Abstract
Researches on host preference, variability and management of Helicoverpa armigera (Hubner) in different vegetables were studied. Host preference and management studies of H. armigera were carried out at the field and IPM lab of Entomology Division, Bangladesh Agricultural Research Institute (BARI), Gazipur, Bangladesh during October 2007 to August 2008 and March 2009 to August 2010, while variability study was done at the Department of Plant Molecular Biology and Biotechnology, Tamil Nadu Agricultural University, India during September 2008 to February 2009. Five vegetables, viz. tomato, pea, country bean, French bean and brinjal were evaluated against H. armigera for oviposition and feeding preference test under laboratory condition. The highest number of eggs (25.32) was laid on flowering French bean plants followed by tomato flowering plants (21.43), country bean (16.45) and pea flowering plants (9.38) respectively. While, brinjal flowering plants received no egg whatsoever. In feeding preference test, significantly the highest number of fruiting bodies were damaged in French bean (13.25) followed by country bean (9.50), pea (7.75) and tomato (4.00). While, no brinjal fruit was damaged by Helicoverpa. A total of 12 H. armigera population of which 10 population collected from different agro-ecological zones of Bangladesh and two populations from India were tested for their variability. The similarity coefficient based on 138 RAPD markers ranged from 0.000 to 0.777 of the pair wise combination among twelve samples of H. armigera. H. armigera population from Bangladesh had 25 to 45 percent similarity, while 30 percent similarity was observed for population from India. Four botanicals viz. mahogany oil, mahogany seed extract, tobacco leaf extract, neem seed kernel extract along with one synthetic chemical cypermethrin were tested for their efficacies against H. armigera. The lowest fruit infestation, both by number and weight, were observed in neem seed kernel extract treatment (27.15%, 22.29%) which was statistically similar to tobacco leaf extract (27.71%, 23.31%) and cypermethrin (28.87%, 25.44%) treated fruits. While no significant difference was found among mahogany oil, mahogany seed extract and control treatments. The highest yield (18.14 t/ha) and the highest MBCR (2.99) were also obtained from neem seed kernel extract treated fruits. Two microbial insecticides HaNPV @ 0.4ml/L and Bt @ 2g/L along with their combination were tested against H. armigera. The lowest fruit infestation, both in number and weight, were obtained from treatment HaNPV and Bt alternate spraying (11.78%, 9.64%), followed by Bt (13.25%, 10.85%) and HaNPV (17.67%, 13.11%). The highest yield (16.92 t/ha) obtained from HaNPV and Bt alternate spraying plots followed by Bt (16.65 t/ha) and HaNPV (14.73 t/ha). But in case of MBCR, the highest MBCR was obtained from HaNPV and Bt alternate spraying (5.30) followed by HaNPV (4.46) and Bt (3.37). Two egg parasitiods Trichogramma chilonis @ 1g/ha, T. evanescens @ 1 g/ha and one larval parasitoid Bracon hebetor @ 1200/ha and their combinations were tested for their efficacies against H. armigera. The lowest infestation, both in number and weight, were observed in the treatment of T. chilonis + B. hebetor, (15.32%, 12.23%) which was significantly differed from all other treatments. The highest yield (10.90 t/ha) obtained from T. chilonis + B. hebetor treated fruits followed by T. evanescens + B. hebetor (8.37 t/ha). The highest MBCR (6.31) also obtained from T. chilonis + B. hebetor followed by T. chilonis (4.06) treated fruits. Five IPM packages viz. T1-Pheromone trap + Neem seed kernel extract, T2-Pheromone trap + HaNPV and Bt, T3-Pheromone trap + Neem seed kernel extract + HaNPV and Bt, T4-Pheromone trap + T. chillnis and B. hebetor, T5-Pheromone trap + Neem seed kernel extract + T. chilonis and B. hebetor were evaluated against H. armigera. The lowest infestation by number (12.55%) and the highest yield (29.74t/ha) were obtained from T5 followed by T2 (15.49%, 26.77 t/ha). Significantly the lowest fruit infestation by weight (10.60%) was found in treatment T2 followed by T5 (11.73%). Considering MBCR, the highest MBCR was found in T2 (3.41) followed by T5 (3.35). Hence, T2 and T5 packages may be the effective tools for managing H. armigera.