Field observation on the diurnal activities of the Sahelian plague grasshopper Oedaleus senegalensis Krauss (Orthoptera: Acrididae) in northern Nigeria.

Diurnal activities of the adults and nymphs of Oedaleus senegalensis in relation to temperatures of plant shade and sunshine areas on cool and warm days were observed. The activities followed a similar sequence but the time of commencement varied. At dawn and sunset, the movement of the grasshopper was sluggish and the adults and the older nymphs rested on bare ground, while the younger nymphs rested on low vegetation. The insects vacated their positions at sunrise. Thereafter, their activities, such as creeping or crawling, hopping, feeding, flying, courting and copulation, increased with a rise in temperature. The peaks of the activities occurred at about 36 to 370C on warm days and 30 to 320C on cool days. The level of activities reduced at about 380C and the insects fell into a state of heat stupor and immobility at temperatures higher than 40°C. When the temperature fell below 400C the insect resumed activities. The adults and nymphs of the grasshopper were rarely found in the middle of the shades and at heights above one metre. The probable implication of the findings for the control of this. grasshopper is discussed.