32 BULLETIN 647, U. S. DEPARTMENT OF AGRICULTURE. 



Most of the mealybug outbreaks in Los Angeles County orange 

 groves which came to attention during the summer of 1916 did not 

 long remain very severe unless the Argentine ant was in attendance. 

 An outbreak that occurred at Pomona may be cited as an example 

 of what usually occurs under such circumstances. The mealybugs 

 appeared in the orange trees in a certain locality and on walnut trees 

 bordering the groves in April and May and were rather numerous 

 on many trees during the latter month. By June 23. however, they 

 had become so scarce that it was difficult to find them at all. None 

 could be found on the walnut trees, and though some orange trees 

 were found on which 15 out of 18 of the young oranges were infested, 

 there were only from 1 to 10 mealybugs per fruit, hidden under the 

 sepals. Predacious caterpillars, tubuliferan thrips, and small lady- 

 beetles {Scymnus sp.) were also rather common under the sepals of 

 these fruits and apparently feeding upon the mealybugs. The Ar- 

 gentine ant did not occur in this section, and there were no other ants 

 in the worst infested trees at the time of this examination. 



In San Diego County, on the contrary, the mealybug infestations 

 were very bad in some of the groves where there were no ants in 

 attendance at the time of the inspection, June 27 and 28. In the 

 Lemongrove district three orchards were inspected, and all trees 

 examined were infested very badly with mealybugs. In two of the 

 orchards there were no ants of any species on the trees examined, 

 but in the third a few small red ants occurred on some of the trees. 

 The Argentine ant is not yet present in any of the orange groves of 

 ihis county, although it has been introduced into the fairgrounds at 

 San Diego. In the Sweetwater Valley the lemon trees inspected also 

 were infested very badly with mealybugs, but while two species of 

 ants were fairly common on some of the trees, the Argentine ant was 

 not present. The infestations were equally as bad on a number of 

 trees on which there were no ants as on those where the ants occurred. 



In the Chula Vista district the infestation in the last two or three 

 years had been quite as severe as at Lemongrove and in the Sweet- 

 water Valley, but during the summer of 1916 it was so slight as to 

 give no apprehension. This fact is attributed locally to the occur- 

 rence of mealybug enemies, and especially the lady-beetle Crypto- 

 laemus montrouzieri Muls.. in much greater numbers this year than 

 usually. 



In the El Cajon Valley, which is considerably farther inland than 

 the three orange districts previously mentioned, and is almost com- 

 pletely shut in from air currents from the coast by the surrounding 

 foothills, no mealybugs could be found, and Mr. H. M. Armitage, 

 horticultural commissioner of San Diego County, stated that none 

 had been found by the local inspectors. 



