Canopy management of macadamia trees and understory plant diversification to reduce macadamia felted coccid (Eriococcus ironsidei) populations

The macadamia felted coccid, Eriococcus ironsidei Williams, is an invasive pest in Hawaii that causes severe damage and yield losses in macadamia nuts. Developing integrated pest management options including effective conservation biological control is essential. Combining techniques of canopy thinning with the provision of nectar and pollen plant sources for beneficial insects in the understory may result in improved E. ironsidei suppression. The role of canopy modification and understory habitat in enhancing natural enemy effectiveness to reduce E. ironsidei populations was investigated. Plots with pruned trees plus wild plants had up to 48% less E. ironsidei than the control plots, and the pruned-only plots had up to 32% less E. ironsidei compared to the control plots. A greater abundance of natural enemies was found in the treated plots than in the control plots. Predatory beetles were up to 62% more abundant in the pruned trees plus wild plants than in the control plots, and in the pruned-only plots there were up to 54% more predatory beetles than in the control plots. Encarsia lounsburyi (Berlese and Paoli), a wasp that parasitizes E. ironsidei was up to 73% more abundant in the pruned plus wild-plant plots, and up to 50% more abundant in the pruned-only plots than in the control plots. Pruning macadamia trees potentially enhanced natural enemy populations within the orchards increasing predation from 36% to 60% and parasitism from 1.3% up to 4.3% compared to control plots. Yields of macadamia trees were not affected by the pruning during the period of the study, and current results suggest a potential increase in yields over time after pruning. This study provides evidence that pruned macadamia trees and understory plant species diversification support natural enemy populations and may provide enhancement of biological control of E. ironsidei in macadamia nut orchards.