Alder Leaf Beetle.

 

Alder Leaf Beetle.

Agelastica alni (L.)

Many Italian Alders were in the 2010 and 2012 plantings They were joined later by common alder and then Red Alder. After a few years I noticed little blue beetles eating the leaves. By 2018 they were frequent I bothered to look up what they were, Alder Leaf Beetle (ALB) and sent in an observatree report only to be told they were not a problem. Pole stage trees were defoliated by June while eggs could still be found and some beetles could be seen into September. At an Observatree Zoom meeting pictures of them drew a blank, but once people started looking for them they usually found them. My concern was a second generation. Forest research say there is no evidence for a second generation on the continent where it is wide spread but not normally problematic. The defoliated trees do reflush. One year 2021, when we had a high pressure system stuck over the country and cold clear nights with warm sunny days through March and April the beetles became active several weeks before the Alders flushed and were seen feeding on Hazel, Birch, Hawthorn, Cherry Plum and just about anything else that was green.

Their waking up this year coincided with bud burst on Alders.

I took this photo on 4^th April this year. A single horizontal Common Alder shoot on a 3 year old coppice stool. I count 42 beetles, perhaps you can do better. Most of the wood was flooded at least once over the winter so most beetles which hibernate in leaf litter will have died.

After hibernation they feed on Alder leaves but they also eat particularly Birch where I have seen feeding larvae eating. The females abdomens fill with eggs and can be distinguished by the yellow /orange membrane under their wing cases.

The yellow eggs are laid on the underside of the leaves.

The eggs hatch in about a couple of weeks. The 1^st instar are yellow feeding together on the underside of the leaves. The second instar is also gregarious while they do separate out in the final instar. They eat either the top side or bottom surface of the leaf but not both. The whole of one side of the leaf may be removed. They pupate in the litter layer or probably any sheltered crevice. They emerge relatively quickly so adults can be found throughout the year. They then shelter for a diapause time during the heat of the summer before feeding up and hibernating again in the leaf litter. On my light soil they manage to bury themselves shallowly. They are fond of the gap between spirals and a tree trunk.

 

I was aware the beetle was considered Native but declared extinct in U.K, until found in Manchester in 2004. When it spread quickly locally. It can certainly reproduce prolifically and when it is really warm it can fill the air with flying beetles. I invariably find them in the car and on my clothes when I get home in the spring.

 It’s history in Britain is interesting and worth summarising. The following information is lifted from a paper A HISTORY OF AGELASTICA ALNI (L.) (COLEOPTERA: CHRYSOMELIDAE) IN THE BRITISH ISLES BY DON A. STENHOUSE. Which appeared in the ENTOMOLOGIST’S MONTHLY MAGAZINE in February 2019.

There are Alder leaf beetles in the Bronze Age deposits of Flag Fen, so there is no doubt about it being native. Prehistoric archaeological evidence comes from several sites, in the South and East of England and one from the Bristol Channel coast of Wales. There appears to be no evidence for it after Iron Age deposits until the start of the 19^th Century. 19^th and 20^th century records are occasional at best and limited to the south and coasts. Historical records are very infrequent surprising for an easily recognisable obvious beetle if genuinely native. There has long been a debate about whether ALB was/is native or a visitor. The last 20^th century record appears to be from Dorset in 1958. The first UK 21^st century record is from Manchester 2004 this was followed by an increasing number of sightings across an ever expanding area. A similar spread was seen after ALB was recorded on the south coast in Hampshire in 2014.

 The Distribution of Alder Leaf Beetle 

from The National Biodiversity Network