Introduction
Cockroaches are cosmopolitan insects that have undergone millennia of evolution, resulting in a high degree of adaptation to diverse environments (Gondhalekar et al., 2021). Their active habitats include settings with heavy microbial contamination—such as sewers, refuse dumps, and manure heaps—which implies direct contact with carcasses and feces (Vatandoost, 2023). Their lifestyle, feeding behavior, and reproductive biology make them important mechanical vectors of pathogenic microorganisms, including multidrug-resistant bacteria affecting humans and animals, via contaminated cuticle and mouthparts, as well as through regurgitation and fecal deposits (Turner et al., 2021; Vatandoost, 2023; Kakooza et al., 2025). In a large-scale synthesis, Donkor (2020) further summarized and confirmed the carriage and dissemination of numerous pathogens (bacterial, viral, fungal, and parasitic) by cockroaches.
To protect animal and human health, the implementation of integrated cockroach management is recommended (Abbasi, 2025). A key component is the use of baits, in which the insecticidal active ingredient is incorporated into a food matrix with high—often selective—attractiveness to cockroaches. Some bait formulations include denatonium benzoate (Bitrex), a highly bitter synthetic agent used as a deterrent for people and companion animals to prevent accidental ingestion. Baits are applied as gels for placement into cracks and crevices, and as dry, solid baits housed in plastic stations that reduce inadvertent contact or access by non-target animals (pets) and humans. These advantages make baits one of the preferred methods for insecticidal treatments (Hubbard et al., 2024).
Our recent survey documented widespread infestations of the oriental cockroach in industrial pig farms in Bulgaria, with several units (newborn units, sanitary filters, and weaning sections) exhibiting high population densities (Boneva et al., 2023).
The aim of the present study was to determine the efficacy of several commonly used insecticidal baits against the oriental cockroach, Blatta orientalis L., collected from pig farms in Bulgaria, in order to assess their suitability for pest-control applications.
Materials and Methods
Insects
Tests were performed with the oriental cockroach, B. orientalis (L.), collected from seven industrial pig farms in Bulgaria. The identification of B. orientalis adults and fifth-instar nymphs was confirmed based on external morphology (body coloration, pronotal pattern, wing pad development, and antennal segmentation) following the diagnostic characters described by Bell et al. (2007). Before bioassay, insects were acclimated for at least 3 days in laboratory conditions with a temperature of 20–26 °C, relative humidity of 30–50%, and a photoperiod of 9 h light: dark. From each population, experimental and control groups were formed, each comprising 10 randomly selected 5th-instar nymphs.
Food baits
The efficacy of four insecticidal bait formulations widely used in cockroach control was evaluated (Table 1).
Each formulation was tested as received, without additional dilution or modification. All baits were stored in sealed containers at room temperature and used within their shelf-life period. For clarity, the commercial products were coded according to their trade names to avoid brand-related bias. The tested baits included a gel formulation containing 0.6% indoxacarb, a pro-insecticide disrupting sodium channel function after enzymatic activation (code AG), a combined gel containing 2.15% imidacloprid, a nicotinic acetylcholine receptor agonist, together with 0.5% S-methoprene, a juvenile hormone analogue disrupting normal development and reproduction (code MG), an inorganic desiccant gel with 50% diatomite (code Chl.E), and a solid bait combining 50% silicon dioxide, an inorganic desiccant, with 1% tetramethrin, a neurotoxic pyrethroid blocking sodium channels (Code Chl.D).
Test method
A no-choice lethal feeding assay with insecticidal food baits was conducted (Gondhalekar et al., 2011). For each population, treatment groups received 1 g of a test bait as the sole food source; control groups were maintained under identical conditions on the laboratory non-toxic diet. All groups had water ad libitum. Each test set-up was run in triplicate. Knockdown and mortality were recorded every 8 h during the first 24 h, and thereafter daily through day 7.
Knockdown was defined as stimulus-induced immobility rendering individuals unable to move freely, feed, or drink, while still exhibiting vital signs and partial reflex responses (e.g. trembling of legs/antennae) after gentle probing with forceps (Dong et al., 1998). Individuals in complete physiological immobilization with no response to stimuli and no limb movement, which persisted until the end of the monitoring period, were classified as dead. If the mortality of the control group exceeded 5%, the mortality observed in the treatments was corrected using Abbott‘s formula (Equation 1) (Abbott, 1925):
1. Corrected mortality (%)=[(Pt−Pc)×100]/(100−Pc)
Where, Pt is the observed mortality rate (%) in the treatment group and Pc is the mortality rate (%) in the control group.
