Collection of Anastrepha fraterculus on Santa Cruz Island, Galapagos Province, Ecuador

Abstract

Fruit flies of the genus Anastrepha, family Tephritidae, are major pests in the Western Hemisphere, predominantly in the tropics and subtropics (Stone 1942). Previously, they had been reported from the Galapagos Islands from only a single specimen of Anastrepha fraterculus (Wiedmann) collected in a spider web (Foote 1982). Of six species in six genera of tephritids known from the Islands, A. fraterculus is considered to be the only introduced species, the remaining five being endemic (Foote 1982). The paucity of previously known specimens of this genus from the Islands is undoubtedly a result of inadequate sampling, as the data from the present study suggest. Ample opportunity for colonization by many species of Anastrepha exits, as many known host plants (Norrbom 1985), mostly introduced (Wiggins & Porter 1971, Lawesson 1987), occur on the Islands. Psidium guajava Linnaeus, for example, the common guava or guayaba, which is a known host for 18 species of Anastrepha (Norrbom 1985), has spread over extensive areas of San Cristobal, Isabela, Floreana, and Santa Cruz Islands (Lawesson 1987) following its introduction earlier in the century. In April, 1987, two of us (JE and GC) established McPhail traps (McPhail 1937) on the island of Santa Cruz to sample for the presence of Anastrepha. Eighteen traps were placed in a small (<1 ha) grove of guayaba trees located on a farm approximately 800 meters west of Bella Vista at an elevation of ca. 500 m. Traps were each baited with two yeast hydrolysate tablets dissolved in water and were hung at heights of 1.8-2.5 m above ground in trees which were 3.0-3.5 m tall. They were placed only on branches which bore fruit. All traps were emptied weekly, rebaited, and rehung, with collections made on April 17 and 24 and May 1 and 8. Weather during the sampling period was wet, with rain occurring daily. All insects collected were emptied into a sieve, washed, and placed in jars containing 70% ethanol. In the laboratory, they were transferred to Whirl-Pak bags containing 70% ethanol, labeled, and sent to the United States for sorting and identification. All Anastrepha specimens were removed, placed in separate alcohol vials, and identified to species. Each of the 18 traps caught Anastrepha, but no trap caught them on every sampling date. A total of 245 specimens was collected during the 72 trap weeks included in the study (one trap week = one trap operated for one week). Catches ranged from 0 to 34 Anastrepha per trap in a given week and to 38 per trap over the entire four weeks. Mean catches/trap/week were 3.4 +-5.3, while mean catches per trap over the four-week period were 13.6 ?+10.8. Total combined trap catches/week were 11, 72, 115, and 47 for trap weeks 1-4, respectively.