62 THE EEPORT OF THE Xo. 36 



larvge may be found ou the same leaf. Some of the first larvae to emerge may 

 have matured, pupated, and produced adults. For the sake of convenience, the 

 females developed from wintering larvae may be designated, as spring emerging 

 females and those developed from larvae produced the same summer as summer 

 emerging females. The small larvge found on the same leaf with the almost 

 mature larvae may have been produced from eggs laid by late maturing spring 

 emerging females or they may have been produced from eggs laid by a summer 

 emerging female. There results field conditions that would warrant the consider- 

 ing of the species as single brooded, while breeding experiments would show 

 two or more broods. 



It is a matter of record that there is a second lot of larvae produced in 

 the case of Pteroniis ribesii, Lygaeonematus ericlisonii, Taxonus nigrisoma, and 

 various species of Lophynis. The number of larvse produced at this time is 

 always much less than the number produced by the spring emerging females. 

 There is no question but that in many species, only a small number of the larvae 

 produced by the spring emerging females pupate the same season and emerge 

 as adults; the great majority do not emerge until the following spring. So that 

 in most species a full second or third brood does not exist. 



That the great majority of the species of Tenthredinidae are single brooded 

 and the other species partial second or third brooded is also shown by the collec- 

 tion of adults. They are most abundant during six weeks or two months of 

 the spring, May and June or June and July, depending upon the latitude and 

 the altitude of the region. Only a few individuals are taken after this period, as 

 is shovi^n by the many collections that have been received for identification and 

 my own collecting during the past twenty years. The adults are usually taken 

 flitting about on or near the host plants upon which the larvge feed. They are 

 found more abundantly during the early part of the forenoon in sunny places. 

 The great majority of the species are peculiar to the boreal and transitional 

 zones, but in the east and middle west extend into the upper austral zone. A 

 limited number of species extend into the lower austral, while the subfamilies 

 Hylotominae, Schizocerinaa, Acordulecerinae, and certain genera of Selandriinoi find 

 their greatest development in tropical regions. 



The food-plants of the larvae are, therefore, for the most part such species as 

 are peculiar to the boreal and transitional zones. The various conifers, species of 

 Salix, Alnus, Betula, Quercus, various genera of Alices, Populus, Viburnum, and 

 Sambucus harbor the largest number of species. The species of Cornus, C'orylus, 

 Fragaria, Garya, Rumex, Ulmus, and the various kinds of sedges are next in im- 

 portance, while the following are the more important of the remaining host plants : 

 Amelaiichier, Fraxinus, Fyrus, Crataegus, Rosa, Prunus, Rubus, Viola, Robinia, 

 Acer, Juglans, Tilia, Carpinus, Ostrya, Pdygonum, and Vitis. 



Before the taxonomy of any group can be accurately determined, the struc- 

 ture of the forms to be grouped needs to be carefully examined. But little has 

 been done in homologizing the parts of the external skeleton of the larvae of any 

 of the orders with a complete metamorphosis and practically nothing has been 

 written dealing with the anatomy of the larvae of the Tenthredinoidea. This is 

 sufficient reason for a somewhat detailed discussion of their external anatomy. 



The larvae of the Tenthredinoidea, with the exception of the leaf-miners, are 

 cylindrical in form (Figs. 1 and 27), caterpillar-like. They consist of a well dif- 

 ferentiated, globular head and a series of similar segments. The segments are 

 clearly indicated and the thoracic segments can be distinguished by their form 



