924 AN INTRODUCTION TO ENTOMOLOGY 



KEY TO THE SUBFAMILIES OF ICHNEUMONID^ 

 By Dr. H. K. Townes 



A. Spiracles of first abdominal segment situated definitely behind the middle of 

 the segment; sternite of first abdominal segment immovably fused with the 

 tergite or if rarely free, then the abdomen strongly compressed. 

 B. Abdomen more or less compressed; areolet (= a small cell near the center 



of the wing) more or less triangular or absent, p. 927 Ophionin^ 



BB. Abdomen depressed or cylindrical; areolet more or less pentagonal, 

 quadrangular, or occasionally absent. 



C. Sternaulus (a horizontal groove in lower part of mesopleurum) sharp and 

 usually more than half as long as the mesopleurum; ovipositor usually 



surpassing tip of abdomen, p. 927 Cryptin^ 



CC. Sternaulus absent or poorly defined and short; ovipositor not or but 



slightly surpassing tip of abdomen, p. 928 Ichneumonin^ 



AA. Spiracles of first abdominal segment situated near or in front of the middle 

 of the segment; sternite of first abdominal segment usually more or less free 

 from the tergite. 



B. Face and clypeus forming an even undivided surface; male claspers drawn 

 out into a pair of long spines; ovipositor sheaths slightly shorter than the 

 first abdominal segment, rather broad, flat, and somewhat polished; areolet 



large and rhomboidal. p. 927 (tribe Mesochorini) Ophionin^ 



BB. Face more or less separated from clypeus by a groove, or insect otherwise 

 not entirely agreeing with the above. 



C. Ovipositor surpassing tip of abdomen; abdomen often with definite 



elevations and depressions above and usually elongate, p. 924. . Pimplin^ 



CC. Ovipositor not or but slightly surpassing tip of abdomen; abdomen 



without definite elevations and depressions above and not elongate unless 



also petiolate. p. 926 Tryphonin^ 



Subfamily PIMPLIN^ 



Most species of Pimplinae are black with femiginous or banded 

 legs. They are parasites mainly of caterpillars and wood-boring 

 beetle larvae. Their long ovipositors are adapted to reaching hosts in 

 tunnels in wood or in weed stems. 



Megarhyssa ( = Thalessa) is our largest ichneumon fly (Fig. 11 53). 

 It is a parasite of the wood-boring larva of the pigeon horn-tail, 

 Treniex cclmnha. When a female finds a tree infested by this borer 

 she selects a place which she judges to be opposite a Tremex burrow 

 and making a derrick out of her body proceeds with great skill and 

 precision to drill a hole in the tree. At the beginning of the process 

 the excess length of the ovipositor is coiled into a sack formed by the 

 very elastic membrane between the sixth and seventh abdominal 

 segments. When most of the ovipositor is deep in the wood the 

 ovipositor sheaths which do not enter with it form a loop over her 

 back (Fig. 11 53). After the Tremex burrow is reached, a long egg 

 flows down the tube in the slender ovipositor and is left on or near 

 the host. The larva which hatches from the egg feeds upon the 

 Tremex larva by sucking its blood and eventually destroys it entirely. 

 When full grown it pupates in the Tremex burrow. The adult gnaws 

 a hole through the bark to emerge. If the adult is a female, there are 

 males waiting just outside and she is mated just after emergence or 

 even before she can extricate herself from the hole. Females of the 



