THE IIOMOPTERA 207 



around the sides and may more or less cover the body. The animal after 

 its third molt differs so from its former appearance that this stage is 

 often called a pupa, and as the following molt produces the adult there 

 is evidently quite a metamorphosis to justify the use of this term in the 

 group. Honey-dew is produced by these insects. 



White Flies are essentially tropical though a few species live in the 

 northern United States. In greenhouses everywhere the Greenhouse 

 White Fly (Aleyrodes vaporariorum Westw.) is too often a serious pest, 

 for it multiplies rapidly and the tiny nymphs (Fig. 202) are not generally 

 noticed in time to check their increase before the plants have suffered 



FIG. 202. Nymphs of the White Fly on underside of a leaf, enlarged twice. (From 

 Britton, Second Rept. Ent. Conn. Agr. Exp. Sta. 1902.) 



greatly. When they are abundant, fumigation for 3 hr. at night, using 

 between J and J oz. of sodium cyanid to each 1,000 cu. ft. of space in 

 the greenhouse should kill all but the eggs and some of the pupae, and 

 repeating this treatment twice afterwards at intervals of 2 weeks should 

 destroy the others in the stages to which they will have then progressed. 

 If for any reason this treatment is not desirable, syringing the plants 

 with fish-oil soap using from 1 to Ij-^ oz. per gallon of water, giving 

 particular attention to the under surface of the leaves will give some relief. 



In the Southern States and in California, white flies attack citrus fruits and 

 cause much injury. Several species are more or less concerned, the most impor- 

 tant one being the Citrus White Fly (Dialeurodes citri Ashm.). These insects 

 usually check the growth of the tree and fruit, reducing the yield and its size, 

 and also by the production of honey-dew, induce the growth in this of a fungus 

 called "sqoty mould" which interferes with the ripening of the fruit and is also 

 believed to affect its flavor, besides making it look objectionable, so that fruit 

 partly covered with the mould must be cleaned before shipping. The reduction 

 of the vitality of the tree by these insects also favors the more active development 

 of other citrus insects and of diseases. 



