1922 ENTOMOLOGICAL SOCIETY. 19 



Parasites. Two hymenopterous parasites were reared by Ainslie in North 

 Dakota and Utah namely Microbracon cephi Gahan and Pleurotropis utahensis 

 Crafd. The same insects have been taken by us in Manitoba, while two other? 

 Eupelmus allynii French and a species of Eurytoma also are present in some 

 numbers. All these parasites are natives of the country and they occur where- 

 ever infested grasses are met with. Cultivated grasses which are attacked by 

 the sawfly have proved equally suitable to the parasites, but when it comes 

 to fields of grain there is a sudden check which practically leaves the saw- 

 fly free of enemies. 



The sudden check of the parasites when they come to grams is the most 

 important and interesting of the problems before us and a number of details 

 will have to be supplied before we can ultimately define what the causes are 

 that bring about this change. There are, however, several significant facts to 

 be taken into consideration; firstly, both Eupelmus and Eurytoma emerge in 

 .large numbers during August and September, the Ceplius larvae being at this 

 time in their winter quarters in the stubs below the ground where it is doubt- 

 ful whether the parasites would find them. If this is so, in what do the above 

 parasites oviposit during the Autumn months or do they hibernate and remain 

 inactive until the following July ? If the parasites breed in their hosts then they 

 would obviously have to return to the plants harbouring them an'd consequently 

 leave the grain fields. This might well account for the insects' abundance in 

 Maid grass lands, but it would only partly explain the problem before us. We 

 know that Microbracon hibernates in cocoons, either as larvse or pupa?, to emerge 

 . as adults sometime during the following spring, in this case there being probably 

 no secondary host. We must, therefore, look to other causes for the absence of 

 this parasite in infested grain fields. 



Turning to Pleurotropis utahensis we find that this parasite is late in matur- 

 ing, and that it is even more restricted in its habits than Microbracon. It has 

 been found in most of the Ceplius infested grasses and once in fall rye, but 

 not in wheat. It was comparatively rare in 1921. 



The third parasite Eupelmus allynii (French) is a very general one, being 

 known to attack various other grass-infesting insects, but it has not previously 

 been recorded from Cephus. Our specimens emerged in September. The fourth 

 Eurytoma sp. appears in August. It has been reared from both grain and 

 grasses as a host of Cephus. 



The second point is that sawfly-infested winter rye is quite thickly inhabitated 

 by parasites when said rye is found growing as a volunteer crop amid other 

 grasses and weeds of various kinds, but not when it is growing alone. 



Thirdly, infested wheat and spring rye are both found to contain Micro- 

 bracon and Eupelmus around the edges of fields next to grass areas but very 

 rarely towards the centres of fields. All of which points strongly to the para- 

 sites having their home among the grasses, in which they find necessary factors 

 not present in the growing grain. We are still at a loss to know what these 

 factors are, but it is significant that parasites of sawfly larva? may be found 

 in both grain and grasses when those plants are growing together -on land that 

 has been left uncultivated. 



Climatic Control. It is noteworthy that there is a marked fluctuation 

 in the yearly development of the sawfly, even though the species has gradually 

 become more numerous. In North Dakota, for instance, the infestation of 1921 

 did not apparently exceed that of 1917, whereas had the insect developed at what 



