Life History and Ecology of Pulvinaria vitis (L.) (Hemiptera: Coccoidea), the Cottony Scale Attacking Peach in Ontario

Abstract

AbstractThe cottony scale attacking the peach in Ontario is apparently the European species Pulvinaria vitis (L.) and may have been introduced to North America prior to 1897. It is thelytokous and has only one generation per year. The partly grown, adult female overwinters on the bark of its host. The eggs, laid about mid-May, are enclosed in a white, felt-like ovisac that is secreted by submarginal glands in the ventral region of the scale's body. The eggs, which on peach averaged about 4,000 per female, were laid over a relatively short period when the temperature was 14 °C. or higher. Eggs began to hatch after about 200 day degrees above 10 °C. Increasing the temperature increased the rate of hatching, but no close correlation was found between the rate of hatching and the average daily temperature during the hatching period.The newly emerged nymphs were both phototactic and photokinetic, and their establishment on the host plant was affected by several factors including light, humidity, and air movement. For a given set of conditions there appeared to be a maximum number of nymphs that could become established per unit area of host. P. vitis was dispersed by wind at any stage when it was active, but especially at the early crawler stage.Growth of the scales was discontinuous with varying periods when no growth took place. There were three moults: the first 12 to 18 days after hatching; the second 28 to 36 days; and the third 56 to 93 days. At ecdysis only the cuticle of the ventral surface and the appendages was shed. Movement of the scales on the host plant was particularly frequent till the first moult, but some movement took place throughout the summer and early fall except for a period in late August and early September. Only a small percentage of the scales reached the bark from the leaves, probably due to random movement.Feeding appeared to be discontinuous with periods of days when no feeding took place. The scales fed on the phloem, but on twigs the stylets penetrated as far as the xylem and destroyed the cambium in the feeding area.Though parasites and predators exist in the area and appeared to be capable of exercising a large measure of control, the spray programs used in the orchards held them to relatively small numbers. At least one species of parasite was almost absent from sprayed orchards.