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Biological Control of Bradysia odoriphaga Using Coenosia attenuata with Banker Media System and Mulch Layer

  † These authors contributed equally to this article.

Submitted:

31 August 2026

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31 August 2026

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Abstract

Greenhouse cage trials were conducted to evaluate the biocontrol potential of the predatory tiger fly Coenosia attenuata against the Chinese chive maggot Bradysia odoriphaga infesting Allium tuberosum. To enhance pest suppression, we supplemented the predator with alternative prey (Drosophila melanogaster adults), a banana‑based banker medium, and a coir mulch layer across four treatments over 50 weeks. When C. attenuata was released alone (T1), corrected control efficacy against B. odoriphaga larvae ranged from 56.14% to 59.82%. Notably, peak larval suppression was significantly higher in treatments combining the predator with mulch layer (T2: 94.23%) or with the banker media system (T4: 100%). Against adult stages, T1 achieved 32.68%–69.73% corrected efficacy, whereas T2 and T4 reached peak values of 100% and 97.69%, respectively. Predator application also doubled the dry weight of Chinese chive. However, the concurrent use of banker medium and mulch layer (T3) did not produce synergistic effects. Collectively, these findings demonstrate that banker media system and coir mulch layers are effective auxiliary tools for enhancing C. attenuata‑based biocontrol in protected cultivation systems.

Keywords: 
Coenosia attenuata
;  
fungus gnat management
;  
Bradysia odoriphaga
;  
banker media system
;  
mulch layer
;  
Allium tuberosum
Subject: 
Biology and Life Sciences  -   Insect Science

1. Introduction

The Chinese chive maggot, Bradysia odoriphaga infests over 7 plant families, including 30 commercially important crops including Chinese chives, onions, garlic, ginger, and others [1,2]. The soil-dwelling larvae of this fungus gnat feed on these crop roots and stems and can cause significant yield loss [3]. In the absence of insecticide treatments maggot damage can destroy an entire crop [4,5]. Chemical insecticide application is the main approach for B. odoriphaga management in China and elsewhere [6]. Repeated application of chemical insecticides has led to rapid development of insecticide resistance in B. odoriphaga populations and has resulted in environmental pollution and high insecticide residues on marketed vegetables [7,8].
Entomopathogenic nematodes (EPNs) have been reported as potential biological control agents for several species in the genus Bradysia. Heterorhabditis sp. was shown to be effective against B. odoriphaga [9,10]. Ma et al. (2013) evaluated the virulence of 145 isolates from 13 species of EPNs against B. odoriphaga and found a Steinernema feltiae isolate to perform best in field applications [5]. Wu et al. (2015) evaluated EPNs and sticky card combinations and found a S. feltiae isolate in combination with a black sticky card to perform best against 3rd instar B. odoriphaga [11]. Despite their demonstrated potential, EPNs have seen limited application against B. odoriphaga due to their vulnerability to soil conditions. Likewise, thermal control methods, though effective at temperatures exceeding 37°C for 4 hours [12,13], are constrained by practical complexities. Some chemosensory genes and proteins, such as BodoCSP4, BodoCSP6 and BodoCSP7, play crucial roles for B. odoriphaga to identify their host [14,15,16]. However, there is still a long way to go before these genes and their encoded proteins can be applied for pest control [17]. In contrast, the exploration of natural enemy insects for controlling this pest has received little attention.
The predaceous fly Coenosia attenuata is currently thought to be a useful biological pest control agent in greenhouses. It is also known as “tiger fly”, “killer fly”, or “hunter fly” [18,19,20,21]. It has received attention because of its ability to effectively suppress a wide range of agricultural pests, such as fungus gnats, whiteflies, leaf miners, winged aphids, leafhoppers, midges, moth flies, shore flies, and fruit flies [22,23,24,25,26,27,28,29]. The wide range of prey used as food makes them very flexible; hence especially useful. C. attenuata adults live above the soil and feed on flying insects, but its larvae are soil-dwelling and feed on small soft bodied of soil invertebrates like the larvae of sciarids and shore flies. C. attenuata is native to Europe and was likely introduced via plant material. It has since become distributed worldwide and has been documented in several regions of China, including Taiwan, Xinjiang, Yunnan and Tianjin of China [29,30,31,32,33,34].
Our previous research demonstrated that each adult C. attenuata is capable of preying on approximately 18.5 to 20.3 adult B. odoriphaga per day under laboratory conditions [35], highlighting its potential as an effective biological control agent against B. odoriphaga. In this study, the biological control of B. odoriphaga infesting Chinese chive, Allium tuberosum, in greenhouse was carried out using C. attenuata. Drosophila adults (an alternative prey), bananas (a banker medium) and coir substrate (a mulch layer) were used to enhance the control of B. odoriphaga with C. attenuata.

