Lepidoptera

Before NZ was colonised by Europeans it was isolated from the rest of the world millions of years and evolved without the presence of mammalian predators. The long isolation and lack of terrestrial predators allowed for unique characteristics, including flightlessness, to evolve in many species. Also without the presence of many of the species evolved defence mechanisms that are only effective against their natural predators which are mostly birds. The introduction of mammals into this country has been devastating to numerous species of native/endemic flora and fauna including many invertebrates.

Due to the lack of defence mechanisms against many naturalised predators NZ has a high number of threatened and at risk species. Also many animal and plant species have to deal with competition from introduced generalist species that thrive in our environment. This is a huge problem because many of New Zealand’s invertebrate species are specialised to survive on one or a few species of plant so a decline in plant species means a decline in invertebrate species.

One of the largest orders of insects in New Zealand, after Coleoptera and Diptera, is Lepidoptera; the moths and butterflies. It is estimated that there are around 1800 species present in New Zealand with 1600 of them being endemic that’s a whole 89% of NZ Lepidopterans that are only found in New Zealand! Of the 1800 Lepidoptera species only 26 of them are butterflies (17 endemic/native) while the rest of them are moths.

The idea that the loss of plant species is affecting the loss of invertebrate species was put forward as one of the most likely explanations for why more Lepidoptera species are becoming endangered in a 2012 paper: The Conservation status of New Zealand Lepidoptera. In the paper they established that of the species they investigated in 2007, 49 taxa are threatened, 69 taxa are in danger of becoming endangered and 56 were data deficient meaning they could find enough information on the species to establish populations’ numbers. No known taxa have yet become extinct but this could easily change in the future.

As stated before it is likely that the increase in threatened/ at risk species is due to the decrease in plant species they live on. Much of NZ’s once abundant forest has been destroyed and fragmented and many species lost. It was established in the investigation that many of the Lepidopteran species lived in restricted habitats which restricts their poulation numbers. Also many species have become quite specialised including 11% of threatened/ at risk taxa which only feed on a single species of plant and another 20% that only feed on a single genus of plant.

The restrictions on the Lepidopteran species’ habitat and diet aren’t the only factors contributing to the high number of threatened/ at risk species but they are two of the most obvious. Other possible contributing factors are competition and susceptibility to parasitism/ predation which links back to the fact that many NZ species don’t have the right defense mechanisms to protect them against introduced predators and parasites and since many species are specialists, they are easily out-competed by generalist species.