20 



as a bee would do if alighting and instantly stinging an animal. The 

 next move is to let the tip of the abdomen strike the stem and then 

 go back to its proper position, but the tip of the ovipositor does not; 

 on the contrar^^ it catches on the surface of the stem, directly beneath 

 the bod}' of the insect, and by putting its machinery in motion and 

 drawing the stem toward her she slowly forces the ovipositor into the 

 soft, juic}' stem at the point where this is solid and not hollow, as is 

 the case a short distance above and immediately below the joint. The 

 tip of the ovipositor is 'composed of two flattened plates arranged side 

 bv side, the edges of which are sharp, and are propelled with a sort of 

 rotar}' motion alternating with each other. In this way the ovipositor 

 cuts and drills its way to the center of the stem, and an e^g is forced 

 down the interior and left in its proper place in the stem of the plant. 

 The female recovers her ovipositor by again straightening her legs 



and pushing the plant from her. Only 

 one egg is placed in the same location, 

 though perhaps more than one is placed 

 in the same straw by the same female, 

 but if so they are placed above different 

 joints in the straw. The larvae must 

 mature quickly, for, though pupation 

 does not take place until about October, 

 the stem ripens and becomes tough and 

 wood}^, wholly unfit for the food of the 

 larvfe, within less than a month. It 

 would seem that the mother insect is 

 aware of this, as she invariabl}- selects 

 the greenest and rankest growing plants 

 in the more open spots, where the straw 

 matures the slowest and remains green 

 and juicy the longest. 

 Briefly, then, the insect passes the winter in the stubble — with the 

 exception of the few that have been removed with the straw — in the 

 pupal stage. In late March or during April the spring form 

 {inmntum), small, jet-black, ant-like, and with rare exceptions wing- 

 less females, eat their way out of their winter home and seek the 

 young growing wheat plants. They deposit their eggs singly, placing 

 them in the embryo head. These hatch within a few days and the 

 larva? mature and transform to the form c/rande, large, robust, also 

 jet-black, with fully developed wings, in late May and the first two- 

 thirds of June. These last are also females, and without pairing they 

 begin to deposit their eggs in the now nearly fully developed straws. 

 The eggs are placed just above the uppermost joint accessible to the 

 female, usually the second or third below the head. But a single egg 

 is deposited in a place, the object of the mother insect seeming to be 

 to get it in the center of the stem in the more or less solid portion 



Fig. 6.— Method of oviposition of female 

 of summer form {Isosoma grande, 

 Riley): a. female inserting her eggs; 

 6, section of wheat stem showing point 

 reached by oviposition (after Riley). 



