common name: bella moth, rattlebox moth, inornate moth or calico moth
scientific name: Utetheisa ornatrix (Linnaeus) (Insecta: Lepidoptera: Arctiidae: Arctiinae)
Introduction - Synonymy - Distribution - Description - Life Cycle and Biology - Hosts - Selected References
The bella moth, Utetheisa ornatrix (Linnaeus), is one of our most beautiful moths. Unlike most moths, which are nocturnal, the bella moth is diurnal and flies readily when disturbed. Therefore, it is more commonly seen than nocturnal species by the general public.
Figure 1. Adult and larva of the bella moth, Utetheisa ornatrix (Linnaeus). Photograph by Lary Reeves, University of Florida.
The adult bella moth is highly variable in coloration which has resulted in confusion regarding its taxonomy and the assignment of many names to the numerous color "forms". Linnaeus originally described two species in the genus Phalaena -- ornatrix (more whitish or pale specimens) and bella (brightly colored specimens), and Hübner later moved them to the genus Utetheisa. Forbes lumped both forms under the species U. ornatrix. The Entomological Society of America's Common Names of Insects and Related Organisms publication uses the common name "bella moth," but uses the scientific name Utetheisa bella (Linnaeus) instead of U. ornatrix (Linnaeus).
This species is found from Connecticut westward to southeastern Nebraska, and southward to southern New Mexico and Florida. It is more common in southern part of its range.
Eggs: The eggs are white to yellow and spherical.
Figure 2. Eggs of the bella moth, Utetheisa ornatrix (Linnaeus). Photograph by Don Hall, University of Florida.
Larvae: The larvae are orange-brown with broad irregular black bands on each segment. Full-grown larvae are 30-35 mm in length. There are distinct white spots on the anterior and posterior margins of the black bands. Whereas most arctiid larvae have verrucae (elevated wart-like areas on the cuticle) bearing many setae, Utetheisa larvae lack verrucae, and setae occur singly.
Figure 3. Larva of the bella moth, Utetheisa ornatrix (Linnaeus). Photograph by Don Hall, University of Florida.
Pupae: The pupae are black with irregular orange-brown bands and are covered with a loose layer of silk.
Figure 4. Pupa of the bella moth, Utetheisa ornatrix (Linnaeus). Photograph by Don Hall, University of Florida.
Adults: The adult bella moth is a rather small moth (wingspan 3.0 - 4.5 cm). The more common "bella" form commonly has the front wings yellow with white bands each containing a row of black dots, and the hindwings bright pink with an irregular marginal black band. The paler form originally designated "ornatrix" is restricted to southern Florida and southern Texas.
Figure 5. Adult bella moth, Utetheisa ornatrix (Linnaeus), on fruit of lanceleaf rattlebox, Crotalaria lanceolata E. Mey. Photograph by Don Hall, University of Florida.
Figure 6. Adult bella moth, Utetheisa ornatrix (Linnaeus). with wings spread. Photograph by Don Hall, University of Florida.
The bella moth has two generations northward but may breed continuously in the southernmost parts of its range. Eggs are laid in clusters on the foliage. Upon hatching, the young larvae feed on the foliage, but later move to the pods which they bore into to feed on the seeds. Upon reaching maturity, larvae migrate from the host plant to pupate in sheltered situations under loose bark on nearby trees, in thick vegetation, or in debris.
Much of what we know about the biology of the bella moth is due to the fascinating work of Thomas Eisner and his colleagues and graduate students. This work is summarized in his recent book, For Love of Insects. The biology of the bella moth is intricately intertwined with its Crotalaria host plants. Crotalaria (particularly the seeds) are laced with pyrrolizidine alkaloids. Bella moth larvae sequester these chemicals and become poisonous (and usually repellent) to predators. The alkaloids are retained in the pupal and ultimately the adult stages. Thus these stages also are poisonous to predators. The alkaloids appear to have little effect on pathogenic fungi or parasitic Hymenoptera.
Figure 7. Lanceleaf rattlebox, Crotalaria lanceolata E. Mey, in fruit. This plant is a host of the bella moth, Utetheisa ornatrix (Linnaeus). Photograph by Don Hall, University of Florida.
