Macadamia felted coccid impact on macadamia nut yield in the absence of a specialized natural enemy, and economic injury levels

Macadamia nut is among the most important edible crops produced in Hawaii. Macadamia also accounts a significant amount of agricultural land in the state at about 6920 ha of active production. Currently, macadamia has one major insect pest that requires considerably more severe management than others; the macadamia felted coccid, Acanthococcus (previously Eriococcus) ironsidei. Horticultural oils and insect growth regulator insecticides are frequently used to control this pest, without any knowledge of economic injury level currently. This study quantified yield loss and impact on nut quality related to A. ironsidei in Hawaii, on two varieties in two different environments, one mesic, and the other dry. Based on these data, EIL estimates were developed for A. ironsidei on macadamia. There was significant variation in yield loss to A. ironsidei in the two varieties and locations. Some varieties of macadamia nut had severe yield losses under dry-habitat conditions, while others tolerated higher A. ironsidei infestations better, with a lower rate of yield loss. Kernel quality was largely not impacted by A. ironsidei infestation, and reduction in yield was the only impact detected. There were correspondingly variable EILs estimates from the different varieties and environments. The implications of high yield loss in a crop in the absence of a natural enemy of the primary pest are discussed. Results of this study will help to contribute to developing an effective integrated pest management program for A. ironsidei management in Hawaii. •Macadamia nut yield was measured over a gradient of infestation levels of macadamia felted coccid.•Substantial yield reductions occurred, and where most substantial in drier areas.•Economic injury levels are estimated for selected macadamia varieties.•A relatively easily implemented monitoring process is described.