Evaluation of Coffee Canopy Damage by Dirphya nigricornis Olivier (Coleoptera: Cerambycidae)

Abstract

Coffee canopy damage studies with the yellow-headed borer, Dirphya nigricornis Olivier were conducted on mature plants. Single borer infestation of the pest in coffee plantations were established. Age-induced destruction of the coffee canopy was evidenced by the withering of branches, stems and nodes and were correlated to larval developmental days 0-260. Larval frass excretion was immense being 16,214.91 and 12,076.90 g for female and male beetles, respectively and represented direct physical damage by the pest to plants. Analysis of accumulated data of physical measurement on coffee yield components in the three categories of canopy partitions relative to height of the stem above the ground showed that damage to plants by the pest adversely affected them. Generalized non-linear equations relating berries, pinheads, flowers and leaves (P = 0.05 to P = 0.001) to heights of canopy partition above ground level are described. The physical model developed approximates the responses of the canopy to infestation by the beetle, and shows that these were either depressed or enhanced depending on whether the yield components measured were in the bottom, mid or top partitions of the canopy. Threshold damage constants for leaves (0.34), berries (0.41), pinheads (1.54) and flowerbuds (1.07) which caused variability were established.