Methods for the collecting,
preparation and study of
aphid specimens
Where to look for aphids:
On the whole, aphids tend to be most abundant and diverse in disturbed habitats, including those generated by human activity, such as clear-cuts, roadsides, cultivated fields and gardens.
Being sap feeders, they tend to do best where the rate of nutrient translocation is high, that is, on actively growing plants and plant parts.
Terminal growth and areas immediately below developing flowers and fruit are especially favoured.
On trees and shrubs, the leaf petiole and midrib provide the site of highest nutrient flux.
Some aphids (mainly Pemphigidae and Adelgidae) create their own nutrient sinks in the form of specialized galls.
Tree-feeding species are often more abundant on young trees; thus recently reforested areas and nurseries are rewarding collecting sites.
Many aphids (also other Sternorrhynchans) are associated with ants directly (active tending) or indirectly (feeding on sugars (honeydew) deposited on plant surfaces).
Obvious aggregations of ant activity should be investigated.
Often, this is the most profitable method of locating root-feeding aphids.
In late summer and autumn, watch for Vespid wasps gleaning sugar from leaf surfaces; there are likely aphids or scale insects on the underside of the leaves above.
Honeydew deposits also encourage the growth sooty mildew; a blackish coating on leaf or branch surfaces indicates the probable presence of aphids or scales.
Many aphids, however, give no outward sign of their presence and require
diligent and persistent searching to find them.
Field Data:
Standard collecting information (and the data usually included on specimen labels)
includes host, locality, date and collector
(the latter provides a link to field notes and hence to additional data not present on the labels,
and is also useful in tracing ambiguities, deficiencies and errors in other associated data).
Many aphids are most easily identified by a combination of host plant,
colour and pattern, and form and location of colony.
Detailed notes on these aspects should be made whenever possible.
Knowledge of aspects of the biology of most species is very sparse.
Thus information on habitat characteristics, associated insects and behavioural characteristics is always useful.
Collecting Techniques:
- Hand picking:
- Visual inspection and hand-picking individuals is the most reliable method for
determining host association and permits observation of behaviour and other details,
but is time consuming.
- Shaking / Beating:
- This is best accomplished by holding a tray or cloth (we use photographic trays) under a plant and
shaking the plant vigorously or,
for woody plants, rapping it briskly with a heavy stick (axe handles work well).
Short plants may have to be uprooted and shaken over the tray, or even brushed with the hand.
This technique allows sampling of a large number of plants quickly
while still permitting association of the collection to a particular host.
Although finer details of feeding location and colony formation are lost,
this is the best method for general surveys of the above-ground parts of plants.
A combination of beating to locate colonies,
followed by visual examination and hand-picking,
maximizes the "information : effort" ratio.
- Sweeping
Use of a sweep net is of greatest benefit when sampling
a particular species for population or distribution studies.
It is also useful as a method of detecting the presence of aphids
in herbaceous vegetation in order to determine if a more thorough
examination of the vegetation using other techniques
will be profitable.
In addition to the loss of host and behavioural information,
sweeping has a great potential for damage to specimens by other insects and
debris that accumulates in the net.
- Vacuum collectors:
- Vacuum cleaner-like devices are useful for
collecting from low matted vegetation that is not
easily swept or beaten.
It is also an efficient method for retrieving aphids which are difficult to dislodge
or, conversely, that drop to the ground too readily to be easily captured with a sweep net.
Like sweeping, this is a quick indicator of presence or absence of aphids
and the results can used to determine whether more refined
searching is in order.
- Flotation:
- Submersion in water is a useful method of extracting root aphids from soil.
It works especially well with aphids (as well as mealy bugs and other Sternorrhyncha)
because the heavy wax coat produced by many of these insects makes them
very bouyant and hydrophobic.
- Berlese funnel extraction:
- Aphids living in mosses are most easily recovered by the use of Berlese funnel extractors, in which a heat
source above the sample forces mobile insects to the bottom of a funnel into a collecting liquid.
- Pan traps:
- Water, brine or ethylene glycol in a pan, especially a yellow pan,
attracts and traps many migrating aphids.
This is a useful survey technique for some species,
and can give useful information on diurnal, seasonal and year-to-year
variation in flight activity.
- Aerial traps:
- Aerial traps are essentially a fan that draws a known volume of air
through an orifice of known area over a given time interval and deposits anything sucked in into
preservative fluid.
Such devices are often used to monitor flight activity and abundance in
agricultural areas.
Preservation:
- Fluid preservation:
- Aphids destined for morphological examination
should be collected directly into 70% ethanol.
This is also the favoured medium for long term storage.
Other media, such as formalin-based preservatives result in
specimens that are difficult to clear for mounting on
microscope slides.
Some workers use lactic acid for storage.
This has the advantage of preclearing specimens for
mounting, but is not suitable for long term storage,
the material becoming very fragile and overcleared.
- Microscope slide preparation:
- Detailed morphological examination of an aphid specimen ususally
requires mounting on a microscope slide.
Many media have been used for such preparations.
The traditional medium is Canada balsam, and is the medium we favour.
Alternatives include Euparol, Permount, polyvinyl alcohol,
and various water-soluble formulations based on Acacia gum.
Due to the superior optical qualities of the gum-based mountants compared to balsam,
gum mounts (specifically Hoyer's medium) were favoured for some
time in Europe and adopted by some North American workers.
However, such mounts are subject to dehydration if not properly protected.
This is exacerbated by the very low relative humidity found indoors
during the winter in colder climates.
Large numbers of slides prepared using this medium are now unusable
and require remounting.
Do not use it if you expect to keep a specimen more than a year or so.
Follow these links for instructions for preparing balsam mounts and Hoyers gum mounts
- Drying:
- Large aphids may dried using either critical-point drying methods
or through processing with volatile organic solvents.
Such methods are little used except for creating display specimens.
Many characters currently used for identificaton and classification
are not easily observed in such specimens using standard light microscopy.
Examination of specimens using scanning electron microscopy has
been underutilized among aphid taxonomists and is certainly not
a viable tool for general use.
Measurements:
[Text to follow.]
Aphids of British Columbia: last update 1998-09-28
Direct comments or questions about this site to
Eric Maw (mawe@em.agr.ca).
For questions about the project, contact
Robert Foottit (foottitrg@em.agr.ca).