Hazel Catkins under attack

March 3rd 2023

Hazel catkins under attack 

January is not always an exciting time to be out and about in Assynt.  This was particularly so in 2023, but Nature can spring surprises.  It was lunchtime on 26th, and David  was enjoying his sandwich while parked on the waste ground by Achmelvich Bridge (NC082248).  

As he ate, he wandered and looked.  He was looking up at some mature hazels Corylus avellana on the north side of the road, and noticed that many of the unexpanded male catkins were damaged.  It appeared that their ends had been reamed out, leaving a conical hollow with blackened edges.  Out came the camera for a stacking picture of this oddity (photo 1, which consists of 80 individual images).

He emailed the final image to Ian, which made two people who had not seen anything like it.  Ian thought that the ends of the catkins might have been chewed by insect larvae.  Two groups of insects were likely suspects, sawflies and micro-moths, with larvae that can, fortunately, be told apart.  

Detective work on the bookshelves

Sawflies are difficult to identify to species in any life stage, but there is a book that lists all the micro-moths that feed on parts of plants.  This is A Field Guide to the Smaller British Lepidoptera (1988) edited by A.M.Emmett, of which Ian had a copy.  Hazel is obviously a popular foodplant with micro-moths, since the entry for Corylus included 31 species (over 1600 micro-moths occur in the British Isles). 

So, back into the body of the text, to see which part of the tree they attacked.  Fortunately, just two were recorded as feeding on the catkins, only one of which occurs in Scotland, the Nut Bud Moth Epinotia tenerana.  

Fieldwork

On 3rd February Ian and Gwen went out looking at hazel catkins, starting with those on trees planted in her garden ground at Torbreck (NC0824).  Some of these did indeed have blackened damaged areas.  Later examination under a binocular microscope revealed tiny larvae (2mm long) hunkered down in the flower scales of the damaged areas.  A specimen was extracted; it had four pairs of pro-legs, which established that it was a moth larva, a black head capsule and a dark area on the back of the first thoracic segment.  All of which was a good fit for images of the early larva of the Nut Bud Moth found online.

Next stop was the hazels where David had made his original observation – more catkins with patches of damage and some very fine silk, although no larvae as such.  The following day, 4th February, Ian had a look at the old hazels in his garden ground at Nedd (NC1337), and found more damaged catkins and larvae.  

Life cycle

Meanwhile, David had produced several photos he had taken on 13th February 2020, at exactly the same spot as his more recent discovery (a considerable credit to his image filing system!).  These images show a rather larger larva with the same features, hanging on a silken thread from a catkin (photo 2). 

From various sources, we have learned that the adult Nut Bud Moth has a long flight season, July-October, and comes to light.  It is not large, with forewings about 7mm long.  A member of the large family Tortricidae, it is generally reddish-brown, but ‘exceedingly variable’ in pattern.  The eggs are laid in unexpanded catkins, where the tiny early instar larvae feed October-March.  They then move to the unexpanded leaf-buds, where they feed March-May, with a hole in the bud sometimes concealed by leaf fibre.  They then drop to the ground, where they pupate in a cocoon, emerging in July.  

Highland distribution

Although the moth is described as ‘common’ in the British Isles as a whole, there are only about ten records from the Highlands, with just two in the north.  An adult was collected by the late Philip Entwistle at Migdale Wood in East Sutherland (NC6590) on 24th July 1996, and another came to a light trap run by S.M.Palmer at Druim Chuibhe,  Invernaver (NC6861) in West Sutherland on 12th August 2009.  Happily, Gwen had also photographed an adult found during daytime on croft woodland not far from her house on 10th July 2022 (photo 3).  So, David’s discovery of the larval feeding signs, his earlier photographs and our follow-up greatly extends the known range of this species.

David Haines, Ian Evans and Gwen Richards

 

 

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