Distortion, a severe stunting and deformation of plants of guineacorn (Sorghum vulgare) in Northern Nigeria, has been shown to be caused by Heterococcus nigeriensis Williams feeding on the plants.

The symptoms are striking; affected stems are much shorter and wider than normal and leaves are mis-shapen, with irregularly divergent veins and white tissue between the veins. Symptoms in the field vary from small patches of distortion on other normal plants to whole plants affected. The abnormal leaves of a plant with severe distortion are crumpled and remain rolled together. Growth of the plants virtually ceases if the mealybug infestation continues but, in the absence of mealybugs, affected plants recover and produce normal leaves.

Distortion has been found in the field, commonly on Sorghum vulgare, Zea mays and Cynodon dactylon, and once only on Pennisetum typhoides and Chloris pycnothrix, respectively, and has been produced experimentally on Z. mays, C. dactylon, P. typhoides, Triticum aestivum, Oryza sativa and Digitaria exilis by transferring mealybugs from affected guineacorn.