Bulletin of the National Research Centre (Jul 2019)
Integration of some biopesticides against potato tuber moth, Phthorimaea operculella (Zell.), during storage with reference to histopathological changes detected by a transmission electron microscope in the endocrine system
Abstract
Abstract Background The potato tuber moth (PTM), Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is an important pest. It attacks several cultivated solanaceous plants including potato (Solanum tubersum), tobacco (Nicotiana tabacum), eggplant (Solanum melonguene), tomato (Lycopersicom esculentum), and bell pepper (Capasicum annuum). It has also been reported to be found on several wild plant hosts of the following genera: Solanum, Datura, Nicotiana, Fabina, Hyoscyamus, Physalodes, Lycium, and Nicandra. All over the world, it is the most important insect pest in potato field and storage under subtropical warms and dry summer conditions. The larvae attack both foliage and tubers in the field and infested tubers brought into heaps. Aim of work This research focuses on (a) the compatibility of Bacillus thuringiensis (Dipel-2X DF) and granulosis virus (GV virus) with plant basil extract (Ocimum basilicum), an aromatic plant, as a component of integrated pest management system against the potato tuber moth during storage and (b) histopathological changes detected in the endocrine system by a transmission electron microscope. Methods 1. Insect culture rearing A stock laboratory colony of PTM was initiated on potato tubers. The culture was maintained following the method of Sharaby and Fallatah (Bull NRC Egypt 43: 79–85, 2019). The culture and all experiments were maintained under room conditions of 27 ± 2 °C and 70 ± 5% RH with a light regime (10:14 L:D). New clean potato tubers were added every 10 days for egg deposition and to keep a continuous culture. 2. Basil plant extract All parts of the basil plant (Ocimum basilicum) which was obtained from fields in June after 3 months of plantation were dried in a shad place then minced into fine powder in an electric mill. The weight of the plant powder (500 g) was filled into the Soxhlet apparatus and extracted with ethanol (85%) that was used as a solvent. 3. Biological aspects of plant basil extract and the microbial insecticides (Dipel-2X DF (32,000 international units of potency/mg (equivalent to 32 billion international units of potency/KG Registration NO. 26508) and granulosis virus (GV)) Basil extract was mixed with the microbial insecticides in order to study the combined effects on different biological aspects. Five millilitres of each of the tested substances (basil extract + B.t + GV) was mixed with 95-g commercial carrier material (talcum powder) and left to dry under room temperature; then, 1 kg of potato was treated by 25 g of the treated talcum powder w/w (to be used as dust). The three bioagents were tested separately and in different combinations. Two control groups were used (treated talcum powder and the other talcum powder without treatment). Different biological parameters and development of PTM were estimated. Electron microscopic studies The remaining alive treated larvae were collected from inside the treated tubers after 13 days of hatching. Larvae were taken for ultrastructure investigations using the transmission electron microscope (TEM). To investigate the ultrastructure changes on the endocrine glands of the treated larvae, the brain neurosecretory cells, corpus cardiacum, corpus allatum, and prothoracic gland, were examined. Untreated larvae of the same age were used as control. Results In the data recorded, it is clear that there are insignificant differences at P < 0.01 of the mean number of deposited eggs that were laid on potato tubers treated by talcum powder mixed with the three additives (basil extract + B.t + GV) (3.0 eggs/♀) and on tuber treated by powder containing basil extract only (4.6 eggs/♀) and nearly equal difference in the B.t + extract or GV + extract (cleared 4.0 and 5.0 eggs/♀, respectively); no differences in treatments by B.t or GV when used separately were found compared with the two control treatments of talcum powder only or the untreated tubers (38.2 eggs/♀). The most effective combination was the mixture of the three additives: the mean number of emerged adults was 0.4, while it ranged from 1.2 to 14.4 for the other treatments compared with the two controls 35.4 and 37.2 individuals. The percentage of emerged F 1 was greatly decreased by the different treatments, and the lowest percentage (13.3%) was recorded for extract + B.t + GV; for other treatments, the percentage ranged from 25.00 to 54.96% compared with 92.20 and 98.40% in the two control treatments. Histopathological changes on the endocrine glands of the larvae that were detected by the electron microscope have been recorded. Conclusion This research revealed that an additive effect was produced using a combination of three bioagents (basil plant extract + B.t + GV) against the potato tuber moth Phthorimaea operculella. The combination of the three elements in one formulation may reduce the initial amount of potato destruction, decrease insect resistance build-up, and reduce the need for chemical insecticides and their associated risks. The obtained results suggested an interesting opportunity to develop bio-insecticides based on plant extracts for the control of this serious lepidopteran pest and other pests during storage, so usage of the mentioned combined mixture for controlling and protecting the tubers from increasing their toxicity could be recommended.
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