Functional biodiversity: a focus on scale insect pests and enhancement of their parasitoids

Abstract

This project studied scale insects and how to control them. Grapevine scale was the most common species, usually with patchy distribution. Infestations were worse in vineyard edges near perennial crops and buildings since such woody plants are potential alternative hosts. Parasitic wasps were common on vines in summer but species that attack scale insects were rare, possibly due to ants protecting the scale. Vetch groundcovers to distract ants are not ideal for vineyards. Better cover crop options identified in earlier work should be used. Communication activities have been undertaken to communicate recommendations. 

Summary

Rising concern among winegrape growers regarding increasing infestations of scale insect pests – potentially exacerbated by climate change – prompted Wine Australia to fund the present project. The aim of this work was to capture field data that would underpin the development of an expanded range of management (control) options. 

Surveys were conducted over two years across six New South Wales vineyards – primarily in the Riverina region – quantifying scale insect populations on vines. Sampling was undertaken both centrally and along vineyard edges, the latter to detect potential influences from adjacent land uses and vegetation types. In addition to visual inspections, a motorized vacuum sampler was used to collect beneficial insects from vine foliage. 

Grapevine scale (Parthenolecanium persicae) was the dominant species detected, with only occasional observations of frosted scale (Parthenolecanium pruinosum). Scale insects were present at all sites and during each sampling event, though their distribution was highly patchy. While most vines were uninfested, dense localized hotspots were common. Scale were observed across all vine structures, including canes, spurs, petioles, leaves, and berries. Infestation levels varied widely among vineyards, between years, and across seasons. One organically managed site recorded relatively low pest numbers, although scale insects were still present. 

Despite the high level of variability in the data, a potentially important trend emerged: scale numbers were higher in vineyard edges adjacent to perennial horticulture or built infrastructure – both areas supporting a variety of alternative host plants, including ornamental shrubs. Built environments, particularly around cellar doors, often included these woody hosts. Such plants constitute potential scale insect harbourage and allow spillover into vines. Whilst adult female scale insects are sessile, other life stages are mobile. Immature scales (‘crawlers’) can be wind-dispersed and adult males are winged, enabling colonisation from nearby vegetation. These findings point to the importance of inspecting adjacent woody plants, which may serve as “donor vegetation” for vineyard reinfestation. 

Previous Australian studies have highlighted biological control as a promising management strategy. Parasitic wasps, which oviposit into scale insects and developing larvae consume their hosts internally, leave visible emergence holes when mature wasps exit. In the present study, 669 parasitoid individuals across 165 morphospecies were collected. However, only two of these species are known to specialise on scale insects: Metaphycus maculipennis and Ophelosia bifasciata and these were rare in vacuum samples collected from vineyards. 

Earlier authors have suggested that cover crops such as common vetch (Vicia sativa) may attract ants away from vines by providing nectar, potentially exposing scale insects to parasitism. While this approach has reportedly been trialled overseas, it remains untested in Australian vineyards and has logistical complexities such as the tall and climbing habit of this plant. Consequently, growers interested in this strategy are encouraged to consider alternative groundcovers with prostrate, non-climbing habits. An earlier Wine Australia project identified suitable nectar-producing species, such as alyssum and buckwheat, through the Cover Crop Finder Tool. These plants support beneficial insects, including parasitoids of lightbrown apple moth, and may similarly benefit those attacking scale insects (Functional biodiversity solutions for Australian vineyards: Harnessing groundcovers, vineyard surrounds and native plants to deliver key ecosystem services). 

In conclusion, integrated pest management (IPM) remains the foundation of best-practice scale insect control. This includes routine monitoring to detect hotspots – guided by signs such as ant trails, honeydew, and sooty mould - and treatment with paraffin oils during winter or other insecticides in spring. Woody plants near vineyard margins, particularly those adjacent to built infrastructure or perennial crops, should be included in inspections. Heavily infested canes can be removed during pruning and either mulched or disposed of off-site to reduce reinfestation. While commercial releases of predatory beetles and lacewings may be cost-prohibitive at broad scale, they may be considered useful for targeted hotspots. Cover crops, if well chosen, offer multifunctional benefits—supporting biological control agents while reducing pest pressure from scale insects.