I. infensa inhabits tussock grasslands and native forest.

This species was described by Francis Walker in 1857 using a female specimen from Percy Earl and presumably collected at Waikouaiti.

[3] The female holotype specimen is held at the Natural History Museum, London.

[4] In 2019 Robert Hoare undertook a major review of New Zealand Noctuidae.

[2] A. V. Chappell described the egg of the species as follows: Earth-grey; later becoming ringed with brown near the top; finely sculptured.

Hind wings somewhat aeneous, cinereous towards the base; ciliae whitish.

[2] I. infensa inhabits different habitats including tussock grasslands and native forests.

[2] Chappell, when rearing this species, stated that he obtained eggs in December and pupation happened in September.