2. Materials and Methods

2.1. Experimental Bradysia odoriphaga

A colony of B. odoriphaga was initiated from approximately 200 B. odoriphaga adults collected from a greenhouse at Institute of Plant Protection of Tianjin Academy of Agricultural Sciences (Xiqing District, Tianjin, China). Twenty to thirty pairs of newly emerged B. odoriphaga adults were placed in transparent plastic rearing containers (8.5-cm top diameter, 11.5-cm bottom diameter, 6-cm high). The top of the plastic pot was modified to include one 3.0-cm-diameter hole covered with fine screen (0.4-mm mesh openings) for ventilation. A Petri dish (11-cm diameter) served as the bottom. A piece of Chinese chive bulb (4-mm thick), serving as oviposition site, was placed on a piece of filter paper in the Petri dish contained a layer of 2.5% water agar. Adult females oviposited for a period of 2 to 4 days and died. About 3 days later, larvae hatched and pieces of Chinese chive stems were placed on the Petri dish as food. The duration of larvae and pupae was about 25 days and 5 days, respectively. The colony was maintained in a laboratory incubator and held at 24 ± 1 °C, 14:10 (L: D) and 70 ± 5% RH.

2.2. Experimental Bradysia impatiens

The larvae of B. impatiens were used as prey for larvae of C. attenuata because of their shouter development time. A colony of fungus gnats was initiated with about 100 B. impatiens adults collected from a greenhouse at the Modern Agricultural Science and Technology Innovation Base (Wuqing District, Tianjin, China). Bradysia impatiens were reared using a simplified method of that reported by Zou et al. (2021) [33]. Briefly, 300 mL of black peat (Lvdimeijing Science and Technology Co., Ltd., Beijing, China) and 55 to 60 g of dry kidney bean powder were placed in an open plastic box (25.5 × 19 × 7.8 cm3). The mix was then moistened with 250 mL of tap water and 0.2-cm thick layer of moist coir (Shanghai Galuku Agricultural Science and Technology Co., Ltd., Shanghai, China; desalted, EC = 0.5, family pack, common grade) was placed on the top of the mix. Then the open plastic box was placed in a tissue bag (50 × 35 cm2 , 0.4-mm mesh openings). Four hundred to 500 newly emerged adult B. impatiens were placed in the tissue bag and closed with a binder clip. Fresh rearing medium was prepared daily and new cultures were set up daily. The colony was maintained in a laboratory incubator and held at 24 ± 1 °C, 14:10 (L: D) and 70 ± 5% RH.

2.3. Experimental Coenosia attenuata

The C. attenuata used to establish a laboratory colony for this study were collected at Leizhuangzi flower farm of Tianjin, China. Adults were introduced to a cage (50 × 70 × 50 cm3), containing oviposition media consisting of an open plastic box (20 × 29 × 7 cm3) with eggs of B. impatiens on rearing media as described above, and 1-cm thick layer of moist coir placed on top of the rearing media for oviposition. Drosophila melanogaster adults were supplied as prey every day for the adult C. attenuata. Five to 6 days later, the oviposition media was replaced with a new one. The exposed oviposition media was transferred to another cage and second and third instar larvae of B. impatiens were added to the box to feed larvae of C. attenuata. Distilled water was added to the box when the media became dry. About 20 to 21 days later, adults of C. attenuata emerged. The colony was maintained in a laboratory incubator and held at 25 ± 1 °C, 14:10 (L: D) and 70 ± 5% RH.

