260 



Seamans (H. L.). Wheat-Sheath Miner. — Jl. Agric. Research, 

 Washington, D.C., ix, no. 1. 2nd April 1917, pp. 17-25. 



Two wheat-sheath miners, the habits of which are very similar, 

 are Meromyza americana, Fitch, and Cerod&nta {Agromyza) femomlis, 

 Meig. 



Very little has previously been published about the latter, though 

 it is apparently of general occurrence in the north-western States and 

 Canada. The host-plants of C. femomlis are wheat, oats and timothy 

 {Phlemn pratense), and, as the insect is only found in Graminaceosu 

 plants, natives grasses are probably the natural food-plant. The 

 various stages are described. There are apparently three full broods 

 of C. femoralis in a year. The first adults appear about 20th May 

 and oviposit until about 10th June. Immediately after hatching, 

 which takes place in the insectary in about six days, the larvae begin 

 to feed, and it is in this stage that the injury is done. The larva starts 

 from that point in the leaf where the egg was deposited and mines 

 down the leaf towards the stalk, ending in the leaf-sheath, at the 

 crown of the plant, or at the first node. On reaching the base of the 

 leaf-sheath the larva feeds up and down the sheath and sometimes 

 around the stalk, causing the central stalk to wither and die. 

 The injury appears to be identical with that caused by M. americana, 

 but the mine cut by G. femoralis is narrow, clean-cut and almost straight, 

 while that of M. america'na is broad and irregular, with indistinct 

 edges ; the latter enters the stem and eats out the central stalk, and 

 the former may girdle the stem, but does not completely cut it ofi". 

 The length of the larval period varies from about 10 to 20 days. Cool, 

 wet weather apparently retards pupation, which takes place either at 

 the node or at the crowTi of the plant. The pupal period lasts about 

 25 days, and in the insectary, which seems to correspond closely with 

 conditions in the field, the second brood appears about 15th July and 

 the tliird about 7th September. The second brood of larvae cause 

 slight injury to the plants just before blossoming ; this occurs in the 

 leaves only, the central stalk being miinjured. The amount of injury 

 done to winter wheat during the autumn has not yet been ascertained. 



Puparia of C. femoralis have yielded two Hymenopterous parasites, 

 a new Braconid, Dacnusa sp., and the Chalcid, Cyrtogaster occidentalis ; 

 these were not however sufficiently numerous to be effective agents 

 in control. 



No control measures have yet been tried, but the following sug- 

 gestions are made. When wheat is cut for harvest, the straw should 

 be scattered over the field and the stubble burnt, as well as the grass 

 borders surrounding the fields. This would destroy the larvae of the 

 second brood, which are then in the last instar at the crown of the 

 plant or have already pupated. If burning is not practicable, the 

 stubble should be ploughed under about 6 inches and harrowed before 

 planting a spring crop. This would probably bury the pupae deep 

 enough to prevent the flies from emerging. Winter wheat should be 

 sown late, about the third week in September, so that it would not be up 

 until oviposition was over ; this would prevent the main infestation 

 in the spring. As native grasses are natural host-plants of the fly, 

 crop rotation would be useless, but the clearing of grass borders and 

 destruction of self-sown wheat during the fallowing period would be 

 of great assistance in control. 



