1(1 AXMWI. REPORTS OF DEPARTMENT OF AGRICULTURE, 1939 
PRUITFLT INVESTIGATIONS 
Studies in Hawaii an the vapor-heal method of fruit sterilization 
have resulted in data permitting the movement of papaya- in the 
regular channels of trade. Heavy populations of the Mexican fruit- 
fly appearing during the past year bave been traced to the abnormal 
production of a second crop of Sargentia^ a wild native host abun- 
dant in northeastern Mexico. Repellent materials discovered both in 
Hawaii and in Mexico offer a new possibility of protecting fruits 
from attack. In Puerto Rico a study of the movement of adult fruit- 
fly populations indicate- that attack on citrus i- largely incidental. 
depending on the populations which may migrate, and that there 
is no continuous build-up in citrus. 
MEXICAN FRUITFLY CONTROL 
The citrus fruit industry in the Rio Grande Valley of Texas had 
an unprecedented crop of fruit and the Largest number of larval in- 
festations on record. The large crop of fruit necessitated a longer 
harvesting season, and the increased number of larval infestations 
made sterilization of citrus fruit of prime importance throughout the 
last half of the shipping season. 
INFESTATIONS 
Owing to the presence of an extremely large fly population, which 
apparently drifted into the regulated area from northeastern Mexico 
during January and February 1939. there developed in later months 
the most severe infestation of the Mexican fruitny on record in the 
Rio Grande Valley. The situation was further complicated by the 
amount of fruit remaining to be harvested before the beginning of 
the host-free period, at a time when the fruit movement was delayed 
on account of poor market conditions. 
Early in January traps indicated that flies were moving into the 
area, and by February it was realized that a serious problem con- 
fronted the growers, shippers, and quarantine personnel. Larval in- 
festations were found in the regulated area late in February on 18 
premises, in March on 1.404, in April on 704, in May on 8. and in 
June on 3. These infestations varied in intensity from 1 fruit found 
infested to as high as 10 percent of the entire crop on many plant- 
ing.-. On individual trees in numerous groves the damage amounted 
to 80 percent of the crop. 
Outside the regulated area nine incipient infestations were found. 
Seven of these were found in Webb County, one in Dimmit County, 
and one in La Salle County. 
li has long been recognized that the early termination o\ the 
harvesting season has ;> direct bearing on the amount of infestation 
which develops within the regulated area. When the crop was -mall 
enough to be harvested by March l, little difficulty was encountered; 
but when production increased to Mich a degree that a Large quantity 
of fruit remained t<» be harvested in March and April, infestations 
usually developed. During the past season it was necessary to 
tend the period for harvesting grapefruit through May L5, and a- an 
abundance of fruit was available for oviposition, the resulting 
heavy infestation was not unexpected. 
