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Research Article
Impact of host suitability on some biological and behavioral traits of the tachinid Compsilura concinnata
expand article infoMehran Rezaei‡, Mohammad Mehrabadi§, Ali Asghar Talebi§, Maryam Atapour‡
‡ Institute of Agriculture, Iranian Research Organization for Science and Technology (IROST), Tehran, Iran
§ Tarbiat Modares University, Tehran, Iran

Corresponding author: Mehran Rezaei ( mrn.rezaei@gmail.com )

Academic editor: Stefano Maini
© 2025 Mehran Rezaei, Mohammad Mehrabadi, Ali Asghar Talebi, Maryam Atapour.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Rezaei M, Mehrabadi M, Talebi AA, Atapour M (2025) Impact of host suitability on some biological and behavioral traits of the tachinid Compsilura concinnata. Bulletin of Insectology 78: 11-19. https://doi.org/10.3897/bull.insectology.152894
Open Access

Abstract

To better understand the biology of Compsilura concinnata (Meigen) as a potential biological control agent, it is necessary to determine suitability for potential hosts. In this study, laboratory tests were performed to investigate the acceptance and suitability of two key insect pests, e.g. Pieris rapae (L.) and Spodoptera litura (Fabricius) as host species for C. concinnata. In the first experiment, no significant difference was found for larval and pupal development duration, male and female puparium weight, female longevity period, sex ratio, adult yield, and fecundity of C. concinnata between P. rapae and S. litura. However, the parasitism rate and the host larval mortality were significantly higher for S. litura (58.37% and 65.82%, respectively) than for P. rapae (54.21% and 62.26%, respectively), but the values were very close between the two pests. In the second experiment, it was found that the ability of the parasitoid to locate between the hosts was insignificant. Nevertheless, the mean time to deposit two C. concinnata larvae was significantly longer for S. litura than P. rapae (third experiment). Overall, this finding indicates that C. concinnata could effectively contribute to lowering the population size of P. rapae and S. litura. Further studies must be done to apply C. concinnata successfully against these two host species in field and semi-field conditions.

Key Words

Biological control, Diptera, Host acceptance, Host-parasitoid interactions, Parasitoid, Tachinidae

Introduction

Dipteran parasitoids are the second most crucial group of parasitoid insects, which are far less studied than hymenopterans, also due to their relatively low species number (Dindo et al. 2003; Dindo and Grenier 2022). The Tachinidae is the largest and most important family of dipteran parasitoids that comprises approximately 1500 valid genera and more than 8500 described species in the world. This family is divided into four subfamilies, i.e., Exoristinae, Tachininae, Dexiinae, and Phasiinae, of which the Exoristinae is the most species-rich subfamily (Cantrell 1986; Stireman et al. 2006; Sahebari et al. 2018). Some species of the Tachinidae have been used in classical and augmentative biological control programs, especially in the Nearctic and Neotropical regions. Despite the high potential of Tachinidae parasitoids as effective biological control agents, their role in pest management programs has been less considered (Benelli et al. 2018; Dindo et al. 2019; Hammami et al. 2022). Not only in Iran but also in many parts of the world, the tachinid species are not commercially available and only some species of the family have been mass-reared (Dindo et al. 1999; Dindo and Grenier 2022). In the last decade, considerable research has been conducted on the identification and classification of Tachinidae in Iran, and more than 270 species of this family have been reported in the country (Farahani et al. 2018; Sahebari et al. 2018; Gilasian et al. 2022, 2024; Rezaei et al. 2022; Karami et al. 2023; Seyyedi-Sahebari et al. 2019, 2023).

Compsilura concinnata (Meigen) (Diptera: Tachinidae) is a larval, gregarious, polyphagous endoparasitoid of Lepidoptera, Hymenoptera, and Coleoptera which is recorded on about 289 host species (Ichiki et al. 2014; Tschorsnig 2017; Hammami et al. 2022). This parasitoid was described for the first time from Germany (Meigen 1824). In the eastern United States, C. concinnata was released widely to control Lymantria dispar (L.) (Lepidoptera: Erebidae) and other lepidopteran pests from 1906 to 1986 (Kellogg et al. 2003; Elkinton and Boettner 2012). In Massachusetts, percent parasitism by this species exceeded 25% on L. dispar (Fusco et al. 1978). The parasitoid is a prevalent species in northern Iran and has been recorded in four provinces (Guilan, Mazandaran, Fars, and Kohgiluyeh and Boyer-Ahmad) (Karami et al. 2023). This species is considered one of the most important biological control agents of the box tree moth, Cydalima perspectalis Walker (Lepidoptera: Crambidae), in the Hyrcanian forests of Iran (Farahani et al. 2018). Also, C. concinnata was reported as the indigenous natural enemy of the box tree moth in the southwest Mediterranean region (Lopez et al. 2022). As C. concinnata has a vast host range, the potential non-target impacts on native insects are a significant concern in classical biological control introductions (Elkinton and Boettner 2012).

