Effect of vitamin-enriched artificial diets on the biology of the rice moth, Corcyra cephalonica (Stainton)

Introduction

Globally, crop protection strategies are undergoing a paradigm shift away from conventional chemical-dependent pest control practices towards bio-intensive Integrated Pest Management (IPM) approaches. Biological control is an ecologically sustainable and economically viable approach within Integrated Pest Management, using parasites, predators, or pathogens for maintaining another organism's population density at a lower average than would occur in their absence. Approximately 90% of potential pests are already effectively managed through biological control (Shukla and Jadhav, 2014) [11] . Mass production of biological control agents is a fundamental requirement of biocontrol programs, necessitating a steady and sufficient supply of easily maintainable factitious hosts for mass culturing of bioagents. (Wadaskar et al., 2015) [13] . The rice moth, Corcyra cephalonica (Pyralidae: Lepidoptera) is a serious pest of stored commodities, such as rice, wheat, maize, sorghum, groundnut, cotton seeds, coffee, spices and cocoa beans, in India and other tropical and subtropical regions of the world (Devi et al., 2013; Allotey & Azalekor, 2000) [5,1] . The rice moth is employed in a variety of biological control research, development and extension units for the large-scale production of numerous natural enemies (Gauraha and Deole, 2016) [7] . The larvae of rice meal moth, C. cephalonica, is a top choice for mass cultured entomophagous insects including, egg parasitoids-Trichogramma spp., egg larval parasitoid-Chelonus blackburnii, larval parasitoids-Bracon spp., Goniozus nephantidis and Apanteles angaleti and insect predators which includes-Chrysoperla carnea, Mallada boninensis, R. marginatus and Cyrtorhynus feltiae (Neoaplectana carpocapsae). For the mass production of C. cephalonica, a variety of food materials such as rice, sorghum, groundnuts, maize, wheat, ragi, sesame and bajra etc. have been utilized.

Rearing of C. cephalonica larvae on a high-quality nutritional source resulted in high quality eggs (Nathan et al., 2006) [10] . Different diets affect various developmental parameters such as larval growth rate, pupation success, adult emergence, overall growth rates, survival rates and reproductive success of C. cephalonica, making the choice of food material critical for optimizing mass production of this species. Different investigations concluded that, growth and reproductive potential of C. cephalonica increased by providing optimum nutritional components in the diet (Gauraha and Deole, 2016) [7] . Vitamins are vital micronutrients that play a critical role in maintaining internal metabolism by acting as enzyme precursors and are indispensable for proper growth (Elsayeh et al., 2022) [6] . Although several artificial diets have been developed for C. cephalonica, scientific information on the impact of vitamin enriched diets on its biological attributes and egg productivity remains limited. Accordingly, the present study was undertaken to study the effect of different artificial diets enriched with vitamins on the biology of rice moth C. cephalonica with the objective of developing a stable and nutritionally balanced rearing medium.

Materials and Methods

The assessment of different artificial diet enriched with vitamins on the biological parameters of C. cephalonica was carried out at the Biological Control Research Laboratory, ICAR Unit-9, AAU, Anand, during 2024-25, using a sorghum-based diet. The experiment comprised seven treatments with twenty-five replications, laid out in a Completely Randomized Design (CRD) and the diets used for rearing C. cephalonica are detailed below in Table 1:

Maintenance of C. cephalonica culture

The fresh (0-24 hr) eggs of the rice moth infesting the media were taken from the culture maintained at the Biological Control Research Laboratory, ICAR Unit-9, AAU, Anand.

Preparation of rearing cage

The wooden cages (38.5 x 38.5 x 15 cm) used for C. cephalonica multiplication were thoroughly cleaned with a 0.5% detergent wash, rinsed in tap water, wiped with a dry, clean towel and shade-dried. The trays emptied after a cycle of rearing were cleaned with 2% formaldehyde.

Preparation of artificial diet formulations

The required quantities of sorghum grains needed for the experiment were thoroughly cleaned and coarsely milled, breaking them into 2-3 pieces in a flour mill. After that, the grains were sterilized at 100 °C for 30 minutes in a hot air oven to eliminate the residual population of stored product insects and fungal contaminants. Once sterilized, the grains were cooled under a fan in a clean area. Two kilograms of sterilized sorghum (Fig 1A ) were weighed using a mechanical balance and placed into each wooden cage. The broken groundnut seeds (100 g), powdered yeast (5 g) and vitamins (10 g) were added (Fig 1B ) to the respective treatments and the contents were mixed thoroughly. Furthermore, 5 g of wettable sulphur was mixed into each container. The prepared mediums were used for rearing C. cephalonica larvae in the study.