2.4. Biological Control of B. odoriphaga Using C. attenuata in Cages of Greenhouse

Fifteen nylon mesh cages (1 × 1.5 × 1 m3, 0.165-mm mesh openings) were arranged in a greenhouse at the Modern Agricultural Science and Technology Innovation Base (Wuqing District, Tianjin, China). Each cage was fully enclosed on six sides, with an 80 cm-long zipper installed on one side to serve as an access door. Twenty healthy 1-year-old Chinese chive plants were transplanted into each plastic flowerpot (21-cm top diameter, 13.5-cm bottom diameter, 20-cm high) filled with a sterilized substrate containing of equal volumes of black peat and peat moss. Four grams of compound fertilizer (N:P:K = 5:2:1) were added to each pot. Ten labelled flowerpots (numbered 1-10) were placed inside each cage and arranged in two rows of 5 pots. One control CK and 4 treatments (denoted T1-T4) were tested in this study; the treatments comprised different combinations of maggots, tiger flies, mulch layers and banker media with Drosophila flies, as detailed in Table 1. Each treatment was replicated 3 times. Climate data were recorded using HOBO® data logger, model U23-001 (Onset Computer, MA, USA).
The experiment was initiated on 6 May 2025. Adults in each cage were counted weekly using a hand-held counter, while larvae were enumerated from the soil of differently located flowerpots bearing identical numbers. Following larval counting, Chinese chive plants, soil and larvae were returned to their original flowerpots. The corrected control efficacies against B. odoriphaga were evaluated at 3, 10, 20, 30, 40, and 50 weeks after the start of the experiment. Dead Chinese chive plants were replaced with healthy individuals weekly. All chives were mown above ground at the start of the experiment. Dry weight (g; dried at 90 °C for 9 h using a Memmert UFE 600 oven, Germany; measured for all ten flowerpots in each cage), plant height (cm; determined on the ten tallest plants per cage) and chlorophyll content (SPAD value; measured with an SPAD-502 chlorophyll meter, Konica Minolta Sensing, Inc., Japan; readings taken on the middle leaf portion of the ten tallest plants per cage) were recorded every four weeks.

2.5. Statistical Analyses

One-way ANOVA and subsequent Tukey’s HSD test at α = 0.05 were used to compare the plant height, chlorophyll content, dry weight, and corrected control efficacy. When variances were unequal, Welch's ANOVA followed by Games-Howell test at α = 0.05 was ued. All the statistical tests were done using SAS version 9.4. The corrected control efficacy was calculated using the Abbott formula [36].

3. Results

3.1. Corrected Control Efficacy Against B. odoriphaga Larvae in Greenhouse Conditions with Chinese Chive

The corrected control efficacy against B. odoriphaga larvae with different treatments were shown in Figure 1. The fungus gnat larvae were suppressed by C. attenuata larvae during the subsequent 50 weeks with the corrected control efficacy of 56.14% at 40 weeks to 59.82% at 3 weeks in T1. Interestingly, the 100% corrected mortality observed at 10 and 20 weeks in all treatments was attributed to high temperature rather than C. attenuata. The corrected control efficacy against B. odoriphaga larvae was significantly higher for T4 than T2 and T3 at 3 weeks (F = 9.03, p = 0.006).
The fungus gnat larvae were suppressed by C. attenuata larvae during the subsequent 50 weeks with the corrected control efficacy of 42.47% at 3 weeks to 94.23% at 30 weeks in T2 (Figure 1). There was no significant difference in corrected control efficacy in T2, T3, and T4 at 30 weeks. However, the corrected control efficacy against B. odoriphaga larvae was higher in T2 with the help of coir layer than T1 at 30 weeks (F = 4.48, p = 0.04). At 40 weeks, there was no significant difference in corrected control efficacy in T2, T3, and T4, but all of them were significantly higher than that of T1 (F = 18.4, p = 0.0006). At 50 weeks, corrected control efficacy against B. odoriphaga larvae did not differ significantly between T1 and T2. However, T3 and T4, which utilised banker media, exhibited significantly higher corrected control efficacy than T2 (F = 7.62, p = 0.0099).
In treatment T3 with banker media and a mulch layer, C. attenuata larvae suppressed fungus gnat larvae over the subsequent 50 weeks, with corrected control efficacy varying from 50.68% at 3 weeks to 98.46% at 40 weeks (Figure 1). However, treatment T3 exhibited significantly higher corrected control efficacy than that of T2 (F = 7.62, p = 0.0099), but only at 50 weeks. In treatment T4 containing banker media system, C. attenuata larvae suppressed fungus gnat larvae across the subsequent 50-week period, with corrected control efficacy ranging from 73.03% at 3 weeks to 100% at 40 weeks (Figure 1). Treatment T4 exhibited significantly higher corrected control efficacy than treatment T2 (mulch-layer treatment) at both 3 weeks and 50 weeks.

