I had a query from a gentlman asking whether bees would protect his tri-color birch from aphids, or whether it would be safe to use an insecticide to get rid of the aphids without harming the bees.
I hope the gentleman concerned sees this post - I tried to respond, but the email came back 'undeliverable'.
Still, I publish my answer here, in case it helps others.
it's fairly common that bees are seen feeding on what is known as 'honeydew' - which is a type of sweet excretion produced by aphids and scale insects that feed on plant sap. You can read more on this page here.
Ants also like it, and even kind of 'protect' aphids in a form of symbiotic relationship that benefits ant and aphid - sometimes referred to as 'farming'!
This may be seen on a range of trees, including eucalyptus, for example. However, I'm afraid the bees are neither eating nor killing off the aphids, so the presence of the bees will not protect the tree or plant form aphid attack.
- as well as other beneficial insects, so spraying or treating with a toxin is a bad idea.
I think this is a bad idea too! Systemic insecticides (like neonicotinoids) basically create a toxic plant. This means that any flowers produced by the tree or plant, will in turn present that poison to pollinators or other beneficial insects. They may be persistent in soil, and leach to other areas, thus contaminating other plants.
In addition, if the sap sucking insect ingests, then (if it survives long enough) secretes honeydew, the honeydew will in turn quite probably be toxic.
Presumably, the aphids will then be toxic for other creatures (beneficial predators) that might feed on them.
had aphids on my plums several years running (though no bees feeding on the aphid honeydew).
The plum tree recovered each time, and I was relieved because the plums are excellent.
In the case of aphid infestation, I think it would be a good idea to act quickly. This is what I did:
- Removed the leaves that were especially shrivelled and infested - usually the new growth - the very ends of the twigs.
- I then blasted the leaves with water (hose) each day for about a week, then kept an eye on things. I know some people use soapy water - just ordinary very diluted, household liquid soapy water, sprayed on to the leaves.
I have had no aphid problems this year.
Some people also advocate growing onions and alliums nearby (and I have heard of garlic spray being used, but have no experience of this for aphid control, though I have used it to deter slugs from my lupines.
If you are concerned about aphids, you could also invest in lacewing and ladybeetle larvae to protect your plants from aphids ahead of aphid season - although if there are ants around, I suspect they will endeavour to protect the aphids from predators!
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