Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
Why aphid-hunting is important
for control and conservationOn this page: Aphid pest species need to be controlled Aphids as rarities, in biodiversity and conservation
Some aphid species are very important pests, whether of agricultural crops, ornamental plants or forestry trees. Accordingly, we know a great deal more about those few pest species than we do about the others, and our perceptions are biased accordingly.
Aphid pest-species - need to be controlled effectively
One obvious reason for looking for aphids is to reduce their numbers on our crops and garden flowers, or to "nip outbreaks in the bud".
Owing to their parthenogenetic reproduction and winged adults, and consequent high reproductive and ability to invade temporary habitats, aphids are known as classic 'r-strategists'.
Similarly, each summer innumerable winged cereal aphids Sitobion avenae, transported to the upper atmosphere by thunderstorms on the continent, arrive in the UK and rapidly reproduce. Such aphids are common because they exploit a specially favourable environment - large numbers of young rapidly growing plants. Other commonly observed aphids have an abundant but genetically non-diverse host such as sycamore aphids, nettle aphids and rose aphids (pictured below).
Several highly polyphagous greenhouse pest aphids such as Aulacorthum solani and Macrosiphum euphorbiae exploit a specially favourable environment. Yet outside a greenhouse environment they seldom attain such a predominant position.
Given their potential for rapid dispersal and reproduction, many people assume the only reason to search for aphids is in order to destroy them - so they treat all aphids in similar fashion. That simple approach can easily make the pest situation worse....
For example in UK four aphid species occur commonly on apple:
In other words to know what to do when you have 'apple aphids', you need to know which apple aphid. Spraying insecticide to get rid of the (relatively) harmless apple-grass aphid can cause much bigger problems later in the season if you kill off the natural enemies.
Out of about 600 aphid species in the UK (plus an ever increasing number of introduced or invasive species), a mere 20-30 of those species are regarded as serious 'pests' - in other words, under favourable conditions, those species may cause noticeable economic damage. Globally there are about 5000 species of which only about 250 are pests. Paradoxically, most aphids are quite rare, cause no economic damage and contribute greatly to our biodiversity.
Aphids - rarities, biodiversity and conservation
Of the aphids in Britain, a few can be pests, some are invaders, but others are rare and unusual, and even useful.
Many aphid species are little noticed. One such aphid, the large oak aphid Lachnus roboris is pictured below. This species lives on oak and amongst aphids is much more of a 'k-strategist'. The 'k' refers to the so-called carrying capacity at which the population is more or less stable. Such aphids tend to be larger, have a lower reproductive rate and can be strikingly slow to recolonize degraded and restored habitats, such as replanted woodland.
Some of these k-strategists are very rare, such as Lachnus pallipes which live on beech. Only our older fragments of ancient woodland host such rarities of the aphid world.
Most species of aphids of course fall somewhere between the r and K extremes. One should also point out that dividing aphid species into r and k-strategists is simplistic and only reflects part of their life history strategies. But it does highlight the diversity within the group.
Apart from the general benefits of biodiversity in the environment, some aphids bring specific benefits to man. Consider these three species:
These aphids cause little damage, and in Europe bees feeding on their honeydew produced much-prized honey.
At present we probably know less about which species of aphids are found in different parts of the country than any other major insect group. There is quite a high chance of finding a species that has never been recorded before in Britain.