1900] 



58 



MUST AIM). 



Gamma or Silver Y-Moth, l'liini<t i/aunmi, Lmn. 



Plusia gamma. — 1, CRgs ; 2, caterpillar; 3, chrysalis in cocoon; 4, moth. 



Towards the middle of the past summer information was sent me, 

 with specimens accompanyiug, of caterpillars (which proved to he those 

 of the Gamma or Silver Y-Moth) liaving heen causing serious injury 

 to Mustard, and also to Potatoes. In the first case the attacked 

 locality extended for a distance of fully twelve miles in fields adjoining 

 the Humber; in the second, the mischief was reported especially from 

 the neighbourhood of Holbeach, in Lincolnshire. 



The attack is of unusual interest from several points of view, but 

 most particularly because, although these voracious and good-sized 

 caterpillars are very general feeders — as, for instance, on the leafage of 

 Peas, Beans, and Clover, Turnips and Cabbage, Beet and Mangolds, 

 and various other crop and weed plants — yet I have no knowledge of 

 Mustard having ever been recorded as one of the plants on which they 

 feed ; and excepting in 1892, when I had two observations from 

 localities in Kent of the migration of this species of caterpillar to 

 Potatoes from Clover, I have never had notes of them as an infestation 

 to Potatoes. 



In the following pages I have placed the observations under one 

 heading as above, referring back to it from that of Potatoes, placed in 

 its regular order, as from various coincident circumstances the attacks 

 are most usefully recorded together. 



The Gamma eggs are generally laid beneath the leaves, and soon 

 hatch. The caterpillar (figured above, life size) is, when full grown, 

 usually green, and covered with short hairs; the head brownish green. 

 It has six fine whitish lines along the back, and a fine yellowish line 

 along each side; the three pairs of claw-feet green or reddish brown, 

 and the tivo pairs of sucker-feet beneath the body green. One great 

 point of distinction in these caterpillars is that they have only these 



