The biology of the West African bush-cricket, Euthypoda acutipennis Karsch (Orthoptera: Tettigoniidae)

This paper presents the results of the first comprehensive study of the biology of a tropical bush-cricket. The eggs were laid without any external protective structures and lost water readily in unsaturated air; losses of more than 16% of the original fresh weight were usually fatal. Development and hatching took place only if the eggs were in contact with water. The water content increased by about 500% during development. The mean incubation period was 171 and 116 days at constant temperatures of 20oC and 28oC, respectively, but at temperatures fluctuating by±3°C about a mean of 28°C this period was reduced to a mean of 88 days. The eggs failed to develop if exposed to freezing temperatures for more than five days or kept at a constant temperature of 307deg;C or above. The duration of the nymphal period varied from 83 to 131 days at a temperature range of 22-30°C (mean 26° C). There were four or five nymphal instars in the male and five or six in the female. The linear growth of the hind femur conformed to Dyar's law. There was a conspicuous colour change during development, all the first-instar nymphs being leaf green and the adults predominantly brown. In nature the species lives exclusively on the forest floor and is markedly nocturnal in habits, hiding underneath litter during the day. The eggs are dormant during the dry season, hatching at the onset of the rains (March/April at Ibadan). The nymphs reach maturity from July onwards and the adults have mostly died off by the end of the rainy season (October). In the laboratory the species was found to have a temperature preference of 26-32°C, immobilization setting in at 18°C and 42°C, and a humidity preference of 60-80% R.H.; this corresponds with the prevailing conditions in its forest habitat. The nocturnal pattern of activity persisted for several days in continuous darkness, with no marked acceleration. Movement was inhibited for several days by artificial illumination. Reversed illumination reversed the rhythm of activity.