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Rose Aphids - fact sheet
The Rose Aphid, Macrosiphum rosae, is the most common insect pest of roses in Australia. Aphids damage plants by sucking sap from plant tissues using highly specialised sucking mouthparts. The usual symptoms of damage are distortion of new leaves and flowers. Aphids particularly like newly-forming flower buds, and damage done at this stage has more serious consequences than if the buds are attacked later. Aphids also excrete large amounts of honeydew, which can cover the plant. Honeydew is a food source for sooty moulds, which form a black covering over affected areas, severely reducing photosynthesis and aesthetic appeal. Severe aphid infestations can result in defoliation of the plant and loss of the flower crop. Aphids can breed very rapidly and build up vast numbers, especially in warm, humid weather.
Rose aphid life cycle
Rose Aphid females give birth to live young, are parthenogenetic (i.e. do not need to mate to produce young) and have a very short generation time. The generation time decreases as weather gets warmer. A female aphid carries its own grandchildren, i.e. even before they are born, the offspring have their own developing embryos. Males of most aphid species are very rare to nonexistent in Australia because they only arise in sufficiently cold conditions - most of our aphids have been introduced from higher latitudes of the Northern Hemisphere. Female aphids in Australia therefore generally don’t produce eggs, and the offspring are clones of their mothers.
Aphids grow by moult through several stages, finally reaching a reproductively mature adult form. When populations on a plant become insupportably large, juvenile aphids will respond by producing wing buds. They develop into winged adults which can then fly off to look for less crowded plants on which to produce their own young.
Cultural: hosing with a jet of water can control aphids on small plants in the home garden. Simply squashing the aphids using fingers, or a damp cloth with or without insecticidal soap and/or spray oil, is an option if the aphid population is not too large.
Biological: In the early 1990s, scientists from the Waite Agricultural Research Institute at the University of Adelaide successfully introduced a tiny parasitic wasp from Italy, Aphidius rosae, as a biological control agent for the rose aphid. They first bred the wasp in large numbers in quarantine conditions to determine any unwanted, harmful side effects. They found that the wasp was specific to the rose aphid and attacked no other insects (including those that might be beneficial). It was released into the wild in Adelaide, and spread rapidly (over 40 km in one year). The wasps are now spreading successfully through eastern and south-eastern Australia, and were deliberately introduced into the rose garden at the Royal Botanic Gardens Sydney in 1996.
The wasp controls the aphid by laying eggs inside a recently born aphid nymph. When an egg hatches the wasp larva feeds on the aphid’s body contents until it pupates, killing the aphid. The adult wasp emerges from the ‘skin’ of the dead aphid (known as a ‘mummy’) by chewing a hole in the rear of the aphid’s abdomen. It then crawls out and flies off in search of food, mates, and ultimately, prey.
Other natural predators and parasites of the rose aphid - including ladybirds, lacewing and wasps - often do not provide adequate control, especially when pesticides are used. They are extremely sensitive to most of the commonly used pesticides, both synthetic pyrethroid and ‘harder’ chemicals such as carbaryl and maldison.
The only problem that the rose aphid wasp encountered in becoming established at the Royal Botanic Gardens Sydney was the actual presence of hoverflies, lacewings and ladybirds. These predators do not distinguish between parasitised and unparasitised aphids, and eat the wasp larvae along with the aphids. The wasps overcame this obstacle, and have become well established.
Chemical: There are several insecticides registered for control of this pest. Please contact your local nursery for information on them.