This little fella is one of about 4 or 5 similar species, which are easily confused. Indeed we have marked this species MLS due to this fact.
If you find something that looks like this (note this specimen is a little worn), then it is likely one of the five following species;
- Digitivalva pulicariae
- Acrolepiopsis assectella
- Acrolepiopsis betulella
- Acrolepiopsis marcidella
- Acrolepia autumnitella
The reason we have suggested it as A.assectella is that one of the more distinctive marks on this species is a more triangular white mark as shown below.
Apparently the most likely species this could be confused with visually is Acrolepiopsis betulella (1). However the distribution maps for this species show that it’s UK distribution is limited to North England and Scotland (1). The same source also suggests that Digitivalva pulicariae is similar but the white marking is more rectangular and reaching faintly towards the front of the forewing (known as the Costa), which is clearly not the case in this specimen. Also D.pulicariae has a second white mark towards the head end which out little friend above is missing.
Acrolepiopsis marcidella in the UK is distributed and limited locally towards the south coast (1), so likely ruling it out for the Bristol area.
Acrolepia autumnitella in Brislington is perhaps the most likely alternative species this could be. Indeed as of 2008 it was perhaps the more widespread of the two species in Bristol (2). However we feel A. assectella is the more likely species, based partially on appearance but also on the larval food plant of the species. A. assectella larvae feed on a Alliums, including Onions, which our neighbour at the time was very fond of growing (sometimes to enormous size), where as A. autumnitella larvae feed on Nightshades mainly, a rare group of plants in this area.
So for now we will stick with A. assectella as the MLS. The next question therefore is what’s this little fella all about. Well as we have already stated it feeds on Alliums but in the UK it remains rare enough to not be the pest it can be on the continent (3). Indeed it is now a considerable pest in North America as well, to the extent that in Canada the controversial step of biological control has been trialled.
According to the Cornell University College of Agriculture and Life Sciences (4), in 2010 a natural predator of A. assectella was introduced in the Ottawa area to help control it’s numbers. The predator chosen was Diadromus pulchellusis, a solitary wasp native to central Europe. The method of control is via the female D.pulchellusis laying it’s eggs into the pupal host.
The larvae of A. assectella are fairly well protected from pesticides as they mine the foliage, stem and bulb of the onion, hence selecting a predator which attacks the moth during its pupal stage, which occurs outside the host plant, probably makes good sense.
However here is Brislington we shouldn’t jump to conclusions if we see internal damage to any onions we may have been growing. Other invertebrates such as Delia antiqua (the Onion Fly) also feed in a similar way, but we are yet to spot this in our garden. Either way if you find a larva munching within your onions, if it has legs its a caterpillar and may be the species above. If it doesn’t have legs, it may be the maggot of the Onion Fly.
Brislington has a number of allotment sites, so it would be interesting to know if this species is becoming a pest in these locations.
- Sterling, P. and Parsons, M. Field Guide to the Micro moths of Great Britain and Ireland. 1st Edition. UK. Bloomsbury 2012
- Barnett, R.J. Andrews, R.M. Bailey, M.A. Corner, T. Higgins, R.J. and Martin, J.P. Moths of the Bristol Region. 1st Edition. Bristol Regional Environmental Records Centre (BRERC). H. Charlesworth & Co. Ltd. 2008
- Author Unknown, UK Moths, https://www.ukmoths.org.uk/species/acrolepiopsis-assectella. Accessed 02/12/2021
- Tilton, S.H. Cornell University College of Agriculture and Life Sciences – Biological Control, https://biocontrol.entomology.cornell.edu/parasitoids/diadromus.php, Accessed 02/12/2021