10 U. S. NATIONAL MUSEUM BULLETIN 2 1 6 part 3 



degrees of modifications for this habit. In Gamhrus some of the spe- 

 cies attack cocoons in tunnels in succulent herbage. These are 

 weakly specialized for parasitizing borers. They have a somewhat 

 compressed ovipositor with the apical teeth in the form of subvertical 

 ridges, a tendency for the last tarsal segment and its claws to be en- 

 larged, and a tendency toward a cylindric body shape and inflation of 

 the female front tibia. For some reason, they and other parasites of 

 borers commonly have a median apical tooth on the clypeus. Some 

 genera related to Gamhrus seem to be regular parasites of cocoons in 

 grass culms, and show a stronger modification. In these the oviposi- 

 tor is rather short, definitely compressed, and the teeth appear as 

 vertical ridges. The body shape is cylindric and head subspherical. 

 Mallochia, Kriegeria, and Amauromorpha are examples of this group, 

 and some species of Isotima show the same modifications, or are 

 intermediate. A second group of genera, also related to Gamhrus 

 and not to be separated sharply from that genus, are parasites of 

 cocoons or other hosts in herbaceous stems or in soft twigs. These 

 have the same kinds of modifications as the group parasitic in grass 

 culms but the body is less compact, clypeus wider and usually with 

 a stronger median apical tooth, ovipositor usually longer, and teeth 

 on ovipositor tip more widely spaced. Aritranis, Caenocryptus, 

 Caenocryptoides, and Idiostoma are the genera involved, and probably 

 also Pycnocryptus or part of the genus. The group parasitic in 

 grass culms is largely tropical or subtropical; that parasitic in her- 

 baceous stems mostly temperate in distribution. A third group of 

 borer parasites, mostly tropical or subtropical, is parasitic on hosts 

 in twigs, branches, woody stems, or tree trunks. They are rather 

 highly specialized for these kinds of hosts, to the extent that they 

 form an easily recognizable, and largely (entirely?) natural group. 

 They are separated here as the new subtribe Echthrina. In these 

 the body shape tends to be cylindric, head subspherical, clypeus 

 wide and usually with a median tooth, lower tooth of mandible 

 frequently longer than the upper tooth, female antenna with a special 

 sensory area at the tip, female front tibia strongly inflated, fourth 

 tarsal segment of female with an apical compact group of stout 

 bristles, spiracle of first tergite usually near the middle, ovipositor 

 more or less compressed, teeth on tip of ovipositor tending to be in 

 the form of vertical ridges, lower valve of ovipositor nearly always 

 with an apical dorsal lobe that encloses or partly encloses tip of 

 upper valve, and subapical abdominal segments of female enlarged 

 (to accommodate a high development of ovipositor muscles). All 

 these characters are more or less directly associated with the habit 

 of parasitizing borers, and are approached or sometimes matched by 

 other mesostenine genera with hosts similar to those of the present 