The biology of C. concinnata was explained by Culver (1919). It is mentioned that three to four generations of the parasitoid occur per year, with the larvae overwintering in host larvae or pupae. Ichiki and Shima (2003) investigated the development, location, and respiration of C. concinnata larvae within the body of the silkworm, Bombyx mori (L.) (Lepidoptera: Bombycidae). The development times of C. concinnata from larviposition to pupation and initiation of cocoon spinning to pupation in fifth instar larvae of B. mori were 10 and 4.3 days, respectively, at the temperature of 23 °C. The parasitoid larvae usually emerge from the host body to pupate during or after the host’s prepupal stage. Averages of 2.1 (from 1 to 5) and 1.8 (from 1 to 4) parasitoid larvae per host emerged from the fourth and fifth instar larvae of B. mori, respectively (Ichiki and Shima 2003). Fusco et al. (1978) evaluated the effect of seven constant temperatures from 15.6 to 32.2 °C on the biological characteristics of C. concinnata. Their findings indicated that successful development from the first instar larva to adult emergence occurred within a temperature range of 15.6 to 29.4 °C. Following this result, Ichiki and Nakamura (2007) demonstrated that successful development from egg to adult was obtained within a temperature range of 15 to 27.5 °C, when Mythimna separata (Walker) (Lepidoptera: Noctuidae) larvae were used as hosts.

The study of biology and alternative hosts of C. concinnata is necessary to increase the parasitoid efficiency in biological control programs. Therefore, the experiment described below aimed at exploring the location, acceptance, and suitability of two key insect pests, i.e. Pieris rapae (L.) (Lepidoptera: Pieridae) and Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) as host species for C. concinnata. Both macromoth species have been reported as natural hosts of C. concinnata in previous studies (Cantrell 1986; Iwao et al. 1989; Wold-Burkness et al. 2005). These species were selected as case studies in the present research because they are getting more and more harmful to different host plants in Iran. The results may allow us to estimate the potential role that C. concinnata may play in controlling these invasive insect pests.

Materials and methods

Insect rearing protocols

In the laboratory, C. concinnata was reared on the greater wax moth Galleria mellonella (L) (Lepidoptera: Pyralidae). The original population of G. mellonella L. was collected from the colony kept at the Research Institute of Forests and Rangelands (RIFR) (Tehran, Iran). Galleria mellonella larvae were reared on an artificial diet at constant environmental conditions (30 ± 1 °C, 65 ± 5% RH, and complete darkness) as described by Dindo et al. (2003, 2019).

The original population of C. concinnata was collected from the Hyrcanian forest of Siahkal county, Guilan province in northern Iran (37°06'N, 49°87'E, ALT 253 m). The adult parasitoids were maintained in ventilated Plexiglas cages (45×35×35 cm) at constant environmental conditions (26 ± 1 °C, 65 ± 5% RH, and 16:8 h L:D photoperiod) and supplied with sugar cube and cotton balls soaked in a honey and water solution (20% honey w/w). Also, distilled water was provided via drinking cups with soaked cotton (Dindo et al. 2019). The temperature of 26 °C was selected based on the previous studies conducted on the rearing of C. concinnata and other tachinid species (Fusco et al. 1978; Dindo et al. 2003; Benelli et al. 2018). For colony maintenance, last instar larvae of G. mellonella were used as hosts, since they are the most suitable stage according to Ichiki and Shima (2003). Parasitization was performed by introducing ten mature larvae per mated adult female of C. concinnata into the cages for up to 24 hours (as described by Erb et al. 2001). The exposed larvae were then removed and placed in translucent plastic containers (11×10×4 cm) in the same constant environmental conditions until parasitoid larvae emerged and puparia formed.

