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Monarch caterpillars gone

I planted a swan plant and monarch butterflies quickly came and laid eggs. Soon there were baby caterpillars. But when we went back to look, the caterpillars were all gone, and the plant is infested with tiny orange bugs, which cluster around the stalk. Any idea what they are, and how can I get rid of them in a monarch-butterfly-friendly way?

I think you have two problems here. The first is presence of the tiny orange bugs. These are most likely aphids, which suck the sap from your swan plant, and will cause it to sicken over time. They will not directly harm the monarch butterfly caterpillars, but may compete for food or physically crowd them out.

The absence of caterpillars is most likely caused by predation. Two insects love to eat caterpillars — wasps and praying mantises. Praying mantises may be living on your caterpillars and getting very fat on the spoils. Have a look around the swan plant and nearby plants for any evidence of these green insects. They are usually beneficial in the garden, eating a wide range of pests, so you may be inclined to forgive them. Paper wasps are the likeliest culprits and can wipe out caterpillars on entire swan plants. Look nearby for them and their paper nests on fences and buildings. If you live in West Auckland, the spraying campaign will probably have killed your caterpillars and will continue to do so.

What can you do? Unfortunately you cannot use an insecticide, as the caterpillars, aphids, praying mantises and wasps are all insects. To get rid of the aphids, you could try squashing or removing them by hand. Diluted soapy water may also discourage them, but try to avoid spraying it directly on any caterpillars. With the praying mantises I suggest hunting for them and moving them away from the area. Wasps; I would find their nests and spray with fly spray, wait until evening, then dispose of the nest in a plastic bag. You could try covering the swan plant with fine netting (such as net curtain material), which will physically keep other insects away. Of course you need to let the monarch butterflies land and lay their eggs before you do this, and you will need to remove the netting once the chrysalises are hatching into butterflies. Good luck.

UnitecAdvice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

Reproduced with permission from NZOOM Home and Garden content,
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