Katherine Monroe is a junior at Princeton High School in her second year of the Research Program.
As the practice of rearing insects as a food/feed source becomes increasingly widespread, the question of what to do with insect “frass” (excrement) has arisen. This study aims to explore the potential use of frass from the larval form of the darkling beetle, Tenebrio molitor (commonly known as the mealworm) as fertilizer for Wisconsin Fast Plants, Brassica rapa. It is hypothesized that this use of mealworm frass will positively affect the growth of B. rapa, increasing the bioactive compound content, biomass, overall health of the plant, and expression of chitinase-related genes Bra038727, Bra037699. Increased expression of chitinase could potentially increase resistance to fungal pathogens. This is based on the findings of previous research that suggest that nutrients found in insect frass, including nitrogen, phosphorus, calcium, potassium, iron, and chitin, are beneficial for plant growth (Houben et al., 2020, Lee et al., 2019, Kagata and Ohgushi, 2012). Using the Wisconsin Fast Plants® Growth, Development, and Reproduction Advanced Classroom Kit, a total of 128 B. rapa plants will be grown according to standard practices, divided into 6 experimental groups in addition to a positive and negative control. Experimental groups will be subjected to fertilization treatment using NPK fertilizer, cornmeal-fed mealworm frass, or Styrofoam-fed mealworm frass in either a standard peat/vermiculite potting mix (included in the Wisconsin Fast Plants kit) or a coconut coir/perlite mix. During the plants’ 5-week lifecycle, plant health will be assessed by measuring chlorophyll levels, flowering time, and seed production. After the lifecycle is over, dry biomass will be measured, and an antioxidant assay will be carried out. Additionally, RT-qPCR will be conducted to measure expression of chitinase-related genes. The results of the study could lead to healthier and more abundant crop yields, as well as increased disease resistance.
Why Wisconsin Fast Plants?
The Wisconsin Fast Plant (B. rapa), is a model organism developed for rapid growth. It is closely related to a wide variety of edible plants, including field mustard, cabbage, turnip, mustard, radish, and broccoli. Due to their short 5-week life cycle, Wisconsin Fast Plants are especially useful for studying genetics and heredity, allowing researchers to observe and measure transgenerational changes. Brassica vegetables are known to be rich in bioactive compounds with antioxidant, antibacterial, anti-inflammatory, and antifungal properties (Favela-González et al., 2020). As such, findings regarding their nutritional value have direct implications for human health.
In recent years there has been increasing interest in farming insects as an alternative protein source for human consumption or animal feed. Compared to other meat, rearing insects is significantly more sustainable and environmentally friendly. As this practice grows, insect frass (excrement and waste products) will be generated. Insect frass has potential for use as an organic fertilizer, as it contains nutrients such as nitrogen, phosphorus, potassium, and calcium, which are beneficial for plant growth (Houben et al., 2020). Frass also contains chitin, a polysaccharide found in the exoskeletons of insects and the cell walls of fungi. Research indicates that chitin can increase plant growth, reduce plant pathogens and pests, and increase the quantity of beneficial microbes.
- Wisconsin Fast Plants will be grown according to standard practices in Princeton High School during the 2021-2022 academic year.
- A positive and negative control group will be established, along with several experimental groups. Plants in the positive control group will be grown in a standard peat/vermiculite potting mix, while the plants in the negative control group will be grown in a nutrient-poor medium (coconut coir/perlite). Experimental plants will be grown in the same soil as the negative control, supplemented with insect frass or NPK fertilizer at incrementally-increasing concentrations.
- During the plants’ five-week lifecycle, growth will be observed, with qualitative and quantitative measurements (number of seeds, flowering times, plant height, disease symptoms) taken. Photosynthetic output will also be determined each week with a chlorophyll meter. After seeds are harvested, plants from each group will be washed and dehydrated to measure total dry biomass, and bioactive compound content will be measured.
- Depending on the results, chitinase expression may be measured in B. rapa when raised on either insect frass or commercial fertilizer, in comparison with the positive and negative controls.
This study aims to explore the possibility of using insect frass as a fertilizer by examining the effects of mealworm frass on the growth of the Wisconsin Fast Plant, Brassica rapa. Additionally, the differences in plant growth between treatment with frass and commercial fertilizer will be examined. The impacts on antioxidant content and chitinase expression will also be investigated, along with nutrient acquisition and availability, which could yield results that would have implications for human health and could lead to healthier and more abundant crop yields.
It is hypothesized that the use of mealworm frass as a fertilizer will positively affect the growth of B. rapa, increase the bioactive compound content, biomass, overall health of the plant, and expression of chitinase-related genes.
Chen J. et al. (2018) Genome-wide identification and expression analysis of chitinase gene family in Brassica rapa reveals its role in clubroot resistance, Plant Science, Volume 270, 2018, Pages 257-267, ISSN 0168-9452,
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Favela-González K.M., Hernández Almanza A.Y., De la Fuente-Salcido N.M. (2020, August 3). The value of bioactive compounds of cruciferous vegetables (Brassica) as antimicrobials and antioxidants: A review. J Food Biochem, vol. 44, issue 10, 2020;00:e13414. https://doi.org/10.1111/jfbc.13414
Houben, D., Daoulas, G., Faucon, M. P., & Dulaurent, A. M. (2020). Potential use of mealworm frass as a fertilizer: Impact on crop growth and soil properties. Scientific reports, 10(1), 4659. https://doi.org/10.1038/s41598-020-61765-x
Kagata, H. and Ohgushi, T. (2012, January). Positive and negative impacts of insect frass quality on soil nitrogen availability and plant growth. Popul. Ecol., 54: 75-82. https://doi.o.rg/10.1007/s10144-011-0281-6
Lee, J., et al. (2019) Environmentally friendly fertilizers can enhance yield and bioactive compounds in Chinese cabbage (Brassica rapa ssp. pekinensis). Turk J Agric For 43: 138-150 https://doi.org/10.3906/tar-1807-28
Marecek V., et al. (2017) ABTS and DPPH methods as a tool for studying antioxidant capacity of spring barley and malt, Journal of Cereal Science, Volume 73, 2017, Pages 40-45, ISSN 0733-5210,
Sharp, R.G. (2013) A Review of the Applications of Chitin and Its Derivatives in Agriculture to Modify Plant-Microbial Interactions and Improve Crop Yields. Agronomy 2013, 3, 757-793. https://doi.org/10.3390/agronomy3040757
Wang, X., Wang, H. et al., The Brassica rapa Genome Sequencing Project Consortium (2011). The genome of the mesopolyploid crop species Brassica rapa. Nat Genet 43, 1035–1039 https://doi.org/10.1038/ng.919