THE NANTUCKET PINE MOTH. 749 



bility, then, the insect is doiililo-brooiled, flying in May and August, and wintering 

 in chrysalis. 



Curious as this dilierence in the number of broods between these allied species in 

 Europe and America may seem, it is quite in accordance with what occurs in other 

 Lepidoptera, where analogous species are found upon the two continents. I have 

 not studied this subject in the nocturnal Lepidoptera, but among butterflies I have 

 found that nearly all the species which are identical, or very closely allied, on the 

 two continents have at least one brood per annum more in North America than in 

 Europe. Specifications of half a dozen of these cases will be found in the American 

 Naturalist, Vol. X, pp. 603, 604. This seems to be largely due to climatic causes, 

 and it naturally follows that, when an injurious insect is imported from Europe to 

 America, its ravages here are likely to surpass any thing charged to it in its proper 

 home — a point which should be taken into account by students of economic ento- 

 mology.* 



Retinia, the genus into which this insect falls, is represented in Europe by no less 

 than eleven species, four or five of which are common, and four were found by Ratze- 

 burg more than forty years ago doing extensive injury.t They all feed upon conif- 

 erous trees, perhaps exclusively upon pines, and all live upon the twigs ; according to 

 Ratzeburg again, all are single-brooded with a single exception {R. resinella), where a 

 generation of moths appears only once in two years. When I first observed the injury 

 at Nantucket, no species of this genus had been found in this country ; but since 

 then one or two have been found in this section, and doing a considerable amount of 

 injury to pines.t Now that attention has been drawn to them, no doubt other notices 

 will follow, showing that we have to deal with a whole group of insects, specially 

 destructive to pines, both in Europe and America ; but our Nantucket species proves 

 much more dangerous than the European R. dtiplana and R. sylcestrana.^ 



The dift'erent species of this genus attack the trees in somewhat different methods, 

 but they all agree in selecting the tenderest growing shoots for their ravages, and in 

 destroying this sensitive and essential part by boring into the heart and devouring 

 the sappiest and pnlpiest portion at the base of the needles. Some, like a species 

 recently found by Mr. Comstock of the Agricultural Department in Washington upon 

 Pinus inojis,]] live a part of the time, at any rate, outside of the twig, for their webs 



* Mr. C. V. Riley (2d Rep. Entom. Missouri) asserts that destructive insects intro- 

 duced from America into Europe make no headway against their more "highly 

 developed " allies on that continent, while the reverse is true of European pests 

 introduced here, " the stronger and more favorably organized species overpowering 

 and starving out from Lime to time their less vigorous and less favorably organized 

 competitors." Unfortunately he gives no facts to support this highly organized 

 theory. [The facts in support of Riley's assertion are, it seems to us, very patent. 

 We have always regarded such introdnced species as prepotent, like weeds intro- 

 duced from Europe, which overpower and drive out native plants. The Phylloxera 

 of the vine, however, has multiplied in Europe as rapidly, if not much more so, than 

 in its native country. — A. S. P.] 



t Three of these four have now been found on the Pacific coast of the United 

 States. 



t A brief notice of these will be found in the appendix. 



§ Fernald's Catalogue of Tortricidse (1882) gives eight species, of which, however, 

 only three, including R. frustraiia, are found in the eastern United States. Of the 

 five found on the Pacific slope, where the insect fauna has, as is known, a decidedly 

 European aspect, four are believed to be identical with European species, and among 

 them R. dtiplana and R. sylvestrana occur. 



II Since this was written Mr. Comstock has published his notices of this species 

 (Rep. U. S. Dept. Agric, 1879, pp. 236, 237, pi. 5, fig. 2), which he considers, on Pro- 

 fessor Fernald's authority, to be the same as that here described. There can be no 



