Preferential feeding and damage to cultivars of Nigerian cassava by the variegated grasshopper (zonocenus variegatus)

variegatus to cassava planted during the active period of the "dry season population." Additional investigations include the preferential feeding responses of the grasshopper to Nigerian cassava cultivars. Previous reports of preferential feeding have been observational. The gregarious nature of the insect limits random distribution and leads to questionable conclusions in a non- or poorly-replicated planting. The present test was designed to overcome these deficiencies and to determine if the grasshopper exhibits statistically significant preferences for certain cassava cultivars. Test cultivars used were 53101 and 60444 (Improved Nigerian) and Isunikankiyan (Nigerian local). The three cultivars were laid out in eight 3 x 3 Latin squares. Each plot within a square contained fifteen plants in three rows, five plants per row. The experimental plot was bounded on the south, east and west by primary bush and on the north by an access road and an area free of bush. The plots were kept weed-free during the investigation. Grasshopper counts were made for three months on the center plant of each five-plant row. These counts were made during the morning and care was taken to minimize disturbance of the insects. Defoliation of each cultivar was assessed on six dates. Individual plants were considered defoliated when more than 90% of the foliage was consumed. Initially most grasshoppers occurred on cv. 60444, slightly less on Isunikankiyan, and fewest on 53101. Later, following a massive migration into the planting, there was an almost equal distribution on all three cultivars. Counts dropped sharply on a cultivar after defoliation, except for Isunikankiyan whose bark was also acceptable.