Statistical analysis
Data were analyzed using UNIANOVA, with post hoc comparisons by Tamhane’s T2 or Tukey’s HSD test, depending on the outcome of Levene’s test for homogeneity of variances. Analyses were conducted using SPSS software, version 26.0.
Assessment
Efficacy was interpreted according to OECD guidance (OECD, 2013): in a no-choice test, efficacy is generally considered sufficient when a mortality rate ≥95%, corrected according to Abbott, is achieved by the end of the assay.
Results
All baits showed excellent acceptance by B. orientalis (Table 2).
Cumulative mortality across the MG, Chl.D, and Chl.E treatments exceeded 95% by the end of 168 hours, whereas AG produced 100% knockdown without recorded mortality (R²=0.995). MG showed the highest knockdown effect (66.7%) at 48 hours and a mortality of 96.7% at 168 hours (R²=0.918–0.954). Chl.D and Chl.E achieved 100% mortality at 168 hours with a slower dynamics of the knockdown effect (R²=0.833–0.997).
Discussion
Insecticidal baits have emerged as the leading and preferred method for chemical control of cockroaches in infested premises, increasingly replacing contact sprays. They are targeted at the insects and leave low toxic residues (Rutgers NJAES, 2020; UF/IFAS Extension, 2022). High water content and optimized phagostimulants — especially in gels and pastes —enhance attractiveness and consumption (and thus uptake of active ingredients) relative to solid baits (Lucero et al., 2025).
Among the widely used active ingredients in modern cockroach baits are indoxacarb and imidacloprid, as well as inorganic desiccants, such as silicon dioxide and diatomite. Indoxacarb acts on the insect nervous system and belongs to the oxadiazine class, blocking voltage-gated sodium channels of the pyrazoline type (Rezende-Teixeira et al., 2022). Imidacloprid, a neonicotinoid, also targets the nervous system through the activation of postsynaptic nicotinic acetylcholine receptors and is increasingly incorporated into bait formulations (Naveen et al., 2022). To enhance the overall efficacy of neonicotinoid-based formulations, juvenile hormone analogues, such as S-methoprene are sometimes included to provide long-term population suppression by disrupting insect development and reproduction (Jindra & Bittova, 2020).
Desiccant actives are another common option for bait matrices. Natural diatomite (diatomaceous earth), a geological material composed of fossilized siliceous skeletons (diatoms and other algae containing amorphous silicon dioxide), is considered safe and recommended for eco-friendly pest management (Korunic, 1998). Desiccant particles damage the cuticle by absorbing cuticular hydrocarbons and abrasion, increasing water loss and causing death by desiccation (Faulde et al., 2006).
In our laboratory, in lethal no-choice feeding assays with oriental cockroaches from pig farms, the tested baits showed excellent acceptance and high cumulative efficacy (Table 2). Using the indoxacarb gel (AG), we recorded a strong knockdown: 80% of cases by 48 h and 100% by 96 h. Although no mortality was recorded by the end of the monitoring period (168 h), the complete immobilization (inability to move, feed, or drink) indicates high practical efficacy and a trajectory toward eventual lethality. Indoxacarb acts as a pro-insecticide that requires bioactivation by insect esterases and amidases to form the toxic N-decarbomethoxyllated metabolite (Wing et al., 2000). In cases where paralysis occurs rapidly, this enzymatic activation may be disrupted, preventing the full conversion to the active form and thus reducing or eliminating mortality. This mechanism could account for the 0% mortality observed in the AG group by the end of the experimental period. The very high coefficient of determination (R²=0.995) supports a strong effect attributable to the active ingredient. High field performance of related products has been reported in apartments infested with German cockroaches, achieving 75.1% and 92.1% population reductions at two and four weeks, respectively (Wang & Bennett, 2008).
For the combination gel (MG; imidacloprid + S-methoprene), knockdown was more moderate (66.7%) at 48 h, while mortality increased over time—reaching 73.3% at 144 h and approaching a maximum (~96–97%) by the end of the observation period. High coefficients of determination (R²=0.918; 0.954) again indicate a strong causal link between the measured outcomes and the applied insecticide(s).
Using the two inorganic desiccant products (Chl.D and Chl.E), knockdown remained weak (<25%) with negligible, statistically non-significant differences between products. Nevertheless, both achieved complete (100%) mortality by 168 h. Mortality occurred earlier and reached satisfactory levels with the pyrethroid-fortified Chl.D (76.7% at 72 h), whereas the diatomite-only Chl.E reached an effective mortality of 86.7% at 120 h. Coefficients of determination ranged from moderate for knockdown (R²=0.662; 0.833) to high for mortality (R²=0.945; 0.997).
