

22 



BULLETIN 647, U. S. DEPARTMENT OF AGRICULTURE. 



known or suspected enemies, while the activities of the ants were 

 observed on the unprotected tree. The results are summarized in 

 Table II. 



Table II. — Influence of the Argentine ant on abundance of mealybugs on orange. 



Louisiana, 19L'f. 



Date. 



Ants present. 



Number 

 of sound 

 mealy- 

 bugs on 

 tree. 



Number 

 of para- 

 sitized 

 mealy- 

 bugs. 



Number 

 and kind 

 of mealy- 

 bug ene- 

 mies on 

 tree. 



Ants excluded. 



Number 

 of sound 

 mealy- 

 bugs on 

 tree. 



Number 

 of para- 

 sitized 

 mealy- 

 bugs on 

 tree. 



Number 

 and kind 

 of mealy- 

 bug ene- 

 mies on 

 tree. 



Mav 7. . 

 May 13. 



May 21. 



June 3.. 

 June 12. 

 July 29. 

 Aug. 15. 



593 

 234 







110(31.9 



per cent j. 



3 (1.3 per 



cent). 



1 T. 



2 T. 



4D,3T, 

 .1L.1S, 

 1C. 







IP 











1,126 

 859 



209 (19.5 



percent). 



90(11 per 



cent). 



IT. 



4 T, 3 L. 



3 L, 1 C, 

 1 S. 



2D,1 L. 



0. 

 0. 

 0. 



Symbols: T=tubuliferan thrips; L=larva of the pyralid moth Laetilia coccidioora Comst.; D=larva3 of 

 the dipteron Leucopis griseola Fallen.; C=eoeeineUids; S=Syrphus fly larvse; P=the mealybug parasite 

 Paraleptornastii abmrrnis Gir. 



At the time of beginning the experiment, May 7, there were 593 

 mealybugs on the ant-invaded and 1,126 on the ant-free trees. The 

 mealybugs gradually disappeared from both trees, as shown in Table 

 II, until by June 12 there were practically none. There was consid- 

 erable parasitization and the continuous presence in the mealybug 

 groups of several different predacious enemies. On May 13, for ex- 

 ample, 31.9 per cent of the mealybugs on the ant-invaded tree were 

 found to be parasitized, and 19.5 per cent of those on the protected 

 tree also were parasitized. On May 21 the percentage of parasitism 

 among the ant-attended mealybugs was 1.3 per cent, whereas among 

 those on the protected tree it was li per cent. Predatory enemies 

 occurred among or near the mealybugs on both trees as long as the 

 mealybugs lasted. The more common ones were predacious thrips, 

 coccid-feeding larva? of the moth Laetilia coccidivora Comst. (identi- 

 fied by Dr. Harrison Gr. Dyar), and the two-winged fly Leucopis 

 griseola Fallen (identified by Mr. Frederick Knab), unidentified 

 lady-beetles, and larvae of syrphus flies. At least one parasite, 

 Paraleptomastix abnormis Gir. (identified by Mr. A. A. Girault), was 

 found on one of the leaves of the ant-infested tree. There was no 

 evidence that the mealybugs were being attacked by fungus or other 

 disease. 



The slightly greater persistence of the mealybugs on the ant- 

 frequented tree has little practical significance and in part was ac- 

 counted for by the following circumstance: On June 12 a strip of 



