FUMIGATION OF CITRUS TREES. 77 



The orchards in Riverside and San Bernardino Counties are seldom 

 as severely infested as elsewhere. These observations explain why 

 scale-insects are less destructive in these two counties than in regions 

 nearer the coast. The hot weather appears to be almost as efficient 

 as some insecticide treatments. 



THE EFFECT OF FUMIGATION ON LADYBIRDS (COCCINELLIDJE) 

 AND SCUTELLISTA CYANEA MOTSCH. 



Several writers on fumigation have mentioned that ladybirds are 

 less easily killed by hydrocyanic-acid gas than the scale-insects of 

 the citrus. In order to prove this contention, specimens of the two 

 common ladybirds (Coccinella calif ornica Mann, and Hippodamia con- 

 vergens Guer.) were suspended under a fumigation tent in an open 

 cage 6 to 7 feet above the ground, while others were placed right on 

 the ground. Schedule No. 1 was used. The tent was left on the 

 tree one hour. The temperature was 60° F. The insects were 

 examined about ten minutes after the tents had been removed, but 

 exhibited no signs of life whatever; all appeared to be dead. The 

 following morning a second examination showed that many had 

 revived from their previous stupefied condition. A count made of 

 those suspended from 6 to 7 feet above the ground showed that out 

 of a total of 64, 32, or just 50 per cent, were killed. Of 85 on the 

 ground 33, or about 39 per cent, were destroyed. Both species 

 appeared equally resistant to the gas. 



It thus appears that the insects on the ground survive a gas treat- 

 ment somewhat more readily than those toward the top of a tree. 

 When it is considered that the strength of gas was as great as is ever 

 used in commercial work against the common scale insects of citrus 

 trees, in fact somewhat stronger than is used by most fumigators, and 

 also that in regular operations many of the ladybirds after becoming 

 stupefied fail off onto the ground, where they are less affected by the 

 gas, it would seem safe to presume that the larger number of these 

 insects on a tree at the time of fumigation will survive the treatment. 



Scutellista cyanea Motsch. is a small hymenopterous parasite of the 

 black scale which was introduced into California from South Africa 

 several years ago. The larva? feed on the eggs of the black scale, 

 usually one in each scale, although there may be 2, 3, or even 4 

 present. Frequently as high as from 50 to 75 per cent, or even more, 

 of the black scale on a tree have been seen attacked by this parasite. 

 The work of this insect is remarkably good, yet not sufficiently perfect 

 to allow the fruit to come into the packing house in a clean condition. 

 This necessitates fumigation as though the parasites were not present. 



This is not meant to depreciate the usefulness of this parasite, even 

 though it fails to keep citrus trees entirely free of the black scale. 

 By destroying, as it does, a large percentage of eggs it confers a 



