4 MISSOURI AGRICULTURAL EXPERIMENT STATION BULLETIN 177 



with all the Missouri nurserymen and it has been his pleasure to make per- 

 sonal visits with practically every nurseryman in the state and, especially 

 with those located in communities where San Jose scale is prevalent. He 

 has worked with them and helped them treat their nursery stock for scale 

 and other injurious insects. While engaged in the work, many problems, 

 confronting the nurserymen, concerning the eradication of San Jose scale 

 from nursery stock, have been brought to his attention. As a result, a 

 number of experiments have been made to test the effect of the different 

 materials commonly used upon infested and non-infested stock, with the 

 object in view of determining which remedy is the most practical from all 

 standpoints, under Missouri conditions. 



Life cycle of San Jose scale. 'The mature San Jose scale is yellow with 

 a sac-like body which is covered with a soft, waxy secretion the scale. 

 This covering serves as a protection for the pest. The insect passes the 

 winter in a half-grown stage, all other stages being killed by winter condi- 

 tions. These half-grown insects are found under a small black scale just 

 visible to the naked eye. About 95 per cent or more of these are male 

 insects, they being greatly in excess. About the first of May, the males 

 pupate and in a short time emerge as delicate two-winged insects. The 

 females at this time have arrived at the stage of impregnation and in a few 

 days the males disappear. The females reach maturity about a month later 

 and begin to give birth to living young. 



Most of the other scale insects deposit eggs which later hatch, but this 

 is not true of the San Jose scale. The young are developed in a mem- 

 branous sac which corresponds to an egg, but they usually burst out of 

 this before being born. Thus the San Jose scale is usually oviviviparous, 

 but it may be partially oviparous. A single female is capable of giving 

 birth to 600 young in a period of about six weeks. It is doubtful, however, 

 if a female gives birth to more than 100 or 200 insects and many of these 

 are males. Even at this rate of reproduction, from one single female the 

 total number of off-spring at the end of a season reaches into the millions. 

 The newly born insects are very tiny, yellow in color and have six legs. 

 They soon push their way out from under the scale of the mother and crawl 

 around for a day or so finding a suitable place to settle down. On the apple 

 the young scale seem to push out towards the tender growing tips to settle 

 down, while on the peach they stay more on the old wood. It is at this 

 stage, while the young are crawling about, that the pest is likely to be scat- 

 tered from one place to another upon the feet and bodies of birds, beetles 

 and other objects. If the branches of two trees intermingle, the young 

 easily crawl from tree to tree and it is often in this manner that the pest 

 spreads. 



When a suitable place is found, the young settle down and begin to 

 work the long proboscis, which is three or four times the length of the in- 

 sect's body, into the tissue of the host and begin developing a scale cover- 

 ing. Within two or three days, this covering of cottony and waxy fibers 

 becomes matured into a pale grayish scale which gradually becomes darker. 



Male and female scales are similar in size, shape and color until the 

 first molt, which takes place in from twelve to fourteen days after the emer- 

 gence of the larva. Up to this time the male and female are indistinguish- 