The original population of P. rapae was collected from common cabbage fields in Pishva county of Tehran province in the north of Iran (35°31'N, 51°68'E, ALT 923 m). Chinese cabbage (Brassica pekinensis Ruprecht Hero veriety) was grown in plastic pots (10 cm diameter, 9 cm high) as a host plant under greenhouse conditions (25 ± 5 °C, 65 ± 10% RH, and 16:8 h L:D photoperiod). The 5-week-old plants were used to maintain P. rapae population in ventilated cages (45×35×35 cm). Aqueous honey solutions (40% honey) were placed in each cage as a source of carbohydrates for adult nutrition. The colony was maintained in a growth chamber at constant environmental conditions (26 ± 1 °C, 65 ± 5% RH, and 16:8 h L:D photoperiod).

The original population of S. litura was collected from corn and beet fields in the same location as P. rapae. The colony of S. litura was kept on the artificial diet developed by Shorey and Hale (1965) at constant environmental conditions (26 ± 1 °C, 65 ± 5% RH, and 16:8 h L:D photoperiod).

Experimental design

Biological characteristics of Compsilura concinnata on different hosts

The newly emerged adults of C. concinnata were kept in a ventilated Plexiglas cage (45×35×35 cm) and fed as described in the rearing procedure for five days to ensure they had the opportunity to mate and develop fertile eggs. The pre-oviposition is reported five days (Fusco et al. 1978; Weseloh 1980; Bourchier 1991). According to Culver (1919), the parasitoid copulation lasted from 26 min. to 1 h. and 50 min. If the male is 2–4 days older than the female, the copulation occurs more readily. Accordingly, we ensured the females were completely developed to conduct the experiments. A pair of parasitoids (1 female and 1 male per cage) was placed inside the ventilated Plexiglas cage (45×35×35 cm) and fed as described in the rearing procedure. The females used in the experiment were inexperienced (i.e., they had never encountered a host). The last instar larvae of P. rapae and S. litura were daily exposed to parasitoids from emergence until death. It is reported that the last instar host larvae are the most suitable for parasitism by C. concinnata (Weseloh 1984; Bourchier 1991; Ichiki and Shima 2003). The newly-moulted last instar larvae were detected by the presence of moulted head capsule or detached cuticle. The larvae were exposed to the parasitoid females within 48 h. after the ecdysis (Sanchez 1995). For each host species, 10 larvae per cage were placed and removed after 2 h. (as described by Fusco et al. 1978). The exposed larvae were provided with the host plant leaves or artificial diet in translucent plastic containers (11×10×4 cm). The leaves or diets were replaced with fresh ones every two days. After pre-pupation (i.e., cessation of feeding), the host larvae were maintained without food. Since the parasitoids emerged from the host to pupate, the parasitized larvae were monitored daily until the parasitoid larvae emerged or died. The parasitoid larvae were then placed individually into a 20 ml plastic cup without food until puparium formation. For each host species, different parameters of the parasitoid, including larval and pupal development period (day), adult longevity (day), adult yield (%), puparium weight (mg), sex ratio (%), host larval mortality (%), percent parasitism, and fecundity (larvae/female) were evaluated. Also, the size and weight of the host body were investigated. Body length was measured from the anterior to the posterior end, excluding appendages, using a calibrated ocular micrometer under a stereomicroscope. The percentage of adult yield was estimated as the number of parasitoid adults emerged/number of puparia × 100 (Simoes et al. 2004). Puparium weight was measured seven days after puparium formation as a parameter of body size (Ichiki et al. 2014). The sex ratio was determined upon adult emergence based on female offspring. The percentage of larval mortality was evaluated as the number of larvae from which puparia were obtained + dead larvae that did not produce puparia/total number of larvae ×100 (Simoes et al. 2004). The percent parasitism was calculated as the number of parasitized larvae/total number of larvae ×100. Fecundity was estimated as the total number of parasitoid puparia obtained from host larvae parasitized by a female throughout the life span. The experiment was performed at 26 ± 1 °C, 65 ± 5% RH, and 16:8 L:D photoperiod with 20 pairs of adult parasitoids per host species and each pair of the parasitoid was considered a replication.

