630 



Criddle (N.). The Hessian Fly and the Western Wheat-Stem Saw- 

 Fly in Manitoba, Saskatchewan and Alberta. — Dominion of Canada 

 Dept. Agric, Entom. branch, Oltaiva, Bull. 11, 1915, 23 pp., 4 figs. 

 [Received llth August 1915.] 



The attacks of Mayetiola destrucioi (Hessian fly) are usually confined 

 to wheat, rye and barley, although spelt and Agropyron tenerum are 

 probably also infested. The life-history diiTers considerably according 

 to the latitude and geographical conditions under which it occurs. 

 In Manitoba there is one full brood, with a supplementary summer 

 brood averaging about 20 per cent, of the spring brood. Flies emerge 

 from over-wintering pupae about 15th May, and continue to appear 

 until the end of that month. Eggs are deposited almost immediately 

 after emergence, being usually placed on the upper surface of the 

 leaves. The larvae, which hatch in from 10 to 12 days, work their 

 way down between the sheaths towards the roots. Tlie main shoot 

 is ultimately killed. Puparia occur in the second half of June among 

 the dead leaves at the base of the plant. From about 20 per cent, 

 of the spring brood adults begin to emerge at the end of June, increasing 

 in numbers until about 10th July, after which they gradually diminish. 

 Eggs from these adults are deposited on leaves above the second joint ; 

 puparia are present late in July and the winter is passed in this stage. 

 FJies emerging late in July or August, deposit eggs on late barley and 

 self-sown wheat. Young plants attacked in spring show at first a 

 bluish tint, while the central shoot is stunted ; later they become 

 yellow at the tips and either die outright or survive by throwing out 

 new lateral shoots. Control measures consist of : (1) ploughing all 

 infested stubble between 15th August and the middle of the following 

 May ; (2) burning stubble and straw piles between the same dates ; 

 (3) sowing strips of grain about 20 feet wide between infested stubble 

 and newly planted grain to attract flies on occasions of severe outbreak. 

 The strips should be planted early and ploughed down about the 

 middle of June. Excess of rainfall combined with warmth, particularly 

 in early summer, favours development of the insect, while dryness has 

 the opposite effect. Hymenopterous parasites are important in 

 checking the pest. Early maturing wheat Avould probably suffer less 

 than late-ripening varieties. 



Cephus occidentalis (western wheat-stem saw-fly) has gradually 

 spread from wild grasses of the genus Agropyron to cultivated grain 

 crops, including wheat, rye, spelt and barley. Adults begin to appear 

 about the second week in June. Eggs are deposited at the end of 

 June, usually above the topmost joint, either between the sheath and 

 the stem or inside the stem. The larvae hatch in three or four days, 

 and gi-adually pass down to the lowest joint. The stem is gnawed 

 through from the inside, and in the basal part the larva constructs a 

 cocoon in which it remains until the following May. Pupation then 

 occurs and the adult emerges in June. The only means of distribution 

 are by flight or by artificial carriage in the adult stage. Dispersal by 

 flight does not amount to more than a few miles annually. All infested 

 stubble should be ploughed not less than 5 inches deep between 1st 

 August and the end of the ioUowing May. Infested grasses, such as 

 western rye grass, timothy and prairie grasses, near growing crops, 

 should be cut between 10th July and 1st August. By this means. 



