Mite (Acari) Communities Associated with 'Ohi'a, Metrosideros polymorpha (Myrtaceae), at Hono O Na Pali and Kui'a Natural Area Reserves on Kaua'i Island, Hawaiian Islands

Abstract

Native 'Ōhi'a trees (Metrosideros polymorpha) were sampled for mites at two natural area reserves on Kaua'i Island, Kui'a and Hono O Nā Pali. Ninety samples of leaves, flowers, bark, leaf litter, and soil under the 'Ōhi'a canopies were taken. Mites were extracted with use of Berlese-Tullgren funnels. One hundred sixty-four species were found, with the suborder Prostigmata having the greatest number of species (74), followed by Mesostigmata (43), Oribatida (43), and Astigmata with the least (4). Leaf litter, leaf litter with soil, and bark have the most species, composed of predaceous mesostigmatic and prostigmatic mites, but a certain amount of overlap of mite species between the leaf litter and soil habitats was observed. The predominance of Collembola in the soil and litter samples indicates a stable food source for the predaceous mites, partly explaining the high number of mites in those habitats. Oribatid mites were collected from leaves, but the species composition differs from that on flowers and litter. Preliminary residency status of identified taxa shows 12% endemic, 17% adventive, and 71% of unknown status.

Mites or Acari are one of the largest and most biologically diverse groups of the arachnids, rivaling insects in the extent to which they have successfully colonized aquatic and terrestrial habitats (Evans 1992). Mites are an important part of the Hawaiian ecosystems. Although approximately 630 species have already been named and reported (Nishida 1997, Swift and Norton 1998), mites remain one of the most poorly known arthropod groups in the Islands. Studies of Acari associated with particular plants, soils, and litter habitats are relatively uncommon in the Hawaiian Islands. Although sampling of litter from an area or location to determine its mite fauna has been done, there has been little systematic collecting from specific plant hosts or habitats. In the early 1970s, the International Biological Program (IBP), through the Bishop Museum, sampled mites in soil and litter in an elevational transect of 'Ōhi'a forest east of Mauna Loa Trail on Hawai'i Island. From these collections, work by Radovsky and Tenorio (1981) on the soil Mesostigmata (Parasitiformes) and Collembola gave an indication of the diversity of soil and litter fauna living under the canopies of the nativè 'Ōhi'a. Gagné (1979) sampled arthropods including mites from 'Ōhi'a and Koa canopies with pyrethrum fogging. Unfortunately, the mites recovered from the canopy-sampling technique on 'Ōhi'a and Koa and most mites collected from the Maunaloa Trail transect currently remain unstudied.

'Ōhi'a, Metrosideros polymorpha (Gaud.) (Myrtaceae), is a dominant native Hawaiian tree found from sea level on wetter slopes up to 2590 m elevation. It is distributed on the six largest islands in areas with annual average rainfall ranging from 75 cm to 11.5 m (Corn and Heisy 1973). 'Ōhi'a was the subject of intensive research for over 20 yr because of periodic breakdown of stands known as " 'Ōhi'a rainforest dieback" (Mueller-Dombois 1985). Although the effects of arthropods (e.g., wood borers) were studied extensively, the possibility of mites as a causal organism for 'Ōhi'a dieback was never considered. This study seeks to identify mite species associated with Ōhi'a and to expand the general knowledge of arthropods associated with this native tree. It is well known that sustainable management of any forest requires reliable knowledge of arthropod species and their ecological roles in the forest ecosystem.

Because of the current incomplete state of acarine systematics in many parts of the world, there has been a reluctance to designate residency for mite species described from Hawai'i (Goff 1987, Swift and Norton 1998). The preliminary designations for species associated with 'Ōhi'a in this report are for the primary purpose of assessments of the conservation status of the natural area reserves. For the purposes of this report, endemic refers to taxa found only in the Hawaiian Islands; adventive refers to those taxa that are immigrant species but not intentionally introduced; and introduced refers to...