3.2. Corrected Control Efficacy Against B. odoriphaga Adults in Greenhouse Conditions with Chinese Chive

The corrected control efficacy against B. odoriphaga adults across different treatments was shown in Figure 2. Fungus gnat adults were suppressed by C. attenuata adults in T1 over the subsequent 50 weeks, with corrected control efficacy ranging from 32.68% at 30 weeks to 69.73% at 50 weeks. There was no significant difference in corrected control efficacy in T3 and T4, but both of them were significantly higher than that of T1 and T2 at 3 weeks (F = 9.82, p = 0.0047). Consistent with the observations for larvae, the 100% corrected control efficacy against adults was also attributable to high temperature at 10 and 20 weeks.
The fungus gnat adults were suppressed by C. attenuata adults during the subsequent 50 weeks with the corrected control efficacy of 65.94% at 3 weeks to 100% at 30 weeks in T2 (Figure 2). Especially at 30 weeks with the lowest temperature, T2 and T3, which utilised mulch layer, exhibited significantly higher corrected control efficacy than T1 and T4 (F = 27.72, p = 0.0001). Compared with B. odoriphaga adults, adults of C. attenuata and D. melanogaster lost activity under low-temperature stress and possessed poor low-temperature tolerance. At 40 weeks, there was no significant difference in corrected control efficacy in T2 and T4, but both of them were significantly higher than that of T1 (F = 7.28, p = 0.0113). At 50 weeks, corrected control efficacy against B. odoriphaga adults did not differ significantly among treatments T2, T3, and T4. Nevertheless, T2 (mulch-layer treatment) and T4 (banker media treatment) exhibited significantly higher corrected control efficacy than T1 (F = 6.2, p = 0.0175).
In treatment T3 with banker media and a mulch layer, C. attenuata adults suppressed fungus gnat adults over the subsequent 50 weeks, with corrected control efficacy ranging from 68.38% at 40 weeks to 87.61% at 30 weeks (Figure 2). Further, treatment T3 exhibited significantly higher corrected control efficacy than T1 and T2 at 3 weeks (F = 9.82, p = 0.0047). In treatment T4 containing banker media system, C. attenuata adults suppressed fungus gnat adults across the subsequent 50-week period, with corrected control efficacy ranging from 32.83% at 30 weeks to 97.69% at 50 weeks (Figure 2). At 3, 40, and 50 weeks, treatment T4 exhibited significantly higher corrected control efficacy than treatment T1 (mulch-layer treatment) (F = 9.82, p = 0.0047; F = 7.28, p = 0.0113; F = 6.2, p = 0.0175, respectively).

3.3. Plant Height of Chinese Chive in Greenhouse Conditions

Across all treatments, Chinese chive plant height increased under high-temperature conditions and decreased under low-temperature conditions. For CK, T1, T2, T3, and T4, plant height varied from 7.96 cm (9 December 2025) to 31.74 cm (16 September 2025), 10.51 cm (9 December 2025) to 37.18 cm (19 August 2025), 10.91 cm (3 March 2026) to 37.33 cm (19 August 2025), 10.39 cm (9 December 2025) to 33.63 cm (19 August 2025), and 11.21 cm (9 December 2025) to 34.34 cm (19 August 2025), respectively (Figure 3).
No significant differences in Chinese chive plant height were detected among all treatments and CK on 27 May 2025, 24 June 2025, 11 November 2025, and 3 February 2026 (F4, 71.69 = 0.899, p = 0.47; F4, 71.56 = 1.237, p = 0.303; Games-Howell test, all p > 0.05; F = 1.48, p = 0.2105, respectively). CK exhibited significantly lower plant height than T1, T2, T3, and T4 on 19 August 2025, 14 October 2025, and 9 December 2025 (Games-Howell test, all p ≤ 0.048; Games-Howell test, all p ≤ 0.014; F = 5.68, p = 0.0003, respectively).
The Chinese chive was significantly lower for CK than of T1 and T2, but not significantly lower than of T3 and T4 on 22 July 2015 (Games-Howell test, p = 0.029, 0.008, 0.093, 0.152, respectively). In treatment T2 with a mulch layer, Chinese chive exhibited significantly higher plant height than CK, T1, T3, and T4 on 16 September 2025 (Games-Howell test, all p ≤ 0.001). Similarly, on 6 January 2026, treatment T2 exhibited significantly higher plant height than CK, T3, and T4 (F = 6.93, p < 0.0001). With the help of banker media system, T4 exhibited the highest plant height on 3 March 2026, 31 March 2026, and 28 April 2026. However, no significant differences in Chinese chive plant height were detected between T3 and CK on 3 March 2026, 31 March 2026 (Games-Howell test, p = 0.96 and 0.89, respectively), and 28 April 2026 (F = 6.79, p < 0.0001) (Figure 3).

