Location: Biological Control of Pests Research
2025 Annual Report
Objectives
1. Expand studies on discovery, culturing, production and evaluation of natural enemies for biological control and insects as animal feed.
1.a. Behavior and evaluation of black soldier fly as feed and fertilizer.
1.b. Characterization of traits for high efficiency of food conversion and development of Tenebrio molitor for mass production as animal feed.
2. Develop improved rearing methods and artificial diets to reduce costs of insect mass production.
2.a. Test of prey recognition and consumption rate of lady beetles reared on artificial diet or factitious food for multiple generations.
2.b. Determine the effect of diet on the nutritional value of Tenebrio molitor produced for animal feed.
Approach
The invertebrate predator Coleomegilla maculata De Geer (Coleoptera: Coccinellidae) will be used as a model invertebrate in this test. It is an omnivorous predator that has the capacity to utilize microalgae and synthetic pollen as food to obtain essential nutrients not present in unsuitable prey (Riddick and Wu, 2015). This colony has been in continuous culture without any addition of wild type individuals for more than 50 generations in a climate-controlled room (24°C, 50%–60% RH, 16 h photophase). Individuals originating from the colony and used in this experiment have been mass-reared for more than 10 consecutive generations on a proprietary mixture of freeze-dried, powdered brine shrimp eggs Artemia franciscana Kellogg, freshwater microalgae (Chlorella vulgaris Beijerink), and fatty acids, stearic acid (18:0) or myristic acid (14:0) (Riddick, unpublished data). Larvae and adults have no prior exposure to H. illucens. Yet, published work using larvae and adults from this colony, indicated that the eggs of the common housefly Musca domestica L. (Diptera: Muscidae) were suitable prey in experimental trials (Riddick et al. 2014). All life stages have been maintained in separate cages in the same climate-controlled room (24 °C, 50%–60% RH, 16 h photophase) for more than 10 years at the National Biological Control Laboratory (NBCL), USDA, ARS, in Stoneville, Mississippi.
Cultivated strawberry (Fragaria × ananessa Duch. cv. Chandler) will serve as model plants to test the effects of H. illucens larval frass, as a fertilizer, on plant health. Approximately 1,000 bare root individuals will be purchased from a commercial nursery in Redding, CA, as mentioned in previous research (Riddick et al. 2019). All individuals will be removed from cold storage in NBCL, then transplanted into “flats” over the course of several consecutive days. Excess dead roots will be trimmed away, using stainless steel scissors. Once in flats at a spacing of approximately 6 cm between individual plants, a light covering of peat soilless media will be applied over the roots; then watered using tap water. All plants will be setup on metal benches in a temperature-controlled greenhouse (20-22°C, natural lighting) in Stoneville, Mississippi, USA. One month later, the healthiest plants will be transferred to plastic (1.3 L) pots, one plant per pot, containing the same quantity of soilless media in each pot.
Progress Report
Progress was made by ARS researchers at Stoneville, Mississippi on mealworm diet refining and evaluation. Based on results from mealworm self-selection studies one diet (diet 2) was selected as the reference diet to develop more refined formulations as diet variations. The first experiment was designed to determine if adding taurine could improve biological traits, such as growth, development time, and survival. Also, a variant of the reference diet (diet 2A) was formulated by replacing the canola meal by soybean meal. This first experiment was completed in May 2024 showing no effect of taurine addition and negative effects of switching from canola meal to soybean meal. The second experiment consisted of replacing canola meal with sunflower meal (diet 2b), testing the effects of adding fiber (20% and 30%), to eliminate defatted rice bran and corn DDGS (dry distilled grain with solubles) (diet 9), and to test a new formulation using corn meal (diet 12). Results of this experiment showed negative impact of replacing canola meal with sunflower meal. Similarly, the addition of fiber reduced growth rate and survival. However, a diet without defatted rice bran showed some promise while providing a simpler formulation. Also a diet with corn meal showed promise by outperforming the reference diet in growth rate and food utilization efficiency. The downside of the corn-based diet was its cost as compared with the reference diet. The third experiment was designed to test the replacement of oat fiber with peanut shells in a variant of the reference diet; refining the diet lacking defatted rice bran by reducing fat content and increasing protein (diet 9c); refining the corn-based diet to reduce costs (diet 12a); and to test a simplified version of the reference diet (diet MP-1) consisting of only four ingredients instead of 6. The first phase of the third experiment was completed on May 26, 2025, and results showed significant improvements in growth rate, food assimilation, and food conversion efficiency in diets the new modified diets as compared with the reference diet. The second phase of this experiment is in progress, but insects in several of the new formulations have already completed development ahead of the control diet and significantly earlier than the reference diet. These diets include the refined simplified diet eliminating defatted rice bran, a variant of the corn-based diet, and a variant of the reference diet replacing oat fiber with peanut shells. A fourth experiment started on July 1st designed to test the addition of sugarcane bagasse as a substitute for oat fiber and peanut shells in two diet variations is and it is currently in progress. Four new diet variations were formulated, which are being compared to the reference diet and the control. Current overall results show three new diets that outperform our best diet. These diets include the corn-based, a simplified diet that eliminated defatted rice bran, and a variant of the reference diet using peanut shells instead of oat fiber.
