The Behaviour of Nymphs of Schistocerca Gregaria (Forskål) (Orthoptera, Acrididae) in a Temperature Gradient, With Special Reference To Temperature Preference

[Observations were made on the behaviour of second instar nymphs of Schistocerca gregaria in a temperature gradient. Hopping was seen at low and high temperatures, but not within the range 32-43° C. At higher temperatures active ventilatory movements and marked avoidance reactions were observed. The preferred temperature range in which the hoppers became quiescent was about 34-45° C with a peak at 40-41° C. Following prolonged starvation the response disappeared. It was impossible to separate starvation from desiccation with certainty, but the former seemed to be more important with respect to its effects on temperature preference. There was an apparent increase in preference in later instar nymphs, but this may not have been a real change and did not materially affect the range. The same is true of a possible slight fall in the peak preference in the latter part of each instar. Preference did not vary following preconditioning at different temperatures and humidities, but the peak preference was affected by the activity of the nymphs and their point of entry into the gradient. It is suggested that the reaction results from a reduced output from the central nervous system in the preferred temperature range. This arises as a result of the direct effect of temperature on the nervous system modulated by the sensory input from widely distributed peripheral thermal receptors. Experiments showed that the antennae and tarsi were not particularly important as sites for thermal receptors and the overall response was to air temperature rather than surface temperature. The preferred range of temperature is wide, but constant and it also appears to be much the same, with a peak at about 40° C, in all but one of the grasshoppers so far studied. It is suggested that temperature preference is a behavioural mechanism tending to keep the insect within a range of temperatures which is optimal for most basic metabolic processes., Observations were made on the behaviour of second instar nymphs of Schistocerca gregaria in a temperature gradient. Hopping was seen at low and high temperatures, but not within the range 32-43° C. At higher temperatures active ventilatory movements and marked avoidance reactions were observed. The preferred temperature range in which the hoppers became quiescent was about 34-45° C with a peak at 40-41° C. Following prolonged starvation the response disappeared. It was impossible to separate starvation from desiccation with certainty, but the former seemed to be more important with respect to its effects on temperature preference. There was an apparent increase in preference in later instar nymphs, but this may not have been a real change and did not materially affect the range. The same is true of a possible slight fall in the peak preference in the latter part of each instar. Preference did not vary following preconditioning at different temperatures and humidities, but the peak preference was affected by the activity of the nymphs and their point of entry into the gradient. It is suggested that the reaction results from a reduced output from the central nervous system in the preferred temperature range. This arises as a result of the direct effect of temperature on the nervous system modulated by the sensory input from widely distributed peripheral thermal receptors. Experiments showed that the antennae and tarsi were not particularly important as sites for thermal receptors and the overall response was to air temperature rather than surface temperature. The preferred range of temperature is wide, but constant and it also appears to be much the same, with a peak at about 40° C, in all but one of the grasshoppers so far studied. It is suggested that temperature preference is a behavioural mechanism tending to keep the insect within a range of temperatures which is optimal for most basic metabolic processes.]