The capacity of Trichogramma chilotraeae (Hymenoptera: Trichogrammatidae) to parasitize Spodoptera frugiperda reared with natural diet vs artificial diet vs alternate host

Parasitoids can be mass-produced easily using artificial diets or an alternate host. This research examined Trichogramma chilotreae’s ability to parasitize S. frugiperda (reared on different diets) and Corcyra cephalonica eggs (alternate host). The research was conducted using a completely randomized design. The treatment used is the type of egg (50 eggs of S. frugiperda fed on a natural and artificial diet during the larval stage and 50 eggs of C. cephalonica). These eggs were exposed for 24 hours to one mated female of T. chilotraeae and then reared until the emergence of adult parasitoids. Results show that T. chilotraeae parasitized more S. frugiperda eggs fed on a natural or artificial diet than C. cephalonica eggs. However, the parasitization rate was the same between the three. Similar to the sex ratio of the resulting T. chilotraeae offspring, S. frugiperda eggs fed on a natural diet produced more female offspring than S. frugiperda eggs fed on an artificial diet or on C. cephalonica eggs, indicating that mass rearing of T. chilotraeae can be carried out using a host in the form of S. frugiperda eggs from adult fed on artificial diet during a larval stage or by using C. cephalonica eggs.


Introduction
Spodoptera frugiperda has recently encountered Indonesia.Spodoptera frugiperda may reduce yields, as it did in Africa [1] and America [2].Spodoptera frugiperda was first reported to be found in Indonesia at the end of 2018 in West Sumatra and has now been found in almost all regions of Indonesia, starting from Sumatra, Java, and Kalimantan [3].In 2020, this pest was also reported to be found in Ende, East Nusa Tenggara [4].The infestation of S. frugiperda ranges in intensity.Trisyono et al. [5] reported a severe S. frugiperda infestation of corn plants In Lampung.However, Nurkomar et al. [6] reported that some areas of Yogyakarta had a low level of S. frugiperda infestation.Even so, the presence of S. frugiperda requires serious attention since it potentially causes severe damage [7].
Pest management using biological control is an eco-friendly method, such as using egg parasitoids to prepare bio-agents that can control S. frugiperda effectively.Egg parasitoids are considered adequate because they can attack the early stages of pests so that plant damage can be avoided.The research results by Tawakal et al. [8] reported an association of Telenomus sp. and Trichogramma sp. as egg parasitoids of S. frugiperda.Easy mass propagation of egg parasitoids means that propagation can be done using an artificial diet for the host [9] and alternative eggs [10] as a substitute host to maintain the continuity of mass multiplication of parasitoids in the laboratory.However, using an artificial diet and alternative hosts must be considered carefully since the host's life history can affect the fitness and ability of parasitoids [11].In a previous study, researchers found that the performance of Telenomus 1346 (2024) 012002 IOP Publishing doi:10.1088/1755-1315/1346/1/012002 2 remus in S. frugiperda eggs from moths whose larvae were raised on natural and artificial feeds varied [12,13].Because T. chilotraeae is another possible natural enemy that S. frugiperda could face, and the performance of T. chilotraeae to control S. frugiperda in Indonesia is unknown, the capacity of T. chilotraeae in parasitizing S. frugiperda eggs obtained from moths whose larvae were reared with different diet sources need to be investigated.
This research aimed to study the acceptability and host suitability of the T. chilotraeae to parasitized S. frugiperda eggs originating from adults whose larvae were reared with natural and artificial feed.This research also aimed to investigate the capacity of T. chilotraeae to parasitize Corcyra cephalonica eggs, an alternate host frequently employed in the large-scale propagation of egg parasitoids.

Materials and Methods
The research was carried out from May -July 2021.Samples of S. frugiperda larvae were collected in several food crop cultivation areas in Dramaga, Bogor, and West Java.At the Biological Control Laboratory, Department of Plant Protection, Faculty of Agriculture, IPB University, insects were raised.A fully randomized design was used for the research.The treatment is the kind of egg used, and each treatment was repeated 15 times.

