DIAMOND-BACK MOTH. 109 



The time spent in chrysalis state may vary (as given by various 

 writers) ; it may occupy from rather over one to about three weeks, 

 but there may certainly be two broods during summer or autumn, and 

 the chrysalids from the last brood of the year remain in this state 

 through the winter. 



The food-plants of the Diamond-back caterpillars are, by prefer- 

 ence. Turnip, Cabbage, and other cruciferous * plants, including notably 

 what we know in England as "Charlock" (Sinajjis arvensis, L.), in 

 Scotland as " Bunches " or " Skellocks." It also attacks, amongst 

 other weeds, " Jack-by-the-hedge " (Sisymhrium alliaria, Scop.), a 

 common hedge- or ditch-side plant of early foliage ; also the Hedge 

 Mustard or Flaxweed [Sisymhrium sophia, L.). 



The insect is widely distributed, and is one of the well-known 

 crop attackers on the Continent of Europe, a fact which probably 

 bears very largely on the sudden appearance of the caterpillars 

 amongst the Turnip crops on our eastern coasts. Notes of the vast 

 flocks of the moths noticed, a few weeks before the first outbursts of 

 attack at various localities on the coasts, with coincident observations 

 (which will be found in the following pages) from entomologists light- 

 house keepers and fishermen, besides agricultural observers, appear to 

 me to leave no opening for doubt that the attack of the past season 

 was wind-borne to our shores, and that, the crops being just in a 

 condition for attack, the results were what we know only too well. 



Particulars of Diamond-back Moth Attack in 1891. 



On the 8th of August, in compliance with the request of Mr. Clarke 

 (Secretary of the Koyal Agricultural Society) that I would prepare a 

 paper on the Diamond-back attack, embodying such amount of infor- 



* The specific scientific name appended to that of Plutella (namely cruciferarum) 

 is a very appropriate one, as it well describes the habits of the caterpillar in mainly 

 feeding on cruciferous plants, namely those of the Cabbage kind. The word Xylo- 

 stella appended to Cerostoma, by which synonym this moth was formerly known, 

 refers to the habit it was, in early days of observation, supposed to have of feeding 

 on the Lonicera Xylosteum, L., the upright or two- flowered honeysuckle, a shrub to 

 be found in thickets, and more especially in Sussex. 



Here, however, it seems to me that there may have been some confusion of 

 species. As the case stands at the present day, the Cerostoma Xi/lostella of Stainton's 

 ' Tineina,' p. 70, is distinguishable by several clear characteristics from Plutella 

 cruciferarum. 



The moth of C. Xylostella, besides being rather broadly yellowish-white along 

 the hinder margin of the upper wings, " has an extremely narrow oblique white 

 streak running half across the wing beyond the middle." Also, the caterpillars are 

 green, with a hroad red stripe on the hack, and are tapering to the head end, and 

 make a firm cocoon. 



During my own investigations, I found a very few green caterpillars striped with 

 brown or reddish brown, which may possibly have been of this kind. 