New mealworm selected lines for high growth rate and short development time. This year we initiated two new mealworm lines designed to reduce development time and increase size. Line 16:190 is a modification of line 16:180, in which selection criteria for pupal size changed from a lower limit of 180 mg to 190 mg and a higher limit of 219 mg to 229 mg. Both lines will maintain a development time selection of 16.85 weeks as maximum development time. The second new line 17:190 is the result of a cross breeding between previous selected populations (17:S and 17:L) with selection criteria of a maximum development time of 17.85 weeks, a minimum pupal weight of 190 and a maximum of 239 mg. This selection parameters allow for a larger pupal size than in the 16:180 and 16:190 lines. Two full generations of selection have been applied at the current time and the third generation is in the process.
Insect powder for poultry feed. A total of 85 lb (34 kg) of freeze dry mealworms and an equal amount of freeze dry crickets were processed into powder and shipped to cooperators from Penn State University as part of an evaluation study on the potential of mealworm powder as a feed ingredient for broilers. For a second study by the University of Minnesota, 37 kg of cricket powder and 37 Kg of mealworm powder were processed and shipped. This experiment consisted of providing insect meal-based feed to commercial poultry farms. These experiments are currently in progress and are part of the agreement number 6066-25-00 0065957 with the University of Connecticut “Systems-based integrated program for enhancing the sustainability of antibiotic-restricted poultry production”, which involves multiple institutions and Universities.
Accomplishments
1. Diets for mealworms and crickets composed of agricultural by-products. Currently there is not a consistent commercial source of feed specifically designed to grow crickets and mealworms. Mealworms are currently grown using wheat bran and some fresh vegetables and crickets are mostly produced using modifications of chicken feeds. ARS scientists at Stoneville, Mississippi developed diets for mealworms and crickets composed of 80% or more by agricultural by-products, such as rice bran (whole and defatted), spent brewery grain, corn distilled grain, canola meal, and brewer’s yeast. These new diets are specifically formulated to enhance growth and reproduction in mealworms and crickets, making them superior to the existing diets used by commercial producers. These diet formulations, if commercialized, could provide much better feed to raise mealworms and crickets for animal feed.
2. Determination of heritability of two high plasticity characters associated with biomass productivity in the yellow mealworm. ARS researchers at Stoneville, Mississippi believe the yellow mealworm is one of the most important industrialized insects with potential to substitute unsustainable sources of animal protein for animal feed formulations. Methods for improving mealworm’s biomass productivity are critical for its commercial application. Three years of continuing research culminated in the determination of heritability of two traits of high plasticity (developmental speed and body size) in the yellow mealworm associated with biomass productivity. Larval development time showed a heritability of 63.37%, which is higher than expected given the level of impact that environmental factors exert on this character. Pupal weight had a heritability of 37.69%. These findings show that both traits are liable to show change in phenotypic frequencies by selection, which could provide a path for genetic improvement of mealworm lines. Ongoing three-generational selection studies show preliminary results that strongly support this assumption. These results show great potential for the development of improved mealworm lines with high biomass productivity. Such lines would benefit the existing industry and could significantly reduce the cost of insect biomass for animal feed.
3. Evidence for seasonal effects delaying and blocking pupation in the yellow mealworm. Over the past 10 years, ARS scientists at Stoneville, Mississippi, have received multiple inquiries from yellow mealworm producers about mealworms failing to pupate and remaining in the larval stage until they die. This phenomenon has also been observed in experimental colonies at USDA-ARS Stoneville, MS. Through three years of continuous observations, scientists have documented that mealworm development time is affected seasonally, even under controlled conditions of temperature, humidity, and light. Development time peaks during summer and decreases during winter. This evidence confirms that the phenomenon observed by producers is real and not due to their rearing procedures. Scientists are now focused on identifying the cause and finding solutions, which will benefit commercial mealworm producers, insect farmers, and consumers of insect meals.
