THE TERRAPIN SCALE. 61 



The nonfeeding instars: Third instar (prepupa), length 2 days — 

 metamorphosis; fourth instar (pupa), length 6 days — development 

 of 'adult structures; fifth instar (imago) dormant phase, length 2 

 days — hardening of exo-skeleton; active phase, length 1 day — migra- 

 tion and copulation. 



SEASONAL HISTORY. 



There is one generation of the terrapin scale annually. This species 

 passes the winter as immature females. At the start of hibernation 

 these are very plump and the ventral part of the abdomen crowds 

 against the surface of the host, so that there is no vacant space be- 

 neath the scale, but by the middle of March the abdomen has 

 shrunken until there is a dome-shaped cavity beneath it. When the 

 spring growth starts the specimens become plump again and the space 

 beneath the scale disappears. Most of the specimens reach maturity 

 during the middle of June and begin at once to produce young. 

 The majority of the scales reproduce for a period of about one month, 

 but an occasional female may continue actively reproducing for as 

 long as 3 \ months. On the second day after the first young are born 

 they begin to emerge from the brood chamber of the parent, mostly 

 through the anal cleft. During the first 5 weeks there is a heavy 

 migration of larvae to the leaves. This migration reaches its maxi- 

 mum during the first week of emergence. It then gradually declines, 

 until by the end of the fifth week it amounts to less than 5 per cent 

 of the maximum emergence. (See figs. 2 and 4.) At the beginning 

 of the sixth week after the appearance of the first young the female 

 larvae start migrating from leaf to twig. By the end of the seventh 

 week the females are ready for copulation and the males migrate to 

 the twigs. Copulation occurs at this time and the males die at once, 

 but the females start upon a period of rapid growth, during which 

 they excrete a vast amount of honeydew, which is responsible for 

 most of the injury caused by this scale. After 2 or 3 weeks of extreme 

 activity their growth gradually slackens, but it continues until cold 

 weather forces the partly mature females into hibernation, after which 

 they remain dormant until the following spring, dying about mid- 

 summer after the production of young. 



MORTALITY. 



There is more or less mortality at all seasons of the year. Ordi- 

 narily there seems to be comparatively little due to winterkilling, 

 though at times this may be considerable. The amount of winter- 

 killing depends mainly upon the vigor of the host plant and upon the 

 severity of the winter. During 1912-13, upon well-nourished trees, 

 the mortality from this source was not more than 5 per cent of the 

 hibernating scales. During 1913-14, however, scales upon trees 

 of low vitality had a mortality as high as 40 per cent. 



