Insect-Larva eating Bust on Wheat and Flax. 491 



which we give for what it is worth. It is well known tliat 

 the Hessian fly, whicli also belongs to tlie genus Cecidomyia^ 

 is the worst enemj to the wheat-crop in the United States, 

 while rust does much less damage there than in Australia. 

 In this country the reverse is true ; rust is the great evil, 

 while the Hessian flj is at present unknown *. Have these 

 facts any relation to each other ? Taken in the light of the 

 above observations on a species of Cecidomyia feeding on rust, 

 it may not seem too fine-spun a speculation if we suggest 

 that tliere may be a connexion. Let us suppose the larvas of 

 the Hessian fly to prefer rust as food if available, but to fall 

 back on tlie juices of the wheat-plant when tlie rust gives 

 out. This might account for the comparative rarity of rust 

 where the Hessian fly is abundant, which is the case in 

 America. All this is from the mountain-top of speculation. 

 If, however, it should lead to an excursion into the valley of 

 observation and experiment, some good may come of it. 



Not that we would suggest the introduction of the Hessian 

 fly for the sake of getting rid of the rust, even if the above 

 suggestion should turn out to be well founded. We would, 

 however, call attention to the need of further observations on 

 the relations between fungi on the one hand and insects and 

 mites on the other. It has already often been noticed that 

 certain fungi are commonly accompanied by certain insects 

 and mites. What, if any, is the relationship in these cases? 



It remains to describe these larvee in such terms as to 

 make them recognizable to other observers. In this we are 

 aided by the four accompanying illustrations. 



The larva undoubtedly belongs to the family Cecidomyidae, 

 and in many respects, if the published figures are to be 

 trusted, it comes very close to the larva of the true Hessian 

 fly {Cecidomyia destructor^ Say). It is composed of twelve 

 segments, exclusive of the head and the so-called " supple- 

 mentary segment," and possesses the characteristic two-jointed 

 antennae as well as the curious thoracic appendage called the 

 " breast-bone " or " anchor-process." Tiie head is retractile 

 and is capable of being withdrawn witliin the flrst thoracic 

 segment ; and in every otiier structural detail it coincides with 

 what we knowof the larvas of the genus Cecidomyia. An exam- 

 ination of these specimens clearly shows that the " supplemen- 

 tary segment " pertains to the liead and not to the thorax. 

 No further proof of this assertion is required than the state- 

 ment that the eye-spots are situated in this additional somite. 

 In the illustration the eye-spots appear to be within the ante- 



* The pest has, however, been recorded from the Wellington district, 

 New Zealand, where it is said to have caused iiiiifh damage. 



