The Microlepidoptera Fauna of Santa Cruz Island is Less Depauperate than that of Butterflies and Larger Moths Jerry A. Powell1 and David L. Wagner2 'Department of Entomological Sciences, University of California, Berkeley, CA 94720 2Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT 06269 long-distance dispersal events (Carlquist 1974). Abstract - Surveys of Lepidoptera on Santa However, impoverished species numbers and Cruz Island, California, indicate that the fauna disharmonic biotas also occur on islands of small to minute leaf mining moths from six situated near the mainland (Pielou 1979; families are proportionately better represented MacArthur & Wilson 1967). Some organisms relative to the nearby mainland fauna, than are are obviously under represented in island larger microlepidopterans (Tortricoidea and faunas, for example, large vertebrates that phycitine Pyralidae) or macrolepidopterans require expansive home ranges, particularly (Papilionoidea, Hesperioidea, Arctiidae and predators, are rare or absent; and organisms ennomine Geometridae). Collectively, 71% of that are poor dispersers, such as fresh water the central coast leaf mining species occur on vertebrates, wingless insects and plants having Santa Cruz Island; whereas in the other 5 propagules that are neither able to float for groups surveyed 30-62% of the mainland fauna long periods nor adapted for transport by birds are resident. Species with small adults or with are lacking from distant islands (Thorne 1963; larvae that feed internally occur in higher Williamson 1981). proportion than do large and external feeding A question that has not received much Lepidoptera. In three well-sampled host plant attention in island biogeography is the one we genera (Ceanothus, Quercus and Salix) used by pose here: Is species richness uniformly both leaf miners and butterflies, 87% of the depressed across taxa of similar biological roles, mainland leaf miner species are recorded for such as phytophagous insects within one Santa Cruz Island, whereas only 35% of the Order? On nearby continental islands of butterflies are present. We postulate that this moderate size, such as Santa Cruz Island disharmony in species richness is due to the (SCrl), the representation often seems sporadic smaller areas required to maintain effective and absences require subtle explanation. For populations of leaf mining moths, which example, the butterflies are the best surveyed enhances the survival rates of these minute group of insects on the California Islands; there insects in small patches of host plant. have been only two additions to the SCrl faunal list during the past 15 years and both of these are widespread species which are characteristic of weedy habitats and are believed to have Introduction colonized recently (Powell 1981; Miller 1985). Two of the most consistent and conspicuous There are 34 species recorded on SCrl, features of island biotas are that they have approximately half the number of resident fewer species than comparable mainland areas, species in a region of equivalent area and and those present comprise an unequal elevational range on the adjacent Santa Barbara taxonomic representation of mainland coast (Miller 1985). communities. Such unbalanced or We expected commensurate levels of disharmonious faunas and floras are most depauperateness for other groups of pronounced on distant oceanic islands where Lepidoptera (Powell 1985). However, after our the species are derived almost exclusively from fieldwork in 1984, which added 80 species to Third California Islands Symposium 189 Table 1. Species accumulation during recent surveys of Santa Cruz Island. Taxa arranged from largest mean size of individuals at top, to smallest at bottom of column. Total Species Added % Added Taxa Species 1979* 1984* after 1978 Bombycoidea & Sphingoidea 7 0 0 0 Hesperioidea & Papilionoidea 34 1 0 3 Noctuoidea 116 8 5 11 Geometroidea 69 4 3 10 Pyraloidea & Pterophoroidea 74 0 5 7 Tortricoidea etc.** 80 3 8 14 Gelechioidea 102 1 34 34 Tineoid & primitive leaf miners 73 2 29 40 (includes Marmara, 3 spp.) * 1979: UCB, Feb.; SBMNH, May; LACM, June (5 days, 1 collector each) 1984: UCB, May (5 days, 3 collectors). ** Tortricidae (n = 46), Cossidae (2), Carposinidae (1), Sesioidea (3), Yponomeutoidea (7), Copromorphoidea (1), Tineidae (14), Incurvariidae (6). the inventory (15% of the total), we realized Methods that species representation in small To obtain an adequate census of microlepidoptera seemed to be proportionately Lepidoptera, three general approaches were richer than the island macrolepidoptera fauna. employed: 1) observation and net collection This was because we found no new butterflies during the daytime for butterflies and diurnally and few larger moths, while the roster of active moths, which are occasional members of Gelechioidea and leaf mining taxa increased all superfamilies; 2) nocturnal sampling at dramatically (Table 