Potential of the predatory pentatomid Eocanthecona furcellata (Wolff) as a biocontrol agent on American bollworm in cotton in Myanmar
Potential der Raubwanze Eocanthecona furcellata (Wolff) als die Biologische Bekämpfung in Baumwollefeldern in Myanmar
by Khin Thein Nyunt
Date of Examination:2008-05-22
Date of issue:2008-06-02
Advisor:Prof. Dr. Stefan Vidal
Referee:Prof. Dr. Hans-Michael Poehling
Referee:Prof. Dr. Teja Tscharntke
Referee:PD Dr. Martin Worbes
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EnglishThe American Cotton Bollworm (Helicoverpa armigera Hübner)(ABW) is one of the most serious pests of cultivated crops, especially in cotton in Myanmar. Insecticide applications to control this insect pest are too expensive for smallholder farmers; moreover residues are frequently washed from the plants by continuously light rainfalls in Myanmar. An alternative approach for controlling the herbivorous pests aims at enhancing the abundance of predators, naturally occurring in this crop. A number of promising natural enemies were identified in the cotton agro-ecosystems, and among them the predatory bug Eocanthecona furcellata (Wolff)(EO) holds potential for controlling the American Cotton Bollworm. Diamondback moth (Plutella xylostella L.)(DBM) is most damaging vegetable pest not only in Myanmar than also in most tropical countries, where cabbage plants and ideal temperatures for high DBM populations prevail throughout the year. Due to frequent insecticide applications development of resistance towards specific compounds, including Bacillus thuringiensis, has been reported in several regions. We wanted to experienced a predatory bug (Eocanthecona furcellata Wolff), native to Myanmar and commonly found in the field, for its effectiveness to prey on DBM. Therefore, this study aimed at testing the effectiveness of biological control measures by: 1. Testing the effect of host plants on the oviposition preference and larvae performance of American Bollworm Helicoverpa armigera Chickpea, cotton and tomato, and wild cabbage plants were used for ovipositing preference and larvae performance of American Bollworm Helicoverpa armigera. The highest numbers of H. armigera eggs was recorded on chickpea plants followed by tomato, cotton and cabbage plants. The best performance of H. armigera larvae was recorded on artificial diet followed by wild cabbage, cotton, chickpea and tomato plants. 2. Testing the predation efficacy of E. furcellata on American Bollworm Helicoverpa armigera Predation efficacy of EO was tested with American Bollworm from four different host plants (Cabbage, Cotton, Chickpea and Tomato) and larvae reared on artificial diet. Majority of EO (30-60 %) directly approached towards cotton plants eating ABW larvae. When ABW larvae and their faeces were wrapped with Para film "M", the prey selecting efficacy was reduced up to 20-40 %. 3. Evaluating the effect of temperature and prey density on the predation efficacy of E. furcellata Developmental time and predation efficacy were tested with three different temperatures and eight prey densities; and four extreme temperatures. Developmental time was significantly shorter in high temperature (35°C) but the highest predation rate of EO was found at 30°C. Developmental time increased with increasing prey density but prey consumption percent reduced with increasing prey density. Predation rate increased with nymph instars of EO and the highest predation efficacy was found on 5th instar EO nymph at 30°C. EO could not survive at two extreme temperatures (15°C and 40°C) and EO was able to survive at these two constant temperatures; however EO was unable to lay the eggs at 20°C and even though they could lay the eggs at 37°C, no eggs was able to hatch to nymphs. Therefore no viable offspring were recorded in four tested extreme temperatures. 4. Testing the prey searching and feeding behavior of Eocanthecona furcellata under laboratory and greenhouse conditions Prey searching and feeding behavior of EO was tested with two different preys (American bollworm ABW and Diamondback moth (DBM), two different host plants (cotton plant and wild cabbage plant) and three different conditions (normal plant, wounded plant, and insect infected plant) under laboratory condition and green house conditions. Searching time and prey consumption time of EO was significantly lower on ABW larvae than on DBM larvae. Searching time of EO on ABW larvae on the wild cabbage plant was significantly longer than on cotton plant but prey consumption of EO on ABW larvae was not significant on both host plants. Visiting time of predatory bug on the insect infested plant was significantly longer than on narmal plant and mechanical wounded plant. 5. Observing of host choice behavior of E. furcellata towards ABW and DBM larvae in Olfactometer Host choice behavior of EO was studied in Olfactometer and the attractiveness % of ABW and DBM were 43% and 30%. The searching time of EO was not significantly different in both larvae.
Keywords: Biological control; Myanmar; Helicoverpa armigera; <i>Eocanthecona furcellata</i>
Baumwolle ist eine der wichtigsten Feldkuturen in Myanmar und wichtig für die Exportindustrie. Einem höheren Ertrag steht jedoch entgegen,dass Baumwolle zu den Feldkuturen mit dem höchsten Schädlingsdruck gehört. Die Einsatz von Insektizidenführt zu den klassischen Problemen. Die Suche nach alternativen, angepassten Bakämpfungstrategien hat dazu geführt , das Versuche mit der Raubwanze Eocanthecona furcellata , um das Potential dieser Wanze für Bekämpfungsstrategien näher zu erfassen und mögliche unerwünschte Seiteneffekte ausschließen zu können.
Schlagwörter: Biologische Bekämpfung; Birma; Helicoverpa armigera; <i>Eocanthecona furcellata</i>