Artificial diet
An artificial diet was made, according to Sari et al. [14].1000 mL of distilled water was used to soak 125 grams of red beans for 24 hours.After that, the beans were blended and drained using the same amount of distilled water.The mixture was then supplemented with ingredients like wheat germ (100 grams), yeast (62.5 grams), casein (50 grams), vitamin C (66 grams), sorbic acid (3 grams), and methylparaben (5 grams).For two minutes, 24 grams of agar were cooked in 1000 milliliters of distilled water.Tetracycline and a vitamin mix were added to the red bean mixture after the cooked gelatine had been combined.After that, the prepared dough was put into a 20 cm x 20 cm x 10 cm storage container and refrigerated.
Diet was administered in tiny (2 cm by 2 cm) portions.Larvae fed an artificial diet were raised in petri dishes with a diameter of 86 mm.The provided artificial diet had its humidity regulated.The fresh diet was used in its place if the old one dried out.

Insect rearing
Larvae of S. frugiperda were taken from the field and raised in a lab.The field-collected larvae were raised and multiplied in 35 cm x 27 cm x 7 cm insulated rearing containers.To prevent cannibalism, larvae were positioned on each of the container's partitions.The pre-pupal stage was reached by feeding the diet (baby corn) daily.Insects were housed in sterile sand containers as a pupation medium shortly before they developed into pupae.After developing, the pupa was placed in a cylindrical container (15 cm in diameter and 30 cm in height) for raising adults.To feed the adult, a 25% honey solution was utilized.To obtain the first generation, rearing was necessary.The first generation's eggs hatched into larvae were then preserved and multiplied using the same technique.The eggs were attached to the tray after they were harvested for experimental purposes.
Corcyra cephalonica was produced over several generations in a laboratory.The larvae were raised using maize flour as a medium in 34 cm x 26 cm x 7 cm plastic containers.The moths were kept in a cardboard nesting box with a diameter of 8 cm and a height of 20 cm during their adult phase.Twentyfive mesh wire mesh covered the carton's top and bottom.The remaining eggs were used for laboratory multiplication after the existing eggs were collected and affixed to a tray for experimentation.
Eggs of S. frugiperda were collected in the field to produce T. chilotraeae.After that, the eggs were raised in a tube-shaped rearing container measuring 2 cm in diameter and 10 cm in height until the adult parasitoids appeared.The emerging parasitoids were fed a diet containing 25% honey.Mature female parasitoids were exposed to S. frugiperda eggs raised in a lab and fed a natural diet (baby corn) after two days of emergence.The eggs of S. frugiperda that had been parasitized were raised in the same container until the next generation of adult parasitoids appeared.After that, the parasitoids were used in experiments.

The ability of T. chilotraeae to parasitize S. frugiperda eggs and alternate host.
A group of 50 eggs of S. frugiperda, which came from an adult fed both natural and artificial diet during the larval stage, and 50 eggs of C. cephalonica as alternate hosts, were arranged on a 1 cm by 5 cm tray.The egg-filled trays were subsequently placed inside a maintenance container that was shaped like a tube and had a diameter of 2 cm and a height of 10 cm.The eggs were left in contact with one mated adult T. chilotraeae female for a full day.After that, the parasitized eggs were kept alive until the adult T. chilotraeae emerged.
Several parameters were noted, such as the number of parasitized eggs (parasitism rate), which is indicated by the change in egg color to black, the number of parasitoids that emerged, the sex ratio of the progeny, and the success of parasitism (parasitization rate).

Statistical Analysis
The abilities of T. chilotraeae, such as parasitism and parasitization rate, were analyzed using one-way ANOVA.The Tukey test was employed at a significance level of 5% to examine any further differences in the mean value of each parameter in each treatment.SAS version 9.0 was used to analyze the data.

Results
The findings demonstrated a significant difference in the parasitism rate (F=5.96,dF=2, P=0.0052) of T. chilotraeae (Figure 1) on S. frugiperda eggs raised on natural diet, artificial diet, and C. cephalonica eggs (Figure 2A).The highest parasitism rate occurred in S. frugiperda eggs.Meanwhile, the parasitism in C. cephalonica eggs happened at a lower level.Meanwhile, there was no difference in parasitization rate for each type of host egg used (F=2.94,dF= 2, P=0.06) (Figure 2B).