A total of twenty-five eggs from each treatment were kept under a microscope and observed for hatching. The incubation period was calculated from the date of egg laying to the date of hatching.

A small representative sample consisting of 25 eggs from each treatment was kept separately in small Petri dishes (90 mm) to determine the number and duration of different larval instars and the total larval period (Fig 2B). Moulting was identified under a stereomicroscope by the presence of cast-off head capsules, as well as changes in larval size and color. The larval period was calculated by summing up the number of days from the date of egg hatching to the date of pupation, including the time required by larvae to undergo different instars.

To study the sex ratio, laboratory-reared adults were critically examined to determine their sex. The ratio was determined by distinguishing males and females based on their labial palps, which were smooth and forward in females and blunt and unnoticeable in males.

f. Adult longevity (days): The longevity of male and female moths was calculated from the date of their emergence to their death.

The period from eggs to adult emergence was considered the total developmental period, which was calculated by summing the incubation period, larval period, pupal period and adult longevity i.e. the periods from egg to adult stage.

h. Pre-oviposition, oviposition, post-oviposition periods (days) and fecundity: Five pairs of freshly emerged male and female adults were collected from the host commodity and released into plastic jars fitted with mesh. A 50 per cent honey solution (1:1 honey and water) was provided as food daily. The eggs laid by each female on the surface of the jar as well as on the inner surface of the mesh were counted daily using a moist camel hair brush under magnascope and the total number of eggs laid by each female was recorded.

The period between the female's emergence and the commencement of egg laying was considered the preoviposition period. The period between the start and cessation of egg laying was referred to as the oviposition period. The period between the cessation of egg laying and the death of the female was considered the post-oviposition period.

i. Growth index: The growth index of C. cephalonica was calculated for different host commodities as per formula (Singh and Pant, 1995) [12] ,

Growth index = The data obtained was subjected to statistical analysis.

Results & Discussions

The effects of different artificial diets enriched with vitamins on the biological parameters of Corcyra cephalonica are presented in Table 2 & 3.

There was no significant variation in incubation period of C. cephalonica when reared on artificial diet enriched with different vitamins (Table 2). The treatment T 2 (Sorghum + Groundnut + Powdered yeast + Vit A) showed the shortest larval period of 26.56 days whereas, the longest larval period of 35.80 days was noticed in the treatment T 1 (Sorghum + Groundnut + Powdered yeast) (Fig 3). The sex ratio demonstrated a dominance of females and it was varied from 1.80: 1 to 1.10: 1. A maximum sex ratio of 1.80 was noted in the treatment T 2 (Sorghum + Groundnut + Powdered yeast + Vit A), while the lowest sex ratio of 1.10 was noticed in the treatment T 1 (Sorghum + Groundnut + Powdered yeast). In the present investigation, the growth index was determined using the adult emergence percentage and the average developmental period of rice moth. Seven different vitamin enriched artificial diets were evaluated using the growth index and the values are represented in The result obtained in the present investigation are in close agreement with the findings of several workers. House (1965) [8] reported that dietary Vitamin A acetate significantly accelerated the growth rate of axenically reared A. affinis larvae on a chemically defined diet and enabled the resulting adults to reproduce. Similarly, House (1966) [9] found that Vitamins A and E accelerated the growth and development of A. affinis, increased adult emergence, particularly improved male development, and corrected the previously abnormal sex ratio. In a similar study, Babu (2013) [3] reported that the fecundity of H. armigera increased with higher concentrations of Vitamin E in the artificial diet and gradually improved over generations when reared on multivitamin-enriched diets, additionally, adult emergence was higher (80.0%) in multivitaminsupplemented diets compared to the control (70.0%).

According to Begum and Qamar (2015) [4] , diet D 5 enriched with vitamin E exhibited superior performance in C. cephalonica compared to other dietary formulations containing Vitamin B and H, leading to the highest fecundity (399.2) and food efficiency index (8.45).

Conclusion

Biological control involves the effective utilisation of natural enemies such as parasitoids, predators and microbial agents, which necessitates the mass rearing of bioagents.

The rice moth, continues to rank as the most widely used factitious host for mass culturing entomophagous insects due to its ease of mass production, adaptability to varied rearing conditions and its favorable influence on the quality of natural enemy progeny. The present investigation highlighted the influence of vitamin fortified artificial diets on the biological attributes of Corcyra.

References

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