From a practical standpoint, the temporal dynamics of knockdown and mortality should guide product choice. Under heavy infestations, products delivering rapid knockdown and/or faster mortality are preferable to curb migration and the spread of pathogens.
The high efficacy of bait-based insect control, confirmed by our findings, has been documented for nearly half a century (Rust & Reierson, 1978) and by numerous contemporary studies (Wang & Bennett, 2008; Kostina et al., 2020; Rahayu et al., 2021). Field applications have produced substantial population reductions, typically 80–96.4% within four weeks, across different settings (Appel & Benson, 1995; Ree et al., 2006), and most baits have remained effective against field populations (Fardisi et al., 2017). Taken together, these data support incorporating insecticidal food baits into integrated cockroach management programs for infested pig farms.
Conclusion
Insecticidal food baits are an effective method for controlling cockroaches in livestock facilities. All the products tested met the European Chemicals Agency (ECHA) criteria for effectiveness against B. orientalis. Given their high consumption rates, selectivity, and practical benefits, these baits should be an essential part of an integrated approach to managing cockroaches.
Limitations
The main limitation of this study is the laboratory-based design, which may not fully reflect real farm environments. Future field studies are required to confirm the observed efficacy under practical conditions.
Ethical Considerations
Compliance with ethical guidelines
There were no ethical considerations to be considered in this research.
Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.
Authors' contributions
All authors equally contributed to preparing this article.
Conflict of interest
The authors declared no conflict of interest.
Acknowledgments
Thanks to Vladimir Petrov, Faculty of Veterinary Medicine, Trakia University, Stara Zagora, Bulgaria.
References
Abbasi, E. (2025). Cockroaches as urban pests: Challenges, public health implications, and management strategies. IJID One Health, 9, 100086. [DOI:10.1016/j.ijidoh.2025.100086]
Abbott, W. S. (1925). A method of computing the effectiveness of an insecticide. Journal of Economic Entomology, 18(2), 265–267. [DOI:10.1093/jee/18.2.265a]
Appel A. G., & Benson, E. P. (1995). Performance of abamectin bait formulations against German cockroaches (Dictyoptera: Blattellidae). Journal of Economic Entomology, 88(4), 924-931. [DOI:10.1093/jee/88.4.924]
Bell, W. J., Roth, L. M. & Nalepa, C. A. (2007). Cockroaches: Ecology, behavior, and natural history. Baltimore: The Johns Hopkins University Press. [Link]
Boneva, B., Zhelev, G., & Marutsov, P. (2023). A survey of the distribution of synanthropic cockroaches in animal farms and food processing plants in Bulgaria. Trakia Journal of Sciences, 21(3), 216–223. [Link]
Dong, K., Valles, S. M., Scharf, M. E., Zeichner, B., & Bennett, G. W. (1998). The knockdown resistance (kdr) mutation in pyrethroid-resistant German cockroaches. Pesticide Biochemistry and Physiology, 60(3), 195–204. [DOI:10.1006/pest.1998.2339]
Donkor, E. S. (2020). Cockroaches and food-borne pathogens. Environmental Health Insights, 14, 1178630220913365. [DOI:10.1177/1178630220913365] [PMID]
Fardisi M., Gondhalekar, A. D., & Scharf, M. E. (2017). Development of diagnostic insecticide concentrations and assessment of insecticide susceptibility in German cockroach (Dictyoptera: Blattellidae) field strains collected from public housing. Journal of Economic Entomology, 110 (3), 1210-1217. [DOI:10.1093/jee/tox076]
Faulde, M. K., Tisch, M., & Scharninghausen, J. J. (2006). Efficacy of modified diatomaceous earth on different cockroach species (Orthoptera: Blattellidae) and silverfish (Thysanura: Lepismatidae). Journal of Pest Science, 79(3), 155–161. [DOI:10.1007/s10340-006-0127-8]
Gondhalekar, A. D., Appel, A. G., Thomas, G. M., & Romero, A. (2021). A review of alternative management tactics employed for the control of various cockroach species (order: Blattodea) in the USA. Insects, 12(6), 550. [DOI:10.3390/insects12060550] [PMID]
