Moths Remember Lessons Learned While Caterpillars

John Roach for National Geographic News

March 5, 2008

Adult moths can remember their "childhoods" as caterpillars, a new study has found.  Recently scientists trained tobacco hornworm caterpillars in the lab to avoid a nail polish-like odor delivered in association with a mild shock.  These bugs then entered the pupal stage and metamorphosed into moths. As adults, they also avoided the nail-polish odor—showing that they had retained their larval memory.  "We concluded that indeed the association does persist and is accessible to the adults in this artificial scenario," said study senior author Martha Weiss, a biologist at Georgetown University in Washington, D.C.  The finding also supports the idea that a piece of the caterpillar brain persists through metamorphosis, she added.  (Related: "Scientists Rethinking Nature of Animal Memory" [August 22, 2003].)  Weiss and colleagues report their research today in the Public Library of Science journal PLoS ONE.  Memory and Metamorphosis  Scientists have long wondered whether memory could survive the dramatic reorganization of the moth brain during metamorphosis, Weiss noted.  "The transition from a caterpillar to a moth or butterfly is really very dramatic," she said.  (See a picture of caterpillar larvae that look like bird poop.)  For example, caterpillars and moths move, eat, and sense the world differently—not to mention appear nothing alike.  The study also showed that memory retention depends on the maturity of the developing caterpillars' brains.  Caterpillars younger than three weeks old learned to avoid the nail-polish odor but could not recall the information as adults.  However caterpillars conditioned to avoid the odor in the final larval stage before pupation, called the fifth instar, retained the lessons.  Larvae trained during the third-instar stage also demonstrated an aversion to odor as fifth instars, but they did not avoid the odor as adults, the authors said.  The findings jibe with the idea that memories are retained in one lobe of a mushroom-shaped part of a caterpillar's brain that forms during the late stages of larval development and survives metamorphosis.  "Basically, the brain is not completely taken apart and rebuilt from scratch," Weiss said.  Reinhard Stocker, a biologist at the University of Fribourg in Switzerland, studies the nervous system of fruit flies.  In an email, he noted that Weiss team's data appear strong, but he said that the moths' memory retention only after the fifth instar was perplexing. "Metamorphic rewiring of the brain is generally thought to be completed only in later stages of metamorphosis, which for the moth would be well after the fifth instar," said Stocker, who was not involved in the new research. "Thus it should essentially not make any difference if one trains third- or fourth-instar larvae. I don't have any simple clue to interpret such an observation." Shock and Odor  The research may help explain how adult female moths that can eat a variety of food choose to lay their eggs on the same type of plant they fed on as larvae.  Study author Weiss describes it as an "if it was good enough for me, it's good enough for my kids" type of selection.  If the moths retain some memories from their larval stage, as this research shows, then they could remember what they ate as "kids."  Other researchers have theorized that moths have what's called a chemical legacy from their larval stage that could cue them what to eat.  "That could look like the larva is actually remembering something," Weiss noted.  Her research team was careful to show that larval memory was based on the formation of an association between a shock and an odor—not a chemical legacy, she said.  "For me, it is exciting to think that a learned association really can be transferred from one phase to another through this very radical transition."  Story

Moths or butterflies retain what they learned as caterpillars

Wed, Mar 5 01:35 PM

Washington, Mar 5 (ANI): It's well known that butterflies and moths undergo a prominent metamorphosis - from crawling caterpillars to winged adults. Now, researchers at Georgetown University have found that a physical change in appearance doesn't necessarily change memories formed at the larval or caterpillar stage.

It was found that tobacco hornworm caterpillars could be trained to avoid specific odours delivered in association with a mild shock. After emerging from the pupae, adult moths also avoided the odours, showing that they retained their larval memory.

This study, led by Martha Weiss, an associate professor of Biology at Georgetown University, is the first to demonstrate conclusively that associative memory can be retained through metamorphosis in Lepidoptera, the order of insects that includes moths and butterflies. This study also leads to further new questions about the organization and persistence of the central nervous system during metamorphosis.

"The intriguing idea that a caterpillar's experiences can persist in the adult butterfly or moth captures the imagination, as it challenges a broadly-held view of metamorphosis -- that the larva essentially turns to soup and its components are entirely rebuilt as a butterfly," said Weiss.

"Scientists have been interested in whether memory can survive metamorphosis for over a hundred years," says Doug Blackiston, one of the authors of the study.

During the pupal stage, the brain and nervous system of caterpillars undergo drastic reorganization and it's still not clear if memory could survive such dramatic changes.

These findings indicate that the retention of memory relies on the maturity of the developing caterpillars' brains.

Caterpillars younger than three weeks of age learned to avoid an odour, but were not able to recall the information as adults, whereas older caterpillars, conditioned in the final larval stage before pupation, learned to avoid the odour and recalled the information as adults.

Besides, these results have both ecological and evolutionary implications, as retention of memory through metamorphosis could allow a female butterfly or other insect to lay her eggs on the type of host plant that she herself had fed on as a larva. This behaviour could actually shape habitat selection and eventually lead to development of a new species.

The findings are published in the recent edition of the journal PLoS ONE. (ANI)

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DANGER FROM MICRO MOTHS

A team of Zoologists has collected over 7,000 specimens referable to more than 500 species of microlepidotream moths. JK Grewal, formerly of the Department of Zoology at the Handique Girls’ College led the quest.

Of the collected specimens, 50 are authentically identified. This work is a part of the All India Co-ordinated Project on Taxonomy (AICOPTAX) Research on Microlepidoptera, initiated by the Ministry of Environment and Forests. Dr H. S. Rose of Punjab University, Patiala, an eminent lepidopterists, is the Co-ordinator and Chief Principal Investigator.

For the smooth operation of the project, five zones have been set up in the country and Dr Grewal heads the NE region zone. On March 1, 2000, the project started its operation and it will continue till March 31, 2004. The project is aimed at capacity building in taxonomy and it envisages establishment of centres for research in identified priority gap areas — as for example, virus, bacteria, microlepidoptera in the field of taxonomy, education and training and strengthening the organisations like the Zoological Survey of India as the co-ordinating units.

The tasks assigned to the coordinators and collaborators under the project are survey, collection, identification, preservation, maintenance of the collections and taxonomic databanks, development of the identification manuals and also imparting training to college teachers, students and local communities in parataxonomy. Grewal and her team colleagues Sarfaraj Newaj and Diganta Sarma, both junior research fellows, have also collected detailed information about the distribution of various microlepidoptera species in the region, like the host plants, place of availability, physical condition of the region, — including climatic and topographical condition etc, through regular intensive and extensive survey-cum-collection trips to various areas, Grewal said.
Her team has surveyed most of the region, including Sikkim and North Bengal, during the pre and post-monsoon season for the last three years. The species of micro-moths are quite large in number compared to the butterfly species. In India, there are little more than 1,500 species of butterfly, whereas the number of species of micro-moths is 200 times ore than the butterflies. But, till date, only about two per cent of the micro-moth species in the country has been studied and identified, she said.

On the significance of the study, she said that the study would finally help the forest departments in evolving plant protection measures. For, she explained, most of the young ones of micro-moths feed on the internal tissues of the plants and make tunnels in the tissues of the leaves, stems, roots and fruits etc and thus act as destructive agents to plants.

Cnophalocrocis medanalis, one of the most destructive insects for paddy plants, also belong to the micro-moth species. This insect folds the leaves of paddy plants around their bodies and feed on the chlorophyll of the epidermal cells of the leaves.

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