Location and acceptance of Pieris rapae vs. Spodoptera litura

A two-choice laboratory test was conducted to assess whether C. concinnata displays a difference in locating and accepting P. rapae vs. S. litura. The experimental design was adopted from Depalo et al. (2010) which was conducted on E. larvarum. The 7-day-old mated females were singly released in a Plexiglas cage (45×35×35 cm) with two targets. The targets included: (a) one P. rapae larva and (b) one S. litura larva. Each host larva was placed on the bottom of the glass Petri dish (5 cm diameter). A target was considered as chosen when the female parasitoid larviposited inside the host body. As mentioned by Ichiki and Nakamura (2007), a small quantity of body fluid is usually gushed out from the wound when a host larva is attacked by a C. concinnata female. However, the host’s acceptance was considered when bleeding had taken place. Forty female flies (40 replications) were tested and each was tested only once. For each female, the two targets were renewed and placed in the cage in a different position to avoid the position effect on parasitoid response. The parameters used to assess location and acceptance of the targets were the number and percentage of female which chose each target and the total duration of time (min) spent by each female in the cage until larviposition (= time to make the choice). A maximum of 12 minutes was considered for the larviposition and the females that did not choose any hosts were excluded from the analysis. The adult parasitoids were fed as described in the rearing procedure. The experiment was conducted at 26 ± 1 °C, 65 ± 5% RH, and 16:8 L:D photoperiod.

Acceptance and suitability of Pieris rapae vs. Spodoptera litura

This experiment was performed to further test the acceptance of P. rapae vs. S. litura as hosts for C. concinnata. Like the former test, the experimental design was adopted from Depalo et al. (2010). Four treatments considered were: P. rapae larvae (a) exposed or (b) not exposed to C. concinnata and S. litura larvae (c) exposed or (b) not exposed to C. concinnata. Each treatment consisted of 20 host larvae and the experiment was replicated four times. The larvae were singly exposed to the female and removed when attacked two times by the parasitoid (the optimal number of larvae per host according to Caron et al. 2010). The larviposition was recognized when the bleeding had taken place. The duration (min) needed to have this larviposition in each host larva was recorded and used as a parameter to assess acceptance. The larvae of P. rapae and S. litura (parasitized or unparasitized) were placed individually into the translucent plastic containers (11×10×4 cm), supplied with leaves or diet and daily monitored. The leaves or diet were exchanged for fresh ones every two days. To assess suitability, the number of successfully parasitized larvae (= larvae from which puparia were obtained) was recorded for treatments (a) and (c). Moreover, the total number of dead larvae was also calculated for all treatments. The adult parasitoids were fed as in the rearing procedure. The experiment was conducted at 26 ± 1 °C, 65 ± 5% RH, and 16:8 L:D photoperiod. Two indices (DI = Degree of Infestation, SP = Success rate of Parasitism) summarizing the host-parasitoid interactions, adapted from Martini et al. (2019), were scored. The DI measured the proportion of host larvae that, following exposure to C. concinnata, died due to the parasitoid larval activity (not necessarily resulting in puparium formation). This index was estimated as (T-di)/T, where T and di were the number of adult months that emerged from control larvae (T) or larvae exposed to C. concinnata flies (di). The SP measured the probability that an infested host (= a host containing larvae of this gregarious parasitoid) would give rise to at least one adult fly. This was estimated as pi/(T-di), where pi was the number of moth larvae exposed to C. concinnata, which produced at least one adult fly. When pi > (T-di), SP was set as 1.

Statistical analysis

Data were first checked for assumptions of normality with the Kolmogorov-Smirnov test. An arcsine transformation was used to transform percentage values for analysis. Comparison between the two host species was assessed with a t-test (P < 0.05), after checking for homogeneity of variances using Levene’s test. A χ2 analysis was run to determine if there was any deviation from the expected female choice of 1:1 (second experiment). All statistical analyses were done using IBM-SPSS v.22.0 software (IBM, Armonk, NY, USA).

