FAIRY FLIES AND THEIR HOSTS. 



49 



thirty specimens from a clump of rushes, and though so plentiful we 

 have not yet discovered the host egg, though we have bred numerous 

 specimens from various growing plants. 



In my endeavour to trace out the hfe-histories of the Mymaridae, 

 I have often placed all kinds of eggs before the living Fairy Flies. 

 In one instance I tried the following experiment : I bred a number 

 of Alapti from eggs of Psocus fasciatiis, and, desiring to ascertain 

 whether they would oviposit in eggs of other insects, I carefully gummed 

 twenty eggs of different insects on to a rose-leaf, and at the extreme tip 

 a single egg of Psocus. I then placed an Alaptus on the leaf ; it ran 

 about and touched the first egg with its antennae and turned from it, 

 then sounded the second and refused it, and so on ; every one of the 

 twenty eggs was refused. I then guided the Alaptus up the midrib ; 

 it ran along and reached the egg of Psocus, touched it and instantly 

 mounted it, inserted its ovipositor and placed an egg into it. By 

 some marvellous power it was able to recognize the right host egg. 

 I have proved that Alaptus will not oviposit in any other species of 



egg- 

 Unfortunately, our knowledge of the value of parasitic insects 

 is very small, and the question has often been asked of the writer, 

 viz. : " What good are these minute Fairy FUes ? " — and the remark 

 has frequently followed : " They are too small to be of any service." 

 Of course such questions are only asked by those who do not appreciate 

 or take notice of " creeping things." I think one instance will sufhce 

 to prove that nothing has been created in vain, and that all insects 

 perform the function for which they were intended. 



Many times have I found patches containing hundreds of eggs 

 of Cabbage Moth, every one of which has been destroyed by a 

 minute Fairy Fly, Trichogramma evanescens which lays its eggs 

 in those of the Cabbage Moth, and so lessens the chance of the 

 caterpillars that would otherwise have been bred from the eggs. 

 Surely the most ignorant and prejudiced individual will not deny 

 that this tiny parasite should have the credit due to it. 



VOL. XL. 



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