340 



influence which depletes or checks the growth of the plant. An interesting question 

 arises in this connection, namely, whether a mild attack of Hessian fly may not be 

 an actual benefit, because I believe that effective stooling is a desideratum in all winter 

 wheat regions. At least it used to be so in my farming days, and the policy of sowing 

 thin rather than thick was based upon the tendency to stool. 1 believe that two 

 months hence, or during the winter season, the appearance of the plants badly 

 infested and those but little affected by Hessian fly will be totally changed ; i. e. the 

 badly infested field will be much more yellow in appearance than the non-infested. 

 This is what I meant, and what has probably led you to believe that I did not agree 

 with you in the appearance of affected plants. It will be very interesting to have 

 this experiment repeated, of Professor Plumb's choosing, in a field not affected by 

 rust. In such case you would have to depend entirely on the greater tendency to 

 stooling of the infested plants, and not be guided very much by color. Is this not 

 so, or do you claim that the work of the Hessian fly, in addition to causing the stool- 

 ing, also induces a darker color of leaf ? — [September 24, 1890.] 



House-fly Parasites. 1 



* * * Inclosed you will find some common house flies which are infested with 

 parasites. I first discovered them last season and not infrequently find a fly upon 

 which I can count a dozen with my naked eye, and, as soon as the fly is killed, they 

 walk off briskly on their six legs. It has been a matter of remark that flies are 

 scarce this year and can it be possible that these mites are decimating the pests ? — 

 [Miss Sarah Parker, Gouverneur, St. Lawrence County, New York, September 22, 

 1890. 



Reply. — " * * The mites which you found upon the common house fly are the 

 young forms of the species which Professor Riley described in the first report of the 

 United States Entomological Commission as Tromhidium mnscarum, and it is very 

 common in this country as well as in Europe, where the larval form was previously 

 described as Jstoma parasiticum by the French entomologist Latreille. This six- 

 legged form which you have noticed is a larval form. After leaving the fly it crawls 

 away and sheds a skin, coming out as a reddish colored eight-legged mite. — [Septem- 

 ber 25, 1890.] 



Night Swarming of Lace-wing Flies. 



Inclosed you will find an insect that has fairly taken possession of our little islands. 

 It works in the night, and at daylight hides in cracks and out of the way places 

 where the sun's rays do not penetrate. * ^ * [James J. W. Doyles, first assistant 

 keeper, Cape Flattery Light Station, Washington, Aug. 30, 1890. 



Reply * * * The matter proves to be one of considerable interest, as the insect 

 is one of suspected abnormal habits. It is one of the lace- winged flies and is known 

 as Polystcechotes pimctatus. While the majority of the insects of this family are air- 

 breathers in their larval states, it has been suspected that the larvse of this creature 

 are aquatic, but in all of them the larvae are predaceous and carnivorous and as they 

 feed very little or not at all as adults, they are beneficial rather than injurious in- 

 sects. If the supposition concerning this species is correct, it should be breeding in 

 great numbers in some fresh-water stream or pond near your light, or possibly at 

 some distance, as they are strong fliers. It is a matter which would be very interest- 

 ing to investigate as they are present in such large numbers, and it seems that with 

 careful watching you ought to see the females lay their eggs. It ought not to be 

 much trouble to watch the eggs hatch, and thus ascertain the habits of the larva. 

 The place of oviposition would indicate a good deal. 



We should be very glad to have you look into the matter a little and to report any 

 observations which you may make. — [September 11, 1890.1 



