Fourth- and fifth-instar hoppers and adults of Locusta migratoria migratorioides (R. & F.) were expected to three fluctuating remperature regimes in Weyco climatic cabinets and weighed daily. The regimes were 30 ± 0.25, 30 ± 10 and 30 ± 15°C., the change from one extreme to the other in the last two being made every two hours. Temperatures were accurately determined, by plantinum-resistance thermometers whose dimensions approximated to those of adult locusts, and were automatically recorded. The three thermorhythms were analysed by methods based on Fourier’s theorem, whereby a given wave form can be described in terms of a basic sine weve and a series of superimposed harmonics.

The rates of growth (weight increase) in the 4th-instar and adult at 30 ± 10°C/ were higher than at 30 ± 0.25°C. and were within 10 per cent. of the means of the rates at constant temperatures of 20 and 40°C., whereas the frowth rate in the 5th instar, and the pre-copulation and pre-oviposition periods of adults and their rate of weight loss when starved, were the same under both regime. At 30 ± 15°C., 5th-instar hoppers did not survive and, in comparison with the other regimes, the growth rates of 4th-instar hoppers and adults were very much lower, the pre-copulation period of adults was the same but the pre-oviposition period was much longer and their rate of weight loss when starved was doubled. Adults locusts were also tested at 30 ± 17.5°C., but most of them died within 24 hours and all within three days.