30 PESTS OF COFFEE 



are that both these ants have a marked influence in in- 

 creasing the numbers of green bugs on a coffee tree. 

 The presence of these ants, according to the results of his 

 experiments, are beneficial to the green bug in four 

 ways :-T- 



.1. The death rate of green bugs is much smaller 



where ants are present than where they are 



absent; 



2. The development of the gTeen bug is more 



rapid where they are present; 



3. They serve to prevent the parasitising of green 



bug to a considerable degree ; and 



4. Their presence leads to a great increase in the 



progeny of the green bug. 



Of the two ants, Plageolepis longipes had a very 

 much more beneficial effect upon the development and 

 multiplication of green bug than did Dolichoderus hitu- 

 hercidatiLS. 



While the experiments of van der Goot deal with 

 the direct effect of the ants on the development of green 

 bug on a tree, he does not appear to have carried out any 

 experiments to decide whether any ants play a role in the 

 spread of the pest. As has already been stated, reports of 

 observations of the actual carrjdng of the green bug by 

 ants have been received. In addition, the junior author 

 observed the cock-tail ant {Cremastog aster sp.) carrying 

 green bugs and when these were followed, it was noticed 

 that they dropped them into the dry hollow of a coffee 

 tree where there was no chance of the bugs obtaining any 

 food. Where green bugs are found in ants' nests formed 

 out of the leaves of coffee tree or other host plants, they 

 too may feed and multiply within the iiests themselves. 

 But where nests are made in the ground it is difficult to 

 understand what the object of the transfer is. Do the 

 bugs in these cases quit the nests soon after they are 

 brought in or do they remain dormant to tide over the 

 uufavourable conditions wbicli may prevail in more ex- 

 posed situations ? To decide these points, if possible, the 

 following experiments were carried out. 



Two coffee plants in pots were placed in shallow 

 trays containing kerosened water. One of these was 

 infested with green bug and the other not. A nest of 

 the red tree ant (OecophyUa smaragdina) was introduced 

 into the uninfested pot on the 13th March 1915. On 



