122 



The Ohio Naturalist. [Vol. IV, No. 6, 



OVIPOSITORS. 



Gall-making insects deposit their eggs by two methods, either 

 on the surface of the plant or within the tissues. Those insects 

 which deposit their eggs on the surface usually have mouthparts 

 developed for sucking, while those which deposit their eggs 

 within the tissues usuall}- have mouthparts developed for biting. 

 Those which deposit their eggs on the surface of the plant are 

 the Acarina, the Hemiptera, and the Diptera. Those which 

 deposit their eggs within the tissues are the Hymenoptera and the 

 Lepidoptera. In this paper we have made a careful study of the 



ovipositors of Cecidomyia gleditsiae, of Nematus sp , Drj^- 



ophanta palustris, Amphibolips radicola, Andricus cornigerous, 

 A. semiuator, and Rhodites radicum. A number of others were 

 examined, but because of the uncertainty as to determination are 

 not figured. 



The Cecidomyia ovipositor (Fig. 92 J is not suited to punctur- 

 ing tissues. The gall is never formed until after the hatching of 

 the larva. In this case it is evident that the stimulus, whether 

 mechanical or chemical, is produced by the larva. 



Insects belonging to the genus Nematus deposit their eggs 

 either on the surface of the plant or in slits made by the ovipositor 

 (Figs. 93a, b). It is said that the galls are formed from these 

 wounds before the larva escapes from the egg, and in these cases 

 it is claimed that the irritating cause is a drop of fluid secreted 

 by the parent insect. Westwood claims that the egg increasing 

 in size is a result of imbibing sap from the wound in the plant. 

 It is well known that the eggs of some insects increase in size as 

 a result of the growth of the embr3'o within the egg. I have so 

 far been unable to make any satisfactory observations upon the 

 Nematus galls, but it is probable that the eggs increase in size 

 from the growth of the embryos and not as a result of the absorp- 

 tion of plant sap. It is also possible that the gall may be the 

 result of the mechanical irritation of the ovipositor or the enlarge- 

 ment of the egg or both. The wound caused by the ovipositor 

 of the Nematus is very much more severe than the woiuids caused 

 by the ovipositors of the Cynipidous insects. 



Adler, after a careful observation on Nematus Vallisnierii, says: 

 "This fly, which is armed with a finely serrated terebra, cuts 

 into the tender leaves of the end of the shoot of the Salix amyg- 

 dalina, and inserts her egg into the open wound, frequently plac- 

 ing several in the same leaf. At the same time the glandular 

 .secretion flows into the wounded leaf. A few hours after this 

 injury the leaf surface presents an altered appearance, and new 

 cell formation begins freely, leading to a thickening of the sur- 

 rounding leaf surface. After the lapse of about fourteen days 

 the green and red-.'^haped gall is fully grown. If it be now 



