This fascinating talk covers every aspect of the aphids lifestyle, including their predators and what we should and shouldn’t be doing to control them.  The information is based on the latest research by the Rothamsted Institute at Harpenden and ends with some hints for gardeners on aphid control.
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The is the first of our Society’s talks for 2020 and hopefully the timing and advice on aphid control is very appropriate!

After a career in computing, Colin has used his retirement to develop an eclectic range of interests including art appreciation, science, healthcare, local history and marionettes.  He is an active member of the Watford & District U3A, and a volunteer speaker for Diabetes UK.
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Colin recently gave this talk to the Radlett U3A where it was very well received.

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Most aphids are clones. One of the reasons why aphids can reproduce so quickly, is that the clones are born fully formed, female and with the next generation already ovulated inside them.

 This is a video of an aphid giving birth (Aphid Parthenogenesis (Cloning)) https://www.youtube.com/watch?v=Yup6spoUpv0

 Aphids grow so fast, that with unlimited food and no predators, one aphid would produce enough offspring to form a 149Km layer over the earth in only 18 weeks.

Aphids can produce winged offspring if they need to move for any reason.

Many of the summer host plants die or are harvested, so many aphids have a summer and winter host plant. The eggs are laid on the winter host.

 This shows the movement from winter to summer host plants for the Peach Potato Aphid.

Longer autumn nights trigger the birth of males. Winter eggs are very cold hardy, so this is a strategy to overcome hard winters when the adults would be killed off.

No eggs from any region survived for more than one month at −30 °C, although it is possible that field acclimated eggs of the Arctic species would be able to achieve this. The eggs of the Arctic species had a higher level of cold hardiness than the temperate species. Eggs from all regions were found to be sufficiently cold hardy to survive conditions in their respective environments. In tropical climates, eggs aren’t needed.

Cucumber Mosaic Virus: many serious plant diseases are spread by aphids. The Peach Potato Aphid exhibited a preference for the elevated volatile emissions of infected plants. 

Apart from cucumbers and other cucurbits, the virus also attacks spinach, lettuce and celery and many flowers, especially lilies, delphiniums, primulas and daphnes. 

DECEMBER 2013 
​University of Cambridge researchers have shown that viruses use aphids as pawns, discouraging the insects from permanently settling on already-infected crops and using this forced migration to spread infection to healthy vegetation. 

The work started almost accidentally when about five years ago. A student and I noticed that aphids became sick or died when confined on a virus-infected plant. Dr John Carr 
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The Cambridge team collaborated with researchers at Imperial College, London, using Arabidopsis plants as hosts and monitoring the effect that the crop-infecting cucumber mosaic virus had. It was observed that the virus launched a concerted attack on the plant’s immune system whilst concurrently altering its biochemistry; in this way, the weakened Arabidopsis plant was unable to fight off either its attacker or visiting aphids. The aphids, instantly repelled by the smell and taste of the plant, left for healthier plants, but not before landing on the plant and contracting the virus. In this way, the mosaic virus ensured that the spread of the infection would be self-sustaining and highly efficient.

Aphids secrete honeydew on foliage, stems and fruits, which attracts the growth of sooty moulds. Here you can also see white cast aphid skins.

Aphids are very common and so have many predators. There is even a fungus which attacks them.

A video of ants “milking” aphids for their sugary honeydew.  https://www.youtube.com/watch?v=0TJT90MJmQg&t=1s

A video of ants attacking a ladybird to protect their food supply. https://www.youtube.com/watch?v=S8RTdznEFio

A video of ants attacking a lacewing lava to protect their food supply, but failing to protect against a hoverfly lava, which uses clever chemical deception!  https://www.youtube.com/watch?v=fbRK6E5crbg

Some aphids distort their host plant to form a protective gall. The gall uses the plant’s own “plumbing” to clean the gall of the sticky waste honeydew, which would otherwise clog the gall.

Some social aphids have specialised “soldiers” which can attack predators. This video shows them attacking a lacewing larva https://www.youtube.com/watch?v=TBo_5Op8x2M

The wasp turns aphids into living larders for its larvae, laying eggs inside unfortunate animals that are eventually eaten from the inside out. If it’s unlucky it might itself be eaten by a ladybird before it can hatch.
​See video https://www.youtube.com/watch?v=YuG39V82J7I

If you see aphid “mummies” it’s a sign of parasitic wasp attack. Don’t spray!

The pea aphid has evolved to fight off attacks by wasps with the help of a bacterium and a virus.

In the body of one species of aphid, a bacterium and a virus have formed a unlikely partnership to defend their host from a lethal wasp called Aphidius ervi. But the pea aphid has a defence – some individuals are infected by guardian bacteria (Hamiltonella defensa) that save their host by somehow killing the developing wasp larvae. 

H.defensa can be passed down from mother to daughter or even sexually transmitted. Infection rates go up dramatically when aphids are threatened by parasitic wasps. 

H.defensa‘s is only defensive when it itself is infected by a virus – a bacteriophage called APSE which produces toxins that are suspected to target the tissues of animals, such as those of invading wasp grubs. The phage infects the bacteria, which in turn infect the aphids – it’s this initial step that protects against the wasps. 
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It was important of having both virus and bacteria – with the full alliance intact, less than 10% of the aphids fell victim to the wasp. If one or both of the partners was absent, the wasp successfully parasitized 90% of its potential hosts. Without the phage, the aphids might as well not have been infected by H.defensa at all, for all the good it did.

