Nutritional Ecology of Wild Silkmoths: Consumption and Assimilation

Last Updated: January 28, 2026
Estimated reading time: ~8 minutes
Word count: 1,250

The growth, development, and silk-producing potential of sericigenous insects are fundamentally governed by their nutritional ecology—the quantitative relationship between food consumption, digestion, and body tissue conversion. In the context of wild silkmoths like Attacus atlas, Actias selene, and Antheraea mylitta, understanding bioenergetics is crucial for optimizing host plant selection and rearing protocols. This analysis delves into the gravimetric data derived from Western Maharashtra, examining how these giant moths process energy from host plants like Terminalia catappa and Ficus carica to fuel their metamorphosis and silk synthesis.

Key Takeaways

• Instar Consumption: The fifth instar larva accounts for the vast majority (up to 80-85%) of total food consumption during the larval life.
• Assimilation Efficiency: Attacus atlas demonstrated high Food Energy Assimilation (FEA), peaking at 5.95g in the final larval stage.
• Metabolic Stress: Larvae exhibit “negative growth” and negative respiration values during molting periods, indicating high physiological stress and cessation of feeding.
• Host Plant Impact: Antheraea mylitta kolhapurensis showed superior assimilation rates on Terminalia catappa compared to secondary hosts.
• Bioenergetics Method: The study utilized Waldbauer’s gravimetric method to quantify consumption, excreta, and weight gain.

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Nutritional Bioenergetics in Wild Silkmoths

Gravimetric Analysis Methodology

To understand the nutritional ecology of wild silkmoths, researchers must quantify the energy budget of the larvae. The thesis employed the standard gravimetric method proposed by Waldbauer (1968), a cornerstone in insect physiology. This involves daily measurements of the weight of larvae, food offered, uneaten leaves, and fecal matter (litter) to calculate nutritional indices.

The Energy Budget Equation

The study tracked the flow of matter through the insect system using these parameters:

1. Food Consumed (F): The raw input of leaf biomass.
2. Excreta (E): The undigested waste material.
3. Weight Gain (G): The conversion of nutrients into larval body mass.
4. Food Energy Assimilation (FEA): Calculated as $F – E$. This represents the actual nutrients absorbed by the gut.
5. Respiration (R): The metabolic cost, calculated as $F – (E + G)$.

“The gravimetric method as described by Waldbauer (1968) was used to measure the utilization of food on wet weight basis by the larvae… The actual performance of an insect reduced below its physiological potential by food quality.” (Kavane, 2010, p. 131, 138)

Student Note: In insect bioenergetics, Assimilation Efficiency is a measure of how well the insect extracts nutrients from its food. It is distinct from Conversion Efficiency, which is how well those extracted nutrients are turned into body tissue (biomass).

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Consumption Dynamics and Instar Progression

A critical finding in the nutritional ecology of Saturniid moths is the exponential increase in food consumption as the larva matures. The thesis data indicates that early instars (1st-3rd) act as “tasting” stages with minimal consumption, while the late instars (4th-5th) are the “gluttonous” phases responsible for accumulating the protein required for silk production.

Case Study: Actias selene on Terminalia arjuna

• Early Instars: In the 1st instar, the larva consumed only 0.0381 g of leaf on the first day. By the 3rd instar, consumption rose to 0.0650 g per day.
• The 5th Instar Surge: The consumption skyrocketed in the final instar. On the 19th day (start of 5th instar), consumption was 8.53 g, peaking at 13.92 g on the 34th day.
• Implication: Sericulturists must ensure an abundant and fresh supply of leaves specifically during the final 10 days of rearing, as food deprivation here causes the most significant loss in silk yield.

Fig: Daily Food Consumption (g) of Attacus atlas on Ficus carica

Larval Stage	Day of Feeding	Food Consumed (F)	Weight Gain (G)
1st Instar	Day 1	0.0543	0.0083
3rd Instar	Day 14	2.7208	2.0447
4th Instar	Day 19	3.6477	0.7310
5th Instar	Day 22	6.3581	1.1130
Peak 5th	Day 26	8.7554	4.1176

Professor’s Insight: The massive jump in consumption in the 5th instar is evolutionarily timed to build fat body reserves for the non-feeding adult moth stage (which has no mouthparts) and for egg production.

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Revived by the Professor of Zoology editorial team. Direct thesis quotes remain cited; remaining content is original and educational.

Food Energy Assimilation (FEA) Trends

Food Energy Assimilation (FEA) is the net energy available to the insect after excretion. The thesis data reveals that FEA is not constant; it fluctuates based on the developmental needs of the silkworm.

Assimilation Efficiency

• Attacus atlas: high Efficiency: Reared on Ficus carica, the Atlas moth showed remarkable assimilation. On the peak day of the 5th instar, it assimilated 5.95 g of food energy from 8.75 g of consumption. This indicates a high digestibility of Fig leaves.
• Antheraea mylitta kolhapurensis: When reared on Terminalia catappa, this subspecies showed a maximum FEA of 6.27 g on the 22nd day. This high assimilation rate correlates directly with the successful cocoon formation and high shell ratio (10.46%) observed in the rearing results.

The Cost of Living: Respiration (R)

The metabolic cost (Respiration) increases alongside consumption but drops significantly as the larva approaches pupation. High respiration values in the 5th instar (e.g., 6.77 g for A. selene on day 25) reflect the immense metabolic energy required to synthesize silk proteins (fibroin and sericin) in the silk glands.

