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  • #12790


    Well, it’s mid September and myp lants are being knocked about by aphids – and what eggs I’ve got are already being eaten by wasps. So it was up with the butterfly house today. I bought it at The Warehouse for $99.

    Anyway – about aphids – here’s some thoughts of how to control them from another discussion group. Dale is in the US. Has anyone else got any bright ideas?

    My experience with the aphids on milkweeds, the amber colored ones, is they are specific and will not spread to other plants other than other species of milkweeds. There are many species of aphids…

    Aphids excrete a sugary substance to attract ants to enlist their help in their defense. They multiply so because they are asexual for most of the season, bearing live young, but at some point in the year, will form pupae from which winged adult aphids will emerge. The adults are sexual, mate and then, I assume, lay eggs.

    The ants the aphids attract will take small larva. You will see small holes in the leaves where the larva began to feed, but then was carried away by an ant. If the caterpillar makes it through the first three or four days undiscovered, it grows too large for the ants to attack and is relatively safe from ants. It is now, however, wasp fodder. They prefer them with a little meat on their bones.

    Plants also excrete sugary substances to attract ants for their defense against caterpillars, though I do not know of milkweeds that do. A number of passion vines, however, are known for this. The glands are on the undersides of the leaves. Some even produce small mimic butterfly eggs to fool the butterfly into laying its eggs elsewhere.

    It’s tough being at the bottom of the food chain.

    Dale McClung

    > Milkweed is certainly an aphid magnet. I’m not sure that the aphids cause a problem to the milkweed so much, but my concern is that the aphids will move from my milkweeds to other plants. And being a public garden, that could present a problem. I have also noticed some kinds of ants seem to be attracted to the aphids and I’m not sure if the ants will do damage to Queen or Monarch eggs/cats/chrys’ that may be on the milkweed also.


    > I squirt my aphids with a solution of roughly 2 teaspoons dish soap to a pint of water. Works fairly well but I really have to stay on top of it. Seems like it doesn’t take many of the little bugers to re-establish the whole herd again (or are insects flocks?!).


    > chris

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    More research I’ve found out about Aphids

    Also known as greenfly and blackfly, aphids suck the sap from young leaves. They are very small, plant-feeding insects. They vary in size from 1-10mm long.

    There are about 4,000 species of aphids worldwide and about 250 of them are serious pests for agriculture and forestry, as well as an annoyance for us gardeners.

    The aphid I get on my milkweed is probably the Oleander Aphid. Winged sexual adults will produce generations of female aphids which do not need a mate, but can give live birth without the help of a male. The aphids then become very plentiful.

    At first signs you can easily eliminate them, or at least control them, with diligent daily hosing. Use a strong spray to wash them away. You can also spray them with soapy water, which clogs their breathing apparatus and causes them to drown.

    But these methods will affect your Monarch larvae, pupae and eggs as well.
    Encourage ladybirds, as they will control aphids. The ladybirds will also reproduce, and the larvae that emerge will help knock back the aphids too.

    If your plants are overwhelmed by aphids or there are caterpillars feeding, which need the leaves, you can hand-squish the aphids while they are still on the stems and leaves – this needs to be done daily though. If you do not control the aphids, you will find your plants are further weakened by honeydew and sooty mould.

    An aphid parasite is available – Aphidius colemani. This is a little wasp, about 3mm long. It will not affect your Monarchs.

    The adult female wasp lays its eggs into aphids, and when the wasp eggs hatch, the larvae begin to devour the aphid from the inside.

    The aphidius larvae then develop into pupa and wasps inside the aphid, killing it in the process. The aphid swells and develops a crusty shell and may become golden or silvery in appearance. This is called an aphid mummy.

    The wasp then emerges by chewing a neat, circular hole in the mummy, to mate and reproduce. They feed on nectar and honeydew from the aphids (see below) – this process takes about 10-14 days.

    Each female wasp now parasitises about another 100 aphids, and so the cycle continues. Aphidius colemani can be found in our environment already – but can be purchased and introduced into areas where there are heavy aphid infestations.

    Because aphids breed very quickly, it is important to introduce Aphidius colemani at the first sign of aphids.


    Honeydew is a sugar-rich sticky substance secreted by aphids and some scale insects as they feed on plant sap.

    Ants and wasps may eat honeydew. Ants may even “milk” the honeydew from aphids, which benefit from the presence of ants due to their ability drive away predators such as ladybirds.

    Honeydew can cause sooty mould on plants such as milkweed.

    Sooty mould

    Plants become blackened and are usually sticky. This is more likely in dry conditions as rain washes the honeydew away.

    Although the mould is not feeding on the plant, it restricts light reaching the leaves – and the plant cannot breathe. Pest and disease problems are always more likely where plants are struggling to survive.

    Wipe down as many of the leaves as you can using a damp cloth. This will get rid of most of the sooty mould, and allow the plant to photosynthesise properly.
    Check any branches that have been cut back in case disease has entered via the wounds. These branches should be trimmed right back to clean, healthy wood. If necessary go right back to a main stem.

    Water the plant regularly – even in wet weather. If it is in a rain shadow, then the roots will be very dry, and the plant will be under even greater stress. You must not let your plant dry out.

    Feed with some garden compost, or sifted well-rotted manure. Just a few centimetres on the surface and either watered, or lightly forked in will make a huge difference. Top-dress the surface with leaf-mould now and in the autumn. This is a wonderful soil conditioner, and will make a real difference to the quality of the soil the plant is growing in. An alternative to leaf-mould would be any of the soil conditioners available from your garden centre.



    More about aphids/ants from people in Florida and (I think) India:

    As I’ve been thinking about the aphids, in particular, the
    relationship with ants and the species specific to milkweeds, I do
    not believe this species is harvested or protected by the ants, at
    least not here in FL. The ants, small, most likely argentine or white
    footed ants, roam the milkweed and take the smallest monarch larva
    regularly in the summer here, but do not, in my observation, appear
    to be interested in the aphids. It may be their “honeydew” is not
    palatable to the ants being derived from milkweed sap. The aphids may
    penetrate deep enough to reach the latex, but probably they feed on
    the sap near the outside of the stem or, since they concentrate at
    the growing tips of the plants, are able to reach the latex at that
    point, but that is pure speculation on my part. As there are many
    species of aphids and many species of ants, we simply may not have
    the right combination of species present or there are no ant species
    interested in this particular species of aphid. That, in general,
    also would explain why the lady bug larva and hover fly larva do so
    well. The ants may not be interested in them either since they feed
    on the aphids and absorb their contents.

    Dale McClung

    > >http://www.hort.wisc.edu/mastergardener/Features/insects/aphids/aphids.htm
    > >Some species of ants are attracted to and feed on the honeydew. Ants will
    > >protect the aphids from natural enemies and will actually carry them to new
    > >plants when the food source is depleted. Some ants even go so far as to
    > >build small shelters for the aphids or to keeping root-feeding aphids inside
    > >their own nests. A few species of aphids have become so dependent on their
    > >ants that they won’t even excrete honeydew unless stimulated by an ant!
    > >However, if aphid numbers get too high the ants will feed a few aphids to
    > >their larvae. And the ants are better at protecting their aphid herds from
    > >some natural enemies (such as ladybugs) than others (such as lacewings or
    > >hover fly larvae). No only do they fight off or kill the predators, but they
    > >also remove the eggs of some.

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