Terrestrial arthropod surveys on Pagan Island, Northern Marianas

This report is part of the “Marianas Expedition Wildlife Survey 2010” (MEWS 2010), a U.S. Fish & Wildlife Service (USFWS) project funded by the Department of Defense - U.S. Marines and is tasked to gather natural resource information on fish and wildlife in the Mariana Islands. This information is required by federal regulations to properly determine the potential impacts that will occur due to the shifting of significant military resources from Okinawa to the Territory of Guam and the Commonwealth of the Northern Mariana Islands. As part of this military build-up, Pagan is under consideration as a live fire training area. This report gives the results of a terrestrial arthropod survey conducted by USFWS and NAVPAC personnel on Pagan in the month of July 2010 and gives details on significant findings resulting from material collected on that survey. In addition, a full checklist of terrestrial arthropods known from Pagan Island is given based on the current survey material as well as previous published records. An appendix gives a full bibliography of articles dealing with Pagan arthropods. Staff from the U.S. Fish and Wildlife Service, Pacific Islands Office, and the U.S. Navy conducted collections of terrestrial arthropods from 9-21 July 2010 using a variety of collecting methods including Malaise flight intercept traps, yellow water pan traps, pitfall traps, peanut butter traps for ants, aerial sweep netting, aquatic dip netting, aspirating, and hand collections. Thousands of terrestrial arthropod specimens resulted from these collections, which were sorted by the collectors to order (to class for non-insects) and delivered to the Bishop Museum for identification. A team of entomologists at the Bishop Museum identified a total of 288 different taxa of terrestrial arthropods based on the survey, which included 228 new island records for Pagan (doubling the number of arthropods previously recorded from Pagan) bringing the total number of terrestrial arthropod species known from Pagan to 416. The full list of identified arthropods is given in Appendix II and includes all previously published terrestrial arthropod records for Pagan as well as the new records identified during this study. To put the arthropod fauna into a proper historical context in order to better understand their possible biological status on the island (e.g., endemic, native, nonindigenous), a history of human habitation as well as previous collecting expeditions is given. The vast majority of identified terrestrial arthropods are most likely nonindigenous, having arrived on Pagan via a variety of mechanisms including transport by humans, supply shipments, and commerce. Verification of true status requires study of the known distributions and potential vagility of each species, which was outside the scope of this report. Although the island has undergone numerous geophysical and human land use changes resulting in what we are calling a synanthropic arthropod fauna, there are still pockets of native arthropods that survive. Eight endemic species are recorded, three of them are new to science. In addition, one new genus was found. The littoral zone has been a neglected area for previous collectors, and a number of new marine and littoral faunal records have resulted from collecting during this survey. None of the arthropods identified are any threat to the megapode or fruit bat populations on the island. The crazy ant, Anoplolepis gracilipes, may pose a potential threat to food resources of the bat and megapodes if the populations on the island ever form what are called supercolonies. Their population levels now are large but not dangerous.