Butterfly-Ant Symbiosis

Many of the 6,000 species of the butterfly family Lycaenidae associate with ants. The complexity and beauty of such interactions in the Malaysian tropics attracted research on the subject. Lycaenid caterpillars may have special organs that attract and appease ants and some species cannot survive without them. For example, some lycaenid caterpillars are taken by ants into the nest and allowed to eat ant larvae in exchange for a sweet secretion from the caterpillars. Some even evolve ant-like pheromones, so they pass as ants instead of invaders.

A Malaysian Blue caterpillar (Anthene emolus) can develop into an adult without the help of ants, but has a much greater risk of falling prey to predators and parasites. Female blues look for both host plants and Weaver Ants (Oecophylla smaragdina), laying eggs when the ants are present. Weaver Ants, a numerous and aggressive species, offer caterpillars reliable protection. The ants transport young caterpillars around host plants to help them find food. In return, they “milk” the older larvae for a sweet secretion.

Former entomology Ph.D. student Emily Saarinen traveled to Malaysia to research ant-caterpillar association. She discovered that different ant castes play different roles in tending caterpillars, and that major ants fight minor ants for the right to tend caterpillars. This defies standard theory that ants act in unity for the common good of the ant colony.

Chemical Ecology of Heliconius

Larvae of Heliconius butterflies feed exclusively on cyanide-producing passionvines. The caterpillars of this genus have developed the ability to counteract the effects of the cyanogenic glycosides in their Passiflora host plants, but the exact mechanisms for counteracting these cyanogens are unknown. McGuire Center research associate Mirian Medina Hay-Roe focuses her studies on the chemical interactions of Passiflora plants and their herbivores of the genus Heliconius. The investigation approaches insect/plant co-evolution at various levels. At the morphological level, she investigates genetic variation in life history characteristics, as well as, the influence of environmental factors (specifically, larval diet) and maternal effects. At the physiological level, her research investigates the fate of plant secondary compounds, the patterns of toxicity exhibited by Heliconius adults fed cyanogenic glycosides as caterpillars, and the mechanisms of detoxification used by the larvae. The evolutionary implication of her research focuses on an understanding of the evolution of mimicry rings based on plant toxicity.

Mimicry Diversity, Evolution and Ecology of Ithomiine Communities

Ithomiines (see Systematics and Classification of Ithomiinae) dominate butterfly communities in neotropical forests, from sea level to more than 7,800 feet elevation. Ithomiines may comprise up to 50 percent of all butterflies in the forest understorey, and in many places up to 60 species fly together. Understanding how such diverse communities coexist is a central goal of evolutionary ecology, and ithomiines are an ideal study group. Ithomiine caterpillars feed almost exclusively on plants of the family Solanaceae, and each ithomiine species is usually confined to a single hostplant species. There is evidence of adaptive radiation, with more diverse plant clades supporting more diverse groups of ithomiines. Ithomiines are also notable for being unpalatable to predators and thus warningly colored, and extensively involved in mimicry rings. However, rather than all species converging on a single warning color pattern as predicted by mimicry theory, there are diverse complexes of mimetic species occurring together.

Keith Willmott and Julia Robinson Willmott are working with colleagues from Edinburgh and Cambridge universities to determine how mimicry diversity is maintained in two distinct ithomiine communities in eastern Ecuador.

Their hypothesis is different mimicry complexes occur in different microhabitats, such as ridge tops or stream sides, where distinct predator species occur, so predators rarely encounter more than one kind of color pattern and thus the selection for convergence of different mimicry complexes is weak. The microhabitats where butterflies occur may be constrained by the microhabitats where their food plants grow, so they are rearing ithomiines to identify host plant usage. They are also mapping the height and microhabitat distribution of butterflies, plants and insectivorous birds to quantify niche space for these groups. They also are deriving molecular and morphological phylogenies for certain ithomiine genera to test whether adaptive shifts in warning color pattern, host plant or microhabitat have been important in speciation.

Learn more about Ithomiinae Immature stages.

Sound Production in Heliconius Butterflies

A few butterfly species have been reported to produce or hear sounds. The best-known example is the butterfly genus, Hamadryas, which has several species known to produce loud clicks in flight. Mirian Medina Hay-Roe has discovered that Heliconius cydno also produces audible wing clicks during encounters with members of the same species and other Heliconius species. This finding suggests wing clicks may play a role in intra- and inter-specific communication in Heliconius. In collaboration with Richard Mankin of the U.S. Department of Agriculture, Hay-Roe is trying to determine the evolutionary importance of sound production in the genus Heliconius.

Night Roosting in Heliconius

Communal roosting occurs when multiple insects of one or more species assemble in close proximity to one another for a certain period of time. Some species within the genus Heliconius display gregarious night roosting behavior. This particular behavior has been addressed several times over more than a century, but an explanation for it remains obscure. To better understand this behavior former Ph. D student Christian Salcedo studied clustering behavior, roost structure and patterns related to the sex, age and size of individual Heliconius butterflies. This research includes work with captive-bred colonies utilizing the McGuire Center’s unique facilities, in addition to field studies in Central and South America.

Speciation in Heliconius

Heliconius comprise a colorful and widespread butterfly genus distributed throughout the tropical and subtropical regions of the New World. These butterflies have been a subject of many studies due to their abundance and relative ease in breeding under laboratory conditions as well as due to the extensive mimicry occurring in this group. Studying this model group is helping scientists to understand how species are formed and why they are so diverse.

Former entomology Ph.D. student Christian Salcedo studied Heliconius sexual selection and speciation processes in the Colombian species, Heliconius heurippa. This species is known to have an intermediate morphology and a hybrid genome, and in the study its intermediate wing color and pattern was recreated through laboratory crosses between H. melpomene, H. cydno and their first-generation hybrids (Nature 2006 – see below). Mate preference experiments showed the phenotype of H. heurippa reproductively isolates it from both parental species. There is strong assortative mating between all three species, and in H. heurippa the wing pattern and color elements derived from H. melpomene and H. cydno are both critical for mate recognition by males.

NOTE: Nature 2006: Speciation by hybridization in Heliconius butterflies

Life-history Evolution of Hawkmoths

Hawkmoths are one of the most charismatic groups of moths. With incredible proboscises that can reach more than a foot in length, they are a primary focal group to understand life-history evolution. Building on the phylogeny of Kawahara et al. (2009) and others, McGuire researchers are constructing a molecular phylogeny of hawkmoths and mapping different life-history traits to understand how such a remarkable group became so successful. Through an NSF-funded project with the Barber Lab at Boise State University and Ian Kitching at the British Museum, scientists are examining the evolution of anti-bat ultrasound production and hearing in hawkmoths.

Phylogenomics of Leaf-mining Moths

Insect herbivores and their hosts dominate terrestrial biomes and may constitute nearly 50 percent of the Earth’s biodiversity. As herbivores and pollinators, Lepidoptera are one of the primary insect groups responsible for the radiation of flowering plants. Since the pioneering work of Ehrlich and Raven (1964), there has been great interest in trying to detect and understand macroevolutionary patterns in insect-plant associations. Most macroevolutionary studies on herbivorous insects have focused on external plant feeders, and few have examined patterns of life history evolution for internal herbivores such as leafminers. Moths in the family Gracillariidae constitute the primary group of plant mining Lepidoptera. Gracillariid larvae feed on a wide range of host plant families, typically consuming the soft tissue between the outer leaf surfaces. With a team of international collaborators, McGuire researchers are utilizing available fossil data to understand the evolutionary history of Gracillariidae and their host associations. The project utilizes next-generation sequencing to build on the study of Kawahara et al. (2011).