The Tetrastichine egg-parasite {potetrastichiis) on the other 

 hand is a comparatively slow breeder, taking fully twice as long 

 as a Mymarid to complete its life-cycle or longer still. It how- 

 ever probably produces twice as many eggs as the other and is, 

 so far as is known, entirely parthenogenetic, no male having 

 ever been seen. If we judge the effectiveness of the two para- 

 sites merely on rate of increase (reckoning the life cycles as 20 

 and 40 days respectively), and suppose that the Mymarid pro- 

 duces 20, the Tetrastichine 40 female young, at the end of six 

 months the latter will have produced four thousand and ninety- 

 six million descendants, but the Mymarid in the same time will 

 produce more by one million times. In reality no case is of this 

 simple nature, the habits and constitution of the parasites have 

 to be considered. Thus the Mymarid is much more delicate 

 than the other, and liable to be decimated by storms, but it 

 lays its eggs within a very short time of emergence, while in 

 Ootctrastichus the period of egg-laying is extended over weeks. 

 The latter, besides its robust nature, has this advantage, that 

 each individual is bred at the expense of tJic ivholc contents of an 

 egg-chamber of the leaf-hopper, while of the Mymarid each 

 individual is bred at the expense of only a single egg. 



If we consider the effectiveness of the four egg-parasites. 

 Paraiiagnis optabilis, P. perforator, Anagrus freqiicns, and Oote- 

 frasticlius beatiis, in areas K'Jiere all are zvell established, we must 

 rate the first-named as at present by far the most effective. As I 

 have previously pointed out, this species is capable by itself of 

 destroying about 50 per cent of the cane-hopper's eggs and 

 Anagrns frequens and P. perforator, extraordinarily numerous as 

 they appear, where seen alone, are but as isolated examples in 

 the crowd, where all are well established in one spot. The 

 Ootetrastiehns slowly but steadily increases in numbers, and on 

 many plantations I expect that it will ultimately be the most 

 efficient of all parasites. I do not think that it can show its full 

 value till 1908, for eSch harvesting of the cane crop is neces- 

 sarily a very great setback to its natural increase. Anagrus 

 frequens, under which name are probably more than one species, 

 or at least one or two distinct races of a single species, although 

 it appears at a disadvantage, when in company with Parajiagrus 

 optabilis, is nevertheless a most abundant parasite. In Part VI 

 of this Bulletin I have compared the habits of the two and need 

 not refer to the matter here, but I may say that as many as 

 eighty or a hundred exit holes of the Anagrus have been count- 

 ed in a single cane-leaf, so that its great utility is unquestion- 



