The case of the Monarch butterfly vs. Painted Lady
butterfly (also Viceroy butterfly)
An orange butterfly fluttered by. Was it a Monarch
butterfly (Danaus plexippus)? Or a
Painted Lady butterfly (Vanessa cardui)?
If it’s a Monarch, it is species of Special Concern listed under the Species at
Risk Act and is not a crop pest. Instead, it’s larvae feed solely on milkweed (Asclepias spp.), typically found in
wetland areas. Painted Lady larvae, on the other hand, feed on a wider range of
plants including sunflower, canola, mustard, borage, soybean, Canada thistle,
burdock, knapweed, wormwood and many other plant species. While neither species
overwinter in Canada, Monarchs have regular
migratory routes into Canada from Mexico through the USA;
Painted Ladies are accidental tourists that are on occasion blown up from the
US.
One important distinguishing characteristic is the distinct
black band with white dots that outline the wings of Monarchs. Painted Ladies
do not have this band; instead they have thin white markings along the
scalloped wing edges.
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Monarch butterfly (Danaus plexippus)
cc by sa 3.0 Kenneth Dwain Harrelson |
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Painted Lady butterfly (Vanessa cardui)
cc by 3.0 Jean-Pol Grandmont |
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Viceroy butterflies (Limenitis archippus)
cc by 2.0 Benny Mazur |
Viceroy
butterflies (Limenitis
archippus) are even more difficult to tell from Monarchs. Viceroys are
smaller than Monarchs and sport a black line running through the middle
(side-to-side) of the hindwing. Like the Monarch, Viceroys are not crop pests
as their larvae feed exclusively on trees of the willow family (willow, poplar,
cottonwood).
The case of the innocuous versus the evil twin: When making pest management decisions, be sure that
the suspect is actually a pest. This can be challenge since insects often mimic
each other or look very similar. An insect that looks, moves and acts like a
pest may in fact be a look-alike or doppelganger.
Doppelgangers may be related (e.g. same genus) or may not be related, as in the
case of monarch butterflies (Danaus plexippus) and viceroys (Limenitis
achrippus). Doppelgangers are usually relatively harmless but
sometimes the doppelganger is a pest yet their behaviour, lifecycle or hosts
may be different.
Correctly identifying a pest enables selection of the most accurate scouting or
monitoring protocol. Identification and monitoring enables the application of
economic thresholds. It also enables a producer to select and apply the most
effective control option(s) including method and timing of application.
For the rest of the growing season, the Insect of the Week will feature insect
crop pests and their doppelgangers.
