27o 



against parasitation by Diplosis. That the presence of the gramang 

 ant is not of itself antagonistic to the development of the scale was 

 proved in experiments in which Diplosis was absent. The practice 

 of refastening to the cacao trees pods which have been plucked and 

 emptied is useful only in plantations where the black cacao ant occurs. 

 These data refer to P. crotoms and do not necessarily apply to other 

 mealy bugs. For instance, P. citri, Risso, appears to thrive equally 

 well on both ant-free and ant-infested trees. The lamtoro Coccid 

 (P. virgatus), which is not much visited by ants, and P. adonidum, 

 which is usually ant-free, also thrive in their absence. 



The injuriousness of the gramang ant depends on the plant involved. 

 In cof!ee plantations it is a most dangerous pest owing to its influence 

 on C. viridis. On many estates this scale is present in such small 

 numbers as to be practically negligible and such infestation remains 

 stationary until the gramang ant appears, when it rapidly increases. 

 It has been stated by Keuchenius that the gramang ant kills many 

 insect pests, hinders the development of sooty fmigus on coJSee bushes 

 and is an important distributor of Cephalosporium lecanii [see this 

 Review, Ser. A, iii, p. 646]. The first of these conclusions has already 

 been dealt ^vith and data are adduced to prove that the other two 

 are incorrect. In cacao x^lantations the gramang ant is also injurious, 

 for it drives away the black cacao ant and does not itself efficiently 

 protect Pseudococcus crolonis against Helopellis. In this con- 

 nection it is suggested that HelopeUis is disturbed by the active, 

 dense masses of the black cacao ant, an effect which the sparse 

 and smaller numbers of the gramang ant cannot produce. Cacao 

 planters have sometimes ascribed a lessened fruit production to the 

 gramang ant and the author states that in places where gramang 

 infestation borders on black cacao ant infestation, the difference 

 in production was very remarkable. This will be further investi- 

 gated. 



As regards the control of P. longipes [see this Review, Ser. A, iii, 

 p. 664:] it is pomted out that the removal of fallen leaves and other 

 debris only causes the ants to enter the soil without leaving the 

 plantation. The employment of other ants is madvisable in coffee 

 plantations and, though the black cacao ant may safely be introduced 

 into cacao plantations, it has httle chance of survivmg in the presence 

 of P. lo)igipes. Attempts to poison the latter have failed, because 

 the ants soon discover the poisons and avoid them. Traps made 

 of sections of bamboo stuffed with dried leaves proved expensive 

 and incapable of entirely ridding a plantation. For use in coffee and 

 cacao plantations, when these ants abound, carbon bisulphide may 

 be recommended, the minimum quantity required being 5 pints 

 per acre. Trenches measm-mg about 5 feet long by 2 feet and 8-12 

 inches deep are dug at regular intervals, about 140 being required 

 per acre. In cacao plantations tliis amounts to one trench per tree. 

 Many small trenches are preferable to a few large ones. The 

 plantation is thoroughly cleaned up and the fallen leaves are placed 

 in the trenches, any surplus being burnt. At 20-inch intervals 

 bamboo pipes are thrust into the mass of leaves which is then carefully 

 covered \^-ith earth so that only the pipes stick out. Twenty cubic 

 centimetres of carbon bisulphide are required per trench and this 



(C375) a2 



