at all possible they should be based on several samples
collected at different times of year and in more than one locality. Most of
the undescribed material in the BMNH collection does not fulfil these
criteria. Also, descriptions of new species are best included in revisions of
the groups concerned, so that they can be adequately compared to existing
species. Nevertheless, we believe that by including undescribed species in
the host lists and keys we can at least make known their existence, so that
this material can be borrowed and included in future taxonomic studies. Aphid morphology and key
characters Fig. 1 illustrates
the characters and morphometric parameters of a typical aptera of the tribe
Aphidini which are in common use in the keys, and the abbreviations. Fig. 2 shows the
principal features of two aphids of different genera within tribe
Macrosiphini. Fig. 3
illustrates features of the terminal segments of the rostrum (R IV+V); the
number of accessory hairs is frequently of taxonomic importance. The
morphology of a generalised alate aphid is illustrated in fig. 8. For
more detailed information on aphid morphology consult Miyazaki (1987), or
Blackman & Eastop (2000). Many of the discriminants used in the keys are
morphometric, and require measurement of parts of the aphid such as antennal
segments with a micrometer eyepiece or a digital measuring system. Some of
the commonest measurements are shown in more detail in fig. 9.
Correct and accurate calibration of the measuring device is obviously
extremely important. The parameters measured are mostly as in Ilharco &
van Harten (1987), except that it is important to note that in the keys on
this website body length (BL) is always measured to the posterior end of the
anal plate and does not include any projecting cauda. Please also note
that the measurement of the basal width of the cauda in our fig. 9 also
differs from that shown in Fig.1.3.13 of Ilharco & van Harten (1987). Key couplets may offer a choice between two
ranges of measurements or ratios. Sometimes when species are particularly
difficult to separate these ranges are contiguous, or even overlap. For
reliable identifications one should therefore ideally examine a series of 10
or more apterous adult aphids, so that if necessary the range of variation in
the sample can be assessed and compared with the range given in the key. Keys will not work if applied to immature aphids,
and in several groups, especially when the adult cauda is broad and rounded
as in Lachninae, Greenideinae and many Eriosomatinae, it can be difficult to
distinguish between late instar immatures and apterous adults. If the form of
the adult cauda is not distinctive, then the presence of rudimentary
gonopophyses, and of fully-formed and clearly defined anal and genital
plates, can provide recognition features for adults, but even these are not
wholly reliable. To be confident about the recognition of adults in difficult
cases it may be necessary to examine a number of specimens of different sizes
from the same colony, in order to establish what are the particular features
of the adult insect in that species. In any case collection and examination
of a large sample should be the general rule, because identifications should
always be based on an examination of the fullest possible range of variation. |