The Use Of Biogeographical Techniques In The Study Of Migrant Noctuid Moths

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The use of biogeographical techniques for monitoring, mapping and predicting seasonal changes in the distribution of migrant noctuid moths in a country or region, can lead to timely and effective control of infestations of the larvae of international pest species like the African armyworm, Spodoptera exempta (Wlk.); the American bollworm, Heliothis armigera (Hub.); the Black cutworm, Agrotis ipsilon (Hufn); the cotton leafworm, Spodoptera lilloralis (Boisd.) etc., and hence to the protection of crops and pasturelands. Methods of data collection include the establishment of national and regional networks of monitoring devices such as light and pheromone traps, and the introduction of regular or periodic standard procedures for recording, reporting and assessing infestations of larvae. Techniques for collecting and analysing the data include the use of: (a) dots, circles or similar marks on topographic or weather maps to plot the occurrence of moths and/or larvae at the latitudes and longitudes of outbreak sites, followed by the dates when infestations were confirmed; (b) numerical symbols (e.g. 1-12 for January to December) on the above maps in order to summarize periodic (e.g. monthly) shifts in the distribution of populations within or across neighbouring countries; (c) colour codes or other graphic symbols to plot maps of pest distribution and migration over the required time-scale, followed by the study of appropriate synoptic weather charts, particularly streamline wind charts showing surface and low-level wind convergence zones over the distribution areas. Successful application of these techniques have included studies of changes in the distribution and migration of: (a) A. ipsilon worldwide; (b) Desert locust in Africa and Asia; (c) S. exempta in Africa and S.W. Arabia etc. In the 1981/82 outbreak season, for example, dots (e) were used to map out and date south-to-north displacement of populations of S. exempta across eastern Africa from Tanzania to Ethiopia between November 1981 and June 1982; while in 1980/81, numbers (1-12 for January-December) were plotted to summarize outbreaks developing between Ethiopia and Tanzania. Successful monitoring and assessment of mass movement of moths between Tanzania, Kenya and Uganda early in the 1981/82 season, for example, enabled the Armyworm Forecast Service to issue accurate forecasts for the first cross-border migrations of moths between the three countries from the second week of February 1982, leading to effective control of larvae to save cereal crops, sugar-cane and pasture grasses in East Africa.
East African Agricultural And Forestry Journal, 8 (4/5/6), p. 551-559