عنوان مقاله [English]
Introduction: The tomato leafminer (TLM), Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is an important pest on tomato, potato and other Solanaceous with a great economic importance. Tomato borer can be regarded as a serious threat to tomato production in Iran. TLM larvae cause losses of up to 100% by attacking tomato leaves, flowers, stems, and especially fruits. TLM larvae act as leaf miners, and in high numbers, they can totally destroy the plant foliage; TLM infestation can destroy crop production early on by infesting both developing and ripe fruits. Management of the pest can be problematic, particularly when the infestation pressure is high. One of the main tools in its management is the use of conventional synthetic insecticides, however, this overreliance on the use of synthetic insecticides quickly leads to problems of insecticide resistance. The use of natural compounds such as plant essential oils is considered as alternatives to chemical pesticides due to their lower toxicity on the non-target and low persistence in the environment. In recent years essential oils of medicinal plants have received much attention as pest control chemical agents. The discovery of active compounds that are less persistent will be beneficial for both the environment and agricultural product consumers.
Materials and Methods: The egg, 2nd larval instars, and adult of TLM were used to determine the fumigant toxicity of the C. cavi. The essential oil of aerial parts of C. cavi, was extracted by hydrodistillation using a modified Clevenger-type apparatus. Conditions of extraction were: 50g of air-dried sample, 1:12 plant material/water volume ratio and 4h distillation. The obtained oil was dried over anhydrous sodium sulfate and stored in the refrigerator at + 4°C until used. The fumigant toxicity of essential oil on larvae 2nd (inside leaf) and egg were tested in macro plastic container volume 1800 ml, The vials were contained leaves containing larvae mines with ten larvae (2nd instars) or 20 eggs, separately. Fore 2nd larvae (outside leaf) and adults bioassay experiments in glass vial volume 600 ml that contained ten larvae (2nd instars) or 10 adults, separately. No. 1 Whatman filter paper disks attached to the undersurface of vials. Filter papers were impregnated with series of pure concentrations of essential oil ranging from 20-100 µl L-1 air, 3-7 µl L-1 air, 0.1-1 µl L-1 air and 0.5-1 µl L-1 air were used in the main bioassay tests for the egg, 2nd larval instars (inside leaf and outside leaf) and eggs, respectively and each concentration and control included three replicates. The mortality was recorded for 2nd larvae and adults after 48 hours. Experiments were carried out at 27±2°C and 65±5% R.H. The rate of mortality was recorded after 48 hours. The type and amount of constituents of the essential oils were analyzed by GC/MS.
Results and Discussion: Results showed that the essential oil of C. cavi had high mortality on the different stage of TLM after 48 hours exposure. There was no mortality in controls. The essential oil showed strong adulticidal, larvicidal and ovicidal activity. The results showed that by increasing oil concentration, the mortality was increased. Based on Probit analysis, the LC50 values for egg, 2nd larvae inside the leaf, 2nd larvae outside leaf and adults were 44.24, 4.652, 0.335 and 0.624 µl L-1 air, respectively. The major constituents of C. carvi was Benzaldehyde, 4- (1- methyl ethyl) – (c) (21.26%)
Conclusions: Essential oil extracted from C. carvi proved to be very toxic different stage of TLM. On the basis of these LC50 values, larvae (outside leaf) and adults were much more susceptible than eggs and larvae (inside leaf). It should be noted that C. carvi showed remarkable insecticidal activity without any apparent phytotoxicity for leaves of tomato plants. The results showed that the caraway essential oil has high potential in controlling tomato leaf miner and will have purely to be advised for the safeguarding of the environment and the health of the user. Especially that application of synthetic insecticides arise development of resistance and pollution of the environment. In summary, results indicated that these essential oils have good fumigant toxicity on TLM.