3.4. Leaf Chlorophyll Content of Chinese Chive in Greenhouse Conditions

Consistent with the pattern observed for plant height, leaf chlorophyll content of Chinese chive increased under high-temperature conditions and decreased under low-temperature conditions across all treatments. For CK, T1, T2, T3, and T4, leaf chlorophyll content ranged from 35.26 SPAD (9 December 2025) to 51.6 SPAD (22 July 2025), 40.41 SPAD (9 December 2025) to 52.66 SPAD (22 July 2025), 39.85 SPAD (11 November 2025) to 54.46 SPAD (28 April 2026), 35.05 SPAD (9 December 2025) to 50.91 SPAD (24 June 2025), and 37.42 SPAD (9 December 2025) to 52.42 SPAD (24 June 2025), respectively (Figure 4).
No significant differences in leaf chlorophyll content were detected among all treatments and CK on 27 May 2025, 22 July 2025, 19 August 2025, 16 September 2025, 11 November 2025, 6 January 2026, and 3 March 2026 (Games-Howell test, all p > 0.05; F = 0.67, p = 0.6174; F = 0.83, p = 0.5087; F = 1.03, p = 0.3922; F = 1.45, p = 0.2211; F = 1.13, p = 0.3441; F = 1.46, p = 0.2172, respectively). CK exhibited significantly lower leaf chlorophyll content than T1, T2, T3, and T4 on 24 June 2025 and 14 October 2025 (Games-Howell test, all p ≤ 0.0007; F = 5.18, p = 0.0006, respectively).
No significant differences in leaf chlorophyll content were observed between CK and T1 on 3 February 2026, 31 March 2026, and 28 April 2026 (Games-Howell test, p = 0.971, 0.97, 0.985, respectively). Benefiting from the mulch layer, T2 achieved the highest leaf chlorophyll content across these three sampling dates mentioned above. No significant differences in leaf chlorophyll content were found between T4 and CK on 9 December 2025 and 3 February 2026 (Tukey's HSD test, adjusted p = 0.558, 0.869, respectively), as well as on 31 March 2026 (Games-Howell test, p = 0.079). Even with both the banker media system and mulch layer, T3 exhibited significantly lower leaf chlorophyll content than T2 on 9 December 2025 and 3 February 2026 (Tukey's HSD test, adjusted p = 0.0003, 0.0205, respectively), as well as on 31 March 2026 and 28 April 2026 (Games-Howell test, p = 0.0003, 0.0002, respectively).

