THE ARGENTINE ANT IN RELATION TO CITRUS GROVES. 37 



experiments to determine the effect of the ants. In a test conducted 

 upon young orange trees colonized with the scales, two of the trees, 

 on which there were 5,425 and 334 young scales, respectively, were 

 handed to exclude ants, while a third, on which there were 3,100 

 scales, was left accessible to the ants for comparison. The number 

 of scales gradually diminished on all the trees, accompanied by a cor- 

 responding increase of parasitized scale remains, until within two 

 months from the time of starting the experiment practically all had 

 been destroyed. 



The destruction of these scales was caused almost exclusively by 

 parasites, the percentage of parasitized scales increasing, with slight 

 fluctuations, at the same rate on the tree frequented by ants as on the 

 two trees from which ants were excluded. There was nothing in the 

 condition of the trees or in their suitability as a food plant of this 

 scale to prevent the scales from thriving, as was shown by the fact 

 that a few sound scales which had secured perfect shelter from para- 

 sites remained on the trees as late as October, three and one-half 

 months after all those not sheltered had been destroyed. 



It was plainly seen in this experiment, and many other observa- 

 tions bear out this conclusion, that the internal parasites are the 

 most effective enemies of the soft brown scale in Louisiana and that 

 the Argentine ant does not extensively prevent the work of these 

 insects. A considerable number of adult parasites were seen on these 

 trees during the examinations, and fully as many on the ant-invaded 

 trees as or. the noninvaded ones. Two species of chalcids, 1 viz, 

 Eupelmus coccidis Gir. and Goccophagus ooccidis Gir., were reared 

 from ant-attended soft brown scales in Louisiana. 



While an orange tree occasionally would be found in Louisiana 

 with one or more small branches very heavily infested with the soft 

 brown scale, assiduously attended by the ants, the worst infestations 

 that came to notice were on plants other than citrus. For example, 

 in an orange grove at Buras, where this scale was present in small 

 numbers and scattered on orange trees, one limb of a rosebush was 

 found infested so severely that in a space 1 foot long on a branch 

 about one-eighth inch in diameter there w r ere 1,440 scales. 



Large groups of this sort sometimes are found in which there is 

 very little evidence of parasitism, but usually from 2 to 60 per cent 

 or more of all the scales occurring in such groups either contain the 

 parasites or show their exit holes. 



The soft brown scale undoubtedly is held in check in Louisiana 

 orange groves, regardless of whether ants are present or not, by its 

 natural enemies and particularly by the internal parasites. 



1 Identified by Mr. A. A. Girault. 



