354 THE STUDY OF INSECTS 



The wheat joint-worm, Harmolita tritici. — This is a well-known pest 

 which infests the stalks of growing wheat and certain grasses. It causes 

 a woody growth which fills up the cavity of the stalk, and sometimes also 

 causes a joint to swell and the stalk to bend and lop down. The presence 

 of this insect is often indicated by pieces of hardened straw coming from 

 the threshing machine with the grain. There is but a single generation 

 of this species in a year. The insect remains in the straw and stubble 

 during the winter, the adults emerging in the spring. The methods of 

 control of this pest are rotation of crops, burning or deep ploughing under 

 of stubble when practicable, or harvesting of stubble in spring with a 

 horse-rake and burning it before the adults emerge. 



The wheat straw-worm, Harmolita grandis. — This species is often a 

 serious pest of wheat west of the Mississippi River; it also occurs in the 

 East, but is rarely so injurious in this section as is the wheat joint-worm. 

 The adults differ from our other, species of Harmolita in that the meso- 

 notum is smooth, polished, and shining. This species also differs in that 

 it exhibits a seasonal dimorphism. There is a summer generation, which 

 consists only of winged females, and a winter and spring generation which 

 consists of both males and females. These are smaller than the summer 

 form and are frequently wingless. The adults of the winter and spring 

 generations emerge in April and the females deposit their eggs in the 

 young wheat plants; the larvae eat out and totally destroy the forming 

 heads of wheat. The adults of the second generation deposit their eggs, 

 about the time the wheat is heading, just above the youngest and most 

 succulent joints which are not so covered by the enfolding leaf-sheaths as 

 to be inaccessible to them. The larvae pupate by October and the winter 

 is passed in the straw or stubble. 



Another species that is of economic importance is the clover-seed 

 chalcid, Bruchophagus Junebris, which infests the seeds of red and crimson 

 clovers and alfalfa. This insect usually winters over in the seed as a 

 well-developed larva; the pupal stadium is rather short and the adult 

 lays her eggs in May and June. 



The fig-insects. — These are remarkable chalcids that live within figs 

 and fertilize them. There is but a single species in the United States, 

 Blastophaga psenes, which was introduced into California in order to 

 make possible the production of the Smyrna fig in that state. 



The fruit of the fig-tree consists of a hollow receptacle on the lining of 

 which the flowers are borne. At the apex of the fig there is a more or 

 less distinct opening leading into the interior; it is through this opening 

 that the female fig-insect leaves the fig in which she was developed and 

 enters a young fig in order to oviposit. 



The eggs are laid at the base of a modified form of pistillate flowers, 

 known as gall-flowers, that are found in wild figs; and the larvae produce 

 little galls in which they develop. The female fig-insect when leaving the 

 fig in which she was developed becomes covered with pollen which is 

 thus carried into the young fig which she enters to oviposit, and thus the 

 flowers in this fig are fertilized. 



The male fig-insect is wingless. It crawls about over the galls in the 

 fig in which it was developed and when it finds a gall containing a female 

 it gnaws a hole in it and then thrusting the tip of its abdomen through 

 the puncture fertilizes the female. 



It is only in the wild figs that the gall-flowers are developed; for this 



