Scale insects

[goosey]

Last year I found about 15 of these scale insects on a holly stalk.
I didn't find out which type they were, but they were all dead females. They were about 3mm long but the white woolly looking excretion was actually covering and protecting their eggs and young. The males are apparently very tiny indeed.



Today I found some more (I presume they are also scale insects) on the Viburnum dawn. There were four of them, none with the woolly excretion, also 3mm but more rounded in shape and much darker in colour. I wondered if this was more to do with camouflage as it was a good match to the stalk.




Does anyone know what their actual purpose is, apart from to mate and die? And do they actually do damage to plants?

[paul m]

There are quite a few coccoids - homopterans: bugs related to aphids.
Scale insect - Wikipedia, the free encyclopedia

The large ones producing 'cotton wool' are likely to be Pulvinaria regalis the horse chestnut scale although I've never seen that on holly. That is not at all host-specific although many others are.

Like all homopteran bugs they live by sucking sap from plants. They can be very damaging. Citrus crops in particular suffer from three or four species.

They're quite peculiar, the males are very small and have no scales - they mate and disappear. Classically the females live in the soil over winter (or summer if it's that sort of climate) then climb up trees or other plants to feed and grow. The large final scales, as you say, are dead females which have returned down the tree to lay their eggs and die - the eggs and young are then protected by the scale and, in some cases, the 'cotton wool' or other exudates.

They are not easily attacked by predators although chilocorine ladybirds (such as the pine ladybird) specialise on them. Notably, the very first successful use of an insect to biologically control a pest was Rodolia cardinalis first used over a century ago to control a scale Icerya purchasi

Vedalia beetle - Rodolia cardinalis - Wildlife Photography

[goosey]

Thanks Paul - incredible to think that there are approx' 8000 species of scale insects.
I haven't noticed the ones in my garden being "a pest" but looking at the ones in the second photo they are on a damaged bit of wood so it would probably make feeding off the sap of the plant easier.

2 down 7998 to find .

[paul m]

Interesting how people view things differently. When I read about "8,000 species", I thought, 'That's not many'! Compared to the numbers of some families of beetles, flies and Hymenoptera .... it's all a matter of personal perspective.

They are an interesting group and not all are well-studied (the non- or minor pest species) and a lot could be learned from people observing them regularly. Probably not the arboreal species - that would involve us climbing up trees in the summer!

Originally Posted by goosey

Thanks Paul - incredible to think that there are approx' 8000 species of scale insects.
I haven't noticed the ones in my garden being "a pest" but looking at the ones in the second photo they are on a damaged bit of wood so it would probably make feeding off the sap of the plant easier.

2 down 7998 to find .

[goosey]

Well, I am totally fed up with scale insects! The ones on the holly are not causing me trouble but the ones on the Viburnum Dawn have multiplied beyond belief and the leaves are coated in the honey dew - a way that the scale insects get rid of excess sugar, they secrete this sticky substance and it drips on tho the leaves beneath. At the weekend I washed the "sticky" leaves with water - but the next day they were sticky again, so I tried a drop of washing-up liquid in with the water. This worked much better but now the honey dew is really thick. The weird thing is the smell - it smells like petrol or parafin. It looks like I am fighting a losing battle - anyone got any pine ladybirds I can borrow .

[paul m]

I lost my sense of smell years ago but don't recall a petrol smell ... mmmm
I do think that the only way to control the scales/honeydew/subsequent fungus is what you have tried - weak detergent in water. Not really useful if you have a large tree ... but it was the only way we could control scale on small citrus plants.

If you have any street lime (Tilia) or sycamore (or other Acer spp) nearby, you will probably find a few Exochomus quadripustulatus which you might persuade to come and owrk for you ....

Good time of year as they are mating and egg-laying at the moment ....

Originally Posted by goosey

....... At the weekend I washed the "sticky" leaves with water - but the next day they were sticky again, so I tried a drop of washing-up liquid in with the water. This worked much better but now the honey dew is really thick. The weird thing is the smell - it smells like petrol or parafin. It looks like I am fighting a losing battle - anyone got any pine ladybirds I can borrow .