Results

Biological characteristics of Compsilura concinnata

No significant difference was found for the larval (t = -1.969, df = 38, P = 0.056) and pupal (t = -1.939, df = 38, P = 0.060) development duration of C. concinnata between two host species as shown in Fig. 1. Also, the male and female puparium weight were not significantly different (t = 1.019, df = 38, P = 0.077; Fig. 2). Results for the female longevity period, sex ratio, and adult yield of the parasitoid were not significantly different between P. rapae and S. litura (Table 1). The percentage of parasitism and host larval mortality were significantly influenced by the host species. The maximum values of the mentioned parameters were estimated for S. litura (58.37% and 65.82%, respectively). The number of parasitoids per parasitized host and fecundity did not differ significantly between the two hosts. The mean number of parasitoid puparia obtained from host larvae throughout the life span of a female parasitoid was evaluated as 111.95 and 105.70 (puparia/female) for P. rapae and S. litura, respectively (Table 1). There were significant differences between P. rapae and S. litura for the body size (t = 11.581, df = 38, P < 0.001) and body weight (t = 2.834, df = 38, P < 0.01). The mentioned body parameters were higher for P. rapae (32.33 mm and 222.30 mg, respectively) than for S. litura (27.52 mm and 209.65 mg, respectively), as shown in Fig. 3.

Figure 1. 

Mean (± SE) larval and pupal development duration (days) of Compsilura concinnata reared on two hosts, Pieris rapae and Spodoptera litura.

Table 1.
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Female longevity, sex ratio, adult yield, parasitism, host larval mortality, number of parasitoids per parasitized host, and fecundity of Compsilura concinnata reared on two hosts, Pieris rapae and Spodoptera litura.

Parameters Host species Statistics
P. rapae S. litura t df P
Female longevity (d) 13.9 ± 0.67a1 12.7 ± 0.65a 1.282 38 0.208
Sex ratio (female %) 52.21 ± 0.56a 54.08 ± 0.76a -1.971 38 0.056
Adult yield (%) 93.30 ± 0.44a 92.13 ± 0.47a 1.817 38 0.077
Parasitism (%) 54.21 ± 0.84a 58.37 ± 1.19b -2.846 38 0.007
Host larval mortality (%) 62.26 ± 0.88a 65.82 ± 1.46b -2.089 38 0.043
No. parasitoids/parasitized host 2.33 ± 0.04a 2.38 ± 0.03a -1.106 38 0.276
Fecundity (puparia/female) 111.95 ± 8.95a 105.70 ± 8.96a 0.494 38 0.624

1 Means within a row followed by different letters are significantly different (t-test: P < 0.05).
Figure 2. 

Mean (± SE) male and female puparium weight (mg) of Compsilura concinnata reared on two hosts, Pieris rapae and Spodoptera litura.

Figure 3. 

Mean (± SE) body size (mm) (a) and body weight (mg) (b) of two host species, Pieris rapae and Spodoptera litura. Means within a panel capped with different letters are significantly different (t-test: P < 0.05).

Location and acceptance of Pieris rapae vs. Spodoptera litura

The results regarding female choice are shown in Fig. 4a. This parameter was not significantly influenced by the host species (χ2 = 1.600, df = 1, P = 0.206). The percentages of females that chose P. rapae and S. litura were 60% and 40%, respectively. Also, the time spent by the female parasitoid to choose P. rapae and S. litura larvae was not significantly different (t = -1.058, df = 38, P = 0.297; Fig. 4b). The estimated parameters for P. rapae and S. litura were 3.75 and 4.25 minutes, respectively.

Figure 4. 

Choice (%) by Compsilura concinnata females between the two host species, Pieris rapae and Spodoptera litura. A target was considered as chosen when the female larviposited in the host (a). The mean (± SE) of the total time spent by C. concinnata females to choose P. rapae and S. litura larvae (b).

Acceptance and suitability of Pieris rapae vs. Spodoptera litura

The mean time (± SE) to have two C. concinnata larvae deposited in the host larva was 5.14 ± 0.10 and 5.68 ± 0.10 min for P. rapae and S. litura, respectively. The difference between the two host larvae was significant (t = -3.846, df = 6, P < 0.01). The females spent a significantly longer time to larviposition in S. litura compared to P. rapae. Regarding the indices summarizing the host-parasitoid interactions, the DI values exceeded 90% and were not significantly different between P. rapae and S. litura. However, the SP values were 100% for the two host species (Table 2).

Table 2.
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Indices (% ± SE) summarizing host-parasitoid interactions for two host species, Pieris rapae and Spodoptera litura.

Parameters Host species Statistics
P. rapae S. litura t df P
DI: degree of infestation 93.0 ± 1.4a1 91.8 ± 1.5a 0.602 6 0.569
SP: success rate of parasitism 1002 100

1 Means within a row followed by different letters are significantly different (t-test: P < 0.05). 2 No statistical analysis was conducted.

