27 



pupa, state at the time its host was subjected to the poisonous gas, was 

 not affected by the gas to the same degree it would have been if in the 

 perfect or adult state, since I have repeatedly proven it to be a fact that 

 larvae and pupae of insects are not affected by this gas to the same de- 

 gree that the adult insects are. At the same time, when a scale is in- 

 fested with one of these parasites and is sprayed with a resin wash 

 sufficiently strong to kill the scale, this also proves fatal to the included 

 parasite. This is one of the many advantages which the gas treatment 

 possesses over any kind of a wash for destroying scale-insects. 



Besides the gas treatment and the resin wash, both of which are re- 

 ferred to above in the article treating of the Red Scale, another remedy, 

 which has the advantage of being very simple and nearly always at 

 hand, consists of spraying the trees with a solution of common brown 

 laundry soap — 1 pound dissolved in 3 gallons of water. I have seen all 

 of these scales on small orange trees entirely destroyed by a single ap- 

 plication of this remedy. 



The Hemispherical Scale. 

 (Lecanium hemisplicericum Targ-Tozz.) 



My collection contains three different forms of Lecanium which are 

 here commonly known under the name of L. hemisphwricum. The 

 largest individuals of the largest form measure 5 mm long by 4 wide 

 and 3 high; these I have found upon pear and orange trees, and also on 

 Sycamore (Platanus racemosus). Wild Lilac (Ceanothus divaricatus) and 

 on California Holly (Heteromeles arbutifolia). The largest individuals 

 of the medium form measure only 3J mm long by 3 wide and 2 high; 

 these I have found only on orange trees. The third and smallest form 

 I have found only upon the Hare's-foot Fern (Davalliacanariensis), where 

 they occurred in such large numbers as to kill the plant infested by 

 them. The largest individuals measured only 3 mm long by 2 wide and 

 1J high. The largest form is evidently the Lecanium hibemaculorum of 

 Boisduval (originally described as a Ohermes), since it agrees very well 

 with che description of this species given in The Entomologist's Monthly 

 Magazine, Vol. xxn, p. 78. This description is by Dr. J. W. Douglas, who 

 has made this group of insects his special study, and who had before him 

 specimens identified by Dr. Signoret, the highest authority upon scale- 

 insects. The medium form found upon orange trees is evidently the 

 true hemisphwricum, while the smallest one is just as certainly the Le- 

 canium filicum of Boisduval (also originally described as a Ohermes). 

 Mr. Mask ell, of New Zealand, another well-known authority upon scale- 

 insects, considers hemisphcericum and filicum as belonging to one and 

 the same species, and is inclined to consider hibemaculorum as being 

 only a larger variety of the above species ; it is very doubtful, however, 

 that he had the true hibemaculorum before him when making his ob- 

 servation, since the measurement he gives (one-ninth of an inch in di- 



