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Lepidoptera Inventories in the Continental United States


by
Jerry A. Powell
Essig Museum of Entomology
University of California,
Berkeley
Lepidoptera (butterflies and moths) make up about 13% of the described and named 90,000 insect species of North America (11,500 named) and are among the better known large orders, although no complete inventory of Lepidoptera species exists for any state, county, or locality in North America.
The rationale for local or regional inventory of insects is related to their importance in biodiversity. Insects make up 75% of all described animals, and in natural communities their species outnumber those of all other higher organisms combined. Thus interrelationships between insects and other organisms form the most prevalent and comprehensive elements of the fabric of biological communities.
Lepidoptera are the major group of plant-feeding insects, and local inventories of Lepidoptera can help indicate the stability and diversity of plant communities. When we have several reasonably complete local inventories of Lepidoptera in different regions of the country, we will be able to make predictions about overall insect--and therefore biological--diversity, and about relationships between plant and insect species richness on a local or regional basis. Such knowledge will lead to more efficient methods of assessing the health and loss of biological diversity.
Once a baseline inventory is done, monitoring of changes in species richness and abundance to assess the ecological health of the community can be carried out. Inventory of a diverse group of insects such as the Lepidoptera must involve various approaches and collecting procedures. This article summarizes the status of local and state inventories of Lepidoptera and suggests a model for planning comparable faunal inventories of major insect groups.

Lepidoptera Surveys
To gather information on the status of current inventories, I mailed a one-page questionnaire to 25 lepidopterists thought to be developing local or state lists. Nearly all responded, and several are conducting more than one census. Early in 1993 I published a request for information on inventories in the News of The Lepidopterists' Society, which is distributed to about 1,000 members in North America. The responses were fewer than I had expected; there may be many more inventories in progress than those reported to me. For completed local and state lists, I searched the literature, but the results are likely to be incomplete because such lists are lengthy and often are published in obscure literature not well referenced by abstracting services.
A thorough local inventory must depend upon diverse methods: daytime searches for butterflies and diurnal moths, nighttime collections of moths attracted to ultraviolet (UV) or mercury vapor lights, and rearing caterpillars (larvae) to the adult stage. In some regions a fourth approach, "sugaring," the attraction of moths to sweet, fermenting bait, is effective for many species not readily attracted to lights. Generating an inventory for a large group of insects such as Lepidoptera is difficult because the season that each species can be found may be short; species abundance varies widely from year to year; several techniques and specialists' experience are needed to complete a thorough census; and, beginning early in the survey, individuals of vagrant species are encountered.
A major problem in compiling an inventory is the identification of species. This is easily accomplished for butterflies (6% of the Lepidoptera), and there are hundreds of local and state lists (Field et al. 1974). Identifications are accessible for the larger moths (macrolepidoptera), including inchworm moths (Geometridae), giant silkworm moths (Saturniidae), hawk moths (Sphingidae), owlet moths (Noctuidae), and related families. However, for many so-called "microlepidoptera" (primitive suborders, leaf miner and leaf roller moths, etc.), 10%-90% of the local species in some families are undescribed. As a result, most state and local lists have dealt only with macrolepidoptera or have treated the microlepidoptera species only cursorily.

Inventories and Trends
There are published Lepidoptera lists or surveys in progress from at least 30 states, and local inventories of at least macrolepidoptera for 35 or more reserves, counties, or islands in the continental United States. The tendency of lepidopterists to compile state and local lists, which had been expressed primarily by faunal studies of butterflies (Field et al. 1974), increasingly has encompassed moths. Half of the state lists and 85% of the local inventories have been published since 1964, and there are an even larger number in progress. More of these include microlepidoptera than before probably because of considerable progress in the descriptive taxonomy of most families during the past 35 years (e.g., Covell 1984).
State Lists
The older and more comprehensive state lists are in the eastern United States (Fig.1). The most complete state lists of Lepidoptera are those for New York (Forbes 1923-60), New Jersey (Smith 1910; Muller 1965-76), and Maine (Brower 1974-86), although these lists have many identification problems. The most active are in Ohio, Kentucky, Mississippi, Florida (Kimball 1965), and Texas. There are lists primarily or only of macrolepidoptera for some states, including Arizona (Bailowitz et al. 1990), Michigan (Moore 1955), Pennsylvania (Tietz 1952), and Maryland (D.C. Ferguson et al., National Museum of Natural History, unpublished data). Lists of described species for the western states are now being done (Fig. 1).

