Effect of ascorbic acid, sorbitol and mannitol carbohydrates on feeding indices and immune system of Ephestia kuehniella (Lep.: Pyralidae)

It is proved that nutrients have an important role in growth, reproduction, immune and activity digestive enzyme. If insects feed on suitable and valuable food, they will have a strong immune capacity and could be better against foreign agents. In addition, larval feeding lead to produce of insects that they have high fecundity potention. This is important purpose of rearing of intermediate hosts for parasitoides. So, in the present study, some physiological properties of Ephestia kuehniella by feeding with vitamin C and sorbitol and mannitol were determined as a dietary supplement in vitro. Condition of rearing was 25±1 ºC, RH=45% and L: D=14:10 h. Treatments were including first treat: flour (99 g) + ascorbic acid (1 g), second treat: flour (97g) +sorbitol (3 g), third treat: flour (97 g) +mannitol (3 g) and forth treat: flour (100 g) as control. Experiments were done with completely randomized design. Relative growth rate (RGR) showed a significant increase in all treatments compared to control. Third instar larvae reared on nutritional diet containing vitamin C and mannitol had the highest efficiency of conversation of ingested food (ECI) (7.66±0.66%) and highest feeding deterrent index (FDI) (37.2±2.72%). The highest index of efficiency of conversation of digested food to biomass (ECD) (16.38±0.9%) was found in larvae fed on diet containing vitamin C. Chymotrypsin activity significantly increased in larvae fed on vitamin C–enriched food. Whereas, the activity of another protease, trypsin, increased by both sugars and vitamin C treatments compared to those of control. Nutritional diets containing sorbitol and mannitol sugars increased the activity of carbohydrase enzymes, alpha (0.74±0.07) and beta glucosidase (0.44±0.008) µmol/min/mg protein compared to other treatments, and decreased lipase activity in larvae fed on diet containing sorbitol (1.3±0.06) and vitamin C (0.6±0.01) µmol/min/mg protein. Mannitol did not have a positive or negative effect on lipase activity. Regarding immunology, injection of Beauveria bassiana (isolate 47) to third instar larvae resulted in a significant increase in total blood cell and immunocyte counts 4 h after treatment. In fact, the role of vitamin C was clearer in altering blood cell counts (625±48.7) in mm3 hemolymph compared with other treatments. The number of blood cells showed a decreasing trend over time up to 24 hours. In general, among the treatments, vitamin C and mannitol sugar can be considered as good choices in the Mediterranean flour moth diet. It seems that improving the quality of the larval food is effective in their digestion, digestive enzymes, and insect physiological defense potential and the objective of rearing of Ephestia kuehniella as an alternative host to natural enemies will be achieved more strongly.