MORPHOLOGICAL ADAPTATION IN INSECTS — GRANDI 213 



IV. LARVAE OF HYMENOPTERA SYMPHYTA (CEPHIDAE, 

 TENTHREDINIDAE) 



Also among Hymenoptera Symphyta, there are many species whose 

 larvae develop within plants and many ectophytic species which ex- 

 hibit behaviors interesting in the light of the facts under discussion. 



It is well known that the larvae of these Hymenoptera, for the most 

 part phytophagous and of generalized type, are polypod, cruciform 

 larvae like those of Lepidoptera, from which they dififer in the three 

 following characteristics : A single lateral ocellus, the presence of 

 abdominal legs also on the second urite, and the absence of the par- 

 ticular thricotaxis characteristic of the caterpillars. Now we shall 

 examine particularly some of those having a specialized diet and ob- 

 serve their behaviors. 



The larvae of the tenthredinid hoplocampinous Caliroa limacina 

 Retz., devour ectophytically the upper epidermis and the parenchyma 

 of the leaves of the pear and other trees, passing their lives in contact 

 with flat surfaces. The body is characteristically shaped: flattened 

 on the ventral side, convex on the dorsal side, gibbous in the anterior 

 portion. The head capsule is nearly invisible from the upper side, 

 because it is not only turned downward, but also recurved backward 

 and therefore strongly metagnathous ; ocelli are displaced dor sally and 

 the antennae conspicuous and well supplied with large sensillae, the 

 thorax has the prosternum very reduced in length with a membranous 

 integument and also two very conspicuous fingerlike glandular promi- 

 nences, which, when the insect feeds, converge forward and come into 

 contact with the labrum. The legs are exceptionally shaped, having 

 an enormous coxa, a stout femur-trochanter and tibiotarsus, and a 

 large claw. Obviously these modifications are correlated with the 

 larval habit of feeding on the surface, but not on the edges of the leaf. 

 To the question whether these modifications were necessary, we should 

 answer negatively. However, we cannot assert, at least for some of 

 them, that there may not be some moderate use and above all an inti- 

 mate correlation with the particular insect behavior. 



On the other hand, the larvae of the cephid hartiginous Janus com- 

 pressus F. bore centripetal galleries within the twigs of pear trees, 

 pushing the gnawed substance behind them, and they are very curi- 

 ously formed. In fact the head capsule of the full-grown larva is 

 clearly, although only slightly, asymmetrical as a result of a moder- 

 ate clockwise rotation of its anterior portion following the lowering of 

 the right side of this portion. Clear signs of it are the behavior of the 

 anteclypeus, the displacement of the invagination pit belonging to the 



