BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 39 
the flies became so numerous and so widely distributed that they could 
readily spread into citrus groves across the border. Survey crews 
operated in the States of Tamaulipas, Nuevo Leon, and Sonora and in 
Baja California, in areas contiguous to citrus plantings in Texas, 
Arizona, and California. Infestations were found on citrus trees 
in all the areas except Baja California. 
The work was done in cooperation with the Mexican Department of 
Agriculture and local Mexican blackfly committees. A number of 
Bureau inspectors and supervisors worked with a larger number of 
inspectors supplied by the cooperating Mexican agencies. More than 
375,000 trees on almost 30,000 properties were inspected. Blackfly 
infestations were found on 924 citrus plantings. Many of the infesta- 
tions were very light; most were on dooryard plantings rather than 
on trees in groves. Application of sprays, under the exclusive direc- 
tion of the Mexican Department of Agriculture and the Mexican 
blackfly committees, gave excellent control of the fly. 
Citrus blackfly fought in Mexico 
Research on the citrus blackfly continued in cooperation with 
Mexico. 
Experimental attrition spraying in the Guaymas area reduced the 
number of infested properties from 282 to 58 and the number of trees 
in the spray program from 20,000 to 8,000. Citrus blackflies on the 
remaining infested trees were reduced to negligible numbers. 
A new infestation on April 30, 1951, near the main highway in 
Hermosillo, Sonora, received a first clean-up spray application begin- 
ning May 3. 
In the generally infested area in the east citrus production has 
been doubled in groves sprayed experimentally twice a year. Both 
speed and hydraulic spraying have given effective commercial control 
in this area. 
Extremely dry weather, both in the west and in the east has slowed 
up multiplication of the blackfly and in the east where infested plants 
in the wilds have lost their leaves because of drought it apparently has 
eliminated a number of infestations. Immature stages on leaves in 
undefoliated areas, however, survived a freeze of 23° F. and multipli- 
cation continued. 
Traps attractive to blackfly adults were used in the field to evaluate 
the progress of clean-up spraying and to determine the spread of 
the fly. 
Experiments using processed oils of high paraffin content and vis- 
cosity resulted in the development of a dip for packed limes that does 
not injure the fruit or affect its flavor, yet kills the blackfly. Dips 
using horticultural oils have either injured the fruit or given it an 
off -flavor. 
Imported citrus blackfly parasites thrive in Mexico 
Four of the seven species of parasites imported by the Bureau from 
semiarid sections in India and Pakistan and released early in 1950 
in dry areas in Mexico have become established and are increasing in 
numbers and spread. One of them, Prospaltella smithi Silv., has 
gone through the dry season with a steady increase in the rate of 
parasitization. Nearly 30,000 adults of the species were collected 
