Tree Beetle Infestation

[BethB]

Hi. 
Apologies if this is the wrong place to post. 
I have 10 Alder trees, with a Tree Preservation Order lining my garden. 
These trees are covered in what seems like millions of black beetle, possibly Alder Beetle. This happened last year and they shredded the leaves and they’ve returned this year. 
They’re all over the trees, surrounding shrubs and lawn.

How can I control these and will they damage my other shrubs? Do I need to get professional help…. 
Any advice would be gratefully received. 
Thanks. 
Beth 

[ABtrees]

Hi Beth,

I'm no expert but those do look like Alder Leaf Beetle (Agelastica Alni), and you certainly seem to have plenty of them !   And it seems once you've got them, you've got them !   Roughly whereabouts are you (in the UK ?)?  

I'm not sure what you aim is - to 'protect' the trees / other plants or just to get rid of the beetles ?

I am in France and we have loads of these but don't notice so much because we also have loads of Alder trees (200 +) along the brook.  Because they're endemic here we also have loads of predators (and therefore a nice ecological balance).  These beetles were (very) rare in the UK until a decade or so ago and it may well take time for the local predators to catch on !

I attach a link to the RHS website which basically says that it is unlikely that they will kill mature trees, spraying anything other than small trees / shrubs is likely to be ineffective as well as damaging to other (possibly predatory) insects.  It also mentions other host plants .

Good luck !

AB

 

https://www.rhs.org.uk/biodiversity/alder-leaf-beetle 

[Stere]

Dunno if its worth the hassle  but im thinking u could try sucking them up with a cordless hoover 🙂

Edited April 7 by Stere

[BethB]

@ABtrees thanks for your comprehensive reply, I appreciate your help. Just in response to your questions I live in Newport, South Wales. 
My main priority is protecting the trees and definitely the surrounding shrubs. That said, I would like to remove the beetles or even just get some control over the numbers. They’re coving my lawn too, clustered over my fence posts and many are on my windows/ conservatory windows. 
I think you’ve raised a brilliant point around predators and the possibility things will find natural balance. I just really hope that is true as I’m not keen on the idea of using pesticides. @Stere thanks for your response. It’s creative and I may just get to a point where I am desperate enough to try it! 

[Dan Maynard]

Reading there it overwinters as adults, one of those things that would have been reduced more by some decent frosts but we've just had warm wet weather. We might get loads of wasps this year too, who knows.

 

I don't think your other shrubs are really in danger, they have the lovely alder tree leaves to eat.

[Anno]

I've been monitoring the spread of these for some time and it is eveident that they are not host specific as I have found them on many different species of trees up here in Cheshire.

In basic terms they defoliate and move on and are in quite alarming numbers once they have colonised, however I think the damage is mostly cosmetic and shouldn't be too alarming.

[BethB]

Thanks @Anno. Interestingly I am seeing them settle on numerous shrubs, not just my trees but I can see no evidence, as yet, of them damaging my other shrubs. I’ve shared some more photos to illustrate where they are settling if you have an interest. You’re right, the numbers I am seeing are scary and from advice given they’re likely to multiply further during July and August. 

[Anno]

Wow there are one or two of them!

A couple of them are mating, keep an eye out for some looking like they have swollen yellow abdomens,usually lifting the wing cases, they are the gravid females who will produce next years mob!