3.5. Dry Weight of Chinese Chive in Greenhouse Conditions

Across all treatments, Chinese chive dry weight fluctuated with mean temperature: it peaked in September and dropped to the minimum in December under the lowest mean temperature, followed by an upward increase from February as temperature rose (Figure 5). The dry-weight ranges for CK, T1, T2, T3, and T4 were 0.21–7.31 g, 0.63–12.97 g, 0.78–17.07 g, 0.57–12.61 g, and 0.65–11.44 g, corresponding to 9 December 2025 (minimum) and 16 September 2025 (maximum), respectively (Figure 5).
No significant differences in dry weight were detected among all treatments and CK on 27 May 2025, 24 June 2025, 22 July 2025, and 28 April 2026 (F4, 4.25 = 6.35, p = 0.0567; F4, 4.334 = 0.8425, p = 0.5578; F4, 4.56 = 3.01, p = 0.1394; F = 1.91, p = 0.1852, respectively). CK exhibited significantly lower dry weight than T1, T2, T3, and T4 on 19 August 2025, 16 September 2025, 14 October 2025, 3 February 2026, and 3 March 2026 (F = 12.67, p = 0.0006; Games-Howell test, all p ≤ 0.0499; F = 11.65, p = 0.0009; Games-Howell test, all p ≤ 0.048; Games-Howell test, all p ≤ 0.048, respectively).
Treatment T2 had a numerically higher dry weight than T1 on 19 August 2025 and 16 September 2025, although no significant difference was detected between the two treatments (Tukey's HSD test, adjusted p = 0.7915; Games-Howell test, p = 0.2627, respectively). By contrast, T2 showed a significantly lower dry weight than T1 on 3 March 2026 (Games-Howell test, p = 0.04).
T3 exhibited numerically greater dry weight than T2 on 3 March 2026, although no significant difference was observed between the two treatments (Games-Howell test, p = 0.557). Likewise, dry weight did not differ significantly between T3 and T4 on 3 March 2026 (Games-Howell test, p = 0.793). Both T3 and T4 had significantly greater dry weights than T2 (Games-Howell test, p = 0.045 and 0.004, respectively), whereas no significant difference was found between T3 and T4 on 31 March 2026 (Games-Howell test, p = 0.987).
Across the one-year experiment, the total mean dry weight of Chinese chive per cage was 29.28 g (CK), 62.09 g (T1), 63.03 g (T2), 58.00 g (T3), and 59.40 g (T4). Yield of Chinese chive was enhanced in T1, T2, T3 and T4 following the release of C. attenuata, compared with the CK treatment without C. attenuata.

4. Discussion

At 25 °C, B. odoriphaga adults live only 3.62–4.39 days [37], while C. attenuata adults survive approximately 20 days longer. To exploit this disparity, we introduced a banker media system (banker media, M. acuminata, and alternative prey D. melanogaster) to enhance biocontrol efficacy in Chinese chive fields (Figure 6). Similar in concept to banker plants, this system prolonged C. attenuata population persistence, increasing predation on B. odoriphaga adults. Consequently, the combined strategy nearly doubled the dry weight of A. tuberosum under greenhouse conditions, a value comparable to that of plants treated with entomopathogenic nematodes and imidacloprid [38]. Leaf chlorophyll content of Chinese chive was not significantly affected by feeding damage from B. odoriphaga larvae throughout the experiment. Therefore, leaf chlorophyll content is not suitable assessment parameter for evaluating whether underground roots and stems of Chinese chive are damaged by B. odoriphaga larvae.
From July to September in this study, field populations of B. odoriphaga nearly disappeared under sustained mean temperatures above 22 °C, leading to 100 % corrected control efficacy against this pest. These observations align with earlier studies documenting reduced adult survival of B. odoriphaga [39,40,41]. Therefore, besides natural enemies such as the predator fly, high temperature itself can effectively suppress B. odoriphaga populations. Under high-temperature conditions, releases of natural enemies may not be necessary.
