A Simple Penetrometer for Measuring Leaf Toughness in Insect Feeding Studies

The effects of leaf toughness on the feeding activities phytophagous insects have been discussed by many workers, but only a few have undertaken quantitative measurements of this parameter. Rao and Venkatraman (1941), Rao (1947) and Khanna et al. (1947), all studying top-borer infestations in sugar-cane, measured a variety anatomical features such as degree of lignification, and thickness of cell walls in stem sections, and attempted correlate such toughness indices with the incidence of pest attack. Williams (1954) working on the Acrididae, followed by Tanton (1962) on the mustard beetle, Phaedon cochleariae F., attempted direct measurements of toughness using a simple penetrometer. In this device, an entomological pin with a light card reservoir mounted on top of it was forced through a piece of taut leaf by adding dry sand to the reservoir. The weight of sand required cause penetration of the leaf was then used as an index of toughness.