26 



BULLETIN 647, TJ. S. DEPARTMENT OF AGRICULTURE. 



from which ants were excluded, remaining, on July 17, about one- 

 third as heavy as on May 17. 



Up to July 17, therefore, the presence of the ants had a very 

 notable effect in increasing and maintaining mealybug infestation. 

 On this date the band was removed from one of the branches so that 

 reinfestation under ant attendance might be observed, and one of 

 the branches previously free to ant attendance was banded. Xo 

 marked results were obtained from this test. As indicated in Table 

 IV, a slight reinfestation of mealybugs occurred on all the branches 

 free from infestation on July 17, but there was a general decrease of 

 infestation on both types of branches and on the entire tree through- 

 out August. The only living mealybugs remaining on either set of 

 branches during August were young which were scattered over the 

 leaves, the insects being destroyed by their predatory enemies before 

 reaching maturity, and by September 2 the entire infestation on the 

 tree was reduced to an insignificant amount. In other words, on 

 this particular tree the effect of the ant in increasing and maintain- 

 ing the mealybug was marked up to the middle or end of July, but 

 this effect was practically lost during August. 



Table IV. — Effect of the Argentine 



ant 



on 



abundance 



of mealybugs 



on 



orange. 





Los Angeles County, Gal., 1916. 









Ants present. 



Ants excluded. 







From Apr. 14 to Sept. 2. 



From July 17 to 

 Sept. 2. 



From Apr. 14 to Sept. 2. 



From July 17 to 

 Sept. 2. 



Date. 



S 



> 



a 



S a 



li> 



n bo 





*— © 



CO 

 (9 

 > 



to - - 



a op, 

 •5 „• Us „ 



k. 



CO 



CD 



> 



to - - 



5 ^ ft 



j>> 





— © 



— to 



v- 3 

 OJ2 



a m 



3 2 



- — 

 >> 



'C © 



*B 



o © 



of lea 

 ined. 



of Hv 

 ybugs 



9 to 

 3 2 



S'O 



— © 



of liv 



ybugs 



nmu 



ybug. 



£.g 



© 



c.a 



of liv 



llUK'S. 



num 

 ybugs 



©S 



11 





- 9 



e"3 



© c3 



S © 



g a g © 



© cfl 



fc. © 



£ a 



g § ]£,© g ° 



Ch 3 



© s 



2 s ■«,© ig ® 





■2 « 





b c cj 



>J3 tO 



•2* -2s 

 a® a B 



fea^ 



•2 * 



|a ss^f s 









H° 



titi 



2 



3-° 



a® 



a® 



a a ' ©.5 "i a 5 





3 



3 



> o.2 



3 3 



> =5 





3 





> o^s 





3 



3 



> O.S 



3 — 





fc 



55 



< 



Z 



£ !fc 



•< 



•A 



Z 



B 



< 



Z 



£ 



& 



-< 



fc 



Aug. 7 



50 



1,000 



20 



9 



189 21 



0.111 







405 



81 



0.2 







150 



30 



0.2 



1 



Aug. 16 



153 



O/O 



3.6 



31 



382 71 



.18 



1 



251 



122 



.4 



2 



128 



19 



.14 



17 



Sept. 2 



' 1,750 



216 



.12 







i 1, 465 50 



t 



.03 







i 1,690 



43 



.02 



e 



1645 



49 



.07 







1 All of the leaves examined. 



The efficiency of natural enemies, as affected by the ant, was seen 

 in the first period of the experiment, from April 14 to July 17. 

 From April 14 to May 17 the number of mealybug enemies occurring 

 on the branches from which ants were excluded did not differ widely 

 from that on branches to which ants had access; yet, although by 

 the latter date these enemies had reduced greatly the number of 

 mealybugs on branches kept free from ants, their effect on mealy- 

 bugs attended by ants was negligible. It appears that the mealybug 

 predators are able to avoid capture by the ants, but are incapable 

 of reaching the mealybug groups closely attended by them. 



