Abstract
Penetrometry studies were conducted on sorghum and mango, in order to assess plant organ hardness as a potential factor of crop resistance to insect pests. Particularly, the hardness of developing kernels and growing stems of sorghum, and that of ripening mango fruits, were evaluated. Respectively two sorghum cultivars differing by their resistance level to the paniclefeeding bug (=head-bug) Eurystylus oldi, two sorghum cultivars differing by their resistance level to the stem borer Sesamia cretica, and two mango cultivars differing by their resistance level to fruit flies (Diptera: Tephritidae), notably Bactrocera zonata, were evaluated. Between 10-17 days after complete anthesis, developing kernels of head-bug resistant Cirad 441 were significantly harder than those of head-bug susceptible ICSV 197. Two weeks after tillering, growing stems of stem borer susceptible Safraari were marginally significantly harder than those of stem borer resistant Majeeri. At the ripe stage, the skin of fruit fly less susceptible Tommy Atkins fruits was significantly harder than that of fruit fly susceptible Cogshall fruits. The relevance of plant organ hardness as a factor of crop resistance to pests, and of its assessment via penetrometry studies, thus depend on whether damage is inflicted via oviposition or feeding, and in the latter case whether it is via piercing-sucking or grinding mouthparts