108 THE ENTOMOI-OCilST'S RECORD. 



There seems, instead, to be a certain connection between the 

 relative specific importance of the different broods, and their disappear- 

 ance in the localities where their number diminishes ; Gomj^teryx 

 rhamni, L., emerges, for example, at/the end and flies at the beginning 

 of the season in regions where it has a single brood, and, in those 

 where it has three, the hybernating one is the primary ; Colias croceus, 

 F., and Pontia iiaplidicc, L., fly at the end of the season in the first 

 case, and the third brood is the primary in the second case. 



The numerical proportion between the individuals of the various 

 broods is not, however, constant (specific) in the majority of cases ; it 

 IS rather determined by the environment (climate, vegetation, parasites, 

 etc.), and these are distinctly " local proportions." In some localities, 

 these external causes can actually suppress the development of a brood, 

 which, in localities not far distant from the same regions, are very rich 

 in individuals (''suppressed broods"); the Pian di Mugn one offers a good 

 example in the total, or almost t()tal, disappearance of the third brood 

 of various species {fiodalirius, napi, si^a/ds, rliannn, cleojiatra, lathonia, 

 ae(jeria), or of the second of other bigenerates (iiriniiiniR, semiargns, 

 alcetas, cardiii), whilst the first mentioned generally afford a great 

 number of individuals in Tuscany ; the cause of this phenomenon 

 is, perhaps, the summer drought in the Pian di Mugnone, where 

 springs of water are wanting. 



Another phenomenon rather nearly related to the' above mentioned 

 consists in the " annual variations " presented by the frequency of the 

 various species in the same locality ; they are so great as to seem 

 incredible and inexplicable in the species with one brood ; these, in 

 fact, disappear almost entirely in certain years, and are most abundant 

 in others ; in the Pian di Mugnone, for example, theie were found 

 only six ^ $ and one ? of Agriadea eRcheri in 1916, notwith- 

 standing assiduous search during all the season of its appearance ; in 



1917, there were collected 50 males and 81 females ; in that year, it 

 was most abundant on the Monte Fanna, which overlooks the said 

 Piano ; on the other hand, in the park of the Eoyal Villa of Petraia, 

 where it is often abundant, only half-a-dozen individuals were found; 

 in the Pian di Mugnone, in 1915, during all the good season, there was 

 found only one Breutliia dia in June; on the other hand, in 1917, 

 there appeared a few examples in April and a few in June, while 

 no less than 35 were collected in August and September. Only a few 

 isolated specimens of Zj/f/aeiia appeared on the wing near Florence in 



1918, whereas several species were quite abundant in previous years ! 

 Also the Grypocera and Bliopalocera were all much scarcer last year. 



These remarkable annual fluctuations are difficult to explain, 

 because one must either admit an accentuated tendency in the $ $ 

 to move from one locality to another for Qgg depositing, which does 

 not correspond with observed facts in many species, whose 2 5 are, 

 on the contrary, very sedentary, and never move from a very restricted 

 zone, or a frequency of nymphosis lasting two or more years, which is 

 not confi med by breeding;* perhaps parasitism and other pathological 

 causes offer more admissible explanation, although still very obscure 

 and insiiffirierit. 



* The biennial nymphosis has been proved in a small number of individuals 

 of Euchloe crumeri : the emergence, after several years, of some Saturniae is well- 

 known ; Ercbia liijea and (Eneia upllo emerge constantly in alternate years 

 {generatio hima.) — R.V. [This is not the ease in Switzerland. — G.W.] 



