Utetheisa ornatrix

• Utetheisa ornatrix ornatrix
• Utetheisa ornatrix bella (Linnaeus, 1758)
• Utetheisa ornatrix saintcroixensis Pease, 1973

The eggs of the Utetheisa ornatrix are spherical in shape and range in colour from white to yellow to sometimes brown.[1]

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.[1]

The pupae are mostly black marked with irregular orange and brown bands. Usually, the pupae are covered with a loose layer of silk.[1]

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.[2] Wings contain white bands containing six bands of irregularly spaced black spots.[5] The hind wings can be bright pink with a marginal black band. The adult Utetheisa ornatrix has a wingspan of 33 to 46 millimetres (1.3 to 1.8 in).[2]

On occasion, bella moth caterpillars cannibalize other eggs, pupae or larvae from the same species.[12] Since PAs are a limited resource, some caterpillars do not reach optimal levels and resort to cannibalism.[13] This behavior is a consequence of PA deficiency rather than hunger, since deficits in alkaloids are the main cause of mortality.[12] Pupae cannibalism is rare because larvae normally pupate far away from the plant where they feed.[12] Egg cannibalism is also rare because eggs provide larvae with very small quantities of PAs[13] and because eggs from the same cluster hatch synchronously.[14] Larvae may also feed on other bella moth larvae that are laden with alkaloids.[12] This is more common since feeding on one single larva is sufficient to compensate for the cannibalistic caterpillar's alkaloid deficiency.[12]

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.[15]

The bella moth presents a polyandrous mating system, where females mate with multiple males.[17] On average, females mate with four to five males over their lifespan of three to four weeks but can mate with and receive up to thirteen spermatophores.[17] Since spermatophores contain nuptial gifts of pyrrolizidine alkaloid (PA) and nutrients, multiple mating helps the female increase the fitness of her offspring.[17] 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.[17] This is equivalent to a 15% increase in egg production.[18] In addition, multiple mating results in increased transmission of alkaloidal gifts to eggs.[19] 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.[19] In contrast, normally most of the sperm used to fertilize the eggs comes from a single male.[16]

Courtship begins at dusk.[20] Stationary females release a sexual pheromone that lures males.[20] They emit these chemicals in short pulses to provide close-range orientation cues to male moths as they seek out the females.[21] 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.[6][22] By doing so, the male emits a specific scent from his coremata that is attributed to a pheromone, hydroxydanaidal.[20] After receiving the scent, the female proceeds to mating.[22]

Copulation lasts for up to 12 hours.[23] 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.[24] The remaining hours of copulation are exclusively used for alkaloid transfer.[24] 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.[24] 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.[24]

Bella moth mating behavior is exceptional in that females compete with other females to obtain more males, as opposed to males competing with males.[25] As in many other moth species, females release sexual pheromones that males can detect over long distances.[25] However, in most species, females do not interact with one another during pheromone release.[25] Female bella moths are unique in that females from the same family often engage in collective pheromone release termed “female pheromonal chorusing”.[25]

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.[25] 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.[25] On the contrary, females do not need time to prepare for their next copulation.[25] Due to the unequal mating rates, males become valuable to females and female-to-female competition rises dramatically as a consequence.[25]

Engaging in pheromonal chorusing allows females to increase the attractiveness of genetic relatives and increase their indirect fitness.[25] Females may also, but less frequently, engage in female chorusing with unrelated females.[25] It has been suggested that chorusing is still beneficial under these circumstances, because cooperation for pheromone release may increase the attractiveness of the entire group and increase each moth's individual fitness.[25] It has been experimentally shown that when females detect other female pheromones they increase the rate of pheromone release and call for longer periods of time.[26] Such observations support the hypothesis that females cooperate with one another to increase mating success.[26]

Although most female moths mate multiply, very low instances of mixed paternities occur.[16] In fact, most progeny in a single clutch is sired exclusively by one male.[16] Females of this species do not select based on age, mating order, between-mating interval, or duration of copulation.[16] Instead, female Utetheisa ornatix demonstrate female choice in mate selection that depends on body size, systemic content of defensive pyrrolizidine alkaloid, and glandular content of the courtship pheromone hydroxydanaidal.[27] Selecting for these males provides the females with multiple benefits such as obtaining sperm packages with more defensive pyrrolizidine alkaloids which results in larger offspring.[18] Offspring fathered by larger males are generally less vulnerable to predation because of their higher alkaloid content, allowing the offspring to have higher viability and fitness.[18]

Larger males with the highest alkaloid content can be distinguished by a specific pheromonal scent that predicts the content of the alkaloidal gifts: hydroxydanaidal (HD).[20] There is a relationship between the size of the male, the type of food the males fed on as larvae, and the composition of its spermatophores.[20] For example, males that fed inside a seed pod rather than on leaves produce higher levels of HD.[20] In addition, these males have higher adult weights and have higher systemic loads of PA, the metabolic precursor of HD.[20] By selecting for HD-rich males, the female moth ensures the receipt of a large alkaloid gift (phenotypic benefit) and genes that encode for large size (genetic benefit).[27]

The female's mating preference is inherited paternally since the preference gene or genes lie mostly or exclusively on the Z sex chromosome.[28] The preferred male trait and the female preference for the trait are strongly correlated; females with larger fathers have a stronger preference for larger males.[28]

After copulating with several males, rival sperm carried by a female do not compete directly for access to the eggs.[16] Females direct a postcopulatory selective process where they choose male sperm based on the intensity of the courtship pheromone that was released prior to copulation, hydroxydanaidal (HD).[7] The intensity of this signal is directly proportional to the amount of alkaloids sequestered by the moth during the larval stages.[7] As a consequence, this pheromone is an indirect indicator of success during larval development and will ultimately determine which sperm will be passed on to the offspring.[7] Once they have selected a male, females use their musculature to channel the selected sperm through the chambers and constructs of their reproductive systems to their eggs.[16]

The spermatophore that males give to the females when mating contains sperm, nutrients, and pyrrolizidine alkaloids (PA), and accounts for up to 11% of the male's body mass.[18] PA plays an important role in preventing predation in Utetheisa ornatrix because it is poisonous to most organisms. Males transmit PA to the females via a sperm package; the females then give this mating gift to the eggs,[30] along with their own alkaloidal supplement and is utilized to protect the offspring from predation.[18] In addition, females also personally benefit from the gift through protection and nutrition. After mating with a PA-rich male, the received PA is quickly allocated to all body parts.[30] As a result, females become and remain unacceptable as prey to numerous organisms such as spiders.[30] Another problem that females face is the risk of incurring a PA deficit due to the large amount of eggs they lay. Spermatophores is one way for females to compensate for this loss in PA.[19]