Fig. 1. Distribution of state and local inventories of Lepidoptera in the contiguous 48 United States. States having comprehensive lists (all families) published or in progress, those with macrolepidoptera lists, and those with preliminary lists in progress are indicated. Dots indicate locations of 35 local inventories of single sites, reserves, and islands, either published or in progress.
Local Inventories
Thirty-five local inventories have been published or are in progress (Fig. 1). These vary greatly in moth families included, geographic size, and number of years in progress. Several inventories, including those of Martha's Vineyard and Nantucket, Massachusetts (Jones and Kimball 1943); Mount Desert Island, Maine (Proctor 1946); Welder Wildlife Refuge, Texas (Blanchard et al. 1985); Ash Canyon, Arizona (N. McFarland, Sierra Vista, AZ, unpublished data); and three in California (McFarland 1965; Powell, unpublished data) span 10-50 years and are estimated to be 85%-95% complete (Table). Table. Comparison of size, duration, estimated percentage completed, and numbers of species recorded in local inventories of Lepidoptera, listed by state.

State* Area (km2 ) Duration (years) % est. censused No. of species recorded
Arizona macro < 10 13 > 95 900 +
California macro < 10 10 > 95 278
California micro < 10 25 80-85 160
California micro 16 12 85-90 376
Florida macro < 10 2 80-90 318
Illinois micro 200 50 90-95 945
Maine macro < 10 4 < 70 349
New Jersey macro < 10 5 90 410
New York macro 100 30 + > 95 872
Oregon macro < 10 1.5 70-80 360
Texas macro 30 24 + 50-70 ? 481
West Virginia macro < 10 6 90 400
*Macro -- macrolepidoptera
 Micro -- microlepidoptera

Unfortunately, no two inventories can be meaningfully compared because they vary in important parameters. Many have recorded only macrolepidoptera, often only one sampling approach was emphasized, inventories are made of sites that vary greatly in size, inventory duration ranges considerably (Table), and the methods of recording data are often inconsistent.
A Model Inventory
Fig. 2. Species discovery curve for all Lepidoptera at the Big Creek Reserve, Monterey County, California, based on collections during 1980-93. The total (910 species) is believed to be more than 90% of the resident fauna. Points along the curve are indicated when 50%, 67%, 75%, and 90% of the recorded total were reached.
We have been conducting inventories in California to document species discovery rates and other comparative data. The most comprehensive inventory is at the University of California Big Creek Reserve in coastal Monterey County, an area of diverse habitats and elevations. The census has been carried out primarily by specialists' visits. We have sampled in all months, on 175 dates, recording every species in each sample; we spent 180 personnel-days for diurnal species, recorded more than 260 UV light samples, and processed 1,350 larval collections and their rearing. The census (more than 900 species) is believed more than 90% complete, with 3% or fewer of the species in each three-date sample new to the list during dates 155-175 (Fig. 2). Butterflies and diurnal moths make up 16% of the total, and microlepidoptera recorded only as larvae make up another 9%.
The species discovery rate was slow because we could not sample the whole reserve during each visit, and most of the effort followed a consummate fire in the fourth year of our 12-year inventory; many species were first collected in year 9 or 10. Nevertheless, the results provide a realistic idea of the effort required in a complex community to achieve a reliable species accumulation curve (Fig. 2).
The data from Big Creek and other inventories (e.g., Butler and Kondo 1991) demonstrate that short-term effort is inadequate to inventory insects. We cannot determine faunal composition from a few visits to a site or even comprehensive sampling over one season. If a group under study is relatively uniform in biology, one sampling or trapping technique may be adequate and a steeper species accumulation curve can be attained. At Big Creek, all Lepidoptera accumulation did not reach 50% until 25 dates, or 75% until 65 dates (Fig. 2).
Planning Inventories
A comprehensive inventory should employ diverse sampling approaches, as outlined previously. Light trapping alone may be expected to recover about 75% of the species after extended effort. If monitoring changes in populations is a goal, a subset of the fauna (e.g., one or a few well-known families) should be the focus, with sampling standardized by method (e.g., light trap), site, frequency, and so forth, so as to be repeatable. To make local inventories comparable, data should be identified in several ways: (1) results should be recorded by standardized subsets of the area; (2) sampling effort should be quantified and reported (e.g., number of person-hours or days, dates, UV samples); (3) first records for each species should be recorded to document species discovery rates; (4) voucher specimens should be preserved, especially for small moths, because detailed study by a specialist may be necessary to distinguish species. Ideally, every specimen can be bar-coded to the data base, a rapid process if carried out in tandem with data entry initially as is being done in Costa Rica (Janzen 1992).
We do not know how many species of moths and butterflies live in any state, county, or locality in North America. We need baseline inventories that are standardized by area or sampling effort by which different parts of the continent or tropical faunas can be compared to extrapolate patterns in regional, national, or world biodiversity of Lepidoptera.
For further information:
Jerry A. Powell
Essig Museum of Entomology
University of California, Berkeley
201 Wellman Hall
Berkeley, CA 94720
References
Bailowitz, R.A. et al. 1990. A checklist of the Lepidoptera of Arizona. Utahensis 10:13-32.

