Reproductive output and population growth of grapevine scale Parthenolecanium persicae Fab. and frosted scale Parthenolecanium pruinosum Cocq. (Hemiptera: Coccidae) on selected grapevine cultivars

Grapevine (Parthenolecanium persicae (F.)) and frosted (Parthenolecanium pruinosum (Coq.)) scale insects may cause long-term physiological damage to grapevines. Although they persist in major grape-growing regions of Australia, the reproductive and population growth potential of these insect pests is poorly understood. The reproductive output of gravid adult females of grapevine and frosted scales was studied under lab and field conditions on Riesling, Chardonnay and Sauvignon Blanc cultivars of European grapevine Vitis vinifera L. The intrinsic rate of increase of grapevine and frosted scales was also studied on Riesling and Chardonnay cultivars, respectively. Gravid adult females of grapevine scale have a larger body length and body mass and higher fecundity than those of frosted scale. Egg and first instar sizes were smaller for grapevine scale than for frosted scale. Egg incubation period, post-oviposition by adult females, was affected by grapevine cultivars, being 20 days on Chardonnay and 19 days on Riesling for grapevine scale and 18 days on Chardonnay and Riesling and 22 days on Sauvignon Blanc for frosted scale. Neither fertility nor fecundity was affected by grapevine cultivar. The intrinsic rate of increase (r_m) was 0.28 per month for grapevine scale on Riesling and 0.29 per month for frosted scale on Chardonnay. The finite rate of increase (λ) for grapevine and frosted scales was 1.28 and 1.33 months, respectively, and the population doubling time (DT) was 2.5 and 2.40 months for grapevine and frosted scales, respectively. Based on these observations, the population of grapevine and frosted scales is likely to persist in vineyards and may rise to outbreak levels that require management.