STUDIES ON DEVELOPMENTAL STAGES OF THE HORSE CHESTNUT SCALE INSECT, PULVINARIA-REGALIS CANARD (HOM, COCCIDAE), IN THE OPEN LAND AND IN THE LABORATORY

In the presented paper the development of horse chestnut scale insect, Pulvinaria regalis Canard, was studied a on red horse chestnut (Aescu lus x carnea) in the urban area of Bonn. Secondly, the scale insect gr owth was determined on sycamore maple (Acer pseudoplatanus) and horse chestnut (Aesculus hippocastanum) at different temperatures in the lab oratory. The field population displayed an insignificant linear increa se in body length between July and beginning of December. No growth wa s observed between December and March but between mid of March and beg inning of May the body size increased exponentially. By setting up a f requency distribution of the anal plate length and by simultaneous mea surement of new and old anal plate during molting it was possible to s eparate different developmental stages. The length of the anal plates of first instar crawlers/settlers ranged between 0.030 and 0.054 mm, t hat of the second and third instar nymphs between 0.066 and 0.090 mm a nd 0.102 to 0.150 mm, respectively. The anal plate length of fourth in star adult females differed between 0.162 and 0.246 mm, whereas those of male puparians ranged between 0.075 and 0.098 mm. Since the cuticul a of P. regalis is very extensible, the separation of different develo pmental stages was only reliable by using the measure of the strongly sclerosed anal plate. Until 12. August first instar crawlers/settlers and till 29. September second instar nymphs were observed on red horse chestnut in the field. Female third instar nymphs were noticed betwee n 9. September and 28. April and fourth instar adult females from 31. March on. In the laboratory P. regalis individuals on horse chestnut a nd sycamore maple did only grow at 18 degrees C and fluctuating temper ature of 20/14 degrees C (16/8 h). The growth was heavily affected at warm temperatures of 26 degrees C and scale insects lived only a few w eeks. Only at the fluctuating temperature of 20/14 degrees C (16/8 h) some females laid eggs on horse chestnut and sycamore maple from the 4 9. and 48. week on.