Australian painted lady

The Australian painted lady typically uses the native Australian everlastings and other daisies as a host and food plant. However, it also feeds on several introduced species, including capeweed (Arctotheca calendula), Scotch thistle (Onopordum acanthium), and lavender (Lavandula angustifolia).[11] The adults feed on the nectar of flowers.[9]

Eggs have being recorded on Arctotis, Chrysanthemum (family Asteraceae) and Scotch thistle (Cirsium vulgare), but the resulting larvae do not survive past the first instar on these plants. Successful larvae have been observed on capeweed (Cryptostemma) and cudweed (Gnaphalium). The results are limited, usually causing malformations on everlasting daisies Helichrysum bracteatum and Helichrysum bellidioides. If leaves are not sufficient, then they eat flowers. Individuals reared on capeweed produce foul-smelling imagos. Other food plants have been recorded in Australia, but do not appear to be used in New Zealand.[10]

The Australian painted lady's mating system evolved due to a highly dispersed female population. Food and oviposition sites are abundant as females feed on a wide range of host plants; therefore, females do not cluster around hotspots of resources. This tendency makes it impossible for a male to defend the entirety of a female's range. Therefore, the best strategy for males is to defend a territory in which females are likely to travel. Females generally only visit male territories when they are receptive, with the purpose of copulating. However, when an abundant food source attracts a significant number of females, males no longer exhibit territoriality, and are seen searching for mates in areas where females are clustered.[6]

To defend a territory, the male exhibits perching behaviour starting in the mid- to late afternoon until dusk. Some individuals are able to reclaim the same territory several afternoons in a row. The longest period of time recorded in which one male defended the same territory was three days. The males choose sunny spots on hilltops, through which females are likely to travel. If no hilltops are available, the males wait in channels in the vegetation that would funnel wandering females towards them. The perching male sits and waits, scanning the sky for any moving object. Periodically, he executes a patrol flight to get a better picture of the surrounding area. When the male spots a moving flying object, he flies directly towards it. If it is a male, the resident male chases him off his territory. If it is a female, the male chases the female, more slowly and less aggressively than with an intruding male, away from the perch site. The pair lands and copulates, a process which can last more than an hour.[6]

Observations of the Australian painted lady migration date back to the 1960s. In 1963, a large migration took place in a south-easterly direction from late August to late September. It was characterized by the species becoming suddenly common in certain areas where it had previously been sparse. That year was noted to have been unusually wet in Australia. This could be a trait shared with V. cardui, which migrates in Europe during the wet season.[13] The Australian painted lady migrates south in the spring and summer, and north in the autumn and winter.[5]

Migrating butterflies often have smaller and lighter body sizes that allow them to fly longer distances. Additionally, these butterflies tend to have larger wing-to-body ratios. Temperatures and day length have been found to influence development. When larvae were exposed to short days and cool temperatures (20 °C), similar to conditions found in the spring, larval development was accelerated. This produced small adults with low body weights, ideal for migration. A similar phenomenon occurred when the larvae were exposed to longer days at warm temperatures (30 °C), conditions similar to those in the late summer. Seasonal changes could trigger the development of spring and fall body forms that are ideal for the migration patterns described above.[14]

During periods of large migration in Australia, and with the possible help of strong winds, the Australian painted lady migrates across the sea to New Zealand,[5] typically only appearing during October to November.[15] Multiple occurrences of this butterfly in New Zealand were reported in the 1960s. In the spring of 1968, they appeared on the western coast of New Zealand near the sea, and were unusually abundant.[2][16] The species is unlikely to be established in New Zealand, as no instances of larvae or adults hibernating through the winter were found. Although some individuals reproduced and laid eggs, the larvae only developed to the first instar before development stopped.[2] The same phenomenon occurred in the late summer 1969, and coincided with a gale-force westerly wind. This evidence suggests that the butterflies observed in the spring of 1968 and the summer of 1969 were the result of a new migration from Australia, and not the offspring of a generation of previously migrated painted ladies. The migration of butterflies and moths from Australia is not uncommon in summers with strong winds.[17]

Fragmented habitats due to urbanization, as well as disturbances to the environment from humans and introduced species, are harmful to most butterflies. Additionally, threats occur to local vegetation such as recreation, trampling of vegetation, fire regimes, and introduction of plant pathogens, which bring about changes to local plant community. Distribution of butterflies depends heavily on the site characteristics and the density of that species' host plants. Changing plant composition changes the distribution of most butterflies' range, isolating them to pockets where the vegetation is ideal. Because of the variety of host plants used by Australian painted ladies, it has not been significantly affected by these changes.[7] It has been found to use some species of carduine thistles, which are invasive to Australia, as host plants in New South Wales. Australian painted ladies use the plants as hosts during their larval stage, and as food sources. However, they inflict little damage to the plant.[18]