Discussion and conclusion

Many insect parasitoids are highly specialized, attacking only one or a few species of hosts. Compsilura concinnata has a broad and cross-Order host range (Cantrell 1986; Hammami et al. 2022). Host range is often determined by a range of biological and ecological characteristics of the host including diet, growth potential, immunity, and phylogeny (Depalo et al. 2012; Hiroyoshi et al. 2017; Li et al. 2023). The results obtained in these experiments showed that C. concinnata females accepted both P. rapae and S. litura as suitable hosts. It seems that in both species, the physiological state in the hemocoel of hosts was clearly at best for the survival and development of C. concinnata larva. These two macromoth species were reported as natural hosts of C. concinnata in different studies (Cantrell 1986; Iwao et al. 1989; Wold-Burkness et al. 2005). However, endoparasitoids must overcome the host immune response for successful development, and for these reasons, they are often highly co-evolved with their suitable hosts (Li et al. 2023).

The results showed that a lower number of larvae were deposited into S. litura than P. rapae, but the difference between the two host species was not significant. Also, lower larval and pupal duration and longer adult longevity were observed for P. rapae, though the differences were not significant. For percentage parasitism and host larval mortality, although the differences were significant, the values were very close between the two hosts. However, slight differences exist in various measured parameters between the parasitoids reared from both lepidopteran hosts; overall, the parasitoids reared from P. rapae showed comparable parameters to those reared from S. litura. Accordingly, former studies investigated the biological characteristics of C. concinnata on different host species, including Pseudaletia unipuncta (Lepidoptera: Noctuidae) (Kaya 1984), L. dispar (Fusco et al. 1978; Erb et al. 2001), B. mori (Ichiki and Shima 2003), M. separata (Ichiki and Nakamura 2007; Ichiki et al. 2014), and P. rapae (Ramadan et al. 2021).

Parasitoid weight may depend on several factors, including host size, species, sex, and age. It is, however, mentioned that the size of parasitic insects may not be influenced by the size of their parents (Dindo et al. 1999; Ichiki and Nakamura 2007). In this study, the host body size and weight showed significant differences but did not affect the parasitoid weight. This difference between the two host species may arise from their rearing diets, as P. rapae was reared on a plant-based system, whereas S. litura was reared on an artificial diet. In line with the current result, Weseloh (1984) showed that C. concinnata developed faster in larger host larvae than in small ones. Female puparial weight is a good predictor of the potential fecundity of the parasitoid (Caron et al. 2008; Ichiki et al. 2014). It is mentioned that there is a significant positive relationship between the number of ovarioles per adult fly and the puparia weight of female C. concinnata (Bourchier 1991).

Examination of the acceptance and suitability of different host species for C. concinnata is important for determining the parasitoid’s host range (Depalo et al. 2012; Hiroyoshi et al. 2017). In the second experiment, it was found that the ability of the parasitoid to locate between the hosts was insignificant. This result further suggested that P. rapae and S. litura larvae are equally accepted by C. concinnata. Nevertheless, the mean time to deposit two C. concinnata larvae was significantly longer for S. litura than P. rapae (third experiment). By locating P. rapae more quickly, C. concinnata may maximize potential offspring fitness (Caron et al. 2008).

Most studies concerning host selection behaviour have involved hymenopterous parasitoids, for which chemical cues have been shown to play a significant role (Depalo et al. 2010, 2012; Rezaei et al. 2019). Movement might be an important host cue for C. concinnata and the host must be physically contacted before larviposition behavior occurs (Weseloh 1980). Such has been suggested for other tachinids. For Exorista larvarum (L.), Depalo et al. (2010) stated that at close range (e.g., in the cage environment), the tachinid females primarily use visual cues and, in particular, motion signals in the host location. Also, it is reported that living L. dispar was slightly more acceptable than dead ones for C. concinnata (Weseloh 1980). On the contrary, the weight of the host larvae did not influence the time for the parasitoid to contact the host (Caron et al. 2008). Therefore, C. concinnata preferentially larviposits in hosts that are actively moving and it is mentioned that adult tachinids from these hosts produced viable progeny (Hotchkin and Kaya 1983).

