The biology and ecology of two species of army-caterpillar, Persectania aversa Walker and Pseudaletia separata Walker., in New Zealand

Abstract

Two species of army-caterpillar are present in New Zealand - a native species, Persectania aversa Walker and an introduced cosmopolitan species Pseudaletia separata Walker. The general biology of P. aversa and P. separata moths, larvae, eggs and pupae were studied in the field and in the laboratory. This included the life history, flight records of the adults, aspects of the reproductive behaviour, feeding responses in the larvae, a field survey and parasite study and a study of the effect of larval density on the biology. The feeding response of both species was assayed using certain naturally occurring carbohydrates and plant extracts of cereal and pasture crops. The response to the plant extracts listed in order of preference were: P. aversa: rice, maize, barley, Bromus, wheat, oats, Grassland Paroa, Grassland Ariki, Grassland Apanui, Grassland Tama, Grassland Kahu, Grassland Huia, Control. P. separata: maize, Bromus, Grassland Paroa, rice, Grassland Huia, barley, wheat, oats, Grassland Ariki, Grassland Apanui, Grassland Tama, Control, Grassland Kahu. The colouration of larvae found in crowded cultures differed significantly from that of the isolated cultures. The isolated cultures of both P. aversa and P. separata showed a small range of colour variation and were typically light. The crowded culture exhibited a wide range of variation from light to dark colour forms, depending on the population density of the culture. The potential mean colour of a crowded culture was influenced by the population density in the early instars, long before such effects became visible, particularly in P. aversa. No intensification of these colour characteristics could be produced by rearing larvae continuously for three successive generations in a crowded or isolated condition. The density related darkening of larvae found in the laboratory was also found in the field. Crowding increased the larval activity, food consumption, food tolerance, rate of larval development, and decreased the larval head-capsule width, pupal weight, larval duration, adult wing area and wing loading. P. aversa larvae also decreased in the number of instars. Significant correlations were found between larval colour and head-capsule width, larval colour and larval duration, pupal weight and head-capsule width, pupal weight and larval duration, adult wing area and emergence weight. P. aversa larvae were parasitized by Apanteles sp, Macrocentrus rubromaculatus and Pales nyctemeriana. P. separata larvae were parasitized by Apanteles ruficrus, Macrocentrus rubromaculatus, Euplectrus sp., Pales nyctemeriana, Ecthromorpha intricatoria and a gordioid worm.