| Summary: | 碩士 === 國立屏東科技大學 === 熱帶農業研究所 === 90 === Oviposition on tomato, cotton and tropical soda apple by the tomato fruitworm (TFW) Helicoverpa armigera (Hübner), was studied in large nylon net cages. The results showed that TFW female significantly preferred to lay eggs on the flowering stage of tomato and cotton as compared to their vegetative stages. To find out whether the flowers stimulated the female’s ovipositing; tomato plant with flowers removed was compared with another flowering tomato plant at the same physiological stage, the results showed that the presence of flowers did not affect the egg laying behavior of TFW female. Similarly, flowers placed manually on vegetative tomato plant did not have any effect on the egg-laying of TFW. Plants with undamaged tomato fruits attracted TFW female for more egg-laying than the plants with damaged fruits.
Plants with manually placed eggs, naturally laid eggs removed, or eggs killed by UV light did not influence the oviposition behavior of the TFW. However, a mated TFW female avoided egg-laying or laid fewer eggs on tomato, cotton and tropical soda apple that had already had naturally eggs present, as compared to the respective plants not having had eggs present. This deterrence of egg-laying is attributed to the presence of chemical markers deposited by egg laying female. Similar deterrent chemicals were not present in the body scales of TFW females.
Additional studies were carried out to investigate the attractiveness of the volatile chemicals extracted from the tropical soda apple volatile in an airtight acrylic chamber. The bioassay results showed that there was a significant difference in the number of eggs laid on filter papers coated with volatile extracts dissolved in hexane compared to the filter papers coated with hexane alone. The bioassay of the chemicals isolated from the volatile of tropical soda apple indicated that TFW showed significant ovipositional response to the chemical 5-butyldihydro-2 (3H)-furanone.
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