Grains Research and Development

Date: 03.03.2014

Bush allies in the insect wars

Author: Sarah Clarry

Native vegetation in grain-cropping landscapes can provide a habitat for beneficial predatory insects, supporting overall pest-control programs.

Key points

  • Pests and beneficials (beneficial predatory insects) are found in a range of habitats in grain-cropping landscapes throughout the year
  • Pastures, especially weedy pastures, provide habitat for pests
  • Pests are more commonly found on exotic weeds than on native plants
  • Remnants of native vegetation in good condition (containing few weeds and with an intact understorey) can reduce the number of pest species by supporting beneficials

Research is showing that bracketing crops with native vegetation can be an effective long-term control option for crop pests.

Native vegetation, particularly remnant natural bush, provides a haven and natural food source for beneficial insects, which prey on exotic insects attracted to grain crops and also to many weed species.

A GRDC-funded project titled ‘Pest Suppressive Landscapes’ has been monitoring the numbers of key pest and beneficial insects over the past two years. The project, led by Dr Nancy Schellhorn of CSIRO, has surveyed more than 80 sites in six landscapes across New South Wales, Queensland and Western Australia.

Photo of Nancy Schellhorn

Dr Nancy Schellhorn has led the Pest Suppressive Landscapes project for the past two years. The project has found that native vegetation provides a natural food source for beneficial insects that prey on exotic insects attracted to grain crops.

PHOTO: CSIRO

Dr Schellhorn says pests of grain crops move between different habitats throughout the year to meet their needs for food and shelter. This mobility makes it difficult to manage pests on a paddock or farm level so management efforts need to take into account habitats surrounding the farm and across the wider region.

Pest-suppressive landscapes are those with the right mix of habitats to support beneficial predatory insects and allow them to move into crop fields without harming the crops, and simultaneously discourage the build-up of pest insects throughout the year.

Dr Schellhorn’s team sampled habitats including crops, pastures, weeds and native remnant vegetation, gathering more than 30,000 specimens of both pest and beneficial insects.

They found pastures, particularly those that are weedy, provide habitats for pests, while native plants are the preferred habitat for predators of pests.

Pests were also found in weeds that had been allowed to build up in native vegetation.

Weeds that harbour pests include nightshade, capeweed, fleabane, mustard, wild radish and weed grasses such as ryegrass.

Plants favoured by beneficial predators are native shrubs (understorey) and eucalyptus trees.

The research shows that early colonisation of a crop by beneficials is crucial for keeping pest insect numbers low.

Ideally, beneficials should be moving into the crop at the same time or shortly after the pest insects arrive.

FIGURE 1 The difference between the density of predators and pests in New South Wales, Western Australia and Queensland.

Graph showing the difference in density of predators and pests in WA, NSW and Queensland

Crop management implications

  • Weed management in pastures may be necessary to reduce pest outbreaks in crops.
  • Weed-infested native vegetation may also be a source of pests.
  • When considering revegetation look for native plants that support beneficials and not pest insects.

Good-quality native vegetation for the purpose of pest management should comprise the appropriate species (Table 1), have some understorey and not be heavily grazed.

Roadsides that have been maintained as natural vegetation can also be an important resource for beneficial insects.

TABLE 1 Native plants that support beneficial insects.
Region Name Description Predators hosted
Southern NSW White Cyprus pine Fire-sensitive native conifer. Spiders, brown lacewing adults, ladybird beetles and spiny shield bugs.
Southern NSW Melaleuca spp. (paper bark trees) Spring-flowering tree to shrub with papery bark. Spiders, brown lacewing adults, ladybird beetles, spiny shield bugs and damsel bugs.
Southern NSW Wattles (Acacia spp.) Tree to shrub that flowers sporadically in response to rainfall. Spiders, green and brown lacewing adults, ladybird beetles and spiny shield bugs.
Southern NSW Eucalyptus melloidora,
E. macrocarpa, E. albens,
E. polyanthemos, E. blakelyi
Native trees that are a feature of open box woodlands. Spiders, green and brown lacewing adults, ladybird beetles and spiny shield bugs.
SE Queensland Berry saltbush and climbing saltbush Perennial plants that mainly flower spring through to January. Spiders, ladybird beetles, rove beetles and brown lacewings.
SE Queensland Black roly poly Perennial small shrub. Spiders, ladybird beetles, rove beetles and brown and green lacewings, predatory bugs such as the brown smudge bug, damsel bug and spiny shield bugs.
SE Queensland Swamp wattle and sally wattle Perennial plant that flowers mainly during winter.  Spiders, ladybird beetles, brown and green lacewings and spiny shield bugs.
SE Queensland Wilga Perennial plant that flowers winter through spring. Not widely grown due to difficulties in propagation.  Spiders, ladybird beetles, brown and green lacewings and assassin bugs.
SE Queensland Brigalow Perennial plant that generally flowers April through October but not every year. Spiders, ladybird beetles, brown and green lacewings and assassin bugs.
Southern WA Native shrubs and grasses from the families: Anarthriaceae, Cyperaceae, Dasypogonaceae, Haemodoraceae, Juncaceae, Phormiaceae, Restionaceae, Xanthorrhoeaceae Native trees that are a prominent feature of remnant native vegetation patches. Also found along roadsides and laneways. Spiders, predatory mites (pasture snout mites and mesostigmatid mites), ladybird beetles, brown lacewings, rove beetles and assassin bugs.
Photo of man and woman walking

Roma and Doug Parker on their Mingenew property where they have fenced-off remnant vegetation to improve biodiversity, including a larger beneficial insect population.

PHOTO: Evan Collis

Biodiversity blooming

Doug and Roma Parker decided to fence-off large areas of remnant vegetation on their Mingenew, Western Australia, property six years ago to encourage beneficial insect populations and to restore biodiversity generally.

Doug says he has not undertaken any scientific analysis of the consequences, but says there has been a noticeable increase in both insects and birdlife. Not all the insects are beneficial, but he assumes the good and bad are balancing out because he has not seen any significant crop damage.

“What’s really improved is the farm’s aesthetics, although that doesn’t mean a lot to the finances. But the farm really is looking good and in 2013 we achieved an above-average harvest after a season that was looking pretty grim mid-year. We had no rain through June and July.”

Doug attributes the season’s recovery – when the rain finally did come – to two decades of no-till. “The condition of the farm’s soils is very good. The crops can reach deeper moisture and respond well to rain when it falls.”

As part of the 2200-hectare farm’s revegetation program, Doug and Roma have planted oil mallee and sandalwood, which could also be income streams in the future.

More information:

Dr Nancy Schellhorn
07 3214 2721
nancy.schellhorn@csiro.au

This project was led by CSIRO with collaborators from the Queensland Department of Agriculture, Fisheries and Forestry, the University of Queensland and the Department of Agriculture and Food, Western Australia.

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