178 



EXPERIMENTAL FARMS. 



Fig. 7. — The Joint-worm : galls on wheat stems — 

 natural size; fly — enlarged. 



The Joint-worms (Isosoma). — There are probably more species than one 

 belonging to the genus Isosoma which attack the wheat plant in Canada. These 

 injui-ies appear to be of rare occurrence, but have sometimes been serious in certain 

 localities. In 1895 specimens of fall wheat infested by a Joint- worm were received 



from Meaford, Ont., on the Georgian 

 Bay. This attack, although amounting 

 to 5 per cent of the entire crop in the 

 year named, has not occurred since. 

 The galls made by this insect were 

 almost entirely in the sheaths of the 

 leaves and not in the tissues of the 

 stems. Last year infested straws con- 

 taining joint-worms were received from 

 Mr. Wm. Welsh, of Verdun (Bruce Co., 

 Ont.). Although from a district less 

 than 100 miles from Meaford, and 

 further, strange to say, although it is the 

 only other report of noticeable injury 

 by joint-worms to wheat which has 

 been reported to me for some years, it 

 would appear fi'om the different nature 

 of the galls which are entirely in the 

 tissues of the stems and not in the leaf sheaths, that this occurrence may be of a 

 different species of joint- worm. Mr. Welsh writes at the end of the season of 1898 : 

 " The joint-worm, which was so abundant last year has done little injury this season. I 

 made many examinations for the insect but could find very little damage. In the grain 

 after threshing there were very few of the hard broken pieces such as I sent you last 

 spring. This disappearance, I think, may have been due to the very wet spring and 

 early summer we had." Unfortunately, the exact identity of the Meaford specimens 

 could not be determined ; but, through the kind assistance of Mr. Welsh, who has sent 

 several parcels of infested straw from Verdun, large numbers of the flies have been 

 bred. These were chiefly from stubble collected in the spring, April 15, in a clover field, 

 where they had lain on the ground from the time the fall wheat was cut the year 

 before. Specimens of stubble from the same field, but collected in November, 1897, 

 and broken joints from the stems taken from the threshed wheat which had been kept 

 in breeding jars through the winter, failed to produce more than two or three specimens 

 of the perfect insect, whereas the stubble which was left in the field all through the 

 winter gave hundreds of specimens of the gall-former, all the females of which were 

 winged like the males. Besides these there were two kinds of hymenopterous parasites. 

 Specimens of all of these were submitted to Dr. Howard, so as to get an authoritative 

 decision on the species. 



Dr. Howard reports as follows : " The species is undoubtedly Isosoma tritici, Fitch 

 (nee Riley). If you will consult my Bulletin 2, Technical Series, page 17, on Phytophagic 

 Eurytominse, you will find that this is the species called /. hordei by Walsh. I think 

 Walsh's specimens also came from Canada. Among the material sent by you after it 

 was mounted I found two species of parasites, viz., Homoporus chalcidiphagus, Walsh, 

 and Eupelmus epicasie, Walker." 



There are so many discrepancies between the descriptions of the galls and their 

 modes of occurrence and with regard to important points in the life histories of the 

 joint-worms that with a view to working out the identity of the different species I shall 

 be pleased to receive specimens from anyone who may find his crops attacked by joint- 

 worms. The galls will somewhat resemble the figure (Fig.7), given herewith or may be as 

 in the case of the Verdun specimens mentioned above, merely hardened and somewhat 

 curved portion in the straws of wheat, barley or rye. 



Remedies. — There is only one brood of the joint-worms, and as they pass the winter 

 in the straw, for the most part so near to the ground that a large proportion of the 

 larvae occur in the stubble left on the fields, they can be largely reduced in numbers by 

 burning over the stubble or by ploughing it down deeply. The broken off hai'dened 