Coenosia attenuata is active across a broad temperature range (≈12 to 42 °C) [42]. However, our field observations showed that adult C. attenuata exhibited little flight activity under sustained mean temperatures below 15 °C, from mid-November to early-January. Therefore, releases of C. attenuata adults may not be feasible for suppressing B. odoriphaga adults when mean temperatures remain below 15 °C. In contrast, C. attenuata larvae are capable of preying upon soil-dwelling B. odoriphaga larvae.
Maintaining C. attenuata adult populations by provision of Drosophila adults and banker media is a promising strategy to improve the biocontrol efficacy of C. attenuata against B. odoriphaga. This was supported by our present findings, in which treatment T4 achieved higher corrected control efficacy against both B. odoriphaga larvae and adults compared to T1 (which used only C. attenuata). Although C. attenuata adults prefer fungus gnats over other preys [43], the release density of Drosophila adults should not be excessively high. Excess alternative prey can compete with the target pest, likely reducing predation pressure on B. odoriphaga. Furthermore, the flight of C. attenuata individuals was affected by environmental factors and was increased in response to increases in the number of prey flights [44]. Our laboratory observations indicated that frequent flight activity of C. attenuata may cause wing abrasion and shorten adult longevity [33].
Mulch layer is an important habitat modification that benefits development of conservation of naturally occurring biological agents. Some work with chrysanthemum showed that mulch layers support the establishment of astigmatic mites and, as a result, increase densities of soil-dwelling predatory mites [45]. Similar methods have been reported to support the generalist hunter fly C. attenuata with the help of a wood fiber substrate [22]. Martins et al. (2015) found that the addition of coir substrate to a soil substrate improved the rearing efficiency of C. attenuata [46]. Besides, coir substrate could be used as oviposition substrate and rearing substrate in some experiments [22,27,47]. In our study, coir substrate was successful as a mulch layer to enhance the biological control of B. odoriphaga with C. attenuata. Additionally, Figueiredo et al. (2012) found that mucus produced by earthworms induced C. attenuata females to extend their ovipositors and lay more eggs in some situations. They concluded mucus acts as a kairomone [48]. Hence, developing mulch layers with kairomone for supporting C. attenuata in greenhouse crops seems to be a promising method. In treatment T3, the combined application of the banker media system and mulch layer did not generate synergistic effects. This may be because the improvement in biocontrol efficacy was constrained by the carrying capacity of the experimental cage.
The banker media system and/or mulch layer may offer promising, cost-effective and environmentally sustainable management measures for future biocontrol of whiteflies, leafminers, and spotted-wing drosophila (Drosophila suzukii) using C. attenuata. Nevertheless, C. attenuata larvae are unable to feed on above-ground stages including whitefly nymphs, leafminer larvae, or D. suzukii larvae. When releasing C. attenuata adults for suppressing adult target pests, banker media system consisting of kidney bean powder, black peat, coir substrate, and fungus gnat eggs and/or larvae can be deployed in greenhouses, open fields, and orchards. C. attenuata adults can oviposit within the banker media, and newly hatched larvae subsequently prey upon fungus gnat larvae in banker media. Banker media containing C. attenuata eggs and/or larvae can then be transferred to the insectary for rearing; newly emerged adults are thereafter collected, transported and released at target sites. Collectively, our results highlight that banker media systems containing crop-safe alternative prey, or a mulch layer combined with kairomones to stimulate predator oviposition, deserve further research.

