Effect of Micronutrient Fertilizers on Digestive Enzymes Activity of Hippodamia variegata (Goeze) Fed on Myzus persicae (Sulzer)

Introduction The green peach aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) is one of the severe pests of bell pepper Capsicum annuum L. in the greenhouse. Ladybird, Hippodamia variegata (Goeze), is an important general predator in both larval and adult stages to various aphid species, including, M. persicae. In this study, the effect of nutritional interaction among plant-herbivore-natural enemy under the influence of foliar application of iron, zinc, copper and manganese in bell pepper on the activity of digestive enzymes of the third and fourth instar larvae of H. variegata fed on M. persicae was examined.Materials and Methods The experiments were performed as a completely randomized design with four replicates per treatment during 2020-2021 in the greenhouse and laboratory of the Department of Plant Protection, College of Agriculture, Lorestan University. The foliar application of micronutrient carried out at four-to six-leaf stage with a certain amount of each micronutrient fertilizer. Then, sufficient number of the third and fourth instar larvae of H. variegata were randomly collected from each treatment and replication. The samples transferred to 1 mL of distilled water, and homogenized with a hand pestle. Then, the samples centrifuged at 13000 g for 15 min at 4°C. The supernatants as the enzyme source were collected and reserved at −20°C for starting biochemical assays. The activity of digestive enzymes was measured according to the standard protocols.Results The results showed that the amount of digestive enzymes activity of the third and the fourth instar larvae of H. variegata fed on M. persicae reared on the different micronutrient treatments were higher than the control treatment. The total protease and the trypsin activity were higher in the third instar larvae H. variegata reared on manganese (0.583 and 19.296 U/mg protein) and iron (0.574 and 18.426 U/mg protein), respectively. The highest and lowest activity of chymotrypsin, aminopeptidase and carboxypeptidase were found in the third instar larvae in manganese (15.518, 8.95 and 7.536 U/mg protein) and control (7.353, 2.139 and 2.665 U/ mg protein) treatments, respectively. The highest (18.952) and lowest (9.139 U/ mg protein) elastase activity were found in the third instar larvae on iron and control, respectively. The higher activity of α-amylase (25.20 U/mg protein) was observed in the third instar larvae of H. variegata in iron treatments then the other treatments. The total protease (0.183 U/ mg protein) and the chymotrypsin (10.396 U/ mg protein) of the fourth instar larvae predatory had higher activities with iron treatment and these enzymes had lower activities on control (0.036 and 6.763 U/ mg protein) and copper (0.059 and 6.655 U/ mg protein) treatments. The highest activity of trypsin and aminopeptidase were observed in the fourth instar larvae of H. variegata fed on M. persicae reared on iron (6.893 and 2.317 U/ mg protein) and the highest activity of elastase was found on iron (2.486) and zinc (2.251 U/ mg protein, respectively). Also, the lowest activity of trypsin, aminopeptidase and elastase were found on control. The carboxypeptidase activity was higher in the fourth instar larvae H. variegata fed on the all micronutrients than the control. Also, the highest and lowest activity of α-amylase were observed in the fourth instar larvae H. variegata fed on micronutrients of copper and iron (17.64 and 15.04 U/ mg protein) and control (9.160 U/mg protein), respectively.Discussion The results showed that the amount of digestive enzymes activity of the third and the fourth instar larvae of H. variegata fed on M. persicae reared on different micronutrient treatments were higher than the control treatment. Based on the results, the foliar application of plants with micronutrient fertilizers has a positive effect on the performance of predator of H. variegata through nutritional interaction and improving of the growth quality. Thus, the quality of host plants, as the first level of nutrition, has an important effect on the physiological characteristics of the predator on the third level of nutrition and show the positive effect of prey nutrients on the physiological performance of H. variegata that can be used in M. persicae management programs. Conclusion Using different micronutrient fertilizers along with biological control agents such as ladybird H. variegata could be effective in integrated management programs of M. persicae through the growth quality improvement of the host plants.