Mass multiplication of rice meal moth, Corcyra cephalonica (Stainton) on different diets under laboratory conditions

Introduction

The rice moth, Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae), has gained tremendous importance in biological control programmes. Although a serious pest of stored grains under natural conditions, it has been found to be an extremely useful insect as a factitious host for mass rearing of various biocontrol agents (Manjunath, 1993) [11] . One of the outstanding examples of mass-production of a biocontrol agent, using C. cephalonica as a laboratory host, is that of the egg parasitoid, Trichogramma spp. (Hymenoptera: Trichogrammatidae), which are extensively used in the control of sugarcane borers, cotton bollworms, and vegetable pests in several countries including India (Padhy et al., 2020) [15] . The widespread acceptability of C. cephalonica as a laboratory host is unique and undoubtedly a boon to entomologists engaged in mass-production of biological control agents. Attempts to mass-produce C. cephalonica have been made in several laboratories using different natural food media like sorghum (Sorghum vulgare), pearl millet (Pennisetum typhoides), rice (Oryza sativa), maize (Zea mays), groundnut (Arachis hypogaea), and finger millet (Eleusine coracana), but the results have not been uniform with regard to production and economics (Kamel et al., 1977; Medina and Cadapan, 1982) [7,12] . Integrated Pest Management (IPM) is now well recognized globally, where all suitable pest control techniques are integrated to find ecologically sound and environmentally safe ways of pest control. Biological control should be regarded as the backbone of any IPM programme, and about 90% of all potential pests are already under biological control (Shukla and Jadhav, 2014) [19] . The fundamental aim in mass production of natural enemies, viz., Trichogramma chilonis, is their quality production at a faster and cheaper rate. The quality of the natural enemies in the laboratory mostly depends on the quality of the host, which ultimately depends on the host nourishment. Therefore, the diet of the host is potentially of importance to the nutritional quality of host eggs and the survival of Trichogramma chilonis and other egg parasitoids released in the environment as biological control agents (Finney and Fisher, 1964) [6] .

The indiscriminate and non-selective use of insecticides in pest management has created several problems including development of insecticide resistance in major crop pests, pest resurgence, destruction of natural enemies, and ill effects of toxic residues in food and environment (Armes et al., 1992) [1] . Several insecticides that are widely used to suppress various pests can also disrupt the effectiveness of beneficial agents. [18] . Trichogramma adults are most active at 25±2°C. A female parasitizes from 1 to 10 eggs per day or 10-190 during its life span (Smith, 1996) [20] . The life cycle of Trichogramma ranges from 8-10 days in summer and 9-12 days in winter. The short life cycle allows the wasp population to increase rapidly (Scholler et al., 2005) [18] . In light of the above-discussed points, the present investigation was undertaken to study the mass multiplication of rice meal moth, Corcyra cephalonica (Stainton), on different diets under laboratory conditions, with the specific objective to evaluate the effect of different rearing media on biological parameters of C. cephalonica.

Materials and Methods

Preparation of rearing media

The bold, clean grains of rice, wheat, sorghum, and groundnut were ground in a domestic grinder to make 2-3 pieces of each grain. These grains were heat-sterilized in a hot air oven at 100°C for 30 minutes to make them free from any secondary infestation. The material was also treated with streptomycin sulphate @ 50 mg per kg to prevent bacterial infection (Rao et al., 1980). Five grams of dry powdered yeast was added to all treatment combinations to enhance the nutritional quality of the diets. Eight different treatments were prepared as follows:

Observations recorded

Total larval period: The larval period was recorded from the date of hatching to the date when 50 per cent larvae spun the cocoons. The average of 10 larvae for each treatment was worked out.

Pupal period:

The same ten larvae that were about to pupate were kept under observation for recording the pupal period. Each larva was observed till adult emergence, and the average pupal period was worked out.

Percent moth emergence:

The actual number of moths emerged from pupae were counted, and per cent adult emergence was calculated.

Per cent female and male moth emergence: The emerged moths were sexed, and the percentage of female and male moth emergence was recorded separately.

Total egg production (cc):

The total number of eggs laid by females in each treatment was measured in cubic centimeters (cc).

Number of Eggs per cc

The number of eggs per cc was counted to determine the fecundity potential of females reared on different diets.

Statistical Analysis

The data obtained from the experiment were analyzed using suitable statistical methods. The standard error of mean (SEm±) and critical difference (CD) at 5% level of significance were calculated to compare the treatment means.

Results and Discussion

The results on the effect of different rearing media on the biological parameters of C. cephalonica are presented in Table 1 and Figure 1 and 2. The data revealed significant differences among the treatments for all the parameters studied. [8] , who recorded the shortest larval period on sorghum + groundnut diet.

Effect on pupal period

The pupal period ranged from 7.93 to 13.32 days. The shortest pupal period was recorded on T3 (Maize + Yeast powder) at 7.93 days, closely followed by T2 (Rice + Yeast powder) at 8.32 days. The pupal period gradually increased with the incorporation of groundnut and mixed ingredients. T8 recorded the longest pupal period of 13.32 days. The shorter pupal period on sole cereal diets suggests rapid metamorphosis, possibly due to simpler nutritional composition. However, the longer pupal periods on mixed diets with groundnut fortification might indicate better nutritional accumulation during the pupal stage, which could contribute to better adult quality. Padamshali and Ganguli (2019) [14] reported similar trends where rice-based diets resulted in longer developmental periods in all stages compared to jowar + groundnut diets.