Gondhalekar, A. D., Song, C., & Scharf, M. E. (2011). Development of strategies for monitoring indoxacarb and gel bait susceptibility in the German cockroach (Blattodea: Blattellidae). Pest Management Science, 67(3), 262–270. [DOI:10.1002/ps.2057] [PMID]
Hubbard, C. B., & Murillo, A. C. (2024). Behavioral resistance to insecticides: Current understanding, challenges, and future directions. Current Opinion in Insect Science, 63, 101177. [DOI:10.1016/j.cois.2024.101177] [PMID]
Jindra, M., & Bittova, L. (2020). The juvenile hormone receptor as a target of juvenoid "insect growth regulators". Archives of Insect Biochemistry and Physiology, 103(3), e21615. [DOI:10.1002/arch.21615] [PMID]
Kakooza, S., Ssajjakambwe, P., Nalubega, R., Namazi, B., Nantume, A., & Ssentamu, G., et al. (2025). Cockroaches as Reservoirs, Vectors, and Potential Sentinels of Multidrug-Resistant Bacteria in Ugandan Communities: A Retrospective Analysis. Global Health, Epidemiology and Genomics, 2025, 5940509. [DOI:10.1155/ghe3/5940509] [PMID]
Korunić, Z. (1998). Diatomaceous earths, a group of natural insecticides. Journal of Stored Products Research, 34(2–3), 87–97. [DOI:10.1016/S0022-474X(97)00039-8]
Kostina, M. N., & Kostin, F. N. (2020). [Insecticidal activity of acetamiprid in various formulations (Russian)]. Dezinfektsionnoe Delo (Disinfection Affairs), 1, 54–60. [Link]
Lathrop, R., Wong, F., Aronson, M., Chin, A., Clemson, B., & DeFeo, J., et al. (2021). Climate action plan supplemental report: Report of working group on land use and offsets regarding planning, development, and design. New Jersey: Rutgers. [Link]
Lucero, I. M., Gaire, S., & DeVries, Z. C. (2025). Effects of age and environmental conditions on cockroach gel bait performance. Journal of Economic Entomology, 118(4), 1850–1867. [DOI:10.1093/jee/toaf130] [PMID]
Naveen, A., Sahu, M. R., Padhi, K. S., & Maharik, S. S. (2022). Self-poisoning with safer insecticide: A case series on imidacloprid poisoning. The American Journal of Forensic Medicine and Pathology, 43(1), 66–68. [DOI:10.1097/paf.0000000000000685] [PMID]
Rahayu, R., Sari, I. P., Aurida, H., Solfiyeni, S., Jannatan, R., & Mairawita, M. (2021). The effectiveness of commercial gel baits against German cockroach Blattella germanica (Linnaeus, 1767) in Indonesia. Polish Journal of Entomology, 90(2), 63–69. [DOI:10.5604/01.3001.0014.9056]
Ree, H. I., Lee, I. Y., Jeon, S. H., & Yong, T. S. (2006). Field trial on the control effect of fipronil bait against German cockroaches. The Korean Journal of Parasitology, 44(3), 255–257. [DOI:10.3347/kjp.2006.44.3.255] [PMID]
Rezende-Teixeira, P., Dusi, R. G., Jimenez, P. C., Espindola, L. S., & Costa-Lotufo, L. V. (2022). What can we learn from commercial insecticides? Efficacy, toxicity, environmental impacts, and future developments. Environmental Pollution (Barking, Essex : 1987), 300, 118983. [DOI:10.1016/j.envpol.2022.118983] [PMID]
Rust, M. K., & Reierson, D. A. (1978). Comparison of the laboratory and field efficacy of insecticides used for German cockroach control. Journal of Economic Entomology, 71(4), 704–708. [DOI:10.1093/jee/71.4.704]
Turner, M., Peta, V., & Pietri, J. E. (2022). New insight into the relationship between Salmonella Typhimurium and the German cockroach suggests active mechanisms of vector-borne transmission. Research in Microbiology, 173(3), 103920. [DOI:10.1016/j.resmic.2021.103920] [PMID]
University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS Extension). (2022). Assessment-based pest management of German cockroaches (EDIS IN1190). Retrieved from: [Link]
Vatandoost, H. (2023). Biology, medically importance of cockroaches and their control. Journal of Clinical Cases & Reports, 6(S13), 10. [Link]
Wang, C., & Bennett, G. W. (2008). Comparison of organic and inorganic insecticides for control of the German cockroach in apartments, 2007. Arthropod Management Tests, 33(1), J2. [DOI:10.1093/amt/33.1.J2]
