Effect of Diet on Some Physiological and Biological Parameters of Indian meal moth, Plodia interpunctella (Lepidoptera: Pyralidae)

The Indian meal moth, Plodia interpunctella (Lepidoptera: Pyralidae) (Hubner, 1813) is one of the most important and well-known stored-product pests in most parts of the world. The larvae of this insect are omnivorous and have the ability to grow and reproduce on a wide variety of grains, dried fruits, dried vegetables, nuts, oil seeds, chocolate, animal feed and various processed products. Therefore, it causes economic losses to various agricultural and stored products. On the other hand, this insect is used as a host in the rearing of various useful insect species. In general, the Indian moth eats carbohydrate-rich foods, and its growth and development is highly dependent on biochemical compounds and especially the quality and quantity of nutrients in its diet. The enzymes like amylase and pectinase in the digestive system of the lepidoperan larvae, which are secreted by the cells of the midgut, play an effective role in the digestion and absorption of food. Investigating some of the biological and physiological properties of this insect on various types of foods will help to optimize the rearing of this insect for management studies and also as a host for rearing of other pest insect’s predators and parasitoids.
In this study, we investigated the effects of different diets, namely raisin, fig, pistachio, peanut, almond, and walnut, which are known to be the main hosts of the Indian meal moth, on the protein content in the last instar larval gut. We compared their protein patterns and content using SDS-PAGE. Additionally, we measured the activities of the digestive enzymes alpha-amylase and pectinase using the DNS (Dinitrosalicylic acid) assay. Alpha-amylase activity was assessed using 1% starch as a substrate, while pectinase activity was measured using pectin as the substrate. To facilitate a better comparison of the relative enzymatic activities, the activities were calculated as a percentage of the highest enzymatic activity. Furthermore, we compared several biological parameters, including the incubation period, larval period, pupal period, adult longevity, life span, and adult emergence.
The results of the study revealed that the Indian meal moth larvae had the lowest amounts of gut protein when fed on figs and raisins, while the highest amounts were observed in larvae fed on pistachios, peanuts, almonds, and walnuts. The determination of protein levels using the Bradford method and SDS-PAGE gel electrophoresis yielded consistent results, clearly indicating the protein concentrations in the samples. The activity of the alpha-amylase enzyme in the larvae's gut was highest in those fed on pistachios and lowest in those fed on figs. Similarly, the pectinase enzyme showed the highest activity in larvae fed on pistachios and the lowest activity in those fed on raisins. The embryonic period of the Indian meal moth remained consistent across different diets. However, when comparing the duration of the larval period, pupal period, and overall growth period, the shortest duration was observed in larvae fed on pistachios, while the longest duration was seen in those fed on raisins. The length of the growth period tends to increase when the insect is fed on less desirable food sources. Regarding lifespan, the shortest duration was observed in the diets consisting of almonds and pistachios, while the longest lifespan was recorded in those fed on raisins. When examining adult emergence, the diets of almonds and figs showed the highest and lowest values, respectively. In conclusion, pistachios, almonds, and walnuts were found to be more favorable diets for the Indian meal moth larvae compared to peanuts, figs, and raisins.
This study aimed to determine the optimal diet for rearing the Indian meal moth. The investigated diets, which are major food sources for this insect, were found to have an impact on the amount and concentration of intestinal protein in the last instar larvae, as well as the activity of alpha-amylase and pectinase enzymes. Significant differences were observed in various physiological and biological components among the diets. The highest values for all these components were observed in the larvae reared on a pistachio diet, while the lowest values were found in those reared on fig and raisin diets. Based on the findings of this research, it can be concluded that pistachio, walnut, and almond diets are favorable and suitable for laboratory breeding of the Indian meal moth, compared to peanut, raisin, and fig diets. Among these diets, pistachio was identified as the most optimal choice.