1). The relative richness of lights (incandescent and ultraviolet species on the island is especially striking for fluorescent), which attract larger moths more leaf mining taxa. Here we compare the fauna of effectively than small microlepidoptera, Figure 1. Distribution of localities in the central coast of mainland California that have been sampled for moths, 1962- SCrl to that of the mainland for selected especially in cooler climates such as prevail 1987. Open symbols = diurnal and/or nocturnal (blacklight) surveys for adults; closed symbols = leaf miner and other larval groups of Lepidoptera, emphasizing butterflies much of the time in maritime areas and 3) by surveys; half-closed symbols = sampling for both adults and larvae, including abandoned leaf mines. and primitive and tineoid leaf miners. searching for larvae and rearing them to adults in the lab. The last usually is the most efficient Survey for the presence of leaf miner genera way to collect leaf miners and other small is enhanced by the characteristic form of the Table 2. Seasonal distribution of Lepidoptera sampling on Santa Cruz Island, 1934-1984. microlepidoptera, because the adults come to mine. Most species are host specific, and on — Jan. 1-15 YU '73 Jul. 1- 15 lights only sporadically, and often the any given plant species the mines are 16-31 — 16-3 1 YU '67, '68, '70, '75 Feb. 1-14 UC '79* Aug. 1- 15 LA'39; YU'68 taxonomic state of species is too poor to allow consistently distinguishable for each moth 15-28 — 16-3 1 LA'39; YU'71, '74 identification of moths that have not been species. Often occurrence of leaf miner species Mar. 1-15 UC '69*; YU '70 Sep. I- 15 — associated with their host plants. can be censused throughout the season by the LA '4 1; YU '70; UC '76 16-30 UC '78 16-31 characteristic 'calling card' left by the larva. By Apr. 1-15 YU '70 Oct. 1- 15 — Lepidoptera that feed in the larval stage 16-30 JG '34; UC '66; YU '70 16-3 1 YU '72 between the upper and lower epidermis of a contrast, most other Lepidoptera are effectively May 1-15 UC'66,76,77*; YU'70 Nov. 1- 15 — single leaf are termed leaf miners. Mining collected only during a particular, often quite YU '70; SB '79; UC '84* 16-30 — 16-31 occurs in a wide diversity of families, at least brief season, when either the larvae or adults Jun. 1-15 UC '66; YU '70 Dec. 1- 15 — 16-30 GG '78; LA '79 16-3 1 — in the early instars, and several families are are active. characterized by having larvae that are For purposes of this analysis, we defined * = visits in which leaf miner survey was emphasized strongly modified morphologically for this central coastal California as the coastal plain, Specimen sources: GG = G.A. Gorelick collection; JG = J. Garth (Hancock Foundation); LA = Los Angeles County Natural History Museum; SB = Santa Barbara Museum of Natural History; UC = Essig Museum, University of mode of life and are unable to survive outside foothills and contiguous valleys, up to 650 m California, Berkeley; YU = Peabody Museum, Yale University. the mine. elevation, from Big Sur (Monterey Co.) south 190 191 to Palos Verdes Point (Los Angeles Co.) In visit in March, by a lepidopterist, with limited To date we have recorded about 550 species Table 3. Representation of primitive and tineoid leaf southern California this zone extends inland to collecting by 2 other biologists (Comstock, of Lepidoptera on Scrl. This total is mining Lepidoptera on Santa Cruz Island (total number of records in parentheses). include the lower parts of the Santa Monica 1939, 1946). These efforts produced records of approximately equivalent to those compiled Mountains and other ranges in Ventura about 90 species of butterflies and moths during 8-year surveys in suburban areas of No. Species on No. % County and the western San Gabriel (Powell, unpubl. data). In 1966 California Walnut Creek (Contra Costa Co.) and at the Central Coast Species on Species Taxa Mainland Insect Survey (University of California) trips to Big Creek Reserve (coastal Monterey Co.), the SCrl on SCrl Mountains (Fig. 1). The limits of this range (330) (224) were in part defined by localities which have SCrI began, and a series of visits by C. L. only other places in California where Remington (Yale University) commenced in comprehensive lists have been compiled Eriocraniidae 6 4 66.7 been sampled for Lepidoptera during the past Nepticulidae 20 (Powell, unpubl. data). Similarity in 15 75.0 25 years. 1967. We estimate that >90% of available Tischeriidae 9 7 77.8 Butterfly data are compiled from Burns records date from the era since 1965. proportions in taxa of larger moths at Walnut Heliozelidae 7 5 71.4 Creek and Big Creek with SCrl, together with Lyonetiidae 12 10 (1964), Emmel & Emmel (1973), MacNeill The seasonal distribution of Lepidoptera 83.3 the modest species accumulation in these Gracillariidae* 44 29 65.9 (1964), Miller (1985), J. Emmel (in litt.), W. sampling on SCrl is summarized in Table 2.