2911 NOCTUID LARVAE— KIPLEY 49 



represents a departure from the leaf-eating habit and free-living existence, 

 which were most probably characteristic of the ancestral lepidopterous 

 larva. 



There is a correlation between the short epicranial stem and specialized 

 feeding-habit. It will be seen that Types 1 and 2 occur only in leaf-miners, 

 Type 3 being also confined to larvae of this habit except in the seed-eating 

 or stem-boring Prodoxidae, in the wax-eating bee-moth larvae, and in the 

 leaf-rolling Tortricidae. Similarly in the Noctuidae the reduced epicranial 

 stem is always associated with a specialized habit, the subterranean mode 

 of life. The more pronounced this habit the shorter is this suture. 



It has been necessary in order to establish this correlation to find criteria 

 by which we may compare larvae of various species with reference to their 

 subterranean proclivites. Cut-worms have generally been described in 

 economic literature as larvae which hide beneath the ground by day, eating 

 at or beneath the surface during the night. Our experiments have shown, 

 however, that there is considerable diversity of feeding-habit, even within 

 this biological group. Certain so-called cut-worms never enter the soil, 

 others do so only under extreme stress, and some, on the other hand, never 

 come above ground except for ecdysis. In addition to observations made on 

 larvae reared under natural conditions, two series of experiments have been 

 performed to determine the relative extent of the development of the 

 subterranean habit with as many species of noctuid larvae as possible. 

 The first of these determines which species are able to burrow into the soil 

 and to what extent this ability has been developed in each. The second 

 series of experiments determines the extent of the power to resist sub- 

 mergence in water, a resistance which subterranean animals have generally 

 developed. The combined results derived from these two lines of investiga- 

 tion enable us to form a fairly accurate idea as to relative "subterranean- 

 ness" of various species. We will now consider these experiments. 



DETERMINATION OF BURROWING HABIT 



The determination of the relative extent of the development of the 

 power to burrow into the soil in the larvae of various species is the object of 

 the first series of experiments. The logical method for making manifest 

 an ability or tendency to burrow into the ground, however slight, involves 

 the subjection of the organism to an irritating factor to which it reacts in 

 a markedly negative manner, at the same time excluding all means of 

 avoiding this factor except by entering the soil. Lepidopterous larvae 

 generally avoid direct sunlight, a large proportion of them being nocturnal 

 in habit. This is especially true of noctuid larvae, the cut-worms being 

 notoriously active at night. Altho precise experiments on the reactions of 

 these insects to light are much to be desired, anyone who has worked with 

 them extensively will have noticed, without doubt, a generally marked 



