The ecology and biology of nemobius Bivittatus in Tasmania

The ecology and biology of Nemobius bivittatus Walker was studied both in the laboratory and in the field. This species exhibits a univoltine and a semivoltine life-cycle, the semivoltine cycle lasting 19 to 20 months. N. bivittatus shows considerable adaptation to varying climatic conditions. Females lay pigmented, diapausing eggs in summer and autumn; and unpigmented non-diapausing eggs in the spring. Day-length and temperature influence the types of eggs layed. High temperatures intensify diapause during summer and autumn, and low temperatures weaken or terminate diapause during winter. In the laboratory, high initial temperatures intensify egg diapause and low initial temperatures weaken or terminate diapause. Absorption of water occurs before diapause commences. Diapausing and non-diapausing eggs both hatch in the field during summer and autumn, but hatching nymphs show great variation in their development with periods ranging from 8 weeks to 1.5 years. In the laboratory, nymphs develop over a period of 8 to 35 weeks. The eggs, nymphs and adults all show cold-hardiness during winter, with increased levels of glycerol allowing supercooling. The adults survive for 2 to 3 months. The food comprises mainly plants, with some animal material. There is a seasonal variation in the composition of food eaten. The consumption, digestion and utilisation of food by 6th, 7th and 8th instars and adults were also determined These factors vary with the different stages of development. Gross efficiency of food utilization is higher in the nymphs, but the net efficiency is higher in the adult. Calorific values of food plants were determined in different seasons. Food plants measured were grasses, forbes, rushes and mosses. Calorific values were also determined for eggs, nymphs and adults. Oxygen consumption of 7th and 8th instar nymphs and adults was determined at different temperatures. Oxygen consumption of 7th and 8th instars and adults was also determined in the field from the density biomass of these categories in the population. In addition, secondary production of 7th and 8th instar nymphs and adults was determined. Energy budgets at the individual and population levels were calculated from the equation: I = R+P+E Where I represents incoming energy; R the respiratory loss of energy; P energy stored as secondary production; and E energy egested as faeces. Sexual and aggressive behaviour and hierarchical relationships were also studied as was analysis of various kinds of song. The orientation and location of sound signals by females were also completed in this study of behaviour. Circadian locomotory rythms were determined the major activity occurring during daytime. This cricket also exhibits rythms in feeding, mating and oviposition. A redescription of the species is also given, including a study of chromosome numbers and genitalia.