Utetheisa ornatrix, also called the ornate bella moth, ornate moth, bella moth or rattlebox moth, is a moth of the subfamily Arctiinae. It is aposematically colored ranging from pink, red, orange and yellow to white coloration with black markings arranged in varying patterns on its wings. It has a wingspan of 33–46 mm. Moths reside in temperate midwestern and eastern North America as well as throughout Mexico and other parts of Central America. Unlike most moths, the bella moth is diurnal. Formerly, the bella moth or beautiful utetheisa of temperate eastern North America was separated as Utetheisa bella. Now it is united with the bella moth in Utetheisa ornatrix.
The larvae usually feed on Crotalaria species, which contain poisonous alkaloid compounds that render them unpalatable to most predators. Larvae may prey on other bella moth larvae in order to compensate for any alkaloid deficiency.
The bella moth also demonstrates complex mating strategies and is thus an excellent model to study sexual selection. Females mate multiply and receive spermatophores containing sperm, nutrients and alkaloid compounds from numerous males as nuptial gifts. Females choose males according to the intensity of a courtship pheromone, hydroxydanaidal, and carry out a sperm selection process after copulation with various males.
Distribution Utetheisa ornatrix is found from southeastern United States to South America (southeast Brazil). In the southeastern United States, its distribution ranges from Connecticut westward to southeastern Nebraska and southward to southern New Mexico and Florida."Utetheisa Ornatrix." Entomology and Nemotology. University of Florida, n.d. Web. 14 Nov. 2013. This species is found to be more common in more tropical parts of this range, in accordance to the availability of its host plant in more southern regions. It is also found throughout Mexico, South America, and Central America.
Taxonomy In 1758, Carl Linnaeus first characterized two species of the genus Phalaena. Phalaena ornatrix was used to describe the paler moth specimens, and Utetheisa bella, described the bright pink moth specimens. In 1819, Hübner moved these species to a new genus, Utetheisa. For nearly a century, it was difficult to determine this moth's evolutionary history as researchers focused on external similarities (color, shape, patterns, size), rather than determining features specific to the species. This led to great confusion when trying to categorize the different subspecies. In 1960, Forbes combined both species, Utetheisa ornatrix and Utetheisa bella, into the species now known as Utetheisa ornatrix. His conclusion was also supported by Pease Jr. who, in 1966, used genetic testing and determined that any phenotypic differences were based on interspecific variation due to geographic differences (rather than intraspecific variation).
Subspecies Utetheisa ornatrix ornatrix Utetheisa ornatrix bella (Linnaeus, 1758) Utetheisa ornatrix saintcroixensis Pease, 1973
Description
Eggs The eggs of the Utetheisa ornatrix are spherical in shape and range in colour from white to yellow to sometimes brown.
Larvae The larvae are orange and brown with irregular black bands on each segment of the body. The anterior and posterior portions of the black binds are also marked with distinct white spots. Full grown larvae reach 30-35mm in length. Although most arctiid larvae have verrucae, Utetheisa ornatrix larvae lack these.
Pupae The pupae are mostly black marked with irregular orange and brown bands. Usually, the pupae are covered with a loose layer of silk.
Adult These moths are aposematic and use their bright coloration to warn predators of their unpalatability. Their wings range in color from yellow, red, pink, and orange to white. Wings contain white bands containing six bands of irregularly spaced black spots. The hind wings can be bright pink with a marginal black band. The adult Utetheisa ornatrix has a wingspan of .
Predation
During the larval stages, caterpillars feed on leguminous plants of the genus Crotalaria. These plants contain large amounts of toxins, particularly pyrrolizidine alkaloids (PAs), which are found in high concentrations in the seeds. Bella moth caterpillars sequester these toxins and use them as a deterrent for predators. When the adult is disturbed, they secrete a foam containing the toxins from their head, which makes them unpalatable to predators. Since PAs are an extremely valuable resource, individual larvae compete with one another to colonize an entire pod, an elongated seed-containing pouch from the food plant. Larvae that are unable to take ownership of a pod must obtain the chemicals from leaves, where they are found at much lower densities. These caterpillars sequester smaller amounts of PAs and are more susceptible to predation.
Although it is beneficial to feed on seeds, larvae do not enter the pods immediately after they hatch. During the first larval instars, caterpillars feed on leaves and it is not until the second or third instar that they enter the pods. The evolutionary benefits of this strategy are not understood. When caterpillars metamorphose into adult moths, they carry the alkaloids with them, which continue to protect them during the adult stage.