Student Note: High FEA values generally indicate a compatible host plant. If a larva consumes a lot (high F) but has low assimilation (low FEA), it means the plant has low nutritive value or high indigestible fiber content.

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Metabolic Stress During Molting

A fascinating aspect of insect nutritional ecology captured in the thesis is the physiological state during molting (ecdysis). The gravimetric data tables show “negative values” for growth and respiration during these periods.

The Molting Phenomenon

• Cessation of Feeding: During the moult (e.g., between the 4th and 5th instar), the larva stops eating completely. The gut is emptied (frass clearing), leading to weight loss.
• Negative Metrics:
  • For A. selene, specific days showed negative weight gain (e.g., -1.9771 g on day 36).
  • Respiration values also dipped or turned negative in the calculation, reflecting the distinct metabolic shift from “growth” to “structural reorganization.”
• Implication: This period is critical. The “negative” physiological state implies the insect is vulnerable. Disturbing the larvae or changing environmental conditions during these “negative value” days can result in failed molting and death.

Real-Life Applications

1. Artificial Diet Formulation: Understanding the specific protein and carbohydrate assimilation rates (FEA) helps in creating cost-effective artificial diets for indoor rearing, a goal mentioned in the thesis discussion.
2. Host Plant Evaluation: By comparing FEA across different plants, farmers can scientifically select the most nutritious fodder (e.g., using T. catappa over T. arjuna if FEA is higher), rather than just relying on observation.
3. Rearing Schedule Management: Knowing that 80% of food is needed in the last instar allows tribal rearers to manage their leaf harvest more efficiently, preventing leaf shortage during the critical final days.
4. Disease Monitoring: A drop in assimilation efficiency or weight gain outside of molting periods is an early bio-indicator of infection (like pebrine or flacherie) before visible symptoms appear.

Why this matters: Applying bioenergetics transforms sericulture from a traditional practice into a precision science, maximizing output per unit of fodder.

MCQs

1. According to the gravimetric data, which larval instar exhibits the highest Food Consumption (F)?
A) 1st Instar
B) 3rd Instar
C) 4th Instar
D) 5th Instar
Correct Answer: D
Difficulty: Easy
Explanation: The data tables consistently show the highest consumption values (e.g., >8g/day) occurring in the 5th instar across all species studied.

2. How is Food Energy Assimilation (FEA) calculated in the context of this study?
A) Food Consumed (F) + Weight Gain (G)
B) Food Consumed (F) – Excreta (E)
C) Weight Gain (G) – Respiration (R)
D) Food Consumed (F) / Weight Gain (G)
Correct Answer: B
Difficulty: Moderate
Explanation: The methodology section defines Food Energy Assimilation (FEA) as food consumed (F) minus food egested (E).

3. What does a “negative weight gain” value in the daily data typically indicate?
A) The larva is sick.
B) The food quality is poor.
C) The larva is undergoing molting or preparation for pupation.
D) Measurement error.
Correct Answer: C
Difficulty: Moderate
Explanation: The thesis explains that negative growth values occur when the larva stops feeding and empties its gut to molt or spin a cocoon.

4. Which species showed a maximum FEA of approximately 6.27g on Terminalia catappa?
A) Attacus atlas
B) Actias selene
C) Antheraea mylitta kolhapurensis
D) Bombyx mori
Correct Answer: C
Difficulty: Challenging
Explanation: Table data for A. mylitta kolhapurensis reared on T. catappa shows a peak FEA of 6.2787g on the 22nd day.

FAQs

Q: Why is the 5th instar critical for silk production?
A: The 5th instar is the period of maximum food consumption. The nutrients assimilated during this stage are directly converted into silk proteins in the silk glands; poor nutrition here drastically reduces cocoon shell weight.

Q: What is the purpose of the gravimetric method in sericulture?
A: It quantitatively measures how much food an insect eats, how much it excretes, and how much it converts into body mass, helping scientists evaluate the nutritional quality of different host plants.

Q: Do wild silkmoths eat during the adult stage?
A: No. The thesis confirms that adult Saturniid moths (like A. atlas and A. mylitta) have vestigial mouthparts and do not feed; they rely entirely on the energy reserves accumulated during the larval stages.

Q: Why do larvae stop moving and eating for 1-2 days periodically?
A: They are molting (shedding their skin). This is a period of high physiological stress where they detach their old cuticle. The study data shows this as periods of zero consumption and negative weight gain.

Lab / Practical Note

Measuring FEA: To calculate Food Energy Assimilation in a classroom setting, ensure leaves are weighed before feeding. Use a “dummy tray” with leaves but no larvae to calculate natural moisture loss (evaporation) so you don’t overestimate consumption. Dry the excreta (frass) before weighing to get accurate biomass data.

External Resources

• Journal of Insect Physiology – Resource for advanced reading on insect bioenergetics.
• Entomological Society of America – General resources on insect biology and rearing.

Sources & Citations

Kavane, R. P. (2010). Biosystematics of wild silkmoths from Western Maharashtra. (Doctoral dissertation, Shivaji University, Kolhapur). 1-304.

Source Note: All numerical data regarding consumption, assimilation, and weight gain were derived from the “Daily Food Consumption and Utilization” tables presented in the thesis appendix and results sections (pages 149-193).

Correction Invitation: If you are the author of this thesis and wish to provide updates or corrections to this summary, please contact us at contact@professorofzoology.com.