27 



succeeding white straw crop should be avoided after a bad 

 attack. 



Care should be taken to keep fields clear of couch grass and 

 other grasses, and to clear away grassy outsides as much as 

 possible. 



PARASITES. 



Upon wheat ears infested with aphides observers would 

 have noticed many brown bodies, evidently of dead larvae 

 (Plate IV. d). These are larvae in which parasitic flies have laid 

 their eggs, and the maggots from these eggs have fed upon the 

 contents of their bodies. From infested wheat ears placed under 

 glass several flies, of two distinct species, came from these brown 

 bodies, and soon commenced to search actively for living larva 

 in which to place eggs. 



One of these flies was Aphidius avence. This parasite comes 

 from the lower part of the body of its victim. It is a pretty 

 insect with black, shiny body, long antennae, and bright wings, 

 whose expanse is just a quarter of an inch, and the body about 

 the eighth of an inch ; altogether much larger than the Aphis 

 granaria. Curtis, in Farm Insects, describes the process of egg 

 deposition in the body of the aphis larva, as witnessed by 

 Mr. Halliday. " This is done by bending her body under her 

 breast, and by lengthening her tail, the ovipositor is conducted 

 under the aphis, and an egg is instantly inserted in the body 

 under the tail. She then searches for another victim, passing 

 by those that have been inoculated."t This description is most 

 accurate, as the process \vas noticed several times in the last 

 season, as well as the mode of egg-laying of the other species of 

 parasite fly alluded to above, which, however, was not present in 

 such numbers as Aphidius avence. 



This other fly corresponds exactly with that called by Curtis 

 Ephedrus plagiator. It is smaller than Aphidius avence. Its 

 antennae are more curved and much shorter. Its body has an 

 ochreous tinge, and is pointed at the end, and its legs are 

 yellowish ; those of Aphidius avence being blacker. The eggs 

 of this fly were inserted in the backs of the aphides. 



At least 25 per cent, of the aphides on the ears, taken indis- 

 criminately, were infested by one or other of these parasites, and 

 there appeared to be a continuous birth of flies, which at once 

 laid eggs in the aphides near them. The winged aphides were 

 avoided ; only the viviparous larvae were chosen. From the ex- 

 periences of this season it is clear that this action of these 

 parasitic flies must decrease the number of aphides in a very 

 important degree. 



Not many lady-birds, Coccinellidce, whose larvae are wholesale 

 devourers of aphides, were noticed in infested wheat-fields, but 



* A Monograph of British Aphides, by J. Bowdler Buckton, F.E.S. 

 f Farm Insects, by J. Curtis, p. 292. 