4. Mealworm diets that shorten development time while maintaining a high productivity. One of the disadvantages of the yellow mealworm as a farmed insect is the unusually long development time of its larval stage, requiring from 4 to 9 months to reach the pupal stage depending on rearing conditions and seasonal delay. Scientists in USDA-ARS at Stoneville, Mississippi have developed multiple diet formulations, composed of at least 80% of agricultural by-products, which can significantly shorten the larval development time (by up to 1 month) of the yellow mealworm. These diets were the result of comprehensive nutritional studies based on self-selection methods and multiple levels of refinement. Evaluations reveal that some formulations shorten the development time by more than 30 days and can reduce or eliminate seasonal pupation blockage. These diet formulations could potentially solve the seasonal pupation blockage phenomenon experienced by commercial producers. These diets can be used by mealworm producers and farmers and could potentially reduce the production costs of mealworm biomass, making it more competitive to other less sustainable sources of animal protein such as fish meal.
5. Breeding of selected lines of the yellow mealworm to increase body size while maintaining development time stable. Selecting mealworm lines for improved biomass productivity. The yellow mealworm is one of the most important industrialized insects in the world and has great potential to be used as a substitute for fish meal in animal diets as a source of protein and essential nutrients. Fish meal is becoming increasingly unsustainable due to many factors including overfishing. Mealworm powder could provide a good substitute if its current price could be reduced. One way to reduce the costs of production is to increase its productivity. ARS scientists at Stoneville, Mississippi have produced 4 improved populations of the yellow mealworm through selective breeding, which poses high body size and a higher consistence in development time. At the same time, these four lines have been bred to maintain a development time of 16 weeks (not exceeding 17 weeks) using conventional food consisting of wheat bran and potato. Three of the lines produce mealworms with an average of 210 mg of pupal weight compared with an average of 140 mg of a non-selected population. One of the lines is capable to produce an average pupal weight of 240 mg, but their development takes two weeks longer than the other three lines. These four lines produce 15% more biomass than conventional mealworm breeding colonies during the same period and feeding the same diet.
Review Publications
Riddick, E.W. 2024. Evaluating the effects of flavonoids on insects: Implications for managing pests without harming beneficials.. Insects. 15(12), 956.
Morales Ramos, J.A., Macchiano Jr, A., Rojas, M.G. 2024. Estimating optimal temperature conditions for growth, development, and reproduction of tenebrio molitor (coleoptera: tenebrionidae). Journal of Economic Entomology. Vol, No. XX(XX):1-12.
Riddick, E.W., Rojas, M.G., Morales Ramos, J.A. 2024. A simple test of prey (aphid) recognition by laboratory reared Coleomegilla maculata (Coleoptera: Coccinellidae). Insects. 15,852.
Morales-Ramos, J.A., Rojas, M.G., Dossey, A.T., Berhow, M.A. 2020. Self-selection of food ingredients and agricultural by-products by the house cricket, Acheta domesticus (Orthoptera: Gryllidae): A holistic approach to develop optimized diets. PLoS One. 15(1):e0227400. https://doi.org/10.1371/journal.pone.0227400.
Ebrahimfar, J., Shishehbor, P., Rasekh, A., Riddick, E.W. 2020. Effect of factitious diets on development and reproduction of the ladybird beetle Stethorus gilvifrons, a predator of tetranychid mites. Biocontrol. 65:703-711. https://doi.org/10.1007/s10526-020-10033-y.
Zhou, A., Du, Y., Riddick, E.W., Li, L., Chen, J. 2021. Behavioral and electrophysiological response of sugarcane aphids and imported fire ants to 2, 4, 6-trimethylpyridine, an alkaloid from the pink-spotted lady beetles. Journal of Pest Science. https://doi.org/10.1007/s10340-021-01363-6.
Ashworth, A.J., Amorim, H.C., Drescher, G., Moore Jr, P.A., Rojas, M.G., Morales Ramos, J.A., Donoghue, A.M. 2025. Insect frass fertilizer as soil amendment for improved forage and soil health in circular systems. Scientific Reports. 15. Article 3024. https://doi.org/10.1038/s41598-025-87075-8.