Population growth of Monellia caryella, Monelliopsis pecanis, and Melanocallis caryaefoliae and factors affecting seasonal abundance of Monellia caryella at College Station, Texas

Abstract

Field studies were conducted at College Station, Texas in 1982 and 1983 to examine population dynamics of 3 species of pecan aphids. The results indicate that pecan, Carya illinoensis (Wangenheim) K. Koch supports higher densities of Monelliopsis pecanis Bissell for a longer period compared to Monellia caryella (Fitch) and Melanocallis caryaefoliae (Davis). M. caryaefoliae caused the highest defoliation rate and was followed by M. pecanis and M. caryella. Despite the low defoliation rate, M. caryella populations were not sustained on foliage exposed to severe infestations of this aphid. Due to the high defoliation rate, M. caryaefoliae populations diminished in a short period after reaching peak densities. Increase rate of population of M. caryella and carrying capacity of pecan for this aphid were observed to decrease as the pecan growing season progressed. Field surveys and exclusion studies indicated that natural enemies, especially spiders and lacewings, exerted a substantial impact on M. caryella populations. Fluctuations of M. caryella populations appeared to result from combined actions of plant host physiology, natural enemies, prior occurrence of aphids, and weather conditions.