PAs render the bella moth unpalatable to many of its natural enemies like spiders and insectivorous bats. Spiders that capture bella moth larvae or adults release them soon after, leaving them unharmed. In contrast, bella moth individuals grown on a PA-free diet are readily preyed on by spiders. Similarly, bats that catch bella moth individuals quickly release these unpalatable moths without harming them. Unlike other moths of the Arctiidae, the bella moth does not possess an acoustic aposematism system that would enable it to avoid bats altogether. Bella moth larvae and some predators like loggerhead shrikes are not negatively affected by PAs.
The bella moth is able to detoxify PAs due to the possession of the gene pyrrolizidine-alkaloid-N-oxygenase. It has been experimentally shown that bella moth larvae upregulate the expression of this gene when the amount of PAs in their diet increases. In addition, it has been shown that PA rich diets do not have a negative effect on the fitness of these moths, but only affect time of development, which increases with increasing PA concentration in diet. However, caterpillars with longer development times reach similar pupal sizes compared to those with shorter developmental times due to diets containing smaller amounts of PAs.
Cannibalism On occasion, bella moth caterpillars cannibalize other eggs, pupae or larvae from the same species. Since PAs are a limited resource, some caterpillars do not reach optimal levels and resort to cannibalism. This behavior is a consequence of PA deficiency rather than hunger, since deficits in alkaloids are the main cause of mortality. Pupae cannibalism is rare because larvae normally pupate far away from the plant where they feed. Egg cannibalism is also rare because eggs provide larvae with very small quantities of PAs and because eggs from the same cluster hatch synchronously. Larvae may also feed on other bella moth larvae that are laden with alkaloids. This is more common since feeding on one single larva is sufficient to compensate for the cannibalistic caterpillar's alkaloid deficiency.
Kin recognition Bella moth caterpillars may have the ability to recognize other larvae as kin, as larvae are less likely to intrude upon siblings than non-siblings established in seedpods.
Mating Bella moths of both sexes use very complex reproductive strategies, making this species an excellent model system for studying sexual selection. Females mate multiple times over their three- to four-week lifespan as adults. They mate with an average of three to five males, each of whom provides her with a nuptial gift, a spermatophore containing sperm, nutrients, and alkaloids. Adult males invest up to 11% of their body mass to create a spermatophore they provide to a female during mating. The nutrients given in the spermatophore allow the female to produce, on average, an additional 32 eggs.
Mating system The bella moth presents a polyandrous mating system, where females mate with multiple males. On average, females mate with three to five males over their lifespan of three to four weeks but can mate with and receive up to thirteen spermatophores. Since spermatophores contain nuptial gifts of pyrrolizidine alkaloid (PA) and nutrients, multiple mating helps the female increase the fitness of her offspring. In addition, multiple mating also benefits the female directly. Since the spermatophores are sizeable and can be digested within the female, multiple mating allows females to accrue the resources necessary to build additional eggs. This is equivalent to a 15% increase in egg production. In addition, multiple mating results in increased transmission of alkaloidal gifts to eggs. This provides protection to the eggs against predation. However, this does not mean that there is segregated allocation of these gifts. Instead, the PA obtained from numerous males is allocated in admixture so that eggs tend to receive from more than one male source. In contrast, normally most of the sperm used to fertilize the eggs comes from a single male.
Courtship Courtship begins at dusk. Stationary females release a sexual pheromone that lures males. They emit these chemicals in short pulses to provide close-range orientation cues to male moths as they seek out the females. When a male reaches a female, he flutters around her and thrusts two peculiar tufts of scales from his coremata, two yellow spherical structures by the male's genital organs. By doing so, the male emits a specific scent from his coremata that is attributed to a pheromone, hydroxydanaidal. After receiving the scent, the female proceeds to mating.
Copulation lasts for up to 12 hours. It takes the male about two hours to transfer the spermatophore containing all of the sperm and nutrients he is going to offer to the female. The remaining hours of copulation are exclusively used for alkaloid transfer. These alkaloids distribute themselves evenly around the female body, even the wings, and offer her great protection as they render her unpalatable to most predators. Eventually, the female allocates about one third of the alkaloids she receives to her ovaries, where they will be used to confer protection to the eggs.
Female pheromonal chorusing Bella moth mating behavior is exceptional in that females compete with other females to obtain more males, as opposed to males competing with males. As in many other moth species, females release sexual pheromones that males can detect over long distances. However, in most species, females do not interact with one another during pheromone release. Female bella moths are unique in that females from the same family often engage in collective pheromone release termed “female pheromonal chorusing”.
This phenomenon is a consequence of a female-biased operational sex ratio. This means that at any given time, there are more females than males seeking to copulate. This occurs because males lose up to 11% of their body mass during mating and once they are done mating, they need time to sequester resources that will allow them to deliver a spermatophore to the next female they mate with. On the contrary, females do not need time to prepare for their next copulation. Due to the unequal mating rates, males become valuable to females and female-to-female competition rises dramatically as a consequence.