J. W. MiiNRO 17r> 



Parasites liavo already boon used witli succoss in combating other 

 destructive insects ; notably Professor Lefroy's introduction of Rhogas 

 Lefroyi into tlio Punjanl), to combat tlic boll worm, and more recently 

 Pierce and Townsond have shown that Ilymonoptorous parasites play 

 a very important part in controlling the cottonboll weevil in the States. 

 Pierce found that of 2800 weevils, 591 were parasitised, and that of 

 these, in 525 cases the parasite was a Braconid. In 1911 Pierce and 

 Hunter began experiments on the rearing and distributing of the parasites 

 but I am not aware whether a report on these has yet been published. 



As to the possibility of using B. hylohii in combating H. abietis, I 

 have not yet obtained a sufficient knowledge of the former's life-history 

 to make any definite statement, but such observations as I have been 

 able to make lead me to believe there are no special difficulties to over- 

 come. If B. lujlohii is fairly or reasonably common, and there is no reason 

 to suppose it otherwise, there should be little difficulty in obtaining 

 batches of its cocoons, or numbers of its larvae to breed from. The 

 larvae of Hylobius, too, can readily be kept alive if they are not removed 

 from the roots on which they are feeding. I have reared several weevils 

 by removing the smaller roots containing their larvae and keeping 

 these sufficiently moist. The parasite itself is easily reared inasmuch 

 as I bred one batch in an ordinary collecting tube in which I placed a 

 weevil grub as food. 



Out of about 70 cocoons, I have obtained no hyperparasites on the 

 Braconid. This again is favourable. The parasite too is evidently 

 hardy. The plantation from which my specimens were obtained is a 

 bleak hillside near the coast and over 600 feet above sea-level. It is 

 often swept by cold North and East winds. 



Another interesting fact is that B. hylohii attacks the weevil larva 

 in its resting stage, at a time^when the latter is practically inactive. 



The greater increase in numbers of the parasite as compared with the 

 weevil is also interesting. Every weevil grub attacked gives rise to at 

 least five adult parasites. Of these according to Nordlinger's figures, 

 90 per cent, will be females, but from my own observations 60 

 per cent, is a more probable relation. 



Assuming that every weevil grub parasitised gives rise to five adults, 

 three of which are females, and that as in the present instance, 

 30 per cent, of the weevil grubs are attacked in the winter 1913-14, 

 then out of 100 weevil grubs we should get 70 Hylobius adults and 

 90 female Braconids in spring 1914. If we assume further that the 

 rate of increase of Hylobius and of Bracon in a given year is the same, say 



