Scale insects and the vitis vinifera cv. shiraz - reason for high incidence of scales

Abstract

Temperature affects all aspects of the life of animals, especially ectotherms such as scale insects.  Development from first instar to third instar for grapevine scales (Parthenolecanium persicae) occurs from the beginning of summer through to autumn, although the rate can be changed as temperature increases.  Even the development and hatching of eggs is dependent upon the body temperature of the adult females in the spring. 

Biotic interactions between the scale insects and their host plant may vary depending upon cultivar, as previous work has demonstrated that scale populations differ among grapevine cultivars.  A preliminary metabolomics study of grapevine leaves from different varieties indicated that differences exist between cultivars that were more prone to scale infestation and more resistant cultivars.  Expansion of this study has the potential to provide scale control methods independent of abiotic conditions.

Summary

Three survey trips and the use of temperature data loggers were used to determine development of scales from third instars through to the appearance of first instars in Langhorne Creek region. No difference in scale presence on vines was observed despite differences in vineyard management.

Fluctuating temperature conditions were transformed into degree-days to compare scale development in vineyards with laboratory conditions.  The change from third instar adult appeared to correspond to laboratory expectations, but development from adult to hatching of first instar may be slightly different, although the identification of first instar emergence was limited by rain at the November survey.  The pattern of degree-day accumulation may influence the timing of moulting from one scale developmental stage to another between years.  Use of degree-days may aid in chemical control procedures for controlling the vulnerable change from third-instar into adult.

Although timing of moulting is important for determining when scale insects may be susceptible to control processes, the size of insects may also play a role in the way that the plant is affected.  An increase in size between third instar and adult, along with egg production, may remove nutrients, leading to a reduction in plant development.  A second stage that may affect plants is the combined presence of first and second instars, as the most honeydew may be produced then.  The high quantity of honeydew may initiate the growth of sooty mould.