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A characteristic feature of the giant owl butterfly, i.e. Caligo memnon , is its big wing eyespot. This feature could serve as deceiving functionality for the butterfly against predators. As evidenced by scanning electron microscope (SEM) image on black part of eyespot, the scales on wing eyespot contain nanostructured ridges and cross-ribs. Applying direct measurement, statistical method, and Fourier analysis, the authors evidence that these nanostructures display order–disorder in their shape and position. The autocorrelation of SEM image provides average values of characteristic periods of the order–disorder nanostructures together with an estimation of corresponding correlation lengths. Linecuts obtained from the Fourier transform of SEM image were also analysed with the Hosemann function to extract similar information. These analyses indicate that the nanostructured order–disorder may contribute to blackness on wing eyespot. The authors thus conclude that the blackness on wing eyespot of C. memnon could be attributed to contributions from both the nanostructured order–disorder and melanin pigment.

This paper investigates the self-assembled chitin based nanostructures of the Caligo Memnon Nymphalidae Felder (1866) butterfly's scales that are responsible for the colour formation on the butterfly's “artificial eyespot”. The Fourier transform analysis of the digital scanning electron microscope images and the calculation of the corresponding half-width Airy disc allowed an effective estimation of the temporal resolution of this “artificial eyespot” as well as its optical sensitivity and optical absorption/light trapping. It was observed that Land equation remains an excellent tool for computing optical sensitivity of nanostructure materials.

SUMMARY Insects active in dim light, such as moths and many beetles, normally have superposition compound eyes to increase photon capture. But there are nocturnal and crepuscular insects – such as some species of bees, wasps and butterflies – that have apposition compound eyes. These are likely to have adaptations – including large eye and facet size and coarsened spatial and temporal resolution – that improve their sensitivity and thus their visual reliability. Is this also true for crepuscular insects that are active at intermediate intensities? To test this hypothesis, the visual performance of two closely related butterflies, the diurnal blue morpho Morpho peleides and the crepuscular owl butterfly Caligo memnon, were compared. Compared to the diurnal M. peleides, the crepuscular C. memnon does not appear to be adapted to a nocturnal lifestyle in terms of spatial resolution: the interommatidial angleΔϕ is similar in both species, and acceptance angles, Δρ,are only marginally larger in C. memnon. Moreover, temporal resolution is only a little coarser in C. memnon compared to M. peleides. Using a model for sensitivity, we found that the eyes of C. memnon are about four times as light-sensitive as those of M. peleides in the frontal visual field, much of this difference being due to the larger facet diameters found in C. memnon. In summary, greater visual sensitivity has evolved in C. memnon than in M. peleides, showing that adaptations that improve sensitivity can be found not only in nocturnal apposition eyes, but also on a smaller scale in crepuscular apposition eyes.

Efficiencies of food use, growth rates, and consumption rates were measured for larvae of eight tropical insect species, reared upon normal and fertilized Heliconia species (Zingiberales: Heliconiaceae) and Musa sp. (Zingiberales: Musaceae) in Costa Rica. Cephaloleia consanguinea and Chelobasis perplexa (Coleptera: Chrysomelidae, Hispinae) feed only on Heliconia. Caligo memnon and Opsiphanes tamarindi (Lepidoptera: Brassolidae) are oligophagous, with known hosts in two families of Zingiberales. Sibine apicalis, Sibine sp., and Metraga sp. (Lepidoptera: Limacodidae) and Megalopyge sp. (Lepidoptera: Megalopygidae) are polyphagous, with dicot and monocot hosts. Foliar nitrogen content of natural Heliconia imbricata (° = 1.76%) was lower than that of H. latispatha (° = 3.01%) and Musa sp. (° = .30%). The oligophagous brassolids generally had lower growth rates, lower efficiencies of food use, and lower nitrogen accumulation rates on H. imbricata than on Musa sp. The hispines had lower relative consumption and growth rates than any of the lepidopterans examined on any host or treatment. Growth rates and nitrogen accumulation rates for the hispine species were not affected by host plant fertilization. Efficiencies of nitrogen use declined with increasing foliar nitrogen content for the hispines. Several parameters of food use efficiency were correlated with larval feeding specialization. The specialized hispines and oligophagous brassolids had higher efficiencies of food assimilation and nitrogen use on H. imbricata than did the polyphagous limacodids and megalopygid. Other efficiency indices, such as net growth efficiency, were not correlated with feeding specialization. The hispine Ch. perplexa has one of the longest larval developmental times known for a nondiapausing chrysomelid (°200 d). Its slow growth is correlated with a low metabolic rate, which we interpret as a physiological adaptation for starvation resistance. Larvae feed only on rolled Heliconia leaves, which are produced infrequently by host plants, and long fasts are a predictable feature of development. Ch. perplexa's eight larval instars are about equal in duration, and closely match the duration of a rolled leaf's suitability as food for these larvae. After a rolled leaf unfurls, the larvae must either wait for another on the same plant, or search haphazardly for one on nearby plants. The feeding of Ce. consanguinea larvae is apparently moisture limited in this tropical rain forest, and these larvae also have a high resistance to starvation. The oligophagous brassolids have become pests of banana, which is introduced into the Americas. These species increase growth rates with increased nitrogen content of host tissue. They are infrequent on H. imbricata, which has few chemical defenses against herbivores. Thus, the low nitrogen content of H. imbricata may protect it from some herbivory.

In the banana plantations in Costa Rica four species of Lepidoptera pass their life cycle on the banana plant, and their larvae utilize the leaves of this plant for food. The species are Ceramidia butleri, Caligo memnon, Opsiphanes tamarindi, and Sibine apicalis. C. butleri is the most abundant. Laboratory evidence, when compared with observations in the field, indicates that C. butleri populations were not affected by either intra— or interspecies competition. In the field, adults of C. memnon, O. tamarindi, and S. apicalis did not utilize the same food source as C. butleri, and observations of feeding C. butleri adults indicated that they were seldom disturbed while feeding. In the insectary C. butleri adults deposited eggs much more densely on caged plants than was observed in nature. Since the results of competition among larvae appear to be reflected in reduced pupal weights and increased mortality, larvae of C. butleri were reared individually and at different densities on surplus food and restricted food supplies. C. butleri larvae were also reared at different densities with each of the other three species. All larvae were provided banana leaf as food. Densities required in the laboratory to produce a significant decrease in pupal weights or a significant increase in mortality were many times greater than densities observed in the field. Observations of five unmolested populations in nature revealed differences in oviposition sites, larval feeding and resting sites, pupation sites, and habits of the adults. Parasites, predators, and diseases were observed affecting these populations. These factors, however, were not significant in regulating the populations because the small numbers of eggs laid per unit area kept the population densities low.