Rutherglen bug

Summary Top

The Ruther­glen bug is a native species that breeds on a range of native and weed hosts and is a pest of numerous crops across Australia. It is a small, fast moving bug that can build up to high numbers during the warmer months when suitable hosts are available. The pest occurs most commonly in late canola pod set and at windrowing. Damage of Rutherglen bugs can be reduced by parasitoids, controlling weeds and ploughing a deep furrow around emerging summer crops. There are several organophosphates and synthetic pyrethroids registered against Rutherglen bugs but these are disruptive to natural enemies. Insecticide applications will not guarantee a clean crop as Rutherglen bugs can readily reinvade a sprayed area.

Occurrence Top

The Rutherglen bug is a highly migratory native species that is a sporadic pest throughout most of the year. This species is common in New South Wales, Queensland, Victoria, South Australia, and the southern part of Western Australia.

The Rutherglen bug is a native species that is a sporadic pest throughout most of the year, most prominently in spring and early summer.

Description Top

Adults are 4 mm long and grey-brown in color with clear wings folded flat on their back. They have a narrow body with prominent dark eyes, sucking and piercing mouthparts and they are highly mobile. Nymphs are wingless and have a dark red, pear-shaped body.

Lifecycle Top

The Rutherglen bug is a warm-season pest. The species can have up to 8 generations per year and adult females may lay up to 400 eggs on the soil, grasses or flowering parts of plants. In the warmer months a generation time can be approximately 4 weeks. In a crop environment, the pest commonly breeds on prostrate weeds surrounding and under winter crops, or may feed on the lower stems of the crop.

Young nymphs hatch in autumn, slowly develop through winter and mature in spring. As the weeds in the paddock senesce and dry, late stage nymphs and adults move up onto the crop canopy during pod development. Breeding intensifies during late spring and early summer. Watch this video of nymphs of Rutherglen bugs in canola stubble:

Outside the crop environment, Rutherglen bug will breed on a diverse array of plants found throughout arable and more arid environments. As these plants begin to senesce, vast populations of Rutherglen bug will commence migrations which can take them hundreds or thousands of kilometers.

Behaviour Top

Rutherglen bugs are very mobile. Adults will migrate large distances to colonise more favourable environments after the onset of unfavorable conditions, particularly host plant senescence. The migratory influx most commonly occurs in spring and summer. As their host plants begin to dry off, adults and nymphs will walk and fly onto neighbouring crops or plants, sometimes in vast numbers. The video shows an example of mass movement of Rutherglen bug nymphs out of canola.

Rutherglen bugs are an opportunistic pest and can reach plague proportions in some seasons over short periods of time.

Similar to Top

Crops attacked Top

A wide host range, including canola, lucerne, wheat, sunflowers, safflowers, linseed and sorghum. Favoured weed hosts are wireweed and common purslane (summer-autumn) and capeweed (winter-spring).

Damage Top

Rutherglen bugs are sucking insects that most commonly attack crop plants in spring, during seed set, or in summer on emerging or established summer crops or, less commonly, in autumn during emergence of winter crops. In spring, adults and nymphs feed on sap from stems, leaves, flowers and can potentially decrease yield, oil content and oil quality in canola and sunflowers. Damage to susceptible plants can be heightened if the crop is under moisture-stress. Rutherglen bug will often continue to feed on pods after windrowing and at harvest cause problems with seed flow through harvesters, and by raising the moisture content of the grain to above acceptable standards.

Adult and juvenile Rutherglen bugs will feed on canola seed on the ground under windrows, but there is no research on their ability to feed on seeds in pods, and if there is oil/quality loss as a result.

In summer pulse crops, pod set can be reduced and seed can become shriveled. In favorable autumn conditions, feeding by high numbers of bugs can cause cupping of young leaves, retardation of emerging seedlings and seedling death.

Monitor Top

Rutherglen bug can infest crops at any time, but are most common in spring, from pod filling until maturity. Distribution is typically patchy across paddocks. Inspect flowering parts of crops either visually or by shaking flowering heads into a tray or bucket, or onto a beat sheet.

In autumn, particularly if conditions for summer hosts have been favorable, check crop perimeters, paying particular attention to surviving weed hosts.

Economic thresholds Top

Canola:

• Flowering-windrowing: 10 adults or 20 nymphs per plant. Higher number if moisture not limited (Colton & Sykes 1992, Hertel et al. 2013, Berlandier & Baker 2007).

Sorghum:

• Anthesis: 20-25 bugs/head; Milky dough: 25-40 bugs/head; Soft dough: 30-50 bugs/head (unvalidated M. Miles, unpubublished data2009)

Sunflower:

• Spring plant: Budding: 10-15 adults per plant; grain fill: 20-25 adults per plant

• Summer plants: Budding: 20-25 adults per plant; grain fill: 50 adults per plant

• Confectionary grade: 5 adults per plant (Franzmann 2007)

Management options Top

Acknowledgements Top

This article was compiled at cesar by Sandra Hangartner and Garry McDonald (cesar). Melina Miles and Tonia Grundy (Queensland Department of Agriculture) produced the YouTube video.

References/Further Reading Top