Figure 1. Trichogramma chilotraeae
On the other hand, there was a significant difference (77.56%) between parasitism and parasitization of S. frugiperda eggs raised on a natural diet.The rate of parasitism and parasitization of S. frugiperda eggs raised on an artificial diet or other eggs differed less (44%).This showed that T. chilotraeae parasitism was twice as successful on C. cephalonica eggs or S. frugiperda eggs raised on an artificial diet as on S. frugiperda eggs raised on a natural diet.However, the number of female progenies of T. chilotraeae that emerged from each type of host egg used was relatively uniform (F=1.83,dF= 2, P=0.1727).The number of female offspring that appeared was more than 50% of the entire population (Figure 3).

Discussion
Biological control is an effort to control pest populations that are environmentally friendly by utilizing biological agents such as predators and parasitoids as well as entomopathogens.The parasitoid known to attack S. frugiperda eggs is Telenomus sp. and Trichogramma sp.[8,15].Telenomus and Trichogramma are egg parasitoids that have the potential to become natural enemies of many important pests [16], such as Scirpophaga innotata [17], Helicoverpa armigera [18], Ostrinia furnacalis [19], and S. exigua [20].Sari et al. [12,13] has researched T. remus's potential as S. frugiperda's egg parasitoid.Meanwhile, Dequech et al. [21] examined the ability of T. pretiosum and T. atopovirilia as natural enemies of S. frugiperda.This study aimed to study the capacity of T. chilotraeae as another potential egg parasitoid of S. frugiperda.

Origin of host egg
The difference in parasitism and parasitization rates may occur due to several factors, including learning of parasitoids, encapsulation, and super parasitism.Learning is a process that influences the abilities and behavior of parasitoids.Several studies have reported parasitoids' learning ability [22].The type of diet the host receives when the parasitoid is immature will determine its ability to parasitize the host in an adult stage [23].Adult parasitoids prefer hosts that consume the same feed as when they were immature over hosts that consume other types of diet [24].Compared to other treatments, S. frugiperda eggs raised on a natural diet had a higher parasitism rate.This may have occurred because the T. chilotraeae used came from a collection of S. frugiperda eggs in maize fields (reared with a natural diet).The parasitism in the eggs of other hosts occurred because the experiment was carried out without a choice, so T. chilotraeae parasitized the existing eggs.
Encapsulation is a host defense process that can inhibit the parasitization process.Parasitoids are prevented from developing when encapsulated because they die in the host body from a shortage of oxygen and nutrients [25].This study did not observe the presence or absence of encapsulation, making it an important topic for further research.Encapsulation plays a crucial role in both the longevity of biological control in the field and the mass rearing of parasitoids in the lab.Because it impairs biological control through the use of parasitoids, and superparasitism is another factor that can determine the success of parasitization.[26].Nevertheless, this investigation did not find any instances of superparasitism.
Meanwhile, an important aspect of parasitoid biology is the sex ratio, which is critical for controlling pest populations and maintaining the stability of host-parasite interactions in the field.[27].Because female insects play a role in parasitizing and indirectly controlling pest populations as host insects, the abundance of female parasitoid offspring can indicate the sustainability of biological control in the field.

Conclusion
Trichogramma chilotraeae parasitizes more S. frugiperda eggs than C. cephalonica eggs.However, parasitism in the host eggs of C. cephalonica suggests that T. chilotraeae can be propagated using different host eggs as a simple method of egg parasitoid propagation.

Figure 2 .
Figure 2. Parasitism (A) and parasitization rate (B) of Spodoptera frugiperda egg and alternate host egg by T. chilotraeae.Means with different letters are significantly different by Tukey's HSD test (α = 0.05).Lowercase letters indicate a difference between treatments.

Figure 3 .
Figure 3. Sex ratio of T. chilotraeae emerging from the host eggs used