Plant
Doctor Archive
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.
 Advice
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,
from the previous
website of 
The views expressed here are not necessarily those of the RNZIH
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