SPATIAL SAMPLING OF INSECTS, PLANT-PARTS AND INSECT ATTACKS IN THE SOIL OF POTATO CROPS

A method was devised for spatial sampling within the soil in potato cr ops where the soil insects African black beetle, Heteronychus arator ( Fabricius) (Coleoptera: Scarabaeidae) and whitefringed weevil, Graphog nathus leucoloma (Boheman) (Coleoptera: Curculionidae) are pests. The number and position of potato plant parts, the soil insects, and their attacks on potatoes were defined within the hilled-up soil profile of sections of the planting rows. Neither potato tubers, nor insects nor insect attacks were uniformly distributed. Tubers occurred mainly in the middle of the hill, while the insects contrasted in their distribu tion in the soil. Most of the damaging H. arator adults and larvae occ urred in upper middle areas; the damaging G. leucoloma larvae occurred deeper and were more damaging on the under-side of tubers. The method provides a means of simultaneously sampling soil insect populations i n a crop and obtaining a direct assessment of their damage and the eff ectiveness of control measures.