JONATHAN DOWNES: Tell me Y

The Silver Y moth (Autographa gamma, previously known as Plusia gamma) is one of the most well known migratory moths on the British list. The larvae are extremely polyphagous and according to Nancy Fraser (2000), have been recorded feeding on at least 224 plant species, and furthermore she claims that they have also been recorded damaging many crops, especially those of the cabbage family.

They have a complicated life cycle. The adults make seasonal northward migrations into areas where – due to climatic conditions – they are unable to establish a full-term presence. As Fraser writes: “For example, individuals migrate into Britain each spring, and after, one, two or three generations, descendants of the spring migrants return to over-wintering sites in North Africa and the Middle East”.

The species is widespread across Europe, parts of Asia and North Africa and the northerly migrations can reach as far as Iceland, Finland and Greenland – the latter, as far as I can tell, being its only known incursions into the New World. In the United Kingdom they are present in significant numbers from the middle of May until they are killed off by frosts in the late autumn. Many individuals, however, fly south again and winter around the Mediterranean and the Black Sea.

In 2007 the Vermont Co-operative Agricultural Pest Survey (CAPS) reported that although they had not actually found any specimens “the likelihood and consequences and establishment by A. gamma have been evaluated in a pathway-initiated risk assessment conducted by the Department of Entomology from the University of Minnesota, published 2003.

Autographa gamma was considered highly likely at becoming established across the US if introduced: the consequences of its establishment for US agricultural and natural eco-systems were also rated high (ie., severe).”

As far as I am able to ascertain, there have been no records, however, of this species in mainland North America. That is, until – possibly – now.

As editor of an increasingly popular online daily magazine; which covers amongst other things natural history, cryptozoology and out-of-place animals; I often receive photographs for me or our readers to identify. These pictures were sent on 8th August 2010 by my friend and colleague D.R. Shoop in Minnesota. They had been taken the previous Monday (the 6th). My first thought was that they were indeed a Silver Y moth. I have been familiar with this species since I first became interested in British moths at the age of 11 – 40 years ago. My second thought was that they couldn’t be because Silver Y moths are not found in North America. Upon investigation I found that there are forty-three species in the genus Autographa, of which at least fifteen are recorded in North America, and some of these; particularly Autographa californica, Autographa bimaculata, Autographa buraetica, Autographa pseudogamma, Autographa v-alba, and Autographa corusca; are not only found in North America but bear a remarkable resemblance to the Eurasian Silver Y.

I would originally have placed a fair amount of money upon the moths pictured here being the Silver Y species with which I have been familiar for four decades. However, now I am not so sure. I would be very interested in reading the comments of any expert in the North American noctuidae.

REFERENCE

Cirsium Palustre (Marsh Thistle) literature search and habitat potential risk analysis (Nancy Fraser, Canadian Ministry of Forests, Vancouver, 2000)