Accidental indoor rearing

While counting the eleven Nemapogon granella adults in my kitchen late this afternoon, I noticed a fresh-looking Cydia pomonella amongst them.  The N. granella breed in a bag of walnuts brought back from France in 2019.   Peter checked the genitalia of a specimen in 2020.

Nemapogon granella found indoors
Newton Longville, 1st March 2024

The walnuts came from a tree in the garden of my wife's family home.  During a visit in November 2019, we picked up the walnuts from the wet grass beneath the tree and dried them indoors by an open fire before putting them in a carrier bag and bringing it home to Newton Longville.  The wet weather had partly-rotted the pericarp of the walnuts (the fleshy cover over the hard shell beneath) and we didn't really clean this off.  It turns out that this is where the larvae of N. granella were feeding and the same bag of walnuts in the kitchen - more specifically the pericarp on them - has sustained several generations per year of N. granella since then: we decided not to disrupt it by eating the nuts.  There can't be much pericarp left by now.

Cydia pomonella found indoors
Newton Longville, 1st March 2024

We have apple trees in the garden and we definitely have Codling Moth, so it is probable that the C. pomonella got into the house as a larva within an apple earlier this autumn or winter and that it had then found somewhere to pupate and emerged extremely early as a result of the indoor warmth.  We store the in the cold and bring just a few at a time into the kitchen for eating - the last was eaten a month ago - so the larva would have had only a short time in which to emerge from an apple before the apple was eaten.

Alternatively it is just possible that this is another species that has started to breed in the walnuts.  C. pomonella is known to use walnut as a foodplant and I found online a French document from the 1920s that says specifically that they use the pericarp.

Tim Arnold
Newton Longville, Bucks