By Rahul Kumar
Insects play many important roles in the ecosystem. Insect-plant interaction is one of the most imperative areas of modern research which has both ecological and economic significance. Approximately half of the living insects are herbivores and mostly primary consumers. Caterpillar is an immature stage of order Lepidoptera, which are important folivores with a voracious appetite. Their feeding behaviour involves chewing and ingesting plant tissue which results in marked visible damage to plants. Only two fossil caterpillars have been reported to date. A recent collaborative work conducted by a group of Indian scientists has reported for the first time a rare fossil displaying preservation of leaf-feeding caterpillars on their host leaf. This study documents evidence of fossil leaf-feeding caterpillars and their characteristic feeding patterns or markings on the surface of various fossil leaf remains recovered from the Pliocene sediments of Jharkhand India.
This study involves extensive excavation and analysis of a river cutting section of the latest Neogene sediments of Mahuadanr Valley, Jharkhand, India by various experts. This site is a part of the Rajdanada formation from the Pliocene. Shale and sandstone are found in abundance in this area. The excellent fossil preservation indicates the presence of reducing conditions during the time of deposition of sediments. More than 400 leaf fossils were collected, out of which 40 are with different patterns of insect herbivory along with coprolites (fossil feces or frass). Many such patterns include “skeletonization, hole feeding, galling, margin feeding and leaf-mining”. Among all recovered fossils, one is a well-preserved caterpillar fossil having characteristic feeding patterns or markings on the surface of an intact fossil leaf. It has been identified as a lepidopteran caterpillar feeding on Galactia (Fabaceae) leaf. The well-preserved fossil caterpillar has a stout, cylindrical body with head, segmented thorax (3 segments), and abdomen (10 segments). Thoracic segments are fused bearing thoracic legs or true legs and the segmented abdomen has characteristic prolegs. The arrangement of prolegs is typical of a lepidopteran caterpillar, on abdominal segments 3, 4, and 6. Analysis of coprolites also provides evidence of an herbivorous diet.
Figs: Galactia leaf fossil showing a well-preserved fossil of the caterpillar along with its characteristic feeding pattern in images A and C. Image B shows modern Galactia leaf for comparison. D and E show fossil caterpillar in the original photograph and line drawing respectively (Source: Hazra et al., 2021).
This fossil in life association provides important insights into direct plant-insect interactions. The present study provides insights into ancient food webs and ecosystems. It adds new evidence for restructuring terrestrial food webs during Pliocene. This study offers a rare opportunity to understand plant-insect interaction in the Pliocene, especially in the context of lepidopteran caterpillars. These findings confirm the consistency of lepidopteran feeding strategies over time.
For more details, please refer to:
Hazra, T., Spicer, R. A., Hazra, M., Sarkar, S. K., Spicer, T. E. V., Bera, S., & Khan, M. A. 2021: First fossil evidence of leaf-feeding caterpillars from India and their feeding strategies. Lethaia, https://doi.org/10.1111/let.12446. Vol. 000, pp. 1– 15.
Rahul Kumar is one of the Associate Editors of IE. He is working as Assistant Professor of Zoology at Department of Zoology, Sheodeni Sao College (Magadh University), Kaler-824127, Arwal, Bihar, India.
You can contact him at rahuldayanand33@gmail.com
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