Prospects for Biological Control of Macadamia Felted Coccid in Hawaii with Metaphycus macadamiae Polaszek & Noyes, a New Encyrtid Wasp Native to New South Wales, Australia

SIMPLE SUMMARY: The macadamia felted coccid (MFC), Acanthococcus (=Eriococcus) ironsidei (Williams) (Hemiptera: Eriococcidae), is an invasive pest that has devastating impacts on the macadamia nut tree, in Hawaii and South Africa. MFC is a scale insect native to Australia where it has been recorded from smooth- and rough-shelled macadamia variants. Feeding causes discoloration and distortion of plant foliage, premature flower and nut drop, branch die back, and substantial reduction in nut production. Heavy infestations cause severe damage and death to large portions of trees. A survey conducted by Hawaii Department of Agriculture in New South Wales (NSW), Australia, found the undescribed endoparasitoid Metaphycus species is an important biotic factor for MFC. The parasitoid was imported to Hawaii for host specificity tests using closely related hemipterans, scale insect species, and other species of importance in Hawaii. Results indicated that this parasitoid is monospecific to MFC. This promising natural enemy was described as the new species, Metaphycus macadamiae Polaszek & Noyes sp. n (Hymenoptera: Encyrtidae). Laboratory parasitism averaged 30.2%, and parasitoids can feed on their hosts. Field parasitism in Australia is 32.7%. Several coccinellid predators and the aphelinid parasitoid, Encarsia lounsburyi, are local natural enemies of MFC in Hawaii, but their impacts alone are insufficient to suppress MFC populations. Introduction of biological control by release of M. macadamiae is expected to result in an effective long-term, sustainable solution for controlling MFC on macadamia nut trees in Hawaii or other infested areas in South Africa. ABSTRACT: Macadamia felted coccid (MFC), Acanthococcus ironsidei (Williams) (Hemiptera: Eriococcidae), was first discovered in 2005 on the Island of Hawaii. Host plants are restricted to Macadamia species, with Macadamia integrifolia Maiden & Betche (Proteaceae) being grown in Hawaii for nut production. Approximately 6839 hectares macadamia nuts are harvested in Hawaii with an estimated farm value of USD 48.8 million (2019–2020 records). Exploration in Australia started in November 2013 for the evaluation of potential parasitoids being host specific for introduction into Hawaii. A dominant solitary endoparasitoid of MFC from New South Wales was discovered and described as Metaphycus macadamiae Polaszek & Noyes sp. n (Hymenoptera: Encyrtidae: Encyrtinae). Biology and host specificity testing were conducted at the Hawaii Department of Agriculture, Insect Containment Facility, on nine hemipteran and three lepidopteran eggs. Results indicated that M. macadamiae is host specific to MFC. There has been no evidence of parasitism or host feeding on any of the non-target insect hosts that were tested. Parasitoid emergence from the control (MFC) averaged 30.2% compared to 0% on non-target hosts. A low rate of parasitoid emergence in the laboratory (average 30.2%) and an increased rate of MFC nymphal mortality was due to adult feeding. Field parasitism reached up to 32.7% emergence in Alstonville, New South Wales, Australia. We report on the parasitoid performance in native Australia, rearing biology, host specificity testing, and the extant natural enemies associated with MFC in Hawaii. A petition to release this parasitoid for the biocontrol of MFC in Hawaii is pending. Once permitted for release, the colony will be shared with South African Mac Nut Association for their biocontrol program of this invasive pest. They will conduct their own testing before approval for release.