ارزيابي تراكم جمعيت و پارازيتيسم، (Hubner) Helicoverpa armigera و Spodoptera exigua (Hubner)، روي دوازده رقم گوجه فرنگي در شرايط مزرعه

Population Density and Parasitism of Helicoverpa armigera (Hubner) and Spodoptera exigua (Hubner) on Twelve Varieties of Tomato

كرم ميوه ي گوجه فرنگي Helicoverpa armigera و كرم برگ خوار چغندرقند Spodoptera exigua از آفات مهم گوجه فرنگي هستند. تراكم جمعيت اين آفات و ميزان پارازيتيسم آن ها توسط زنبور پارازيتوئيد Habrobracon hebetor رهاسازي شده، روي ارقام گوجه فرنگي، در شرايط مزرعه، طي سال زراعي ۹۳-۱۳۹۲ بررسي شد. شروع نمونه برداري از هفته ي پنجم پس از كشت نشا آغاز و تراكم جمعيت آفات مورد بررسي و ميزان پارازيتيسم لارو آن ها محاسبه شد. ارقام مورد آزمايش شامل، اطمينان، ارس، AB۲، Rio fojiu، Mariana، Gempride، King ston، Super queen، ۹۷۰۴، ۹۷۰۶، ۹۵۵۳ و ۶۵۱۵ PS بودند. نتايج اين مطالعه نشان داد، با وجود اختلاف معني دار تراكم جمعيت اين دو آفت، در تاريخ هاي مختلف نمونه برداري، ميانگين تراكم آفات در ارقام مختلف، معني دار نبود. بيش ترين تراكم لارو كرم ميوه ي گوجه فرنگي در اواخر تيرماه، مصادف با هفته ي نهم و دهم كشت گوجه فرنگي و بيش ترين ميزان پارازيتيسم لارو آن در اواخر تير و اوايل مرداد ماه در مزرعه مشاهده شد. بالاترين تراكم جمعيت كرم برگ خوار چغندرقند در دهه ي اول تيرماه هم زمان با هفته ي ششم و هفتم رشد گوجه فرنگي و بيش ترين ميزان پارازيتيسم لاروهاي آن در اواخر تيرماه در هفته ي سوم پس از رهاسازي اتفاق افتاد. نتايج كلي اين مطالعه نشان داد، استفاده از زنبور پارازيتوئيد H. hebetor به منظور كنترل لارو آفات مورد بررسي در برنامه مديريت تلفيقي حايز اهميت مي باشد. ارقام AB۲ و Kingstone به ترتيب بيش ترين ميانگين تراكم لارو كرم ميوه ي گوجه فرنگي و كرم برگ خوار چغندرقند را داشته و كم ترين ميانگين تراكم لارو آفات به ترتيب روي رقم Kingstone و ۶۵۱۵ مشاهده شد.

Introduction: Tomato, Lycopersicon esculentum Miller has a special place among agricultural products. It is important as a fresh market and industrial product in agriculture. A wide range of pests and diseases causes a damage to tomato. Tomato fruit worm, Helicoverpa armigera (Hubner 1809) and beet armyworm, Spodoptera exigua (Hubner 1808) are two important pests of the Lepidoptera order, which aggress tomato. Chemical pesticide is a conventional method to control their larvae. Overusing these pesticides causes adverse side effects on the environment and human health. Biological control by predators and other natural enemies is an important component of a comprehensive pest management program (!PM). Among the natural enemies, parasitoids have special significance and can be used in biological control of pest plants. Habrobracon hebetor Say (Hymenoptera: Braconidae) is a cosmopolitan, gregarious, ectoparasitoid that attacks the larval stage of several species of Lepidoptera and is considered one of the best potential biological control agent. Study of pest density on different cultivars has an important role in choosing an appropriate method and time control, and is the basis of plant resistance. Therefore, in this study pest density and efficiency of h. hebetor were assessed. Materials and Methods: Population density and larval parasitism by H hebetor were examined on twelve tomato varieties including, Aras, Etminan, Rio fujio, AB2, Mariana, Gem pride, Kingston, Super queen, 9704, 9706, 9553 and PS 6515 under field conditions during 2014. All experiments were conducted in a randomized complete block design. Five weeks after transplanting, sampling was performed randomly. At three-days intervals, egg, larvae and parasitized larvae of each moth were counted on different cultivars of tomato. The whole of each tomato plant was checked for the presence of pests and the number of eggs. 400 and 570 wasps were released in two steps in June 24th and July 23th during 2014, respectively. The number of healthy and parasitized larvae of each pest was counted and recorded to calculate the parasitism percentage. The trichomes density of different varieties of tomatoes was assessed by a stereo microscope with a magnification of 70. Furthermore, the density of trichomes in the leaves after the terminal bud per plant (per square millimeter) was counted and recorded at three points around the midrib. Statistical analysis of data was carried out using Exel 2013 and SPSS 18.0 software. Results and Discussion: The results of the study showed that the pest density had no significant difference among different cultivars of tomatoes, while there were significant differences in different dates of sampling. The highest density of tomato fruit worm and beet armyworm larvae was observed on AB2 and King stone, respectively, while the lowest density of these larvae was obtained on the King stone and 6515, respectively. Moreover, the highest density of h. armigera was in 17 and 22 July2014 that coincided with the ninth and tenth weeks after transplanting in the field. Parasitism percentage of tomato fruit worm and beet armyworm was significant among different dates of sampling but no significant difference was observed among different cultivars. The highest parasitism percentage of tomato fruit worm larvae was obtained in 22 and 27 July 2014. The highest density of pest occurred in 24 and 27 June and 3 July 2014 which coincides with the sixth and seventh tomato growth. The highest larval parasitism of beet armyworm was observed in 17 July 2014, three weeks after parasitoid release. Investigation of tomato leaf trichomes density in different varieties with highest and lowest population of tomato rruit worm larvae indicated that the highest density was observed in King stone variety. Biological and behavioral differences in tomato fruit worm and beet armyworm were effective on host preference by these pests. In addition, chemical compounds produced by different varieties of tomato (repellents and attractants) were effective on host selection for oviposition and influence pest population. Conclusions: The release of parasitoid wasp, H hebetor to control the larvae of the tomato fruit worm and beet armyworm seems to play an eflective role as a biological agent and can be used in a management program of these pests. Due to the compatibility of resistant cultivars with other control methods and environment, more studies are needed to be conducted on the role of trichomes in plant resistance to introduce resistant cultivars of tomato to the mentioned pests.