Biological control of the cabbage white butterfly, Pieris rapae
How to control the Cabbage White Butterfly in an environmentally friendly way
The cabbage white butterfly, Pieris rapae is called the "Small Cabbage White Butterfly" in English speaking Europe, but the "European Cabbage Butterfly" or "Imported Cabbageworm" in America and Canada. It was introduced in North America from Europe at around 1860.
Caterpillars of the cabbage white live on a variety of crucifers and can be damaging on cabbages.
Caterpillars can be up to 2.5 cm long. They are green with a thin yellow line along the body, and their green head is speckled with tiny black dots.
Appearance of Pieris rapae males
Males of the small cabbage white butterfly, Pieris rapae, (Order: Lepidoptera; Family: Pieridae) have white wings with a small, dark spot at the corner of the fore wings and one round, black spot closer to the centre of each fore wing.
The wing span is about 4 cm.
Appearence of Pieris rapae females
Females of the small cabbage white butterfly have, similar to the males, white wings with a small, dark spot at the corner of the fore wings, but they have two round, black spots closer to the centre of each fore wing, instead of one.
The wing span is about 4.5 cm.
Biology of the small cabbage white
The butterflies that have overwintered as pupae appear in spring. They are active during day time and mate towards mid-day, after which the couple flutters around for up to two hours. Eggs are laid singly on the underside of leaves of mainly wild crucifers. The caterpillars pupate on the host plant, and the next generation butterflies lay eggs on cabbages in June. These caterpillars pupate in sheltered places in August-September and overwinter.
Damage of the small cabbage white butterfly
It is especially the second generation caterpillars that is damaging to cabbages. With heavy infestations they leave sometimes only the main veins of the leaves. Moreover, they bore into hearts of cabbages and deep into curds of cauliflower, unlike the caterpillars of the large cabbage white butterfly (P. Brassicae), which only attacks the open leaves. The plants can therefore be fouled by the accumulation of droppings, which causes decomposition resulting in an unpleasant smell.
Natural enemies of the small cabbage white
Many caterpillars will be eaten by birds, especially tits, and wasps (Order: Hymenoptera; Family: Vespidae). Caterpillars are also attacked by small, parasitic wasps, such as Cotesia (Apanteles) glomeratus (Order: Hymenoptera; Family: Braconidae).
This species deposits eggs in young caterpillars, which grows to maturity with the developing larvae inside. Just before it is ready to pupate, the wasp larvae eat its vital parts and eventually crawl out of the dead caterpillar, and pupate on its skin.
Another parasitic wasp, Pteromalus puparum (Order: Hymenoptera; Family: Pteromalidae) attacks the pupae of the small (and also the large) cabbage white butterfly.
- Fine-mesh netting or horticultural fleece will stop butterflies from reaching the crop and lay eggs. The barrier must be complete and without any holes, however, as the butterfly is capable of finding the tiniest holes! When you do find eggs or caterpillars - usually on the underside of the leaves - pick them off by hand.
- Consider placing nest boxes for tits, as their young need large quantities of caterpillars for their development.
- For biological control one could apply Trichogramma, which are tiny wasps that parasitize eggs. Trichogramma can be purchased from biological control companies.
- Do not destroy any wasp nests: the wasps will capture many of the caterpillars to feed their young with.
- Intercropping cabbages with Nastatium, Tropaeolum majus or Chamomile, Matricaria recutita results in fewer eggs laid on cabbage by the butterflies, according to this article.
Links to a few sites of interest
- Effects of mixed cropping of herbs
Journal of Agriculture Science, Tokyo University of Agriculture (Dec 2008) Effects of mixed cropping of herbs on the population and parasitism of cabbage pests Adachi, T.(Tokyo Univ. of Agriculture (Japan). Faculty of International Agricultu
- Imported Cabbageworm
Common name: imported cabbageworm scientific name: Pieris rapae (Linnaeus) (Insecta: Lepidoptera: Pieridae) Distribution - Life Cycle and Description - Damage - Host Plants - Natural Enemies - Management - Selected References
- Pieris rapae | Art Shapiro's Butterfly Site
Art Shapiro's Butterfly Site Monitoring butterfly populations across Central California for more than 35 years.
- Butterflies and Moths of North America | collecting and sharing data about Lepidoptera
Butterflies and Moths of North America collecting and sharing data about Lepidoptera