17- 
RESIDUE STUDIES 
Representative samples of cucumbers from plants treated with 
certain insecticides shortly before or during the fruiting period, or at 
both times, were collected in 1948 and 1949 by W. J. Barbour, resident 
inspector of the Food and Drug Administration, and sent to the Atlanta, 
Ga., office for residue determinations. Similar samples were furnished 
the Division of Insecticide Investigations of this Bureau in 1950. The 
cucumbers were of slicing size, averaging about 2 l/4 inches in diameter 
and 0.65 pound in weight. Some of the 1948 samples were run through a 
brushing and waxing machine, and some of the 1949 samples through a 
more elaborate washing, waxing, and polishing machine. The treat- 
ments of the various samples and the findings of the chemists are shown 
in table 6. 
The quantity of residue from the different insecticides and from 
different samples of certain insecticides varied considerably. The only 
residues of appreciable quantity were those that followed the use of 
gamma BHC in the fall of 1948 during the fruiting period, and of cryolite 
in the spring of 1949. Similar applications of gamma BHC in the spring 
of 1949 and of lindane in the falls of 1949 and 1950 apparently resulted 
in little or no residue at time of harvest. Cryolite residues were rather 
variable and sometimes as high as 82 p. p.m. of fluorine. It is not under- 
stood why plants that received the last cryolite application on May 23, 
1949, before the fruits appeared on the plants, produced fruits showing 
9.6 p. p.m. of fluorine. A control program in which lindane was used 
during the prefruiting period and cryolite thereafter resulted in residues 
of 0.6 p. p.m. of gamma BHC and 2 p. p.m. of fluorine. The fluorine 
residue was reduced to 0.2 p. p.m. by washing and waxing of the fruits. 
DDT, parathion, and methoxychlor residues were low, even when these 
materials were applied on the day of harvest. The lindane and cryolite 
residues were reduced as much as 80 to 90 percent by commercial 
brushing (or washing) and waxing machines. These machines may not 
have reduced the residues to safe levels, however, Similar findings 
for cryolite have been reported by Fulton (11). 
SUMMARY 
The pickleworm (Diaphania nitidalis (Stoll)) and the melonworm 
( Diaphania hyalinata (L.)) are serious pests of fall crops of squash and 
cucumber in the South Atlantic and Gulf States. They also frequently 
cause damage in adjoining States and occasionally as far north as 
Illinois and Connecticut. These insects spread northward each spring 
and summer from semitropical areas. The melon aphid ( Aphis gossypii 
Glov.) and several species of cucumber beetles cause damage to cucurbit 
crops at times. 
