The Effect of Climate on the Migrations and Breeding of Locusta migratorioides in Nigeria

The locust infestation in Nigeria, from December 1929 to April 1931, is studied in relation to the climate and the following preliminary conclusions are made.1. Humidity, precipitation and wind are the relevant climatic elements. Temperature does not seem of importance.2. It is considered that the area of dispersal is limited by the humidity factor. With very few exceptions swarms remain where the mean relative humidity (9 a.m., L.M.T.) is not more than 85 per cent. and not less than 40 per cent., while most swarms are found where the humidity is from 60 per cent. to 80 per cent.3. This humidity belt is similar to the area covered by three main types of vegetation and the swarms move across the belt according to the humidity changes.4. Movement along the belt is largely caused by the prevailing wind.5. Breeding does not commence after the dry season until the humidity rises to 60 per cent. and the degree of wetness, calculated from the monthly rainfall, reaches 2. Breeding does not occur if the humidity is above 80 per cent.6. Through the dry season the adults seem unable to live much more than 22 weeks, and if optimum breeding conditions are not reached within that period death may occur.7. Breeding towards the end of the rainy season follows some 11 to 15 weeks after the locusts become adult, so long as the humidity is not more than 80 per cent., and high humidity may cause a diapause.8. Suitable local conditions during the dry season may allow a third breeding season.These conclusions may be utilised in the following ways :—1. To delimit the total area likely to be infested.2. To forecast when the different zones will be infested by flying swarms.3. To forecast whether and when breeding is likely to occur in each locality.4. To check whether unidentified swarms were of this species of locust.5. To test the possibility of one suspected breeding ground having been infested from another.