EXPERIMENT STATION BULLETINS. 169 



forms occur, all of them being covered with a coat of fine waxy powder, 

 very much like the bloom on the leaves of the cabbage on which they 

 rest. This waxy bloom, no doubt serves as a protection by helping to 

 conceal the insect, but when we come to spray we find that it helps 

 very eftectually to repel the liquid. Lying, as they do, in closely packed 

 colonies, which sometimes cover almost the entire underside of a leaf, 

 one would expect to kill them with ease. One finds, however, on trying 

 to do so, that most spray mixtures slide from them like water from a 

 duck's back. Furthermore it is very difficult to reach them when 

 under the foliage. In order to overcome this last difficulty, we have 

 used a short extension, about three and one-half feet long, with a Ver- 

 morel nozzle set at right angles to the extension. This makes it easy 

 to reach the underside of the leaves and by simply turning the exten- 

 sion in the hand, one can spray downward on the head of the cabbage. 

 The best sprays for the lice that we have been able to find are tak-a-nap 

 soap, used at the rate of one pound to four gallons of water, and 

 Pyrethro-kerosene-emulsion made with whale-oil soap. This is diluted 

 ten times. Both of these sprays killed apparently all the lice that were 

 hit. The difficulty of hitting all the lice with a spray can be appreciated 

 only by those who have made the attempt. 



Cabbage-worms {Pieris rapae, Pontia protodice, Pieris oleraceae). 



Three species of cabbage-worms or cabbage-butterflies grace the State 

 of Michigan. They are, the Northern native white or pure white butter- 

 fly (P. oleraceae), the southern native white or checkered white (P. 

 protodice), and the imported white or common cabbage-butterfly (P. 

 rajiae). The larvae or caterpillars of each of these butterflies feed on 

 cabbage, rape, cauIifloAver and all of their near allies, with such enthus- 

 iasm that it will not be necessary to say more on that score. Before 

 the advent of the now commonest species shown in fig. 18, the pure 

 white cabbage butterfly* fed in peace in the northern United States, 

 inflicting comparatively little damage. The southern cabbage-butterfly, 

 with its checkered, black and white wings did likewise in the more south- 

 erly regions, the two species overlapping in a region that included our 

 State. The accidental importation of the European cabbage-butterfly 

 changed all this, for the native species could not compete with their 

 more vigorous cousins; gradually they faded away before the advance 

 of the aliens, until now they have almost disappeared from certain parts 

 of the country. 



When full grown, the larvae transform to naked pupae, remaining 

 attached to the underside of the food-plants or on some nearby object, 

 later changing to the butterfly stage. 



The writer has seen all three species working together in large num- 

 bers in one field, in Alger County. The larvae differ somewhat, but all 

 are readily recognizable as cabbage-worms. 



REMEDIES. 



From the nature of the case, it is not expedient to use poison on the 

 cabbage, certainly not after the plants have shown a tendency to head. 



* There is a spring form in which the veins_on the under side of the wings are marked with gray 

 scales. 



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