Blanchard, A. et al. 1985. Checklist of Lepidoptera of the Rob and Bessie Welder Wildlife Refuge near Sinton, Texas. The Southwestern Entomologist 10:195-214.

Brower, A.E. 1974-86. A list of the Lepidoptera of Maine. Parts 1, 2. Maine Agricultural Experiment Station, Tech. Bull. 66:1-136; 109:1-60; 114:1-70.

Butler, L., and V. Kondo 1991. Macrolepidopterous moths collected by blacklight trap at Cooper's Rock State Forest, West Virginia: a baseline study. Agriculture and Forestry Experiment Station, West Virginia University, Bull. 705:1-25.

Covell, C.V. 1984. A guide to the moths of eastern North America. Houghton-Mifflin Co., Boston, MA. 496 pp.

Field, W.D., C.F. dos Passos, and J.H. Masters. 1974. A bibliography of the catalogs, lists, faunal and other papers on the butterflies of North America north of Mexico arranged by state and province (Lepidoptera: Rhopalocera). Smithsonian Contributions to Zoology 157:1-104.

Forbes, W.T.M. 1923-60. Lepidoptera of New York and neighboring states, I-IV. Cornell University Agricultural Experiment Station Memoirs 68:1-729; 274:1-263; 329:1-433; 371:1-188.

Janzen, D.H. 1992. Information on the bar code system that INBio uses in Costa Rica. Insect Coll. News 7:24.

 Jones, F.M., and C.P. Kimball. 1943. The Lepidoptera of Nantucket and Martha's Vineyard. Publ. Nantucket Maria Mitchell Assoc. 4:1-217.

Kimball, C.P. 1965. The Lepidoptera of Florida. Division of Plant Industry, Florida Department of Agriculture, Gainesville. 363 pp.

McFarland, N. 1965. The moths (Macroheterocera) of a chaparral plant association in the Santa Monica Mountains of southern California. Journal of Res. on Lepidoptera 4:43-74.

Moore, S. 1955. An annotated list of the moths of Michigan, exclusive of Tineoidea (Lepidoptera). Museum of Zoology, University of Michigan, Ann Arbor, Miscellaneous Publ. 88:1-87.

Muller, J. 1965-76. Supplemental list of Macrolepidoptera of New Jersey. Journal of the New York Entomological Society 73:63-77; 76:303-306; 81:66-71; 84:197-201.

Proctor, W. 1946. Biological survey of the Mount Desert region. Part VII. The insect fauna. Wistar Institute of Anatomy and Biology, Philadelphia, PA. 566 pp.

Smith, J.B. 1910. Report of the New Jersey State Museum for 1909. Trenton, NJ. 887 pp.

Tietz, H.M. 1952. Lepidoptera of Pennsylvania. A manual. Pennsylvania State College, Agricultural Experiment Station, State College, PA. 194 pp.


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