J. of Plant Protection and Pathology, Mansoura Univ., Vol 12 (10):725 -732, 2021 Journal of Plant Protection and Pathology Journal homepage: www.jppp.mans.edu.eg Available online at: www.jppp.journals.ekb.eg . Corresponding author * E-mail address: FatenBader38@yahoo.com DOI: 10.21608/jppp.2021.205746 Potential and Bio-Chemical Effects Of Steinernema carpocapsae (Rhabditida: Steinernematidae) An Entomopathogenic Nematode Against Bactrocera zonata and Ceratitis capitata (Diptera: Tephritidae) Nabawia M. Elhadidy 1 ; Faten A. Badr 2* and A. M. Azzazy 3 1 Department of Zoology, Faculty of Science, El-Arish University, Egypt 2 Department of Horticulture Insects, Plant Protection Research Institute, Agricultural Research Center, Dokki, Giza, Egypt 3 Department of Pest Physiology, Plant Protection Research Institute, Agricultural Research Center, Dokki, Giza, Egypt Cross Mark ABSTRACT The potential and biochemical effects of the Steinernema carpocapsae, an entomopathogenic nematode, against two species of fruit flies in two types of soil texture (sand and sandy-loam) were examined under laboratory conditions. Data obtained revealed that the type of soil altered the potential effect of S. carpocapsae on Bactrocera zonata and Ceratitis capitata. The mortality percentages for B. zonata ranged between 30.00 and 94.43% in sand and between 33.33 and 96.67% in sandy-loam, whereas, for C. capitata, it ranged from 54.43 to 90.00% in sand and from 55.57 to 97.67% in sandy-loam. Generally, the mortality increased with the increase of nematode concentrations. According to LC50 values, S. carpocapsae was more efficient against B. zonata in sand, but the opposite was obtained in sandy-loam against C. capitata. In addition, S. carpocapsae caused variable biochemical changes in activity of certain enzymes of the two fruit fly species, since it exhibited only a significant increase in the acid phosphatase in B. zonata, whereas the other tested enzymes significantly declined. The activity of amylase and acid phosphatase enzymes significantly induced in C. capitata, whereas the activity of trehalase, acetylcholine esterase and alkaline phosphatase significantly decreased. Non-significant effects were obtained in activity of invertase and chitinase within the infected individuals of C. capitata. Thus, the entomopathogenic nematodes could be used as a sustainable bio-control agent in Integrated Pest Management (IPM) programs for soil-inhabitant insects, such as fruit flies. Keywords: Biological control, enzymes, Integrated Pest Management, LC50, soil texture. INTRODUCTION The Mediterranean fruit fly, Ceratitis capitata (Wiedemann) and the peach fruit fly, Bactrocera zonata (Saunders) (Diptera: Tiphritidae) are serious pests of several fruit species. The most tephritid species are polyphagous pests infesting more than 260 fruit and vegetable species (White and Elson-Harris, 1992). These deleterious pests are distributed all over the world and causing direct and indirect effects in both quality and quantity of fruits. The most preferred hosts for C. capitata are apricot, peach and citrus fruits, while in case of B. zonata, are guava, peach and mangoes. The use of chemical insecticides is widespread among large number of insect species and causing many problems as insect-resistance strains; prevent exporting and negative impact on humans, animals and natural enemies. Therefore, the modern world approaches depend on using the biocontrol agents. Among them, the entomopathogenic nematodes, from family Steinernematidae, are consider as effective and safe alternative agents against a wide range of agricultural pests in fruits and vegetables plants (Gaugler and Kaya, 1990; Abd-El Wahed and Elhadidy, 2018). The infective juveniles (IJs) of entomopathogenic nematodes penetrate their host bodies through natural openings and rarely through host cuticle (Shapiro and Lewis 1999) and those belonging to Steinernematidae kill their hosts through the association with the mutualistic bacteria, i.e. Xenorhabdus spp. These mutualistic bacteria release toxins that finally kill the host within 1-3 days. The nematodes then reproduce within the cadavers. The aim of this work therefore is to estimate the potential activity of S. carpocapsae against the late instar larvae of both B. zonata and C. capitata in two types of soil texture (sand and sandy-loam) under laboratory conditions. Further, to determine the biochemical changes in host enzymes after infection with S. carpocapsae. MATERIALS AND METHODS Insect cultures Larvae of the greater wax moth, Galleria mellonella L., were used as suitable host for reproducing the entomopathogenic nematodes. Larvae used in the present study were obtained from bee hives heavily infested with G. mellonella which was collected from the apiary of Plant Protection Research Institute, Dokki, Giza, Egypt. These larvae were reared according to method of Poinar (1975). The nematode, Steinernema carpocapsae, was reared and multiplied on G. mellonella larvae based on method of Kaya and Stock (1997). Nematoda Steinrnema carpocapsae (EGAZ 9) which used in these experiments was isolated from Belbeis, Sharkia, Egypt and reproducted in Pest