Every so often, a 'new' pest appears in the UK and quite often they are relatively new to the country, having arrived on imported plant material or under their own steam. Examples include tomato moth (Tuta absoluta) which is native to South America (1) and rosemary beetle ((Chrysolina americana) from southern Europe (2). However, in the case of the beet moth (Scrobipalpa ocellatella) the 'outbreak' in sugar beet crops in 2022 (3) is not due to the arrival of a 'new' pest.
The beet moth (which coincidentally is from the same family of moths as the tomato moth) is a native of southern England and has been recorded by Lepidopterists for some years. What is hard to explain is why it has 'suddenly' become a pest.
Beet moth has been known as a local and predominantly coastal species of southern England from Suffolk round to Cornwall, Scilly Isles and Channel Islands; rare in south west Wales and single records from north Somerset and the south coast of Ireland. Most inland records were considered as probable wanderers from nearby coastal habitats (4). Its wild host plants are beet and sea beet.
It seems that during 2019-2021, a few more beet moths were seen inland, followed by quite a dramatic move to sugar beet crops in 2022 (3). There is no straightforward explanation for this change in circumstances. Sugar beet is obviously a very suitable host plant and it seems logical that infestations would take off. The question is 'why did they wait until 2022'?
Beet moth occurs widely in Europe including a number of warmer countries and also in Egypt, Libya, and Morocco, where it can be a serious pest and complete up to 5 generations a year (there appear to be 2 generations in England). It seems that hot, dry conditions, such as we experienced in England in 2022, may be very suitable for its development and survival.
A further question concerns its movement and how far it is able to fly, and indeed, did some moths migrate to the UK from the continent in 2022? There is no way of knowing this at the moment, but certainly citizen science monitoring showed that beet moths were also relatively numerous in the Netherlands and Belgium (5, 6).
This is certainly a species to watch from a grower's point of view and one way that beet growers can keep a closer eye on this species is by using pheromone traps to monitor male moths. A pheromone has already been identified for this species and it should not be too hard to obtain some traps commercially.
(3) Beet moth Incidence of Beet moth in UK - Bing video
Images courtesy of BBRO
Article about a talk by Rosemary Collier at BeetTech2023: