Pieris brassicae

Pieris brassicae, the large white, also called cabbage butterfly, cabbage white, cabbage moth (erroneously), or in India the large cabbage white, is a butterfly in the family Pieridae. It is a close relative of the small white, Pieris rapae.

The large white is common throughout Europe, North Africa and Asia.

Distribution

The large white is common throughout Europe, north Africa, and Asia to the Himalayas often in agricultural areas, meadows and parkland. It has managed to establish a population in South Africa and in 1995 it was predicted to spread to Australia and New Zealand.

The large white is a strong flier and the British population has been reinforced in most years by migrations from the continent. Scattered reports of the large white from the north-eastern United States (New York, Rhode Island and Maine) over the past century are of a dubious nature and indicate either accidental transport or intentional release. Such introductions threaten to establish this agricultural pest in North America.

In 2010 the butterfly was found in Nelson, New Zealand where it is known as the great white butterfly. It is classed as an unwanted pest due to the potential effect on crops. For a limited period in October 2013 the Department of Conservation offered a monetary reward for the capture of the butterfly. After two weeks, the public had captured 134 butterflies, netting $10 for each one handed in. As a result of this and other containment measures, such as over 263,000 searches in the upper South Island and the release of predatory wasps, the large white was officially declared to be eradicated from New Zealand as of December 2014.

Eggs

The large white ova are pale yellow, turning darker yellow within twenty-four hours of being oviposited. A few hours prior to hatching, they become black, the shell more transparent, and the larvae visible within.

thumb|Eggs of the large white on the underside of the cauliflower leaf

Larvae

Large white larvae experience four moultings and five instars. The first instar follows the hatching of the egg into large white larvae. The larvae are light yellow with distinctive brown heads and have soft bodies. The larvae appear to be very hairy. Following a moulting, the larvae enter the second instar. They have tubercles covered with black hair. In the third instar, large white larvae display more activity. This instar is when the larvae are observed to eat voraciously, and cause significant amounts of damage to their host plant. At this point, they are observed to be more yellow in colour, studded with black dots. Following the third instar, the larvae go through the fourth instar, with similar appearances as the larvae of the third instar, but with more aggrandized size and feeding behaviour. The large white larvae are observed to be cylindrical, robust, and elongated by the fifth instar, yellow in colour

thumb|Large white caterpillars on [[garden nasturtium leaves]]

thumb|Large white chrysalis, under house eaves

Imagines

For both males and females, the wings are white with black tips on the forewings. The female also has two black spots on each forewing. The underside of each wing is a pale greenish and serves as excellent camouflage when at rest. The black markings are generally darker in the summer brood. The large white butterfly's wingspan reaches 5 to 6.5 cm on average.

Female

The upperside of the female is similar to that of the male, but the irroration of black scales at the bases of the wings is more extended. The black area on apex and termen of forewing is broader, its inner margin less evenly curved. A conspicuous large, black spot also exists in the outer half of interspace 1 near the base of interspace 3. On the hindwing the subcostal black spot before the apex is much larger and more prominent. The underside is similar to that of the male but the apex of the forewing and the whole surface of the hindwing is a light ochraceous yellow, not ochraceous brown. The black discal spots on forewing are much larger. The antennae, head, thorax, and abdomen of the females are the same as for the male.

Reproduction and development

Mating system

These butterflies can be polyandrous, but it is not the predominant mating system. This means that, though some female butterflies can have more than one mate, most of the large white females only have one male mate at a time through a monogamous mating system.

Two generations of butterflies are produced each year. The first brood consists of adults with a spring hatching around April. The second brood is made up of adults that hatch around July. Sometimes, a third brood can be observed farther along in the summer if the weather is warm enough.

Life cycle

Oviposition

These female butterflies oviposit in clusters on the undersides of leaves because the larvae prefer the morphology of leaf undersides over the upper surface of leaves. To oviposit, the female butterflies use the tip of the abdomen and arrange the ova in specific batches. Females tend to use their forelegs to drum on the surfaces of their intended leaves as a test of the plant's suitability for breeding. If they find a suitable surface, female large whites oviposit two to three days following copulation. They oviposit approximately six to seven times in eight days. The females can pair up to mate again approximately five or more days after the previous mating.

Choosing locations for oviposition

Females rely on visual cues, such as the colours of plants, to decide where to lay their eggs. They favour green surfaces in particular to display oviposition behaviour. This colour preference could be due to the fact that the large white's food source also acts as a host plant for oviposition. which are green and ideal plants for the larvae. These plants, used as oviposition sites, typically contain mustard oil glucosides, whose primary function is to help the larvae survive as their essential food source. For instance, previous studies have shown that the large white larvae do not survive if the adult butterflies oviposit on a different host plant such as broad bean (Vicia faba) because this bean does not contain the proper nutrients to aid larval development. However, it has been hard to track entire migratory paths, since these butterflies can migrate more than 800 kilometres; thus, individual butterflies may not migrate the 800 kilometres, but rather that other butterflies start their migrations from where the other butterflies ended.

Territorial behaviour

Males do not display considerable amounts of territorial behaviour. It has been suggested that this could be a reason why there is no observed significant sexual dimorphism between the male and female large white butterflies. Aposematism is not entirely related to Müllerian mimicry; however, large white larvae often benefit from multiple other aposematic larvae from other species, such as the larvae of Papilio machaon.

Relationship to people

Role as pests

The crops most susceptible to P. brassicae damage in areas in Europe are those in the genus Brassica (cabbage, mustard, and their allies), particularly Brussels sprouts, cabbage, cauliflower, kohlrabi, rape, swede, and turnip. The attacks to crops are rather localized and can lead to 100% crop loss in a certain area. In addition, because of its strong inclination to migrate, adults may infest new areas that were previously free from attack. Because many of the host plants of P. brassicae are sold for consumption, damage by these butterflies can cause a great reduction of crop value. Larvae may also bore into the vegetable heads of cabbage and cauliflower and cause damage. High populations of these larvae may also skeletonise their host plants. In present-day areas such as Great Britain, P. brassicae are now less threatening as pests because of natural and chemical control reasons. However, it is still considered a pest in other European countries, in China, India, Nepal, and Russia. In fact, it is estimated to cause over 40% yield loss annually on different crop vegetables in India and Turkey.

Subspecies

thumb|P. b. nepalensis) on China aster (Callistephus chinensis), Laos

Subspecies include the following:

Pieris brassicae azorensis Rebel, 1917
Pieris brassicae brassicae (Linnaeus, 1758)
Pieris brassicae catoleuca Röber, 1896
Pieris brassicae cyniphia (Turati, 1924)
Pieris brassicae cypria Verity, 1908
Pieris brassicae italorum Stauder, 1921
Pieris brassicae nepalensis Gray, 1846
Pieris brassicae ottonis Röber, 1907
Pieris brassicae subtaeniata (Turati, 1929)
Pieris brassicae vazquezi Oberthür, 1914
Pieris brassicae verna Zeller, 1924
Pieris brassicae wollastoni (Butler, 1886) †