The DI (Degree of Infestation) measured the proportion of hosts that were successfully parasitized and SP (Success rate of Parasitism) estimated the probability that an infested host will give rise to an adult parasitoid. Our results confirmed that P. rapae and S. litura are well accepted and suitable for C. concinnata which exhibited the highest level of DI (> 90%) and SP (= 100%). However, this parameter was not significantly different between the two host species. Accordingly, Martini et al. (2019) investigated the acceptance and suitability of C. perspectalis as a host for E. larvarum. They evaluated the values of DI and SP for C. perspectalis as 91.7 and 0%, respectively, and no puparia of E. larvarum formed in any accepted host larvae.

A female of C. concinnata usually attacks the same host several times, with each attack usually being preceded by a period of examination (Caron et al. 2010). Additionally, the female often deposits no eggs even though they attacked the hosts (Ichiki and Nakamura 2007). As shown by Caron et al. (2010), excessive superparasitism negatively affects C. concinnata development time and pupal weight and skews the parasitoid sex ratio in favor of males. Future studies on the current topic are therefore recommended. Additionally, it would be valuable to evaluate the optimal exposure time of the host species to the parasitoid. Tritrophic interactions due to a reduction in the ability of the parasitoid to detect hosts on different plants are also relevant in multi-crop systems (Rezaei et al. 2019). It is reported that C. concinnata has different efficiency and potential on various crops (Caron et al. 2008). Also, Bourchier (1991) showed that L. dispar fed on a diet containing higher levels of tannins, which reduces plant quality to herbivores, produced C. concinnata individuals with longer development time and lower puparium weight. As shown in the previous study (Depalo et al. 2010), the phytophagous-infested plant decreases the attractiveness of S. littoralis larvae to E. larvarum, further experimental investigations are needed to estimate the effects of the host plant (first level) on the biological and behavioral characteristics of C. concinnata. It is mentioned that the mechanisms of host selection in Tachinidae, including the role of host plants, are far less known (Stireman et al. 2006; Depalo et al. 2010; Dindo and Grenier 2022). This highlights the importance of assessing tritrophic interactions in biological control programs since the parasitoid may be released against generalist targets on more than one crop plant (Caron et al. 2008).

Several authors, as an exemplification Elkinton and Boettner (2012), have addressed the risks of biological control as release parasitoids may attack endemic non-target or beneficial species. Although C. concinnata is widely distributed, wide and augmentative release may expand its range, potentially endangering other insect species, such as silkworm farms or endangered butterflies (Li et al. 2023). This issue will be important in univoltine host species as the parasitoid would attack non-target species to complete multiple generations each year after target host larvae are no longer available (Elkinton and Boettner 2012). Since P. rapae and S. litura are multivoltine species, the risks of attacking non-target species by this tachinid may not be seriously considered in augmentative release programs. However, the potential risks of the use of C. concinnata under field conditions should be taken into account.

In conclusion, C. concinnata was adaptable to different hosts and may serve as a model species for further detailed studies of its adaptation mechanism to various hosts in generalist endoparasitoids. Plasticity towards host use in C. concinnata indicates its potential to adapt to exotic hosts (Sanchez 1995; Tschorsnig 2017). However, there can be some fitness costs associated with novel hosts. Host species may differ in quality or size, affecting a parasitoid’s key fitness traits (Caron et al. 2008). Our study demonstrates the possible benefits of using P. rapae and S. litura as the rearing hosts for C. concinnata. Also, P. rapae is available worldwide and easy to be cultured at low cost on host plants. One important factor to consider in rearing biological control agents is cost-benefit (Li et al. 2023). Further studies may be needed to confirm the efficiency of the parasitoids reared from the investigated host species under field and semi-field conditions.

Acknowledgments

We are grateful to the Iran National Science Foundation (INSF) for the financial support of this study. This experiment was conducted as part of the postdoctoral project of the first author (No.: 99026306). The research was supported by the Iranian Research Organization for Science and Technology (IROST) which is greatly appreciated. We acknowledge the laboratory support of Tehran Municipality, Green Area Research, Education and Advisory Center, Area 20 (Iran). We warmly thank Dr. Reihaneh Gholami Ghavamabad (Research Institute of Forests and Rangelands, Tehran, Iran) for providing the G. mellonella specimens. We cordially thank Prof. Stefano Maini (the Managing Director) and two anonymous reviewers for their critical reviews and constructive comments which significantly improved the paper.

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