The pea aphid also has two colour forms. If there are many parasitic wasps, which seem to prefer green aphids, there are more of the red morphs. If there are ladybirds, which like red ones, then there are more green morphs.

The next part of the talk deals with some of the scientific work on aphids at Rothamsted Research at Harpenden. Their Insect Survey has ben running for more than 50 years. Their 2014 anniversary cake shows aphids as well as the Garden Tiger Moth, whose sudden decline was first detected at Rothamsted.

Dr Richard Harrington shows how aphids are collected in giant suction traps around the UK which collect flying insects including aphids, aphid predators and other pest moths, beetles etc. Aphidology Technician Tracey Kruger then shows how the collected aphids are sorted by species, counted and entered in a database. All the material is stored, ready to be used in future research.

These are the agriculturally-important pest species of aphids surveyed and reported on at Rothamsted.

Suction traps kill what they collect. Live specimens are collected in the autumn to monitor the start of egg laying. The aphids are dissected to see whether the offspring are clones or pre-sexual.

Research has shown that the temperature in January and February is a good predictor of when the first aphids will appear, the colder the winter, the later the aphids appear. The data starts in 1965 so it missed the very cold 1963 winter. The winter of 1978-79 was also the coldest winter since the famous 'big freeze' of 1962-63 – see blue dot on the far left in July. Warmer winters in the 2000s show aphids emerging as early as March/April.

Using this method, AHDB (Agriculture and Horticulture Development Board) Aphid News is published in March each year, predicting when aphids will emerge. By 2-8 May 2016, the trap had collected 6 Peach potato aphids, so the predictions are pretty good! 
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Although aimed at farmers, Aphid News is publicly available on the internet at: https://ahdb.org.uk/aphid-news

Water pan traps can be used by farmers to monitor local numbers.
​Yellow attracts aphids better than other colours.

Nets suspended from balloons can sample insects at higher altitudes – important on warm summer days.

The next few slides deal with resistance to insecticides in the Peach Potato aphid – a major pest against which hardly any insecticide is effective. 
With the enormous numbers of aphids born, genetic mutations are bound to occur. Eventually a mutation makes one aphid resistant to an insecticide and it starts cloning itself and number grow despite insecticide being used. The usual reaction to growing numbers is to spray more often, but this simply removes competitor aphids from the food supply and only resistant ones survive. Soon the insecticide is useless.

These are the main commercial insecticide – NOT available to the public.

Knockdown resistance (KDR) was first identified in the house fly in the 1950s. It is also in other insects e.g. mosquitos. 

This graph shows KDR% resistance going DOWN which was odd. There was still a problem with resistance. A new Super- KDR mechanism had evolved. This was more “efficient” in energy terms for the aphid, so it replaced the old KDR mutation. Nearly 98% of this species had the Super mutation by 2013.

Another insecticide useless against this aphid.

Organophosphates where quite effective, but they badly affected human health and were banned. As soon as they went out of use, the mutation for resistance disappeared. This mutation has an energy cost. Without the pressure of the insecticide, the mutated aphids were at a disadvantage and rapidly disappeared.

There is no Neonicotinoid resistance in this species, but the insecticide’s use is very limited because of the effect on the bee population. Over-use of it in Spain has induced a mutation in aphids there, which is likely to spread here eventually if we use Neonicotinoids more widely.

Summary of resistance mutations.

Would genetically modified aphids help to control the populations? NO. Aphids reproduce asexually and so the genes would not be spread.

List of things to try this in your garden!

Nettles: if you can bear to, leave a patch of stinging nettles somewhere in the garden. It will attract a species of greenfly that provides food for early ladybird and hoverfly larvae. These then move on to feast on other insect pests. 
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Early flowers for food: aphids tend to stick to one type of plant, but their predators are not so fussy. To kickstart pest control, make sure you have some early flowering scented plants, such as wallflowers, to attract early pollinators.
Herbs: all helpful insects like aromatic herbs, so plant borage, hyssop, sages, lavender and mint in pots. A few lavender plants among your roses can make all the difference, and a hyssop hedge makes an attractive edging to vegetables or flowers. (It will also deter cabbage white butterflies.) 
Parsley and other umbellifers These attract lacewings, so include fennel, dill or angelica sweet cicely and cow parsley in shadier areas. 
Parasitic wasps and hoverflies are also drawn to flowering heads of dill and fennel, and you could further encourage them by letting some parsley plants go to seed.

Predators by post: Lacewing larvae look like a bargain. Only buy wasps if you have them in an enclosed space like a greenhouse or conservatory, otherwise they will all fly away!

Look after your Ladybirds over winter with a corrugated cardboard “hotel” and leave tidying up dead leaves and plants in the border until spring.

Attract insectivorous birds with feeders and nest boxes. For the garden, the best bets are Great Tits and Blue Tits.

Ants not only protect aphids from predators, some species overwinter aphids in the ants’ nest and they also move aphids around on a plant and between plants. Rid yourself of ants and the aphids are exposed.

A high-pressure water spray is effective, but make sure you get the underside of leaves and try not to damage the plant. There are various recipes for sprays using washing up liquid. Insect sprays from garden centres contain pyrethrum, to which your aphids may be resistant.