Author Contributions

Conceptualization, D.Z., T.C. and H.W.; methodology, D.Z. and Y.L.; validation, W.X., J.X. and H.B.; formal analysis, D.Z. and Y.C.; investigation, D.Z., Y.B. and B.H.; data curation, H.B., W.X. and J.X.; writing—original draft preparation, D.Z. and H.W.; writing—review and editing, T.C., W.X. and J.X.; funding acquisition, D.Z., T.C. and J.X. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Tianjin Finance Bureau, grant number 12000026P33442210233G, Tianjin Academy of Agricultural Sciences, grant number 2022003, and USDA Agricultural Research Service, grant number 5070-22000-037-00-D.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Acknowledgments

The authors sincerely thank the editors and reviewers for their valuable insights and thoughtful feedback, which have significantly enhanced the quality of this manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Corrected control efficacy against Bradysia odoriphaga larvae under greenhouse conditions in different treatments (Values are mean ± SE. Different letters above columns indicate significant differences based on one-way ANOVA followed by Tukey’s HSD test; p < 0.05).
Figure 1. Corrected control efficacy against Bradysia odoriphaga larvae under greenhouse conditions in different treatments (Values are mean ± SE. Different letters above columns indicate significant differences based on one-way ANOVA followed by Tukey’s HSD test; p < 0.05).
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Figure 2. Corrected control efficacy against Bradysia odoriphaga adults under greenhouse conditions in different treatments (Values are mean ± SE. Different letters above columns indicate significant differences based on one-way ANOVA followed by Tukey’s HSD test; p < 0.05).
Figure 2. Corrected control efficacy against Bradysia odoriphaga adults under greenhouse conditions in different treatments (Values are mean ± SE. Different letters above columns indicate significant differences based on one-way ANOVA followed by Tukey’s HSD test; p < 0.05).
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Figure 3. Mean plant height of Chinese chive under greenhouse conditions in different treatments. Values are means ± SE. Different lowercase letters above the bars indicate significant differences among treatments (α = 0.05). Levene's test was used to assess homogeneity of variances. When variances were homogeneous, one-way ANOVA followed by Tukey's HSD test was performed; when variances were heterogeneous, Welch's ANOVA followed by Games-Howell test was applied.
Figure 3. Mean plant height of Chinese chive under greenhouse conditions in different treatments. Values are means ± SE. Different lowercase letters above the bars indicate significant differences among treatments (α = 0.05). Levene's test was used to assess homogeneity of variances. When variances were homogeneous, one-way ANOVA followed by Tukey's HSD test was performed; when variances were heterogeneous, Welch's ANOVA followed by Games-Howell test was applied.
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Figure 4. Mean leaf chlorophyll content of Chinese chive under greenhouse conditions in different treatments. Values are means ± SE. Different lowercase letters above the bars indicate significant differences among treatments (α = 0.05). Levene's test was used to assess homogeneity of variances. When variances were homogeneous, one-way ANOVA followed by Tukey's HSD test was performed; when variances were heterogeneous, Welch's ANOVA followed by Games-Howell test was applied.
Figure 4. Mean leaf chlorophyll content of Chinese chive under greenhouse conditions in different treatments. Values are means ± SE. Different lowercase letters above the bars indicate significant differences among treatments (α = 0.05). Levene's test was used to assess homogeneity of variances. When variances were homogeneous, one-way ANOVA followed by Tukey's HSD test was performed; when variances were heterogeneous, Welch's ANOVA followed by Games-Howell test was applied.
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Figure 5. Mean dry weight of Chinese chive under greenhouse conditions in different treatments. Values are means ± SE. Different lowercase letters above the bars indicate significant differences among treatments (α = 0.05). Levene's test was used to assess homogeneity of variances. When variances were homogeneous, one-way ANOVA followed by Tukey's HSD test was performed; when variances were heterogeneous, Welch's ANOVA followed by Games-Howell test was applied.
Figure 5. Mean dry weight of Chinese chive under greenhouse conditions in different treatments. Values are means ± SE. Different lowercase letters above the bars indicate significant differences among treatments (α = 0.05). Levene's test was used to assess homogeneity of variances. When variances were homogeneous, one-way ANOVA followed by Tukey's HSD test was performed; when variances were heterogeneous, Welch's ANOVA followed by Games-Howell test was applied.
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Figure 6. Banker media system for biocontrol of Bradysia odoriphaga using Coenosia attenuata.
Figure 6. Banker media system for biocontrol of Bradysia odoriphaga using Coenosia attenuata.
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Table 1. Five different treatments in this experiment.
Table 1. Five different treatments in this experiment.
Treatments Chinese chive maggot a Tiger fly b Mulch layer c Banker media and Drosophila fly d
CK Bradysia odoriphaga --- --- ---
T1 B. odoriphaga Coenosia attenuata --- ---
T2 B. odoriphaga C. attenuata coir substrate ---
T3 B. odoriphaga C. attenuata coir substrate banana and D. melanogaster
T4 B. odoriphaga C. attenuata --- banana and D. melanogaster
a Fifteen and 30 pairs of newly emerged B. odoriphaga adults were released in each cage on 26 March 2025 and 3 April 2025, respectively. b One male and 2 females of newly emerged C. attenuata adults were first released in each cage on 29 April 2025. Then 1 female and 1 male, 4 females and 2 males, 3 females and 1 male, 2 females and 2 males, 1 female and 1 male, 2 females and 1 male newly emerged C. attenuata adults were intermittently released in each cage on 13 May 2025, 7 October 2025, 16 December 2025, 17 February 2026, 24 February 2026, and 6 April 2026, respectively. c One-cm thick layer of moist coir was added on the soil surface of flowerpot on 29 April 2025. The moist coir was put on the soil surface of flowerpot again every week after investigation. d Twenty pairs of newly emerged D. melanogaster adults, reared with banana in laboratory, were first released in each cage on 30 March 2025. One banana was put in a plastic pot (15-cm top diameter, 8-cm bottom diameter, 6-cm high) surrounded by flowerpots in the cage and periodically replenished. Then 20, 20, 15, 20, 10, 25, 5 pairs of newly emerged D. melanogaster adults were released in each cage on 3 April 2025, 21 May 2025, 25 June 2025, 10 July 2025, 9 September 2025, 24 September 2025, and 9 October 2025, respectively.
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