We databased all of our ladybird beetles (Coleoptera: Coccinellidae) as part of our recent and ongoing digitization effort, and it’s been fun for me (a hymenopterist, who knows very little about beetle taxonomy!) to poke through our collection as part of this North Carolina Insect of the Week series. Awhile ago I ran into what seemed like an obvious misidentification (Beeria nematocera; and it was misidentified). I thought I found another one this week, at least at quick glance. This week’s species, Stethorus punctillum Weise, 1891, was described (and, until about 60 years ago, known only) from Europe. Yet our collection holds specimens from Mecklenburg county. Alas, a quick search of the Web reveals that this small beetle is reared en masse, as part of the market for natural enemies of spider mites. Now it’s surprising to me that we have so few in our collection!

The species was described (probably) from Germany in 1891 by Weise, though information about type specimens and their repositories appears to be wanting. The species was actually described three times a century earlier: once as Coccinella minima by Rossi in 1794, a name already occupied by Coccinella minima Muller, 1776; then again as Coccinella pusilla by Herbst in 1797, a name already occupied by Coccinella pusilla Muller, 1776; and then yet again as Coccinella atra by Illiger in 1798, a name occupied by Coccinella atra Gmelin, 1790. Weise himself described a species in 1885, Scymnus minimus, that is now considered a synonym of Stethorus punctillum (perhaps that earlier name was itself preoccupied?) Finally, Korschefsky described a species, Stethorus ater, that is now considered a junior synonym of Stethorus punctillum.

Gordon (1985) provides a detailed and technical diagnosis, which reads, in part:
Length 1.35 to 1.57 mm, width 0.90 to 1.12 mm. Form elongate, oval. Color black, antenna, mouthparts, and leg brownish yellow except basal 3/4 of femur brown. Dorsal pubescence short, semierect, yellowish white. Punctation on head and pronotum fine, pronotal punctures separated by about a diameter; elytral punctures coarse, separated by less then a diameter; abdominal sterna with coarse, dense punctures separated by less than a diameter.

As larvae and as adults these small ladybird beetles, like most other known species of Stethorus, are predators of mites, including many species of economic importance.

This species is indeed native to Europe but was introduced in the 1950s. Sources seem to disagree on whether the introductions were intentional or not. Gordan (1985) states that it was unintentional and that the species was first reported in Massachusetts, USA and Ontario, Canada in 1950. McMurtry (1978) claims they were introduced intentionally from Turkey to southern California in 1955 to control brown mites in avocado and citrus. Perhaps both stories are true! It now has a broad distribution in eastern North America, as far south as North Carolina, north to Ontario, and west to about Nebraska (Gordon, 1985). A far western US/Canada distribution is exhibited by a subspecies: Stethorus punctillum picipes

• Stethorus punctillum species page at GBIF.
• Stethorus punctillum species page at BugGuide.
• Gordon, R. D. 1985. The Coccinellidae (Coleoptera) of America North of Mexico. Journal of the New York Entomological Society 93(1): i-iii, 1-912.
• Gordon, RD and EA Chapin. 1983. A revision of the New World species of Stethorus Weise (Coleoptera: Coccinellidae). Transactions of the American Entomological Society 109 (3): 229-276.
• Weise, J. 1891. in Reitter, E., L. Heyden, and J. Weise. 1891. Catalogus Coleopterorum Europae, Caucasi et Armeniae Rossicae. Modling, 420 pp.
• McMurtry JA (1978) Tetranychidae, pp. 3-8, In: Clausen CP (Ed), Introduced parasites and predators of arthropod pests and weeds: a world review. Agriculture Handbook No. 480. Agricultural Research Service, USDA, Washington, DC