Figure 8. A flower spike of lanceleaf rattlebox, Crotalaria lanceolata E. Mey, with carpenter ants feeding at extrafloral nectaries. This plant is a host of the bella moth, Utetheisa ornatrix (Linnaeus). Photograph by Don Hall, University of Florida.
Adults are concentrated in patches of Crotalaria. Males become active approximately 1-1½ hours after sunset and are attracted to females by a pulsed sex attractant pheromone (primarily Z,Z,Z-3,6,9-heneicosatriene) originating from glands at the tip of the female's abdomen.
Males convert some of their Crotalaria alkaloids to a related compound hydroxydanaidal (HD), and upon approaching a female, expose two eversible brushes (coremata) from the tip of the abdomen that contain HD saturated scales. Fanning the female with the coremata stimulates her to raise her wings exposing her abdomen. The male then lands beside her and copulates. In addition to sperm, males also transfer nutrients and Crotalaria alkaloids to the female during mating via the spermatophore. The concentration of HD in the coremata is correlated with the amount of alkaloid carried by the males, and females appear to measure the HD concentration of males and use that information for selecting males with the potential to donate the most pyrrolizidine alkaloids in the spermatophore.
During oviposition, the female contributes not only her own alkaloids, but also those received from the male to her eggs making the eggs toxic to potential predators. Crotalaria lanceolata and C. pallida both have extrafloral nectaries that are often visited in the Gainesville, Florida area by aggressive Florida carpenter ants, Camponotus floridanus (Buckley), and red imported fire ants, Solenopsis invicta Buren. There is experimental evidence that the cavity-nesting ant, Leptothorax longispinosus is repelled by eggs containing the Crotalaria pyrrolizidine alkaloids. It is not known whether the bella moth eggs are protected from carpenter ants and fire ants by the alkaloids.
Adult bella moths live approximately three weeks and females mate on average four to five times -- each time receiving additional nutrients and alkaloids via the spermatophores. The additional nutrients and alkaloids allow the female to lay a larger number of eggs than would otherwise be possible and also to continue to invest sufficient amounts of alkaloids in the eggs.
Because most of our common Crotalarias are introduced weedy species and toxic to cattle, the bella moth plays a beneficial role by eating their seeds and suppressing their reproduction.
Although a variety of plants in the family Fabaceae are listed in the literature as hosts for the bella moth, species in the genus Crotalaria are without a doubt the major if not the only true hosts. It is likely that the other host records are due to the habit of full-grown larvae to wander from the host (and frequently onto other species) prior to pupation.
Only four species of Crotalaria are native to the southeastern U.S. of which two occur in Florida -- Avon Park rattlebox (C. avonensis DeLaney & Wunderlin), which is restricted to Florida, and rabbitbells (C. rotundifolia J.F. Gmel.). Many other species of Crotalaria were introduced into the southeastern U.S. 55-65 years ago for soil improvement and forage. Unfortunately, species of Crotalaria are toxic to livestock due to the presence of pyrrolizidine alkaloids, and can potentially be fatal. Three species have become established and are common in Florida. These are Crotalaria lanceolata E. Mey. and Crotalaria pallida Aiton var. obovata (G. Don) Pohill (formerly Crotalaria mucronata Desv.) which are both native to Africa and Crotalaria spectabilis Roth which is native to Asia. The name Crotalaria originates from the Greek root "crotal" which means "a rattle". It is the same root word as used in the genus name for rattle snakes, Crotalus. The mature dried fruit of Crotalaria rattles like a rattle snake when the pods are shaken or blown by the wind.
Figure 9. Smooth rattlebox, Crotalaria pallida Aiton var. obovata (G. Don) Pohill (formerly Crotalaria mucronata Desv.), with flowers and fruit. This plant is a host of the bella moth, Utetheisa ornatrix (Linnaeus). Photograph by Don Hall, University of Florida.
Figure 10. Showy rattlebox, Crotalaria spectabilis Roth., a host of the bella moth, Utetheisa ornatrix (Linnaeus). Photograph by Don Hall, University of Florida.
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