M. Deyrup and T. Eisner.
A mordellid-meloid mimicry.
Psyche 94:215-218, 1987.

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PSYCHE
Vol. 94 1987 NO. 3-4
A MORDELLID-MELOID MIMICRY
The Mordellidae are small wedge-shaped beetles commonly found in one of the most dangerous of all insect habitats, the open inflorescences of plants. Their chief protection against the many predators that frequent flowers is a series of convulsive leaps fol- lowed by rapid flight, as acknowledged in their common name, the "tumbling flower beetles" (Crowson, 1981). Their escape from a predator's grasp is facilitated by their wedge shape and covering of smooth, backward-pointing hairs, while their movement and pur- chase among stamens and floral hairs may be assisted by rows of tibia1 and tarsal setae strongly reminiscent of the combs of fleas. These escape mechanisms, while undoubtedly effective against many predators (including entomologists), have the disadvantage that they involve abandonment of the feeding site. At our study area in southern Florida (Archbold Biological Sta- tion, Highlands Co.) one species of mordellid appears to belong to a mimetic complex, a strategy by which the beetles might forestall attack. The mordellid, Mordellistena comata LeConte, is a relatively uncommon insect that is found during late summer on flowers of yellow Asteraceae, especially Heterotheca subaxillaris (Lamarck) Britton and Rusby, and Balduinia angustifolia (Pursh) Robinson. The reddish pronoturn and black elytra of this beetle (Fig. 1, bottom) confer a strong resemblance to several species of ne- mognathine meloids, especially Gnathium francilloni Kirby (Fig. 1, lArchbold Biological Station, P.O. Box 2057, Lake Placid, Florida 33852. 'Section of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853.
*Manuscript received by the editor July 6, 1987.



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Fig. 1. The meloid Gnathium francilloni (above) and its mimic, the mordellid Mordellistena comata, on flowers of Heterotheca subaxillaris. Photographs taken at same magnification. Body length of Gnathium = 4.5 mm. ,




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19871 Deyrup & Eisner- Mimicry 2 17
top). At one location in a dense stand of H. subaxillaris covering an area of about 50 X 50 m, we counted 250 specimens of G. francilloni and 6 of M. comata. The meloids often occurred in groups of 2 or 3 (31 pairs were in copula), while the mordellids occurred singly. Visually, as small specks of reddish-brown and black on the brilliant yellow floral discs, the two species are difficult to distinguish. The differences apparent at very close range were not obvious to us at a distance. We had long been familiar with Gnathium at our field site before we noticed the Mordellistena among them. Nemognathines can be expected to be protected chemically by cantharidin, the well-known terpenoid toxin present in meloid blood (Carrel and Eisner, 1974). Meloid beetles typically reflex- bleed when disturbed, a behavior that we could readily induce in G. francilloni, as in other species of Gnathium, by gentle pinching of the body and legs. M. comata, we believe, may avoid harassment through mimicry of these protected models. Whether it is itself fully palatable and therefore (in a chemical sense) a Batesian mimic, remains unanswered. The literature offers no clue to the presence of chemical defensive agents in mordellids. Tests that we did with another species of mordellid, Mordella atrata (Melsheimer), proved this beetle to be edible: six individuals (freshly killed or rendered moribund by freezing) that we offered at our field site in a small dish to tame wild scrub jays (Aphelocoma c. coerulescens) were taken in quick succession by one bird, together with pieces of peanut offered as accompanying morsels. The same bird ate another 29 of 32 M. atrata that were similarly offered several days later, and a second bird ate two individuals of this lot, leaving only one of the beetles uneaten.
Examination of G. francilloni and M. comata by ultraviolet video-viewing (Eisner et al. 1969) showed no differences in ultravi- olet reflectance characteristics. Both beetles are ultraviolet absor- bent over their entire body surface. To the insect eye, therefore, the beetles should also appear similar in coloration. M. comata and G. francilloni have more or less overlapping geo- graphic ranges, according to the fragmentary data available (Black- welder and Arnett, 1975). There are additional species of meloids, such as Nemognatha nemorensis Hentz, and one additional mordel- lid, Mordellistena marginalis Say, that occur on flowers and seem to belong to the red-pronoturn, black-elytra mimetic complex. At the Archbold Biological Station this general complex includes about 90 species, belonging to various insect orders; most of these species



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