The experiment was conducted from May to November 2017 at the laboratory of the Department of Entomology, Hajee Mohammad Danesh Science and Technology University (HSTU), Dinajpur, Bangladesh. Details methodologies of the experiment are described below.
Source and collection of oils: Tested plant oils of mustard, palm, soybean, groundnut, linseed and black cumin were collected from the market of Maldaho Patty of Dinajpur town in separate glass bottles (150 mL). Collected oils were preserved in the refrigerator (4°C) for experimental use.
Data recording procedure: Fifty gram of healthy chickpea seeds were taken in a plastic container (300 ml) and mixed with 5, 7.5 and 10% concentrations of each tested oils (v/v) and then air dried for 30 minutes. Five pairs of newly emerged one day old adult beetles were released in each plastic container and the mouth was closed with its lid. Each treatment was replicated thrice including control. All treated containers were kept at ambient room temperature (28 ± 50C) in the laboratory for oviposition. After 7 days, dead and alive beetles were removed from each container and seeds along with eggs were kept in the laboratory for further development of the insect. The efficacy of plant materials as protectants of chickpea seeds against C. chinensiswas assessed considering oviposition, adult’s emergence, seed infestation and seed weight loss done. For the determination of oviposition of the beetle seeds were collected from each plastic container of each treatment and examined under 10x magnifying glasses and the number of seeds along with eggs (egg bearing seeds) and the number of eggs deposited were counted. After each observation, the grains were returned to the respective containers for the further development of the beetle. The adults were removed daily from each plastic container and the data were recorded. Percent seed infestation and weight loss were determined at the completion of adult emergence. The sample of each replicate were examined carefully and damaged and healthy seeds were separated, cleaned, counted and weighed. Percent seed infestation and weight loss were calculated by using the following formulae:
Infestation (%) = Nb / Tn x 100 (Enbakhare and Law-Ogbomo 2002)
Where Nb=Number of bored seed and Tn=Total number of seeds
Weight loss (%) = IW-FW / IW x 100 (Keita et al. 2001)
Where, IW = Initial weight of seed, FW = Final weight of seed.
Ovicidal and larvicidal efficacies of oils: This test was conducted to investigate whether black cumin, mustard, linseed, soybean, groundnut, and palm oils have ovicidal and larvicidal efficacy. For this, 100 chickpea seeds along with one-day old egg (forovicidal experiment) and 1-2 days old larvae (forlarvicidal experiment) containing one egg or larvae per seed were separately placed in each container and mixed properly with those oils at 5, 7.5, 10% concentrations including control treatment. Each treatment was replicated thrice. Until adult emergence the mouth of the container was closed with its cap and left undisturbed in the laboratory after proper mixing. The number of adults were counted and recorded daily from the first to last emergence and removed from the containers. After completion of adult emergence, the inhibition was computed by using the following formula as stated by Shukla et al.(2007).
Inhibition (%) = Control mean - Treatment mean / Control mean x 100