Effect on moth emergence

The per cent moth emergence varied significantly from 73.13% to 93.27%. The highest moth emergence was recorded in T8 (Sorghum + Rice + Maize + Groundnut + Yeast) at 93.27%, which was significantly superior to all other treatments. T4 (Groundnut + Yeast powder) recorded 86.96%, followed by T7 (Sorghum + Groundnut) at 83.25%. Among the sole cereal diets, T1 (Sorghum + Yeast) showed 78.22%, while T3 (Maize + Yeast) and T2 (Rice + Yeast) recorded 75.19% and 73.63%, respectively. The high moth emergence in T8 can be attributed to the balanced nutritional composition provided by the combination of multiple cereals and groundnut, ensuring adequate supply of carbohydrates, proteins, and lipids essential for complete development. These findings are in agreement with Bhandari et al. (2014) [2] , who reported that corn + groundnut was superior for almost all biological parameters of C. cephalonica, followed by millet + groundnut.

Effect on female and male moth emergence

The female moth emergence ranged from 43.16% (T3) to 59.84% (T8). The highest female emergence was recorded on T8 (59.84%), followed by T4 (53.26%) and T7 (49.35%). The higher proportion of female emergence is desirable for mass rearing programmes as females determine the reproductive potential of the population. Similarly, male moth emergence ranged from 46.29% (T3) to 68.65% (T8).

The treatment T8 again recorded the highest male emergence at 68.65%. The favourable sex ratio and higher emergence on mixed and groundnut-fortified diets indicate the importance of protein supplementation in the adult diet for better survival and reproductive fitness. Mehendale et al.

(2014) [13] also reported maximum total females and fecundity in Corcyra females emerged from sorghum + groundnut + powdered yeast diets.

Effect on egg production

The total egg production is a critical parameter for determining the suitability of a rearing medium for mass multiplication of C. cephalonica. The total egg production ranged from 6.79 cc (T2) to 16.71 cc (T8). Treatment T8 recorded the highest egg production of 16.71 cc, which was more than double the production of most sole cereal diets. T4 (Groundnut + Yeast) recorded 13.37 cc, followed by T7 (Sorghum + Groundnut) at 12.25 cc. Among the sole cereal

diets, T1 (Sorghum + Yeast) produced 7.68 cc, while T3 and T2 produced 7.19 cc and 6.79 cc, respectively. The number of eggs per cc also showed similar trend, ranging from 135,800 (T2) to 334,200 (T8). Treatment T8 recorded the highest number of eggs (334,200/cc), followed by T4 (267,400/cc), T6 (273,600/cc), and T7 (245,000/cc). Sole sorghum, rice, and maize diets yielded significantly lower egg numbers compared to mixed and groundnutfortified diets. The superior egg production on groundnutfortified and mixed diets can be attributed to higher nutritional value, particularly protein and lipid content, which are essential for ovarian development and fecundity in female moths. Laouali Amadou (2019) [9] observed that the addition of cowpea or peanut to cereal diets yielded higher C. cephalonica larval survival and female moths emerging from larvae fed on cereal and legume mixed diets produced higher numbers of eggs compared to those fed on sole cereals.

Comparative analysis of diets

Based on the overall performance, the eight treatments can be ranked as follows for mass multiplication of C. cephalonica. [16] also found that bajra-based medium was significantly superior for most parameters and could be used profitably in mass multiplication of C. cephalonica.

Conclusion

1. The present study clearly demonstrates that the rearing diet significantly influences the biological parameters of Corcyra cephalonica. The following conclusions can be drawn from the study: 2. Among the different diets tested, T8 (Sorghum + Rice + Maize + Groundnut + Yeast powder) was the best treatment, recording the highest moth emergence (93.27%), female moth emergence (59.84%), male moth emergence (68.65%), total egg production (16.71 cc), and number of eggs (334,200/cc). 3. The shortest larval period (29.97 days) and pupal period (7.93 days) were recorded on T3 (Maize + Yeast powder), indicating faster development on sole cerealbased diets. 4. Groundnut-fortified diets (T4 and T7) showed significantly better performance compared to sole cereal diets for parameters like moth emergence, egg production, and fecundity. 5. Mixed diets with multiple cereals and groundnut supplementation provide balanced nutrition and are most suitable for mass multiplication programmes where maximum egg production is the primary goal. 6. For mass rearing of Trichogramma and other egg parasitoids, diets promoting higher C. cephalonica fecundity are preferable, even with a longer developmental period, as they ensure higher output of host eggs for parasitoid production.

The findings of this study contribute significantly to the optimization of mass rearing protocols for C. cephalonica, which serves as one of the most important factitious hosts in biological control programmes worldwide. The results provide valuable information for selecting appropriate rearing media based on the specific requirements of the mass production system, whether priority is given to rapid multiplication or maximum biomass and egg production.

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