660 EXPERIMENT STATION RECORD. 



The origin of the citrus white fly is by circumstances quite definitely indi- 

 cated as Asiatic. In addition to Florida, where about 40 per cent of the orange 

 groves of the State are estimated by the authors to be infested, it occurs in 

 South Carolina, southern Georgia, Alabama, Mississippi, Louisiana, Texas, and 

 California (in which State it was first discovered in 1907). Outside of the 

 United States it is known to occur in Mexico, Brazil, Chile, China, Japan, and 

 India (Northwestern Himalayas). So far as linown it does not occur in Cuba. 

 It is estimated that this species was the source of total loss in value of fruit 

 of $696,700 of the crop of 1907-8 and that the crop of 1908-9 was affected to 

 the extent of $750,000. 



The authors find that A. citri shows a greater degree of adaptation to the 

 umbrella tree than to citrus, that the adults are so strongly attracted by grow- 

 ing leaves of umbrella trees that under certain conditions with umbrella and 

 citrus trees growing side by side more adults collect on 3 or 4 umbrella leaves 

 than are pi-esent on an entire citrus tree of medium size. 



The eggs hatch in from 8 to 24 days, according to the season. " During ordi- 

 nary summer weather from 75 to 100 per cent hatch on the tenth to twelfth day. 

 Infertile eggs hatch as readily as fertile eggs and produce adults of the male 

 sex only. After hatching, the young larva actively crawls about for several 

 hours, when it ceases to crawl, settles upon the underside of the leaf, and begins 

 to feed by sucking the plant juices. It molts three times before becoming a 

 pupa. After the first molt the legs become vestigial; hence thereafter it is 

 Impossible for it to change materially its location upon the leaf. Larval life 

 averages in length fi-om 23 to 30 days. The pupa closely resembles the grown 

 larva and requires from 13 to 304 days for development. The adult fly has an 

 average life of about 10 days, although several females have been known to live 

 27 days. Females may begin depositing eggs as soon as 6 hours after emer- 

 gence and continue oviiX)Siting throughout life. The maximum egg-laying capac- 

 ity is about 250 eggs, although 150 more nearly represents the number laid 

 under grove conditions. Unfertilized females deposit as many eggs as fertile 

 females. The entii-e life cycle from egg to adult requires from 41 to 333 days; 

 the variation in the number of days required from eggs laid on the same leaf on 

 the same day is very remarkable." This variation is absolutely independent of 

 both temperature and humidity influences. The sums of effective temperatures 

 required for the minimum duration of immature stages for individuals develop- 

 ing from eggs deposited between February 23 and August 8 vary from 1,641 to 

 2.153°, with an average of 1,846°, which may be regarded as very nearly the 

 normal for minimum development up to the time when all individuals winter 

 over as pupae. During the course of the year the fly may pass through a mini- 

 mum of 2 generations and a maximum of 6 generations. The generation started 

 by the few adults that emerge during the winter is entirely dependent upon 

 weather conditions and may or may not occur. Each generation except those 

 started after the middle of August is more or less distinctly two-brooded. 



"Specimens of the cloudy-winged white fly (eggs, larvae, and pupse) in the 

 collection of the Bureau . of Entomology show that this species occurred on 

 oranges in the United States as early as 1889. The records in connection with 

 the specimens show that it was collected in Mississippi and North Carolina in 

 1889, in Louisiana in 1890, and in Florida in 1895. Outside of the United States 

 it is known to occur only in Cuba. Its Introduction into the United States 

 from Cuba does not seem as probable as its introduction into Cuba from the 

 United States. Its food-plant differences and adaptations are such that orange 

 trees are not as a rule subject to as heavy infestations as by the citrus white 

 fly, although with grapefruit trees this situation is usually reversed. Most im- 

 portant as a factor limiting the injury from the cloudy-winged white fly is that 



